Queensland University Research

THE UNIVERSITY OF QUEENSLAND

Bachelor of Engineering Thesis

Design Of An Inlet Manifold For A Formula SAEVehicle, Including Experimental Evaluation

Student Name: Francis Martin Evans

Course Code: MECH 4500

Supervisor: Professor Richard Morgan

Submission date: 15/11/2002

A thesis submitted in partial fulfilment of the requirements of the Bachelor ofEngineering degree program in the Division of Mechanical Engineering

School of Engineering

Faculty of Engineering, Physical Sciences and Architecture

Design of an Inlet Manifold for a Formula SAE Vehicle, Including Experimental Evaluation

Francis Evans 2002

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AbstractThe formula SAE competition requires teams to assume a fictitious role of designers,

producing a prototype vehicle to be evaluated for a limited production run. The design of an

inlet manifold for a formula sae vehicle is essentially a problem requiring careful decisions

about methods of manufacture used for a project with a limited budget, little time, and a very

short supply of skilled labour.

The decisions made in the design are influenced by a few principles of fluid flow, and the

characteristics of internal combustion engines. Some decisions require analysis of transient

flow behaviour; which cannot be modelled analytically, and for which prior experimental and

computational results do not appear to be available.

The process of design used in this thesis takes on elements of theory, and gives some

experimental evaluation and verifications. At times, design decisions of a numerical nature

are sought from the somewhat limited personal experience of the designer, and inference from

observations of competitors.

The aim of this thesis is the production of working components and some experimental

evaluation in the hope of giving insight to future competitors and designers.


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Acknowledgements

I would like to express my appreciation to the following people for their valuable contribution

and assistance in the completion of this thesis:

• Mr Keith Lane for his patience, technical tuition, guidance, and for being the only

person to allow me access to workshop machinery to produce the hardware necessary

for this thesis. The production of the hardware for this thesis would have costed in the

region of $5000 for labour alone. I produced every component described within,

except the SLA restrictor, and the welding on the aluminium manifold. The experience

gained from producing this hardware was, I believe, a valuable part of my education at

the University of Queensland.

• Mr Bill Slack, Mr Colin Beech, Mr Wayne Jenkins, Mr Petar Matanovic, Mr David

Paul, once again for technical assistance throughout the year.

• Professor Richard Morgan for being my thesis supervisor, and being available for

“emergency” consultation.

• Professor Hal Gurgenci for making the Formula SAE project available to students at

the University of Queensland.

• Mr Paul Masterson, from Stafford Tune for his patience, and expert engine tuning.

• Mr Mark Fort, from Cadsoft Solutions, for Solid Edge training and support.


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Contents

1 Formula SAE Design Competition.......................................................................................1

1.1 Vehicle Design Objectives................................................................................................1

1.2 Implications of Manufacturability.....................................................................................1

1.3 Intake System Restrictor Rules.........................................................................................2

1.4 Implications of the Restrictor Inspection Process.............................................................2

1.5 Sound Measurement Rules ...............................................................................................2

1.6 Implications of Sound Measurement Process ...................................................................3

1.7 Fuel System Location Requirements ................................................................................3

1.8 Implications of the Surface Envelope Rules.....................................................................3

2 Literature Review..................................................................................................................4

2.1 Engine Fundamentals........................................................................................................4

2.2 Flows and Flaws ...............................................................................................................5

2.3 Manufacturing and Workshop Principles .........................................................................6

2.4 Truths About High Horsepower........................................................................................7

3 Aims.........................................................................................................................................9

3.1 Design Of Aesthetically Pleasing Hardware.....................................................................9

3.2 Design Of Lightweight Hardware.....................................................................................9

3.3 Design Of Prototype Hardware.......................................................................................10

3.4 Design Of Hardware Using Virtual Models ...................................................................10

3.5 Rigorous Costing Of Hardware ......................................................................................10

3.6 Evaluation Of the Effect Of Throttle Sizing ...................................................................10

3.7 Evaluation Of Plenum Volumes .....................................................................................10

3.8 Evaluation Of Restrictor Nozzles ...................................................................................11

3.9 Design Of Hardware That Facilitates Experiments ........................................................11

4 Overview of Hardware ........................................................................................................12

4.1 Air Filter..........................................................................................................................12

4.1.1 Paper Elements.........................................................................................................13

4.1.2 Cotton Wire Elements..............................................................................................14

4.1.3 Foam Elements.........................................................................................................14

4.1.4 The Air Filter Utilised..............................................................................................15


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4.2 Throttle Body..................................................................................................................15

4.2.1 Modify A Conventional Carburettor........................................................................16

4.2.2 Use An OEM Throttle Body....................................................................................16

4.2.3 Produce A Custom Throttle Body By Casting.........................................................17

4.2.4 Produce A Custom Throttle Body By Using A Removable Plug............................17

4.2.5 Produce A Custom Throttle Body By Machining A Billet......................................17

4.2.6 The Final Design Decision For Manufacturing the Throttle Body..........................18

4.3 Additional Components Of Throttle Assembly ..............................................................19

4.3.1 Butterfly ...................................................................................................................19

4.3.2 Throttle Shaft ...........................................................................................................20

4.3.3 Throttle Shaft Bearings / Bushes .............................................................................21

4.3.4 Return Springs .........................................................................................................21

4.3.5 Cable Linkage ..........................................................................................................21

4.3.6 Idle Speed Control Unit ...........................................................................................22

4.3.7 Brackets and Fasteners.............................................................................................22

4.4 Restrictor.........................................................................................................................23

4.4.1 Typical Restrictor Profiles .......................................................................................24

4.4.2 “Type 4” Restrictor Profile Variables......................................................................25

4.4.3 Requirements Of A Restrictor .................................................................................29

4.4.4 Methods Of Producing A Restrictor ........................................................................29

4.4.5 Mounting The Restrictor..........................................................................................32

4.5 Intake Runners ................................................................................................................33

4.5.1 Cross-Sectional Area Of Runners............................................................................33

4.5.2 Length Of Intake Runners........................................................................................33

4.5.3 Mathematical Model For Determining The Length Of Intake Runners ..................35

4.6 Plenum.............................................................................................................................37

4.6.1 Methods Of Manufacturing A Plenum.....................................................................38

4.6.2 Functional Requirements Of The Plenum................................................................38

4.6.3 Volume Of The Plenum...........................................................................................39

4.6.4 The Combinational Effects Of Runners And Plenums ............................................40

4.6.5 Final Plenum Design................................................................................................40

5 Obtaining High Horsepower...............................................................................................42


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5.1 A Theoretical Design Discussed.....................................................................................42

5.2 Engine Operating Conditions..........................................................................................43

5.3 Manifold Pressure Conditions.........................................................................................44

6 Flowbench Testing ...............................................................................................................47

6.1 Measuring Absolute Mass Flow Rates Through Restrictors ..........................................47

6.2 Typical Flow Bench Testing Techniques .......................................................................47

6.3 Description Of Flowbench Hardware .............................................................................48

6.4 Restrictor Test Without Throttle Bodies.........................................................................49

6.5 Modified Area Ratio Test ...............................................................................................50

6.6 Testing With Air Filters And Throttle Bodies ................................................................51

7 Dynamometer Testing..........................................................................................................52

7.1 Plenum Comparisons ......................................................................................................53

7.2 Final Power Readings With Inertia Correction...............................................................54

7.3 Removal Of Air Cleaner.................................................................................................54

8 Track Testing........................................................................................................................55

9 Conclusions ...........................................................................................................................56

10 Recommendations ..............................................................................................................57

10.1 Developing The Restrictor Geometry Upstream Of The Throat. .................................57

10.2 Developing The Restrictor Geometry Downstream Of The Throat. ............................59

10.3 Developing The Pulse Tuning Mathematical Model....................................................59

10.4 Evaluating The Performance Of Symmetric Plenums ..................................................60

10.5 Computational Fluid Dynamics Studies .......................................................................60

References ...............................................................................................................................61

Appendix A Flowbench Principles...........................................................................................i

Appendix B Error Analysis For Flowbench..........................................................................iii

Appendix C Flow Bench Data..................................................................................................v

Appendix D Dynamometer Results ........................................................................................vi

Appendix E Formula SAE Costing ........................................................................................ix

Appendix F Analytical Model Code ......................................................................................xii

Appendix G Rick's Rules For Solid Edge ...........................................................................xvii


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Table Of Figures

Figure 1-1 Surface Envelope Of Vehicle [1] ..............................................................................3

Figure 2-1 Milling Machine-Required For Building Manifolds.................................................7

Figure 2-2 Toronto 2000 Manifold .............................................................................................8

Figure 3-1 Unattractive Hardware ..............................................................................................9

Figure 4-1 Paper Air Filter........................................................................................................13

Figure 4-2 K&N Air Filters [6].................................................................................................14

Figure 4-3 Typical Foam Air Filter ..........................................................................................15

Figure 4-4 RIT's One Piece Design ..........................................................................................17

Figure 4-5 Final CAD Design Of Throttle Body......................................................................18

Figure 4-6 Throttle Shaft Design..............................................................................................21

Figure 4-7 Throttle Assembly...................................................................................................23

Figure 4-8 Typical Restrictor Profiles......................................................................................24

Figure 4-9 Type 4 Restrictor Variables ....................................................................................26

Figure 4-10 Type 4 Design Variables.......................................................................................28

Figure 4-11 A Long CF Restrictor............................................................................................30

Figure 4-12 CAD Image Of Final Restrictor Design................................................................32

Figure 4-13 Typical Plenum Configurations ............................................................................37

Figure 4-14 Cut-away View Of Manifold ................................................................................41

Figure 4-15 Inlet Manifold Installed.........................................................................................41

Figure 5-1 Theoretical Design Visualised ................................................................................42

Figure 5-2 Comparison Of Theoretical And Actual Design.....................................................43

Figure 5-3 Throttle Position For One Lap ................................................................................43

Figure 5-4 RPM Map................................................................................................................44

Figure 5-5 ISO 9300 Required Back Pressure Ratios [8].........................................................45

Figure 5-6 Data Representing Flow Conditions In Plenum [12]..............................................46

Figure 6-1 Comparison Of 2001 And 2002 Geometry.............................................................49

Figure 6-2 Modified Area Ratio Geometries (2002 Device)....................................................50

Figure 7-1 Engine At Dynamometer Testing............................................................................52

Figure 7-2 Plenum Comparison................................................................................................53

Figure 8-1 Fir st Track Testing..................................................................................................55


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Figure 10-1 Envisioned Performance Curves...........................................................................58

Figure 10-2 Upstream Restrictor Geometries...........................................................................58

Figure 10-3 Downstream Restrictor Geometries......................................................................59


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1 Formula SAE Design Competition

1.1 Vehicle Design Objectives

“For the purpose of this competition, the students are to assume that a manufacturing firm has

engaged them to produce a prototype car for evaluation as a production item. The intended

sales market is the non-professional weekend autocross racer.

Therefore, the car must have very high performance in terms of its acceleration, braking, and

handling qualities. The car must be low in cost, easy to maintain, and reliable. In addition, the

car's marketability is enhanced by other factors such as aesthetics, comfort, and use of

common parts.

The manufacturing firm is planning to produce four (4) cars per day for a limited production

run and the prototype vehicle should actually cost below $25,000 (US). The challenge to the

design team is to design and fabricate a prototype car that best meets these goals and intents.

Each design will be compared and judged with other competing designs to determine the best

overall car.” [1]

1.2 Implications of Manufacturability

The components used in the manufacture of an inlet manifold are indeed difficult to produce.

More specifically, it is difficult to produce prototype components that represent a production

item.

Many teams ignore the importance of the manufacturability of their vehicles. The temptation

is to regard horsepower as the ultimate goal of their manifold designs. Inevitably, some teams

design hardware that is extremely difficult to produce. In some instances teams produce

components that are cheap and simple, which may be unsightly or impractical for lean

manufacture.

It must be understood that the hardware produced in this thesis is a serious attempt of

prototyping. It must also be understood that the overall horsepower figures obtained by the


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engine were affected by design decisions made for ease of manufacture, repair, serviceability,

and the limited technical skills of the designer.

Future designers may indeed view these decisions as being weighted too heavily toward

design, and move toward producing more complex prototypes that could certainly yield

higher overall horsepower figures. Future designers may also regard the overall mass of the

design to be more critical, and seek other design options.

1.3 Intake System Restrictor Rules

“In order to limit the power capability from the engine, a single circular restrictor must be

placed in the intake system between the throttle and the engine and all engine airflow must

pass through the restrictor. Any device that has the ability to throttle the engine downstream

of the restrictor is prohibited. The diameter of the restrictor must be no larger than 20.0 mm

(0.7874 inch) for gasoline fuelled cars. The restrictor must be located to facilitate

measurement during the inspection process.” [1]

1.4 Implications of the Restrictor Inspection Process

It is wise to design a restrictor that may be quickly removed and measured during a

competition. It is also wise to consider that a production item would include this same feature

for the “weekend non-professional autocross racer”. The inspection of the throat may be

carried out a number of times throughout the competition.

1.5 Sound Measurement Rules

“All cars must pass the sound test before competing in any dynamic event. The sound level

will be measured during a static test. Measurements will be made at 0.5 m from the end of the

exhaust outlet with the microphone at the exhaust outlet level, at an angle of 45° with the

outlet in the horizontal plane. Where more than one exhaust outlet is present, the test will be

repeated for each exhaust.” [1]


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1.6 Implications of Sound Measurement Process

The intake system will produce considerable sound levels. The total sound level depends on

the design of the intake, and most importantly the type of air filter used. The location and

direction of the inlet manifold may cause a vehicle to fail a sound measurement test.

1.7 Fuel System Location Requirements

“In order to prevent hazards in the case of a roll-over or collision, all parts of the fuel storage

and supply system, and all parts of the engine air and fuel control systems (including the

throttle or carburettor, and the complete air intake system, including the air cleaner and any

air boxes) must lie within the surface defined by the top of the roll bar and the outside edge of

the four tires.” [1]

Figure 1-1 Surface Envelope Of Vehicle [1]

1.8 Implications of the Surface Envelope Rules

It is extremely difficult to design an inlet manifold to fit within the surface envelope of the

vehicle. The length of the restrictor is a typical problem. An obvious solution is to position the

restrictor at some distance from the intake runners or at a significant angle to the intake

runners. The conduits routing flow from the restrictor to the plenum and runners increase the

total plenum volume.

It is important to finalise, or at least formulate specific constraints for the position of the

engine, wheels, and main roll hoop, prior to designing an inlet manifold for a formula SAE

vehicle.


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2 Literature Review

2.1 Engine Fundamentals

It is important to understand the very basic principles behind modern engines. Understanding

the hardware involved with an engine and practicalities of engine remanufacture or redesign is

a must.

The ACL Engine [2] Manual is one of the most thorough and up to date references covering

the remanufacture of modern engines. This book covers the functional performance of every

component in the engine. It even covers gaskets, seals, bearings, cooling systems, oil systems,

and a variety of engine management systems. The ACL engine manual is written from the

perspective of the engine reconditioner, and is a standard reference for any engineer

attempting modifications.

There are a number of texts that specifically cover engine performance modifications. S-A

Design Books publish a performance manual for most makes of V8 racing engine. A notable

book from this series is How To Build Horsepower [3]. This book covers the process of

performance engine modification in the general sense, without listing specific occurrences on

specific engines. The book covers a variety of engine management systems, flow bench

testing, and dynamometer testing, along with the usual guide through cylinder head porting,

camshaft profiles, and valve face geometries.

A comprehensive guide to engine managements systems is The Gregory’s EFI and Engine

Management Manual [4]. This manual has an opening chapter that details the design and

function of nearly every component used in a modern engine management system.

The Motec website www.motec.com.au [5] covers, in a reasonable amount of detail, the

capabilities of their aftermarket engine control units (ECU’s). The software that Motec uses

and engine wiring diagrams are available for download. A Motec training manual [6] is the

next step in understanding the practicalities of aftermarket ECU’s. The training manual covers

the supported hardware and the engine start-up procedure in a logical manner.


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2.2 Flows and Flaws

The design of a formula SAE inlet manifold includes a mandatory flow restriction device.

This device, to be termed “the restrictor” throughout this report, is the primary source of

horsepower limitation. The design of a successful restrictor will affect high peak horsepower

outputs from the engine.

When considering the flow through restrictors, an excellent place to start learning is by

viewing Flow Patterns In Venturis Nozzles and Orifices [7]. This film is part of an

educational series about fluid flows. It is commonly shown to undergraduate engineering

students. The experiments use smoke and ink visualisations. Runstadler and Kline produced

the film at Stanford University in 1966. Even today it stands as an excellent educational

resource.

The standard ISO 9300 [8] details discharge coefficients and designs of conduits upstream

and in the proximity of the throat, for choked flow operation of industrial sonic nozzles. A

journal article that is extremely useful when considering a test methodology for evaluation of

sonic nozzles is ‘Preliminary Considerations In The Use Of Industrial Sonic Nozzles’ [9].

It will be shown in section 5 of this report that the speed at which the engine produces peak

horsepower does not, in fact, cause choked flow through the restrictor. The successful design

of conduits downstream of the throat will lower the non-recoverable losses and increase the

horsepower of the engine.

The flow from the throat is through a diffuser. The Diffuser Data Handbook [10] is a

publication that details turbulent flow discharge coefficients through various diffuser

geometries. A series of performance charts is given for known upstream geometries and

Reynolds numbers.

An obvious problem with analysing empirical data for diffusers is that the flow conditions

upstream of the throat may vary with downstream pressure, and are unknown. Restrictors

should be evaluated with the throttle and air cleaner in place, to create the actual upstream

flow conditions.


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An undergraduate thesis titled Flow Analysis of Three Different Engine Intake Restrictors

[12] includes experimental data from dynamometer testing of a Honda CBR 600 F3 engine.

The experimental data of note is an engine ramp with values of shaft horsepower, mass flow

rate, and absolute plenum pressure; VS engine speed.

The most appropriate resource for choosing an aftermarket air filter is the K&N website at

www.knfilters.com [13]. The superflow website at www.superflow.com [14] outlines the

fundamental principles behind flow bench testing. This site should be viewed, perhaps along

with superflow operator’s manual, before considering an experimental evaluation of restrictor

nozzles using a flowbench. Superflow outline a number of theories concerning what test

pressure should be used to evaluate an inlet manifold.

A flowbench will usually make use of Pitot pressure probes, or orifice plates to determine the

mass flow rate found at a given test pressure. The design of Pitot probes is outlined in

standard ISO 3966 [15], and the design of orifice plates by standard AS 2360 [16].

2.3 Manufacturing and Workshop Principles

It is mush easier to formulate inlet manifold profiles and conduits, than it is to actually design

and construct them. The 3 dimensional CAD assemblies produced for this design, using Solid

Edge, are quite difficult to generate. Rick’s Rules for Robustness in Solid Edge (Appendix G)

is a great guide when attempting solid models that update with significant design changes.

It is essential that the inlet manifold designer understands the fundamentals of rapid

prototyping, design for limited production, and that they possess a considerable amount of

technical skill and experience. Technical skill and experience usually comes with time and

exposure, but any standard trade training text will be invaluable when considering a feasible

design. An excellent material properties resource is available online at

www.matweb.com/search/searchsubcat.asp [17]. Detailed information about rapid

prototyping techniques such as selective laser sintering (SLS) and stereo lithography (SLA)

can be found online at www.3dsystems.com [18].


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Figure 2-1 Milling Machine-Required For Building Manifolds

2.4 Truths About High Horsepower

There does not seem to be any publicly available studies with empirical data for engine

restrictor geometries. In fact there is very little reliable data about any aspect of inlet manifold

design.

A notable publication is Dynamic Inlet Pressure and Volumetric Efficiency of Four Cycle

Four Cylinder Engine [19]. Ohata and Ishida [19] present a theoretical model of the pulse

pressure tuning effect. The study then details a series of experiments using solid-state pressure

transducers, placed in the inlet manifold, to validate the theoretical model.

The design of a successful inlet manifold could be justified by peak horsepower results. In

fact, the design of a successful inlet manifold for a formula SAE vehicle, seeks to maximise

the integral of power available from an engine, over a range of engine speeds, at such times

the throttle plate is in the wide open throttle (WOT) position during racing. The design must

be practical, aesthetically pleasing, and easily manufactured.


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For those who concern themselves solely with dynamometer peak horsepower readings, there

are only a few notably reliable figures. Each year, at the formula SAE competition held in

Detroit, Dynojet Research Ltd makes available a chassis dynamometer for competitors.

The highest horsepower reading ever taken by this test, for a naturally aspirated engine, was at

the 2000 formula SAE competition. The vehicle was the naturally aspirated Toronto

university entrant. The reading taken was 80 bhp (at the rear wheels). The Toronto vehicle

then went on to be placed 6th in the acceleration event, and 12th in the enduro. This vehicle

used M85 fuel, a “v-type” plenum with straight runners (see section 4 of this report for an

explanation of these terms), 13:1 compression ratio, an exceptionally long intake restrictor,

and had a significantly large plenum volume [20].

At the 2001 competition, the naturally aspirated Ecole de Technologie Superieure entrant

produced 79 bhp @ 12 000 RPM. This vehicle also used M85 fuel, a “v-type” plenum,

straight runners, an exceptionally long intake restrictor, and had a significantly large plenum

volume. Ecole de Technologie Superieure then went on to get a DNC in the acceleration event

and be placed 12th in the enduro [20].

At the 2002 competition, the naturally aspirated Rutgers entrant produced 79 bhp. This

vehicle again used M85 fuel, a “v-type” plenum, straight runners, an exceptionally long intake

restrictor, and had a significantly large plenum volume. Rutgers then went on to be placed

83rd in the acceleration event and 14th in the enduro [20].

Figure 2-2 Toronto 2000 Manifold


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3 AimsThe main aims of thesis are design and manufacture of hardware that addresses all aspects of

the formula SAE design rules. The hardware used is designed to facilitate a number of future

experimental studies.

3.1 Design Of Aesthetically Pleasing Hardware

Prototype hardware used in formula SAE inlet manifolds is undoubtedly difficult to

manufacture. Many formula SAE teams design and construct inlet manifolds that function

extremely well, but are certainly not aesthetically pleasing. It was an aim to produce

components that were both functional and attractive.

Figure 3-1 Unattractive Hardware

3.2 Design Of Lightweight Hardware

The previous University of Queensland formula SAE entrant was felt to be significantly

overweight. It was an aim this year for all subsystems on the vehicle to be lighter. The inlet

manifold mass was reduced from 6.2 kg to 2.2 kg. Some of the steps taken to ensure this were

extreme. An example is obtaining aluminium tubing from an overseas supplier, so as that

mandrel bending could be performed.


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3.3 Design Of Prototype Hardware

The previous year’s vehicle was criticised openly by design judges for not being a viable

commercial product. The hardware designed for this year’s vehicle is a serious attempt of

prototyping.

Although the conduits used for this design are in fact very similar to those used last year, the

methods of manufacture are completely different.

Rapid prototyping was used to represent a viable commercial product that is produced by a

different rapid prototyping method.

3.4 Design Of Hardware Using Virtual Models

Every component for this system was design accurately using virtual models. The information

should serve as a resource for future works. Manufacturing flaws have been added to the

virtual models. Drafts are not presented with this report. Instead, a copy of the generic CAD

and a parasolid conversion is included.

3.5 Rigorous Costing Of Hardware

Every component manufactured is rigorously costed as per the formula SAE competition

rules. A database was built for this process, and for the benefit of other team members.

3.6 Evaluation Of the Effect Of Throttle Sizing

The size of the throttle body was deliberately reduced. The effect of a smaller throttle body

was evident during track testing. The performance of the throttle was also evaluated using

flowbench testing and dynamometer testing.

3.7 Evaluation Of Plenum Volumes

The plenum volume was significantly reduced so as to note the effects. The plenum volume

was evaluated by dynamometer testing, and by track testing.


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3.8 Evaluation Of Restrictor Nozzles

The evaluation of small design changes to restrictor nozzles was performed using flow bench

testing.

3.9 Design Of Hardware That Facilitates Experiments

The throttle body was designed to facilitate a further study of restrictor geometries. The use of

a screw thread allows smaller (hence less costly) rapid prototype restrictor profiles to be

made. The plenum and runner geometries were designed in the hope of providing a better

platform for conducting an experimental camshaft development program.


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4 Overview of Hardware

4.1 Air Filter

The primary function of an air filter is to prevent solid particles entering an engine. If this

happens, destructive abrasive wear, or scoring, may result upon the cylinder liners, pistons,

and piston rings. This eventually leads to a loss of combustion pressure and hence

performance [2].

Scoring of these components may lead to excessive “blow-by”, a condition where combustion

gasses enter the crankcase of the engine. Every engine experiences some level of blow-by

[2,3]. In fact the level of blow by can vary greatly between new engines manufactured using

the same processes. The initial level of blow-by is primarily affected by clearances between

the piston and cylinder liner, the surface finish of the cylinder liner, design of the piston ring,

and by the level of cleanliness employed with the assembly of the individual engine [2].

The secondary functional requirement of an air filter is to not restrict the flow of air to an

engine. Obviously, for a filter to actually provide filtration, some restriction is inevitable [13].

Reliable data describing the performance of air filters is extremely difficult to find.

Aftermarket manufacturers typically appeal to the “performance enthusiast”, and it is with

little wonder that their claims cannot be considered reliable.

Air filters used in production vehicles may have additional functional requirements such as:

[2,3]

• Provide an acceptable level of engine silencing.

• Ease of service.

• Reduce throttle shaft icing.

• Be resistant to excessive fuel vapour caused by reversion.

• Be resistant to “sneezing”, a condition where combustion gasses reach the intake tract

under high pressure.


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• Be resistant to “backfire”, when vapour is actually being ignited in the inlet manifold.

When designing an inlet manifold for a formula SAE vehicle, it is important to not cause

significant pressure drop due to a restrictive air filter. Most racing vehicles overcome this

possibility by installing the largest unit that can be fit within the vehicle [13]. Unfortunately a

formula SAE vehicle relies on being very small and light, and the air filter must be placed

within the surface envelope [1]. For this reason it is obvious that a small unit should be

chosen and be subsequently tested for its performance using both a flow bench and engine

dynamometer [2,3,21].

The three main types of air filter elements are: [3]

• Paper Elements

• Cotton / Wire Elements

• Foam Elements

4.1.1 Paper Elements

These are typical for OEM applications. The paper element does not require maintenance and

is replaced at regular intervals. Paper elements are generally used to comply with additional

requirements that need be satisfied in OEM applications.

Figure 4-1 Paper Air Filter


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4.1.2 Cotton Wire Elements

These are generally considered to be the best option in a “performance” application. The

cotton element is cleaned in a solution at regular intervals. The element is then oiled before

re-use. The notable manufacture of cotton / wire elements is K&N engineering. It may also be

noted that this manufacturer employs a very effective advertising campaign.

Figure 4-2 K&N Air Filters [6]

4.1.3 Foam Elements

These units are also considered to be excellent for “performance” applications. The foam

element requires cleaning and oiling at regular intervals. Some critics suggest that for given

levels of filtration, the foam element is more restrictive than a cotton / wire element. It should

be noted that foam elements do not provide resistance to “backfire”. Because the inlet

manifold will employ multi-point fuel injection at a location near the intake valves, a

relatively large plenum, and a restrictor; it is somewhat unlikely that the filter element will

experience a “backfire”.


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Figure 4-3 Typical Foam Air Filter

4.1.4 The Air Filter Utilised

The air filter chosen for this design was a small K&N air filter. Model number RC 2440

4.2 Throttle Body

A throttle is a device used to control the power output of a spark ignition engine. Because the

engine will employ multi point fuel injection, the throttle is simply a throttle body, as distinct

to a carburettor.

Requirements for a formula SAE throttle body are:

• The unit should be lightweight

• The unit should be easy to manufacture

• The unit should represent a prototype of a unit used in a lean manufacture, as per the

formula SAE manufacturing concepts

• The unit should not produce excessive pressure loss at wide-open throttle (WOT)

conditions

• The unit should have simple linkages and brackets for attaching a throttle cable

• The unit must use two (2) throttle position return springs, so that failure of any

component will not cause the throttle plate to be stuck open [1]

• The unit should actuate smoothly


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• The unit should ideally provide progressive actuation to enable greater control at part

throttle conditions (this is very important when using a “performance” throttle)

• The unit should ideally employ an idle speed control unit (ISCU). An ISCU is

basically a solenoid which controls throttle by-pass air through a passage in the body

of the throttle. The air is diverted around the throttle plate. The solenoid is operated by

the ECU by means of pulse width modulation, and is used to control idle speed at all

operating conditions [4].

The five main methods of manufacturing a throttle body are:

• Modify a conventional carburettor

• Use an OEM throttle body

• Produce a custom throttle body by casting the body of the throttle

• Produce a custom throttle body by making a removable plug and laying composite

sheeting to form the body of the throttle

• Produce a custom throttle body by machining the body of the throttle from a billet

The merits of each manufacturing method are discussed briefly.

4.2.1 Modify A Conventional Carburettor

Carburettors typically employ a number of subsystems that would need be modified and made

redundant. The modification of a carburettor is by no means simple, and the attachment of a

TPS is somewhat difficult. Sourcing an adequate unit requires a time consuming search of

automotive or motorcycle wrecking yards. A typical carburettor may not employ two throttle

return springs, and the modification to achieve this may be significant. The redundant systems

of a carburettor typically cause the unit to be large and heavy. This method of manufacture

could certainly not be considered appropriate within the lean manufacturing context of the

competition.

4.2.2 Use An OEM Throttle Body

This is an attractive solution, because an OEM unit certainly has only the systems required for

the application. The difficulty is that few OEM units use small throttle valves. One rarely


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available unit, used on the Ford Ka, has a 33 mm bore. This unit that is extremely difficult to

find. The unit will cost upwards of $600 from a wrecking yard, and its commercial value is

around $1500. It may be possible to use an OEM unit from a modern motorcycle. A

motorcycle throttle body is also quite expensive.

4.2.3 Produce A Custom Throttle Body By Casting

This is by far the most appropriate way to produce a unit that is acceptable for lean

manufacturing methods. The major problem is the high cost involved with producing one

unit. A cast unit still requires quite an amount of machining. The result is a unit that perfectly

satisfies requirements, and is by far lighter than any other method.

4.2.4 Produce A Custom Throttle Body By Using A Removable Plug

This method of manufacture is used to make units that have the throttle and restrictor moulded

as one. The method produces a very lightweight device. The complexity and cost of

manufacturing a removable plug is high. It was considered an extremely time consuming

exercise. The overall cost of this method would be quite low if a student had the technical

ability to produce the plugs.

Figure 4-4 RIT's One Piece Design

4.2.5 Produce A Custom Throttle Body By Machining A Billet

This method will produce a unit that will satisfy all functional requirements. The actual

design process is quite simple. The material costs are low, but the prototype machining costs


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are relatively high. The unit will be necessarily heavier than a cast unit. A throttle

manufactured from a billet has an exceptional visual appeal. Production of a billet throttle

body in lean manufacture was seen to be feasible if machining operations were kept to a

minimum.

4.2.6 The Final Design Decision For Manufacturing the Throttle Body

The decision was made to produce a custom unit by machining the body of the throttle from a

billet. The cost of the aluminium billet was $80, and I personally performed every machining

operation. The body of the throttle was machined from a bar of 2030 T5 aluminium alloy. The

body uses a screw type fitting to attach the restrictor; the justification of this is explained

within the description of the restrictor. The design of the body seeks to minimise weight, and

minimise the number of machine operations used.

The major design decision is weather to resist axial motion of the throttle shaft by allowing

the throttle plate to rub against the body of the throttle; or to locate the shaft axially by use of

another method. By allowing the throttle plate to rub against the body, friction is introduced

to the actuation; and the risk of a sticking throttle plate is increased. The wear of the throttle

body may also cause the throttle shaft to display excessive axial play at an early stage in the

operating life. The positive benefits of allowing the throttle plate to retain axial movement of

the shaft are a simpler and less costly device. OEM devices do not allow the throttle plate to

contact the body. A decision to not allow the throttle plate to contact the throttle body was

made in the interest of safety, and longevity of the unit.

Figure 4-5 Final CAD Design Of Throttle Body


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4.3 Additional Components Of Throttle Assembly

The additional components of a throttle assembly include:

• Butterfly

• Butterfly retaining screws

• Throttle shaft

• Throttle shaft bearings / bushes

• A linkage which transfers the linear cable motion to rotational motion of the throttle

shaft

• Idle speed screw

• TPS

• Return springs, (2) off

• Cable Linkage

• Idle speed control unit (ISCU)

• Brackets and Fasteners

4.3.1 Butterfly

The size of the butterfly valve is a critical decision made in the design process. If the butterfly

valve is too large, it will be difficult to control the power output of the engine. The butterfly

used on last year’s formula SAE entry was is fact far too large. The unit was 46 mm in

diameter. Those who have driven the previous formula SAE entrant have described the

throttle response as “digital”. The vehicle experienced quite high fuel consumption, and this

may be attributed to the throttle valve being too big.

If the butterfly valve is too small, excessive pressure loss will occur at WOT operating

conditions, causing a reduced maximum power level. Only two references have been found

which outline the optimal size of a butterfly valve.

The Delphi Automotive Group suggests that for typical OEM applications the maximum

velocity of air passing by a throttle valve should be 90 ms-1. It is obvious that OEM

applications sacrifice the maximum available power level to ensure the vehicle is easy to


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drive, due to adequate control at part throttle operating conditions. A small throttle ensures

lower fuel consumption figures, because the operator is not inclined to affect unnecessarily

open throttle positions when depressing the accelerator pedal.

HP Books [21] publish a guide for venturi and throttle valve sizing for “performance”

applications. These tables refer to racing engines. The maximum velocity of air passing by a

throttle valve in these applications is between 50 - 60 ms-1.

The decision was made to try and affect maximum flow velocities of 50 ms-1. A decision had

to be made considering the likely output of this year’s engine, and the volumetric flow rate

through the throttle. The output of this year’s engine was precursively estimated to be 55 kW

at 10000 rpm, with a volumetric flow rate of 0.045 m3s-1 across the throttle valve. The ideal

throttle plate size was then found to be 34 mm. A 34 mm butterfly valve was purchased from

an aftermarket supplier.

4.3.2 Throttle Shaft

OEM applications typically call for the use of a hardened steel throttle shaft. This is a costly

component to make for a single unit, and the advantage of decreased wear was not considered

appropriate for the life of the throttle assembly. The other suitable materials for manufacture

are brass and mild steel.

Mild steel has the advantage of being stiffer and stronger per unit mass than brass. The

advantage of using brass is that readily available “free-machining” brass is harder than mild

steel, and the fine surface finishes required for a bearing are easier to generate. Brass is

machined without the use of a coolant. The complex machining operations are easier to

perform without a coolant.

A throttle shaft was manufactured from brass due to its higher hardness; better wear

resistance, ease of manufacture, and minimal material cost.

The throttle shaft features a half-cylindrical design for decreased flow losses. This design

would unlikely be used in lean manufacture. The shape is considerably more difficult to


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produce. It is unlikely a design judge will notice the half-cylindrical shaft design, but it is

certainly worth noting its production to the performance enthusiast.

Figure 4-6 Throttle Shaft Design

4.3.3 Throttle Shaft Bearings / Bushes

Deep groove roller bearings, or Teflon bushes are required for the interface between the shaft

and body of the throttle. Bearings have the advantage of requiring less width than a Teflon

bush to locate the shaft. A bearing can also be used to axially locate the throttle shaft.

Bearings provide marginally less friction than Teflon bushes, and suffer less from premature

wear. The advantage of Teflon bushes is the ease of manufacture.

Typical OEM devices use bearings, and the use of Teflon bushes is usually only condoned

during remanufacture of a throttle body.

Bearings were chosen on the basis of retaining axial movement of the throttle shaft more

easily, and providing a lighter and more compact overall design.

4.3.4 Return Springs

Throttle shaft return springs can be either linear or torsional springs. Linear springs have the

unfortunate characteristic of loading the throttle shaft with considerable bending, which

causes increased wear of the shaft and bearings. Torsional springs have the advantage of

being more compact. Torsional springs are usually used in OEM applications, and were

chosen for this design.

4.3.5 Cable Linkage

When using a large throttle valve to reduce losses at WOT operating conditions, it is

advisable to employ the use of progressive rate actuation. This is achieved by using a linkage

with an elliptical profile. A progressive rate linkage can be produced by one of 4 methods.


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• Fabricate a linkage

• Use an OEM linkage

• Modify an OEM linkage

• Produce a linkage using rapid prototyping methods

Fabricating a quality linkage could be quite an expensive and time-consuming process, and

this method was instantly disregarded. The use of an OEM linkage with or without

modification was seen as an excellent option, although sourcing an appropriate item would be

a time-consuming and tedious task; requiring someone to literally search through hundreds of

units at a wrecking yard, until one with appropriate size was found. The use of rapid

prototyping methods such as selective laser sintering (SLS) or “quick-cast” aluminium

investment castings is an option for producing exactly the component required. Rapid

prototyping methods are quite inexpensive for such small components.

Because the restrictor was to made using SLS, a linkage was made the same way, at the same

time, for very little additional cost.

A brass linkage, not using an elliptical profile, was also produced from a billet. The brass unit

was produced because of concerns about the strength of the SLS model when loaded against

the throttle body stop. In normal use this should not occur, but during dynamometer testing it

is inevitable.

4.3.6 Idle Speed Control Unit

An idle speed control unit (ISCU) was not included in the design due to its complexity and

cost. The use of an ISCU could be considered a “luxury” for a race vehicle. The device is

really only necessary to create steady idle with a cold engine. An ISCU could be easily added

at a later date, should the need be realized.

4.3.7 Brackets and Fasteners

The brackets and fasteners used were designed with the intention of minimising weight.

Countersunk socket screws were used to retain the throttle plate, the idea was to minimise

losses across the throttle. The throttle cable bracket is easily removed by withdrawing two cap

screws. This facilitates throttle linkage removal.


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Figure 4-7 Throttle Assembly

4.4 Restrictor

The purpose of a restrictor is to limit the power output of an engine, creating a safer form of

motor sport. The restrictor must be placed downstream of the throttle and upstream of any

powered device. “The restrictor must have a maximum of 20 mm diameter circular cross

section. All intake air reaching the engine must pass through the restrictor.” [1].

High flow velocities cause excessive pressure losses. The intake flow must be passed through

a convergent and diverging passage that contains the minimum cross sectional area required

by the competition rules. This type of device is similar to what is commonly known as a


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“critical flow venturi”, “critical nozzle”, or “sonic choke”. Such devices are often used in

process industries as simple mass flow rate control devices. [8,9] Throughout the remainder of

this report all such devices will be referred to as “restrictors”.

Reducing downstream pressure will eventually cause “choked-flow”. Once choked, the mass

flow rate passing through the device is predominantly determined by the upstream pressure

conditions and intake geometries. The geometries downstream of the throat have little effect

on the maximum mass flow rate through the device at choked flow conditions [8].

With rising engine speeds, and decreasing downstream pressures, the maximum power output

from a naturally aspirated engine occurs at some time before choked flow is achieved.

[8,12,14,21]. This will be explained in detail in section 5. We wish to minimise losses both

upstream and downstream of the throat.

4.4.1 Typical Restrictor Profiles

The profile used in a restrictor is typically one of 4 types:

• A parabolic profile (type 1)

• An inlet angle, and an exit angle (type 2)

• An inlet angle, radius, and exit angle (type 3)

• An inlet radius, and exit angle (type 4)

Flow

parabolic profile

inlet angle, exit angle

inlet angle, radius, and exit angle

radius, and exit angle (ISO 9300)

Figure 4-8 Typical Restrictor Profiles


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The parabolic profile has the potential to achieve the least loss. Unfortunately it is the most

difficult profile to produce, and empirical data seems unavailable.

A profile without a radius is the easiest to produce using simple internal machining methods.

Unfortunately this profile will cause excessive separation at the throat causing a significant

pressure loss.

The remaining two profiles are similar in design. They are both somewhat difficult to

produce, but with the radius at the throat, have the potential to yield low losses.

A profile using an inlet radius and exit angle is similar, but by no means the same, to an ISO

9300 restrictor profile [8]. There is significant data available about ISO 9300 designs under

choked operation.

For simplicity’s sake the profile with an inlet angle, radius, and exit angle, will be termed a

type 3 design. The profile with an inlet radius, and exit angle, will be termed a type 4 design.

The previous year’s entry was a type 3 design. This year a type 4 design was used in the hope

that the data from ISO 9300 (although relevant for quite different intake geometries) would

suffice to make a good design decision. It will be shown later that this was probably not a

good decision.

4.4.2 “Type 4” Restrictor Profile Variables

When designing a type 4 profile restrictor, there are five variables to be assigned a value.

• The inlet diameter Di

• The choke diameter D

• The exit diameter De

• The radius R

• The exit angle θ


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D i

R

D D e

Figure 4-9 Type 4 Restrictor Variables

The choke diameter D is 20 mm maximum as defined by the rules. The inlet diameter Di is

necessarily that of the throttle valve, 34 mm.

For ISO 9300 profiles the radius R should be between 1.8D and 2.2D to affect a low

discharge coefficient under choked flow conditions. The radius for the type 4 profile was set

at 2D, the value of R being 40 mm.

To reduce losses across the device, prior to choked flow conditions, the exit angle θ is a

critical dimension. If the exit angle is too small, excessive moody-type pipe loss will occur,

too large an angle will cause excessive separation.

The optimal angles for choked flow conditions, with ISO 9300 profiles, are found using

experimental methods with restrictors necessarily having extremely high dimensional

accuracy, and an extremely smooth surface finish [8,9]. ISO 9300 profiles use an exit angle of

2.5° – 6°.

Charts are available for the design of diffusers [10]. The nature of the upstream flow is

necessary to use empirically based charts for diffusers, and in fact a restrictor is not a diffuser

at all, but we assume the diffusive section of the profile to respond similarly. The nature of the

upstream flow is unknown, and is very likely to vary with downstream pressure.

θ


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It is important to remember that empirically derived data is found using repetitive testing

techniques; on devices with exceptional geometric accuracy, and smooth surface finishes

[8,9,10,11]. The upstream flow conditions are known, or at least within some bound, and the

flow is steady state.

The manufacture of a formula SAE restrictor may not comply with the geometric, and surface

finish specifications used to derive data for such charts.

The flow could certainly not be considered steady state, and the path of the fluid leaving the

restrictor may not be collinear with the centreline of the device, nor in a constant direction.

White [11] makes note of the fact that diffusers (and we might also consider restrictors to

behave similarly) perform best in a state of transitory stall, with a slight amount of separation

and unsteadiness. Increasing the length of a diffuser increases the flow separation, and the

performance of the device. Considerable separation will cause the flow to become quite

unsteady. A diffuser with an acute exit angle may afford greater area ratio (hence length)

before excessive separation will occur. When a thin boundary layer exist within intake flow

conditions, a smaller angle is more suitable for a given area ratio.

A larger exit angle will affect design of a shorter, and less expensive restrictor. A smaller

restrictor significantly decreases the overall plenum volume. A long restrictor also requires

significantly higher strength and stiffness. The effects of fatigue due to any bending moment

must be considered, and the length of the device will increase the bending moment

proportionally. The stiffness of the walls of the device must be high enough to resist collapse

due to yielding or buckling from the internal vacuum at small throttle valve openings (or

thought of as external pressure, whichever way one prefers to think). The wall thickness must

also be great enough to resist yielding caused by high internal pressure encountered when the

engine sneezes.

On the basis of cost and complexity of design, without wishing to sacrifice excessive

amounts of horsepower, a 7° exit angle was precursively estimated as optimal for this design.


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The flow, upon exiting the restrictor, will enter a plenum. The plenum volume is necessarily

large, to accommodate the requirements of the intake runners. At this point the flow will

experience rapid diffusion and can be considered a “submerged exit”. The flow might exhibit

behaviour similar to fully developed turbulent pipe flow, and the loss coefficient for such an

exit is known (k=1). Here we note that using a large exit diameter reduces non-recoverable

losses.

Unfortunately, a large exit diameter (a larger area ratio, requiring a more acute exit angle)

means an exceptionally long restrictor. A long restrictor is difficult and expensive to

manufacture. A very important trade-off is required between cost and difficulty of

manufacture, and that of ultimate power levels of the engine.

An exit dimeter of 34 mm was chosen to affect an 82 mm long restrictor, (with 85 cc total

volume) which should produce a small loss at the submerged exit, and will hopefully not

encounter excessive separation.

34 34

R4 0

7°

82

Figure 4-10 Type 4 Design Variables


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4.4.3 Requirements Of A Restrictor

The basic requirements of the restrictor are described below:

• Act as a passage for air to be passed into an engine

• Exhibit exceptionally high dimensional accuracy, especially at the tangency between

the radius and exit angle [8,9]

• Exhibit a smooth surface finish (Ra<0.3µm, at radius) [8,9]

• Resistance to fatigue due to vibration, especially due to any bending moment applied

to the device

• Be resistant to buckling or yielding due to an internal vacuum

• Be resistant to yielding due to a rapid internal pressure build up, caused by “backfire”

or “sneezing” [21]

• Be resistant to transient exposure of fuel vapour [21]

• Provide mounting points that will ensure sealing at a wide range of operating

pressures, and at a range of temperature between 0° – 75° C [3]

4.4.4 Methods Of Producing A Restrictor

Common methods of producing a restrictor include:

• Internally machine the profile from a billet of metallic alloy

• Internally machine the profile from a billet of polymer

• Produce a two-piece plug and wrap with a composite material

• Injection Moulding

• Wrap a one-piece restrictor and throttle body

• Rapid prototyping solids wrapped with a composite material

The relative merits of each method are discussed briefly.

Internally Machine The Profile From A Billet Of Metallic Alloy

The profile can be machined internally using a metallic alloy, such as 6061 T6 aluminium

alloy. The difficulties encountered with this method are due to the size of the choke. With a

20 mm diameter choke a very small cutting tool is necessary to cut the choke area. By using


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such a small cutting tool, one might experience difficulty with the stiffness of the tool. The

process requires very small and time-consuming cuts. The actual billet of aluminium might

cost somewhere between $30-$500 depending on what geometry is to be produced. For the

geometry already discussed, the cost of a billet of aluminium is about $90. The wall thickness

of the device must be large enough to be rigid, so as to conduct machining. This thickness is

necessarily larger than is functionally required and leads to an excessively heavy device. The

profile required is more appropriately produced by CNC machinery. The cost of CNC set-up

for one job is excessive. It is doubtful that a student will gain access to CNC machinery.

Internally Machine The Profile From A Billet Of Polymer

When machining an internal profile from a billet of polymer, the difficulties encountered are

similar to those found using a metallic alloy. Very few polymers, (the notable exception being

nylon), can be finished by polishing. The swarf produced may cause difficulties.

Produce A Two-Piece Plug And Wrap With A Composite Material

A popular method of producing a restrictor is by using an internal two-piece plug and

manufacturing the device by wrapping with a composite material. The resulting device is

quite stiff and strong for given weight, manufactured reasonably quickly, and exhibits a

smooth surface finish. Polishing can finish most composite resins. The difficulties

encountered with this method are in developing the process of laying the composite material.

The process seams reasonable for lean manufacturing methods, but at the cost of being

somewhat time-consuming to set up. The internal plugs require very accurate machining, and

could be considered costly for a one-off application. The internal plugs would need to be

produced using CNC machinery.

Figure 4-11 A Long CF Restrictor


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Figure 4-11 is an image showing a long carbon fibre restrictor. Interestingly, this profile is

used on a turbo charged vehicle. Perhaps a turbo charged vehicle would not need be

concerned with non-recoverable losses. The absolute mass flow rate should be determined by

the geometry upstream, and near the throat. The turbo charger raises the pressure of the flow.

One must also be sure that the turbo charger does affect steady state flow, or a plenum might

be required.

Injection Moulding

Injection moulding could be considered the ideal way to produce a device for lean

manufacture. The appropriate injection moulding method is known as “bridge tooling”.

Bridge tooling is a rapid prototyping technique that is commonly used for productions runs

for between 500-3000 units. The cost of 1000 units was priced at $7600, but unfortunately,

the cost of tooling is $7000.

Wrap A One-Piece Restrictor And Throttle Body

A method of producing a restrictor is to use an internal plug, wrap the device with a

composite material, and produce the throttle body as part of the restrictor. A few American

formula SAE teams have used this method very successfully. The benefits of this method are

that two functional devices can be produced at once, and that a mounting face between the

devices is not required. This method was seen as the next most ideal way to produce these

devices. The method was also seen as somewhat time consuming and intricate for a first

attempt. If a student could produce the plugs, the method would surely be less costly.

Unfortunately, it was seen that no students would have the technical skill to produce the

plugs. Once again the plugs require the use of CNC machinery.

Rapid Prototyping Solids Wrapped With A Composite Material

Rapid prototyping methods such as selective laser sintering (SLS) and stereo lithography

(SLA) can be used to produce a one-off device quite cheaply and simply. The device is

typically produced with a thin wall, and subsequently wrapped with a composite material.

SLS produces a device with reasonably high dimensional accuracy. The material produced

has similar properties to nylon-6-6 [18]. The beauty of this material is that it can be polished

to obtain an exceptionally smooth surface finish. An SLS model might also be seen as a

prototype for an injection moulded product. For these reasons, an SLS restrictor was

produced.


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4.4.5 Mounting The Restrictor

There are three notable methods of mounting the restrictor:

• A flange with a four or six-bolt radial pattern

• A push-on or interference fit accompanied by a clamp

• A screw type fitting accompanied by a clamp

A flange is the most secure and rigid method for mounting a restrictor. The unfortunate

consequence of a flange is the requirement of larger stock for both the restrictor and throttle.

The machining time for each component is also significantly increased. Most OEM

applications use a rigid flange when the diameter of the throttle valve exceeds 35 mm. [21].

A push-on or interference mounting is typically used for motorcycle carburettors with a small

throttle valve. This requires a flexible interface between the throttle and the restrictor.

A screw type fitting with a clamp was seen as a somewhat novel yet fundamentally secure

way of mounting the restrictor. Care must be taken with the relative alignment of the screw

fittings during production. The benefits of this method are a quickly removable device, and a

smaller and lighter throttle. If the restrictor were to be produced using bridge tooling, screw

type plugs would be manually removed from each device after an injection shot. By using

screw type fittings, the size and cost of a SLS component is considerably reduced. Screw type

fittings were used for this design.

Figure 4-12 CAD Image Of Final Restrictor Design


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4.5 Intake Runners

The design details considered for intake runners are the length and cross section of the

runners, and their packaging with the use of bending.

4.5.1 Cross-Sectional Area Of Runners

The cross sectional area of the intake runners determines the flow velocities within. Higher

velocities will promote better mixing of the air-fuel mixture, and more complete vaporisation

of the fuel particles before entering the combustion chamber [21]. Too small a cross sectional

area will cause high flow velocities and excessive moody pipe losses.

It was found that the standard manifold mounts easily accept piping with 38.1 mm OD and

34.9 mm ID. The cross sectional area of the runners was very close to what is used on the

standard manifold. At 10000 rpm this size of tubing should cause average flow velocities of

52 ms-1, and peak flow velocities of 84 ms-1.

The manifold will employ sequential fuel injection near the inlet valve. It may be argued that

the use of sequential fuel injection does not require as high port velocities to affect adequate

mixing, as does other fuel metering methods [21]. It must be noted that some racing vehicles

find higher power levels resulting from fuel being injected very far upstream in the intake

tract. The theory is that thorough mixing is taking place. It must also be noted that OEM

manufacturers claim that lower fuel consumption and emissions are found by using sequential

injection near the intake valve [2,4]. Here we see a classic engineering design trade-off.

The quantifiable effects of this these trade offs can only be found when evaluating a specific

engine under rigorous dynamometer testing [2]. These kinds of studies are extremely

expensive and far beyond the reach of most educational facilities, let alone formula SAE

teams.

4.5.2 Length Of Intake Runners

With the area of the intake runners chosen, it is then necessary to choose the length of the

pipes. The length of the intake pipes causes a harmonic effect [2,4,19,21]. These effects are


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usually referred to as “pulse tuning”, “pipe tuning”, “acoustic tuning”, or “Helmholtz tuning”.

For the remainder of this report the term “pulse tuning” will be used.

The effects of pulse tuning have been known for some time [21], although its documentation

seems somewhat brief and vague. It is probably reasonable to expect that the results were

being evaluated by engineers quite some time ago, but the publication of results were held

within OEM manufacturers or racing teams.

The first significant and detailed published study of such effects was by Ohata and Ishida

[19]. A series of experiments conducted on a four-cylinder engine used solid-state pressure

transducers and data acquisition devices to quantify results.

At some time during induction, very close to 90°after top dead centre (ATDC) the high piston

velocities cause a rarefactive wave to propagate upstream against the incoming flow. This

wave, upon reaching the end of the intake runner (the end of the runner preferably being

submerged in a suitably large plenum volume), inverts and travels back down the intake tract

as a compression wave.

If the compression wave returns to meet the intake valve at near 15° after bottom dead centre

(ABDC), the pressure of the wave will “pack” the cylinder causing the volumetric efficiency,

and hence power output of the engine, to increase. Ohata and Ishida found that the value of

15° ABDC stayed very near constant for the optimal time for the pressure pulse to return.

This value remained constant over a wide range of engine speeds, camshaft profiles, and

engine sizes.

Ohata and Ishida did not ever determine wether the pulse was generated at exactly 90° ATDC.

They then went on to describe secondary pulses generated due to the geometry of the plenum,

and indeed the whole intake system. It is important to note that the effect of the primary pulse

was most significant. The effects of secondary pulses are only felt at lower engine speeds,

when a reasonably small plenum volume is used.


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The design of this formula SAE manifold is performed by only considering the primary pulse;

as the plenum and restrictor are of considerable volume, which render the secondary pulses

insignificant in the engine operating range.

A mathematical model of the described phenomenon is obviously useful in the design

process. It must be understood that no mathematical model could ever capture all the

necessary variables and physical properties required to accurately predict required runner

lengths. Some models will give a good approximation of the experimentally derived optimal

length, and these will indeed reduce the time required for an engineer to find the correct

runner lengths. It is not uncommon to see formula SAE cars with evidence of intake runners

that have been cut to length several times in the attempt to achieve optimal performance.

Unfortunately this process requires significant dynamometer testing time, and considerable

diligence and patience from the engine developer.

The simplest mathematical models should at least include the effect of the transient flow

velocity within the intake runners as the “pulse” is travelling to and from the end of the

runner. One common method of creating a mathematical model is to write an iterative

program. Such a program can easily include the effects of changes in the cross sectional area

of the intake runners along their length.

4.5.3 Mathematical Model For Determining The Length Of Intake Runners

An analytical mathematical model was constructed for the purposes of this study. Code for the

Maple symbolic manipulation program is presented in Appendix F. Variables can easily be

entered at the start of the worksheet, and results found by running down through the

worksheet, evaluating relationships along the way.

The variables used in the model include:

• Cylinder Bore

• Stroke

• Connecting rod length

• Engine RPM

• Intact tract cross sectional area (a constant)


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• Pulse propagation velocity (a constant)

• The angle (ATDC) when the pulse is produced

• The angle (ABDC) when the pulse is to return to the cylinder

The model seeks to find the optimal runner lengths for a given engine speed. The assumptions

of the model include that the runner cross sectional area is constant. After careful

measurement of the standard intake geometry, this assumption was considered appropriate.

Another assumption is that the pulse propagation speed is constant. This is obviously not the

case. The properties of the gas within the intake runners are changing as a function of time.

The “gas” is not homogeneous throughout the length of the pipe, because fuel is being

injected. The propagation velocity was set at a value of 343 ms-1. The angle for which the

pulse is to return to the cylinder is set at 15° ABDC in accordance with the experimental

results found by Ohata and Ishida.

It is important to note the sensitivity of the model to changes in the input variables. The cross

sectional area of the runners is not a sensitive value. An error of 26% in calculating the area

(%14 error in diameter) will cause a 2.7% error in the length of the runners, which

corresponds to about 200 rpm, difference from 8400 rpm. We can see that the cross-sectional

area of the runners, although a very important part of the model, can be approximated as

constant along the length of the tract without adversely effecting the results.

The model is used as a comparative measure, rather than a definitive guide. For instance, we

know that the standard engine produces pulse-tuning effects near 10500 rpm (the original

pipes are 240 mm long). The pulse propagation angle is set at 98° ATDC. We now predict the

necessary pipe lengths for 8400 rpm. This prediction is 308 mm in length.

The maximum power of the engine is expected to occur at around 10000 rpm, so we seek to

set the pipe lengths to produce maximum torque 8400 rpm. The reason for doing this is

because the integral of power across this rpm range should be maximised.


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2002 Formula SAE VS Stock Bike

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

4000 6000 8000 10000 12000 14000

rpm

FSAE 2002 Nm

FSAE 2002 KW

Stock Bike Nm

Stock Bike Kw

4.6 Plenum

The size and shape of the plenum significantly influences the overall packaging of the inlet

manifold. There are four popular designs of plenums and intake runner configurations. A

verbal description of these configurations is unusual. These are:

• A “common log” manifold with a parallel restrictor

• A “common log” manifold with a perpendicular restrictor

• A “v-type” plenum

• A “symmetric” plenum

Figure 4-13 Typical Plenum Configurations

Primary Pulses


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4.6.1 Methods Of Manufacturing A Plenum

OEM applications typically use one of the two following methods of manufacture:

• Cast aluminium

• Fusible core injection moulding

Both of these methods are far too expensive for a formula SAE team. A common way to

develop inlet manifold designs is by the use of rapid prototyping methods such as SLA and

SLS. Again, the cost of rapid prototypes is far beyond the budget of most formula SAE teams;

unless a university owns a SLS machine, such as American teams Auburn and Drexel.

Most formula SAE teams will use light gauge aluminium or steel sheet and tubing to

construct the plenum.

4.6.2 Functional Requirements Of The Plenum

The basic functional requirements of a plenum include:

• Be suitably stiff and strong to resist stress due to bending moment, and vibration

• Be suitably stiff and strong to resist stress due to internal pressures

• Be resistant to fuel vapour exposure

It is obvious that producing a functional plenum is a fairly simple matter. It will also become

obvious that designing a plenum by regarding the flow within important, is somewhat

complicated. It is necessary to consider the basic effects of some designs. The design points

requiring some discussion include:

• Volume of the plenum

• Proximity of runners at the plenum

• Mitre bends

• Sharp runner inlet radii

• Ability to “tune” pipes

• Equal flow distribution


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4.6.3 Volume Of The Plenum

For this report the “volume” of the plenum will include the volume of the intake tract from the

upstream tip of the runners through to the throttle plate. The optimal volume of the plenum is

impossible to determine. There seems to be very little prior data available concerning the

design of a plenum. There is a few “rules of thumb” that appear in the occasional book or

website, but these values should not be considered appropriate for this design.

It is worthwhile to consider the effects of an excessively small, and excessively large plenum.

An excessively small plenum volume will cause the flow in the restrictor choke to move away

from steady state flow toward a cyclic flow. A cyclic flow condition will lower the overall

power output of the engine. It is foreseeable that the flow in the restrictor choke will always

be, in some form, cyclic. We seek to reduce the amplitude of the varying flow rate to an

acceptable level. It is indeed difficult to quantify what an “acceptable level” is. In fact

knowing the effects will only come from dynamometer testing and the use of pressure

transducers, which is expensive and time consuming.

An excessively large plenum volume, upon rapidly opening the throttle, causes a “delay” or

“lag” in the response from the engine [21]. This was very pronounced on last year’s vehicle.

Last year’s formula SAE vehicle used a plenum volume of 3800 cc. The pressure in the

plenum upon deceleration is typically less than 50 kPa. Once the throttle has opened it will

take a short time before the engine reaches maximum volumetric efficiency.

A computational fluid dynamics (CFD) study of a plenum may indeed yield some quantitative

information about the optimal size. It seems that no specific plenum design could be

accurately modelled by one-dimensional or two-dimensional approximations. It does appear

that a “symmetric” plenum design would be more suitable for such approximations. A full

three-dimensional model of the flow through a plenum may yield answers to the problem of

plenum sizing. But it is probably easier to determine an optimal size experimentally, using a

dynamometer, and by driving the vehicle.


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4.6.4 The Combinational Effects Of Runners And Plenums

Mitre bends will indeed cause significant losses at the intake of the individual runners. A

“common log” arrangement with a small diameter plenum will cause the flow to act similarly

to a mitre bend [21].

The inlet radii of the runners should be sufficiently rounded to reduce losses. A small radius,

6 mm, was added to each runner by using a separate component. These components are

termed “air horns”.

The “tuning” of the runners is achieved by literally cutting the length of the pipes. This can be

performed, and an engine dynamometer used to measure the effects. This process was not

performed due to the cost of dynamometer development time. The tuning is far easier with

straight inlet runners.

A plenum design that is not symmetric will cause some uneven distribution in flow to the

runners. The air/fuel mixture ratio may also be unevenly distributed [21]. It is difficult to

quantify to what extent this will occur. Uneven flow distributions often need be accompanied

by individual fuel metering trim for each cylinder [2,6]. This trimming of the fuel metering

system is a time consuming process, and is best performed with the use of individual exhaust

gas temperature sensors and/or exhaust gas oxygen sensors (“lambda sensors”).

4.6.5 Final Plenum Design

The final design decision was to produce a “symmetric” plenum. Each inlet runner uses the

same bend radius, and angle of bends. Each inlet runner is equally spaced from the centre of

the plenum. The final plenum volume is 970 cc. It is important to note that the formulation of

geometry for such a design is an extremely difficult task. The manufacture is not difficult.

This design was chosen because it was believed that ECU tuning would be quicker and less

costly. It was seen inevitable that “tuning” of the intake runners would not occur. It was

believed that a “symmetric” design would most closely affect equal flow distributions to the

runners. The design better facilitated a camshaft development program. It was hoped that


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information from the camshaft development program would support the mathematical model

for pulse tuning. Unfortunately the data gained from the development program was not useful.

Figure 4-14 Cut-away View Of Manifold

Figure 4-15 Inlet Manifold Installed


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5 Obtaining High Horsepower

5.1 A Theoretical Design Discussed

Consider a case where an engine manifold was designed for a formula SAE vehicle where

horsepower is the ultimate goal. The goal would be to produce, say 80 hp, at 12000 rpm.

A large air filter would be sort. The restrictor might use a shallow outlet angle, perhaps a 3°

outlet angle. The final exit diameter of the restrictor might be 60 mm so as to minimise

sudden expansion loses at the plenum opening, without being long enough to cause excessive

separation. The engine might be disassembled and cylinder head shaved to affect a 13:1

compression ratio. The use of “active” or “fly by wire” throttle control might be necessary to

prevent engine detonation below 12000 rpm.

The volume of the plenum would be very large, say 5 Litres, so as to affect strong primary

pulse tuning. Straight, large diameter runners would be used minimise moody losses. The

runners would be tuned after an exhaustive dynamometer development program.

Figure 5-1 Theoretical Design Visualised

The resulting manifold is very large. There would undoubtedly be significant “lag” at sudden

throttle openings. The restrictor would need to be routed along side the driver or above the

driver’s head, so as to stay within the surface envelope of the vehicle. There would certainly

need to be several support mounts for the manifold. The wall thickness of the conduits needs

be quite thick, and the overall production costs are significant. The inlet assembly would

weigh a considerable amount.


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Figure 5-2 Comparison Of Theoretical And Actual Design

Clearly in order to comply with FSAE regulations while still obtaining high horsepower

figures and minimal lag; a balance between the theoretically optimum designs, and

functionally, needs to be reached.

5.2 Engine Operating Conditions

The formula SAE competition has dynamic performance testing events conducted on an

“autocross” circuit. The racing circuit has many short straights and corners, resulting in an

average vehicle ground speed of near 60 km/h.

When considering the final design it is useful to visualise data that describes the operating

rpm, and throttle position, of the engine.

Figure 5-3 Throttle Position For One Lap


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Figure 5-4 RPM Map

From data acquisition (figures 5-3,5-4), we note that the engine operates across an rpm range

of approximately 2500 rpm at WOT throttle conditions. We also see from a 65 second data

log (which corresponds to one lap of the circuit), that full throttle is reached 20 times, and that

each time the throttle position has come from near closed. This data emphasises the need for a

small throttle, and a moderately sized plenum.

5.3 Manifold Pressure Conditions

The absolute mass flow rate obtainable by a restrictor depends on a number of conditions. It is

important to minimise the losses upstream of the throat. The throttle body size and design,

along with the restriction of the air filter has the potential to significantly reduce engine

power.

The ISO 9300 standard [8] and experimentalists such as Miralles [9], specifically state that the

surface finish and dimensional accuracy of the restrictor, under choked conditions, quite

significantly impacts on the discharge coefficient of the device. It is most important that an

exceptionally smooth surface finish (3µm Ra) [8] should be obtained by manufacture. The

dimensional accuracy of the restrictor, especially the tangency between the radius and the exit

angle, must be high.


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For an ISO 9300 restrictor with an exit diameter of 34 mm (an “area ratio” of 2.9), the

backpressure ratio must fall below 0.88 to cause choked flow, in steady state operation.

Figure 5-5 ISO 9300 Required Back Pressure Ratios [8]

An engine will typically not reach the pressure that causes choking until a higher rpm than

where maximum power is reached. With increasing engine rpm, and the restrictor approaches

a choked state [12,21]. The downstream pressure will fall, and affect very little increase in

mass flow rate. The engine needs to expend a significant amount of energy to drive the flow

across the restrictor and manifold. With the onset of choking and rising engine rpm, the

volumetric flow rate is increasing and the density and pressure of the flow reaching the engine

is reducing. The reduced pressure of the flow reaching the engine causes a reduction in

volumetric efficiency, and hence a reduction in effective compression ratio, combustion

pressure, and thermal efficiency. This is the reason a naturally aspirated restrictor engine can

benefit from an increased compression ratio (although it creates the danger of detonation at

lower engine speeds).

The net result is that power levels of the engine are reducing at some time before choked flow

is achieved. It seems obvious that we should achieve small losses at mass flow rates below the

choked state. Efficient flow downstream of the throat will affect higher horsepower readings.

This is due to increased volumetric efficiency for a given mass flow rate.


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A study performed by RIT [12] suggests that average plenum pressures of 94 kPa affect the

maximum horsepower from their engine. The actual figure of absolute plenum pressure at

maximum horsepower may vary considerably with changed manifold designs; different exit

diameters of the restrictor, and minor losses downstream of the plenum should produce the

most significant effects. Reducing the minor losses through the cylinder head (port and

polish) may improve horsepower a little.

An obvious goal is to model the flow as steady state, and either conduct flow bench testing, or

computational studies, at a certain downstream pressure. It might be very difficult,

considering the design of any plenum and restrictor, to state a pressure in the plenum that

causes maximum power output.

Steady state representation of flows from the restrictor to the plenum may be flawed by

another problem. The flow from the restrictor might not be collinear to the centre line of the

restrictor, and the actual direction of flow might vary considerably with time. The result is

that flow bench testing might not yield results that are representative of the flows produced by

the chaotic conditions in a plenum.

Figure 5-6 Data Representing Flow Conditions In Plenum [12]


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6 Flowbench TestingA flowbench is a typical tool, used by performance engine builders, to analyse the

performance of cylinder heads. A somewhat unusual flowbench was constructed for this

thesis. The flow bench was used to measure the performance of the air filter, throttle

assembly, and restrictor only.

6.1 Measuring Absolute Mass Flow Rates Through Restrictors

It would be advantageous to measure the maximum obtainable mass flow rate through the

restrictor. Unfortunately, this type of measurement requires a very large and expensive

blower. The blower required needs power from a three-phase electric motor. There are not

any readily available blowers of this capacity within the department, and the cost of

purchasing one unit might exceed $4000.

As explained previously, measurement of maximum mass flow rate through restrictors

certainly does not provide information about the maximum power that can be obtained from

an engine. It only serves to give information about the efficiency of the design of conduits in

the close proximity, and upstream of the throat.

It would, although, be advantageous to have a blower that had the capability to produce

choked flow. Components could be then tested at both maximum mass flow rate, and at a

series of reduced downstream pressures. The performance of features of the restrictor, both

upstream and downstream of the throat, could then be more easily distinguished.

6.2 Typical Flow Bench Testing Techniques

Typical flow bench testing in industry is conducted at a standardised downstream test

pressure. Modifications are then made to the manifolds, and are subsequently tested in the

same manner. The choice of downstream pressures varies between operators, and might

depend on exactly which components are being tested. Obviously the choice of test pressures

is limited by the power of the blower available to the operator [14]. Typical flow bench

testing techniques do not seek to achieve choked flow.


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A typical commercial flow bench uses manometers across an orifice plate, to measure the

mass flow rate (usually expressed as CFM @ STP) at a given test pressure. A cylinder head,

or a number of cylinder heads, once tested, can then be run on a calibrated dynamometer. The

readings from the dynamometer can then be correlated with mass flow rate results, for a given

test pressure on a given flow bench.

Commercial flow bench units may be supplied with a series of charts that attempt to relate the

mass flow rate through a cylinder head at a given flow bench test pressure, with expected

dynamometer results.

6.3 Description Of Flowbench Hardware

A flowbench was constructed to specifically evaluate the performance of the air filter, throttle

assembly, and restrictor. The flowbench was constructed with geometry to try and mimic the

flow from the restrictor into a symmetric plenum. The flowbench uses a stagnation pressure

probe, and a static pressure probe (“wall tapping”) to determine the peak velocity,

downstream, through a 27.5 mm internal diameter pipe. The pipe has a very rough (corroded

galvanised iron) internal surface finish, and is of sufficient length at ensure fully developed

turbulent flow at the pressure probes. By assuming fully developed turbulent flow, we can

also assume a reasonably consistent velocity profile through the pipe over a small range of

Reynolds numbers.

Pitot probes were chosen over an orifice plate so as to reduce the required power of the

vacuum unit, and hence increase the available test pressure. Manometers were favoured over

differential pressure transducers, to reduce error modes, and so that the device could be used

again without the need for sourcing additional hardware (except a source of vacuum).

It must be stressed that this testing device could never accurately measure the true mass flow

rate through the manifolds tested. It is also important to realize that error analysis for the true

mass flow rate is impossible to formulate.


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The device does provide a very accurate comparison of mass flow rates at a given

downstream (plenum) test pressure. The error analysis for the comparison is easily performed

and yields very encouraging results.

The available blower limits the choice of downstream test pressure. An industrial vacuum

cleaner was borrowed to be the source of vacuum. All testing was conducted at 250 mm of

water, corresponding to absolute plenum pressures near 99.1 kPa.

The temperature of the flow near the Pitot probes was not measured using a stagnant air

temperature probe. Instead, the ambient air temperature was used. It is assumed that this

method did not cause significant error.

6.4 Restrictor Test Without Throttle Bodies

The first flow bench test was a comparison between the current restrictor profile and the

profile used in last year’s entry. Both profiles exhibit a smooth surface finish. The old profile

can be seen to display a slight mismatch at the tangency between the radius and exit angle.

Fittings were used to bring the flow to the restrictors.

Figure 6-1 Comparison Of 2001 And 2002 Geometry

Both units displayed some level of unsteady stall. This is obvious due to a fluctuating

downstream (test) pressure. It can also be heard (and even felt) upstream. The old profile

displayed a greater level of unsteady stall.


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The new profile, despite displaying a reduced level of unsteady stall, passed a significantly

lower mass flow rate. (This is difficult to measure, due to the unstable test pressure without

air filter and throttle body, but a 7% reduction is the ballpark figure)

6.5 Modified Area Ratio Test

The new profile was subsequently modified (more correctly a fitting was modified) to match

the area ratio of the old profile.

Figure 6-2 Modified Area Ratio Geometries (2002 Device)

The unsteady stall became more pronounced with this modification, and the mass flow rate

decreased.

It seems likely the new profile is affecting a lower mass flow rate than the old profile due to

geometries upstream of the throat (for tests without air filters and throttle bodies).

The question remains to be answered as to exactly which geometries upstream of the throat

are more favourable on the older profile. Possible geometric sources of increased flow rates

include:

• The parallel tract length

• Parallel tract diameter

• The presence of an inlet angle

The presence of an inlet angle seems most likely.


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It must be stated that it is somewhat difficult to capture a reading whilst the unsteady stall

condition is present. The same methodology was used for both units, and the difference in

mass flow rates is very obvious, although there is significant inaccuracy in the values.

The modified area ratio test was then performed with the throttle and air cleaner attached. The

flow was steady with the original area ratio, and a slight fluctuation was noted with the

increased area ratio. A reduced mass flow rate was recorded with increased area ratio. The

reduction was 3% +1.9% / -2.4%.

6.6 Testing With Air Filters And Throttle Bodies

The new and old profiles were again tested with throttle bodies and air filters (Note: The new

profile was tested with it’s original area ratio). Both units display fairly stable flow. The 2002

unit is very stable, and the 2001 unit fluctuating very slightly. This is a somewhat puzzling

situation. Obviously the addition of an air filter and throttle body was likely to cause some

reduction in mass flow rate, and hence lower Reynolds numbers.

White suggests that separation increases with boundary layer thickness prior to diffusion. The

addition of an air filter and throttle body might be decreasing the boundary layer thickness.

The level of swirl might also be having an effect.

With the addition of air filters and throttle bodies, the new profile has a lower mass flow rate

at the given test pressure, a reduction of 7% + 1.9% / -2.4%.

Interestingly, dynamometer results show that this year’s engine has decreased in maximum

power (7% ± 1%).

A series of modified dynamometer tests was used to show that the power decrease is due to

components upstream of the plenum. This is explained in detail in section 8.


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7 Dynamometer TestingThe dynamometer testing for this study was performed at Stafford Tune. The dynamometer

operator was Mr. Paul Masterson. Mr Masterson is a renowned dynamometer operator who

specialises with engines using Motec engine management systems. The dynamometer at

Stafford tune is regularly calibrated. Inertia correction, and barometric compensation is also

available. Stafford tune claim their hardware to be accurate within 1%. An SAE J607

correction factor was used for test readings.

The engine was coupled to the dynamometer using a cardan shaft. The inertia corrected power

figures are the values of power at the shaft. The actual engine exhaust system was in place for

dynamometer testing.

The engine systems need be “mapped” before power readings are taken. This means that the

parameters of injector pulse width and spark timing are programmed over a range of throttle

positions and engine speeds.

Once the engine is mapped, it can be run at WOT over it’s operating rpm range, and

horsepower readings taken.

Figure 7-1 Engine At Dynamometer Testing


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7.1 Plenum Comparisons

The first series of comparative tests involved changing between two plenums, whilst using the

new restrictor, throttle body and air filter. The two plenums are both of symmetric design, and

both use the same runner lengths. The difference is that the 2002 plenum has significantly less

volume. The 2001 plenum is 3800 cc whilst the 2001 plenum is 980 cc. The 2002 plenum has

a smaller runner spacing within the plenum.

Plenum Comparison

0.0

10.0

20.0

30.0

40.0

50.0

60.0

4000 5000 6000 7000 8000 9000 10000 11000 12000

rpm

2002 Nm

2001 Nm

2002 Kw

2001 Kw

Figure 7-2 Plenum Comparison

It was found that there was little difference in overall peak power levels. The characteristic

“gurgle” indicating an early primary pulse can be heard from the engine at 7500 rpm. The

torque curve dips at 7500 rpm and rises sharply at 8500 rpm, indicating that the primary pulse

tuning is indeed effective at near 8500 rpm.

It is interesting to note that the “booster” from the primary pulse is much more pronounced

using the plenum with greater volume. These figures are taken without inertia correction.


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7.2 Final Power Readings With Inertia Correction

It is valid to include inertia correction for our testing. The engine produces very little torque

and is accelerating a dynamometer with inertia of 0.037 kgm2, at a shaft acceleration of 250

rpm.s-1.

2002 Formula SAE

0.0

10.0

20.0

30.0

40.0

50.0

60.0

4000 5000 6000 7000 8000 9000 10000 11000 12000

rpm

Nm

KW

The corrected peak horsepower is 50.4 kW @ 10150 rpm (67.6 hp). As mentioned earlier in

section 6 of this report, the engine typically operates over a range of 2500 rpm. We can

clearly see that the integral of power across an rpm range of 2500 rpm is maximised if we

operate the engine between 9000 rpm and 11500 rpm. The engine produces greater than 46

kW (62 hp) across this operating range. The rpm limit of the engine should be set slightly

higher at say 11750 rpm, to encourage the driver to operate the vehicle in the optimum rpm

range.

7.3 Removal Of Air Cleaner

A final test was used to determine the performance of the air filter. The air filter was simply

removed, and the engine was ramped again. The result was an increase of 0.5 kW. This seems

to indicate that the air cleaner is indeed adequately sized.


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8 Track TestingAt this stage there has only been one limited track test of the vehicle. The throttle control

seems to have increased dramatically, although the behaviour is still suited to an experienced

driver. The “lag” from quickly opening the throttle plate seems to have decreased

dramatically.

Figure 8-1 First Track Testing


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9 ConclusionsThe new inlet manifold and throttle body will certainly suit an inexperienced driver more than

the previous year’s hardware. The design is certainly viable for lean manufacture, is more

compact, more aesthetically pleasing, and weighs 2.2 kg compared to 6.2 kg for last year. The

SLS restrictor nozzle has shown no problems with cracking or any other deterioration. The

hardware enables the engine to be installed with the entire inlet manifold connected. The

engine can now be installed in under 20 mins.

The mandatory SAE costing of this hardware is $1600 (AUS) (see Appendix E).

Unfortunately, the peak horsepower reading is down 7% over last year, 50.4 kW Vs 54 kW

(68 hp VS 73 hp). The comparison between ramped power curves was not obtained.

The source of the power loss appears to have occurred due to geometries upstream of the

restrictor throat. The most probable cause is the geometry between the throat and the throttle

body.

The components of the inlet manifold should now be developed experimentally. This will

certainly be an expensive exercise, but should give pertinent data for future designers, and

theorists. A recommended experimental evaluation is given in the following section.


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10 RecommendationsThe development of the formula SAE manifold would likely be achieved through five

separate evaluations. These are:

• Developing the restrictor geometry upstream of the throat.

• Developing the restrictor geometry downstream of the throat.

• Developing the pulse tuning mathematical model.

• Evaluating the performance of symmetric plenums.

• Computational fluid dynamics studies.

10.1 Developing The Restrictor Geometry Upstream Of The Throat.

This development is most easily achieved by flow bench testing. A series of flow bench tests

using a suitably large test plenum, the current throttle body, and air filter, could be used to

determine optimal conduit geometries upstream of the throat. A fixed downstream geometry

would be used.

A suitable downstream geometry might be an exit angle of 5°, and an area ratio of 4. The

upstream geometry might be evaluated for intake angles of 15°, 20°, and 30°. The radius at

the throat might be evaluated for radii of 30, 40, 50, and 60 mm. Performance curves (the

measure being mass flow rate) could then be generated. It would be wise to produce

performance curves for 4 downstream (plenum) pressures. The downstream pressures might

be 250 mm, 500 mm, 750 mm, and 1000 mm of water.

The formula SAE flowbench is indeed suitable for this type of evaluation, but a suitably sized

vacuum source would be required. A suitably large blower, perhaps an ELMO 80H (2.5 kW)

may cost more than $4000. An alternative would be to use a commercial flow bench at the

cost of $500 per day. The nozzles would be most easily produced by SLS, and the support

from The Queensland Manufacturing Institute (QMI) would be required.


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It is imperative that the air filter and throttle body be attached during testing, to affect the

correct boundary layer thicknesses prior to the restrictor. A reasonably clean environment

would be required, to ensure consistent performance from the air filter.

Figure 10-1 Envisioned Performance Curves

Figure 10-2 Upstream Restrictor Geometries


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10.2 Developing The Restrictor Geometry Downstream Of The Throat.

Once an optimal upstream geometry has been found, a second optimisation for downstream

geometries could be carried out.

Using the optimal upstream geometry, the downstream geometry might be evaluated for exit

angles of 3°, 5°, and 7°. The area ratio for each exit angle might be evaluated for a value of

AR = 2, 4, 6, and 8. It would be wise to produce performance curves again for four

downstream (plenum) pressures. The downstream pressures should be the same, set at 250

mm, 500 mm, 750 mm, and 1000 mm of water.

The performance curves would look similar to figure 10-1.

Figure 10-3 Downstream Restrictor Geometries

A dynamometer evaluation of these geometries, for two different plenum designs would be

advisable. Values of mean plenum pressures, at maximum horsepower, might be achievable.

The designer might indeed choose a less than optimal downstream geometry to affect a

practical design.

10.3 Developing The Pulse Tuning Mathematical Model

Subsequent to restrictor optimisation, a series of dynamometer tests could be carried out using

a manifold with variable length pipes. A number of torque curves, for a number of pipe

lengths may serve to validate a primary pulse-tuning model. It is much easier to build such a


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manifold using straight pipes. The manifold should use a suitably large volume, perhaps 5

Litres.

10.4 Evaluating The Performance Of Symmetric Plenums

Subsequent to development of both optimised restrictor, and primary pipe lengths, a

symmetric plenum of suitably small volume might be built and evaluated by a dynamometer.

10.5 Computational Fluid Dynamics Studies

Subsequent to all the above studies being performed a computational fluid dynamics study,

which demonstrates results similar in nature to the experimental studies, might be useful to

future designers. Great care must be taken with applying boundary conditions. The boundary

conditions must be accurately determined through a series of experiments, most preferably

whilst the engine is in operation.


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References

1. The Society Of Automotive Engineers 2002, ‘Formula SAE Rules 2002’, [Online]

Available at: http://www.sae.org/students/fsaerules.pdf

2. Automotive Components Limited 1991, ACL Engine Manual, 1st edn., Gregory’s

Scientific Publications, Sydney.

3. Vizard, D. 1990, How To Build Horsepower, S-A Design Books, California.

4. Gregory’s 1992, EFI and Engine Management Volume 2, Gregory’s Scientific

Publications, Sydney.

5. Motec Pty Ltd 2002, ‘MoTeC Advanced Engine Management & Data Acquisition

Systems’, [Online] Available at: http://www.motec.com.au

6. Motec Pty Ltd (?), ‘MoTeC Advanced Engine Management & Data Acquisition Systems –

Training Manual’, (?)

7. Encyclopaedia Britannica Educational Corporation 1966, Flow patterns in venturis

nozzles and orifices, [U.S.]: Education Development Centre/National Committee for

Fluid Mechanics Films, videorecording.

8. Measurement Of Gas Flow By Means Of Critical Flow Venturi Nozzles, International

Standards Organization, ISO 9300:1995

9. Miralles, B.T. 2000, ‘Preliminary Considerations In The Use Of Industrial Sonic

Nozzles’, Flow Measurement And Instrumentation, vol.11 no.4, pp.345-350

10. Runstadler, P.W. 1975, Diffuser Data Book, Creare Inc., Technical Notes 186, Hanover

11. White, F.M. 1999, Fluid Mechanics, 4th edn., McGraw Hill, Singapore.


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12. Campbell, L.A. 2000, Flow Analysis of Three Different Engine Intake Restrictors,

undergraduate thesis, Rochester Institute Of Technology, New York

13. K&N Engineering, Inc. 2002, ‘Home Of High Performance Air Filters’, [Online]

Available at: http://www.knfilters.com/

14. SuperFlow Corp. 2002, ‘Dynamometers and Flow Benches’, [Online] Available at:

http://www.superflow.com

15. Measurement Fluid Flows in Closed Conduits; Velocity Area Method Using Pitot Static

Tubes, International Standards Organization, ISO 3966:1977

16. Measurement of Fluid Flows in Closed Conduits, Standards Association Of Australia, AS

2360:1993

17. Automation Creations Inc. 2002, ‘MatWeb Material Type Search’, [Online] Available at:

http://www.matweb.com/search/searchsubcat.asp

18. 3D Systems Inc. 2002, ‘3D Systems-Rapid Prototyping’, [Online] Available at:

http://www.3dsystems.com

19. Ohata, A. & Ishida, Y. 1982, ‘Dynamic Inlet Pressure and Volumetric Efficiency of Four

Cycle Four Cylinder Engine’, Society Of Automotive Engineers Journal, SAE 820407,

pp.1637-1648

20. The Society Of Automotive Engineers 2002, ‘Formula SAE Results’, [Online] Available

at: http://www.sae.org/students/fsaeresu.htm

21. Braden, P. 1988, Weber Carburettors, HPBooks, Los Angeles.


Francis Evans 2002

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Appendix A Flowbench Principles

Figure A- 1 Flow Bench Hardware

A flowbench was designed with conduit downstream of the restrictor that is of similar internal

diameter as the plenum used in the engine manifold. A static pressure tap is taken from the

flowbench “plenum”. This static pressure is used as the test pressure. Bypass valves are

adjusted to cause the test pressure to read a certain height at the monometer, indicated P1 in

figure A-1.

The flow continues from the test plenum into a suitably long slender pipe.

The average velocity of flow in the slender pipe is approximately 80 ms-1, which in the 27.5

mm internal diameter pipe creates Reynolds numbers of Red ≅ 1.4 x 106.

White [11] suggests that for Reynolds numbers in this range, fully developed turbulent flow

should develop with a turbulent entrance length Le/d ≅ 44, for smooth pipes. The pipe used in

this hardware has a very rough internal surface, but for sake of being conservative the pipe is

RestrictorP2

P3

P1

Bypass Valves

Pitot ProbePlenum

Static Pressure Taps

Industrial Vacuum Cleaner


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1200 mm in length from the plenum to the Pitot probes (Le/d ≅ 44) to ensure that fully

developed turbulent flow is present.

ISO 3966 [15] suggests that the velocity profile should be measured in order to determine the

mass flow rate. But, for the sake of simplicity, we assume a consistent velocity profile. This

assumption is valid because we operate over a very narrow range of Reynolds numbers. The

device is designed to be comparative rather than absolute.

By measuring the Pitot static pressure at P2, the density of air in the small diameter pipe can

be determined. A thermometer was also used (in ambient conditions) to calculate the density

of air flowing through the pipe. Unfortunately a stagnant temperature sensor was unavailable.

Barometric data from the Bureau of Meteorology weather station was used throughout testing

and corrections are added to all calculations. The Pitot dynamic pressure is measured at

manometer P3. The pressure at P3 is simply the difference between the static pressure in the

pipe, and an adjacent Pitot (stagnation only) pressure probe. The Pitot stagnation probe is

outside the specifications of ISO 3966 [15], being 3 mm in outside diameter.

The peak velocity is calculated by the Pitot formula.

( )ρ

ε 321

PV −=

Compressibility correction (1-ε) is ignored because we are operating at quite low velocities

(Mach 0.23), and over a narrow range of velocities.


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Appendix B Error Analysis For Flowbench

With the flowbench being designed deliberately to give comparative measures, we are

concerned only with errors that alter the comparative performance of the device.

The most obvious, yet unquantifiable sources of error are:

• Diameter of the Pitot (stagnation only) pressure probe

• Position of the Pitot probe in the flow stream

The diameter of the Pitot stagnation probe is outside the specification set by ISO 3966 [15].

The standard suggests, that for the conduit used, a probe with outside diameter of 0.8 mm is

appropriate. A probe of this size was not practical. A 3 mm probe was used.

The probe has been positioned very accurately using a fixture during installation. The

installation procedure should see that the probe is within 1 mm of the centreline of the pipe,

and yaw angles are less than 1°. This should not cause appreciable errors.

The sources of quantifiable error include:

• Misread manometer reading P1



• Flow temperature not moving comparatively with ambient temperatures, or misread

temperature reading.

• Inaccurate barometer readings.

All sources of error are calculated from a baseline average test condition obtained from 27

tests of 9 upstream geometries.

An incorrect test pressure reading, P1 is by far the greatest source of error for this device. An

additional 15 tests were performed using the 2002 restrictor, with the throttle body and air


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filter in place. Each test showed very stable test pressure readings. The test pressure readings

were taken at three positions, 240 mm, 250 mm, and 260 mm. A 10 mm test pressure

difference was averaged to produce a mass flow rate difference of +2% / –3%. The standard

deviation of mass flow rates determined at each test pressure was found to be 0.02%. It seems

unlikely that the operator, within 5 mm, would misread test pressure. This indicates that that

error due to an incorrectly read test pressure manometer, by interpolation, is within +1.19% / -

1.6%.

By mathematical substitution we find: (from the baseline average test condition)

• A misread manometer at P2 of ±5 mm causes a mass flow rate error of ±0.02%.

• A misread manometer at P3 of ±5 mm causes a mass flow rate error of ±0.53%.

• Flow temperature not moving comparatively with ambient temperature within 2 deg C

causes a mass flow rate error of ±0.33%

• Incorrect Barometer Readings within 25 Pascal causes a mass flow rate error of

±0.03%.

• The barometric readings are taken from a weather station, the time at which each test

was performed was recorded, and the data later retrieved.

• All of the above modes off error occurring simultaneously, with an incorrectly read

test pressure, cause a total error of +1.93% / -2.41%.


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Appendix C Flow Bench Data


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Appendix D Dynamometer Results


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Appendix E Formula SAE Costing


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Appendix F Analytical Model Code

#

#

# Heimholtz Tuning Analytical Model,

# Francis M Evans s354079, University Of Queensland

> restart;

> px:=r*(1+n-cos(w*t)-(n^2-sin(w*t)^2)^(1/2));# Position Of Piston wrt

# time

> pv:=collect(diff(px,t),w);# Velocity Of Piston WRT time

> pa:=collect(diff(pv,t),w^2);# Acceleration Of Piston WRT time

> rpm:=10500;

> w:=evalf(Pi*rpm/30);

> T:=evalf(2*Pi/w);

# period in seconds

> stroke:=0.0452;

# stroke in metres

> r:=stroke/2;

> rodtostroke:=2.1;

> n:=2*rodtostroke;

#

> bore:=0.065;

# bore in metres

> boretostrokeratio:=bore/stroke;

> capacity:=evalf(stroke*(bore/2)^2*Pi)*1000000;

# single cylinder capacity in cc's

> plot(px,t=0..T);

# displacement of piston in metres against time

> plot(pv,t=0..T);

# velocity of piston ( ms-1 ) against time

> plot(pa,t=0..T);

#


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# acceleration of piston (ms-2) against time

> flowrate:=pv*Pi*(bore/2)^2:

> plot(flowrate,t=0..T/2);

# ideal flowrate of cylinder (m3s-1) against time

> vave:=(int(pv,t=0..T/2))/(T/2);

# average piston velocity in ms-1

> flowave:=int(flowrate,t=0..T/2)/(T/2);

# average ideal cylinder flowrate in m3s-1

> peaktime:=fsolve(pa=0,t=0..T/4);

# time of peak piston velocity

> peakflow:=evalf(subs(t=peaktime,flowrate));

# ideal peak cylinder flow rate

#

# inlet specs now

> venturi:=34.9;

# venturi diameter in mm

> venturiarea:=evalf(Pi*(venturi/2)^2);

# venturi area in mm2

> avegasvel:=1000000*flowave/venturiarea;

# average gas velocity in ms-1

> peakgasvelocity:=1000000*peakflow/venturiarea;

> mach:=peakgasvelocity/343;

> venvel:=(1000000*flowrate/venturiarea):

> evalf(venvel):

> plot(venvel,t=0..T/2);

> a:=343:# Pulse propogation Velocity

> unassign('crit');

> pulsevelout:=a-venvel:# Relative Pulse Velocity

> plot(pulsevelout,t=T/4..T/2):

> ts:=(T/2)*98/180:# Point of Pulse Generation ie 98 deg ATDC

> te:=(T/2)*crit/180:# Point where pulse refracts .. critical angle

> runnerlengthout:=int(pulsevelout,t=ts..te):


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> pulsevelin:=a+venvel:

> plot(pulsevelin,t=T/4..T/2):

> tf:=(T/2)*(180+15)/180:

> runnerlengthin:=int(pulsevelin,t=te..tf):

> crit:=fsolve(runnerlengthout=runnerlengthin,crit=90..180);

> runnerlength:=int(pulsevelout,t=ts..te); # required runner length for

# given rpm stock pipes

>

>

>

> restart; # restart process and calculate pipe length required for new

# rpm

> px:=r*(1+n-cos(w*t)-(n^2-sin(w*t)^2)^(1/2)); # Velocity Of Piston WRT

# time

> pv:=collect(diff(px,t),w);# Velocity Of Piston WRT time

> pa:=collect(diff(pv,t),w^2);# Acceleration Of Piston WRT time

> rpm:=8400;

> w:=evalf(Pi*rpm/30);

> T:=evalf(2*Pi/w);

# period in seconds

> stroke:=0.0452;

# stroke in metres

> r:=stroke/2;

> rodtostroke:=2.1;

> n:=2*rodtostroke;

#

> bore:=0.065;

# bore in metres

> boretostrokeratio:=bore/stroke;

> capacity:=evalf(stroke*(bore/2)^2*Pi)*1000000;

# single cylinder capacity in cc's

> plot(px,t=0..T);


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# displacement of piston in metres against time

> plot(pv,t=0..T);

# velocity of piston ( ms-1 ) against time

> plot(pa,t=0..T);

#

# acceleration of piston (ms-2) against time

> flowrate:=pv*Pi*(bore/2)^2:

> plot(flowrate,t=0..T/2);

# ideal flowrate of cylinder (m3s-1) against time

> vave:=(int(pv,t=0..T/2))/(T/2);

# average piston velocity in ms-1

> flowave:=int(flowrate,t=0..T/2)/(T/2);

# average ideal cylinder flowrate in m3s-1

> peaktime:=fsolve(pa=0,t=0..T/4);

# time of peak piston velocity

> peakflow:=evalf(subs(t=peaktime,flowrate));

# ideal peak cylinder flow rate

#

# inlet specs now

> venturi:=34.9;

# venturi diameter in mm

> venturiarea:=evalf(Pi*(venturi/2)^2);

# venturi area in mm2

> avegasvel:=1000000*flowave/venturiarea;

# average gas velocity in ms-1

> peakgasvelocity:=1000000*peakflow/venturiarea;

> mach:=peakgasvelocity/343;

> venvel:=(1000000*flowrate/venturiarea):

> evalf(venvel):

> plot(venvel,t=0..T/2);

> a:=343:# Pulse propogation Velocity

> unassign('crit');


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> pulsevelout:=a-venvel:# Relative Pulse Velocity

> plot(pulsevelout,t=T/4..T/2):

> ts:=(T/2)*98/180:# Point of Pulse Generation ie 98 deg ATDC

> te:=(T/2)*crit/180:# Point where pulse refracts .. critical angle

> runnerlengthout:=int(pulsevelout,t=ts..te):

> pulsevelin:=a+venvel:

> plot(pulsevelin,t=T/4..T/2):

> tf:=(T/2)*(180+15)/180:

> runnerlengthin:=int(pulsevelin,t=te..tf):

> crit:=fsolve(runnerlengthout=runnerlengthin,crit=90..180);

> runnerlength:=int(pulsevelout,t=ts..te); # required runner length for

# given rpm new pipes


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Appendix G Rick's Rules For Solid Edge

A sincere thanks to Rick Mason for allowing me to publish this guide to solid modelling.

Rick's Rules for Robustness in Solid Edge - Part 1 (Part Mode)

November 1998

RULE #1: PLAN your work! Remember we are modeling, not "drawing". Spend

a few minutes with a sketch-pad and pencil to:

a) Identify important datums which should be tied to Reference Planes

(these include locating / mating faces, common centrelines, extents of non-

orthogonal features etc.) Placing the major axes of the Part and/or its primary

locating feature onto the base Reference Planes makes for not only a well-

constructed Part, but more robust Assemblies downstream.

b) Imagine the basic set of features which define the part-structure. Is the

part best represented initially by a rotated, linear, lofted or swept protrusion?

Should it be modeled as a piece of bar-stock then material removed as it will be

in the toolroom? If the part is a moulding, casting or forging, does it require a 2-

step process to allow for trimming/cleanup/machining to be defined? Is it one of

a Family of Parts, or of a Handed Pair? This analysis is difficult for a beginning

user of Solid Edge, but it is an essential part of robust technique.

c) Identify common or linked features (eg aligned cutouts) which can be

linked to initial sketch geometry to control their placement without risk of a failed

feature compromising the model. Sketch geometry is a valuable tool in building

robust models and is also a useful way of incorporating 2D reference geometry.

Try to visualise the approximate order in which the model will be built - this will

become easier with experience and experimentation. It is desirable to keep

features as independent of each other as possible, whilst keeping the required

relationships between features - this may seem antithetical at first, but read on!

RULE #2: Build on good foundations. Global (Primary) Reference planes are your

most trusted ally - they are:


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a) Indestructible and immovable (but can be conveniently re-sized

before commencing your model).

b) The most reliable foundation on which to build your model.

c) The most reliable features when placing part-models into assemblies.

RULE #3: Anticipate! Designers change their minds, stock shapes get discontinued,

mating components alter, stresses change etc. Make allowance for:

a) Dimensional changes in your parts. Use driving dimensions to 'test'

that profiles behave predictably when re-sized. Develop techniques which give

maximum flexibility, controllability and reliability in your models.

b) Changes in configuration - If the locating-face changes from front to

back of the part, does it mean 2 minutes or 2 hours to incorporate the change?

With planning and a little experiance, you'll be able to say "Yeah, no problem"

instead of "You wanna do WHAT????"

c) The 'Back Burner' syndrome - don't use such confusing techniques that

when the job's back on the boil after 6 months delay, you can't understand what

the heck you had done so far.

RULE #4: Keep features independent of each other as far as possible. Solid Edge

has a host of tools which allow us to build complex models in various different

ways - some are inherently robust, some not. Try to follow these guidelines:

a) Use primary reference-planes for feature profiles and to attach driving

dimensions at every opportunity. You'll be surprised how often this is, in fact,

possible once you start to practise. AVOID using 'consumable' faces, edges etc.

for profile-planes or dimension attachment. Once you start to re-order features,

the only guaranteed datums are the three primary reference-planes.

b) Practise re-ordering features and using the 'go to' function in Pathfinder.

(you ARE using Pathfinder, aren't you?) See what breaks and what hangs

together when you alter the sequence of your model. Avoid deeply-nested

groups of features which 'lock' you into a set, inflexible path. If a feature cannot

be re-ordered (UPWARD is the only option, by the way) then it has down-line

dependencies which prevent this, or there are no 'break-points' in the model


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above that feature, into which it can be re-located. To bring a feature DOWN

the tree, it may be necessary to cut-and-paste its Profile (using a Draft file as

a buffer) and delete & re-create the feature. Be careful that the robustness of

the Part is not compromised by these changes.

c) Use open profiles to avoid un-necessary interdependence of features.

For example, a boss modeled as a rotated protrusion does not need the open

ends of the profile to be related to the parent model - the boss will always meet

the parent body, so why introduce unnecessary complications? If the boss's

Profile is sketched on a base Reference Plane and dimensioned to the other

2 plane-edges, it becomes completely independent of the parent and therefore

extremely 'robust'.

d) Create a secondary reference plane - either global or feature-specific

(local) - from which to project back onto the parent solid rather than picking a

face on the parent body from which to create a feature profile. This technique

gives the maximum flexibility and independence of features, and eliminates the

possibility of features or relationships failing because the 'supporting' face has

been either altered or removed.

e) Avoid reliance on included edges where there is a likelihood that the

parent feature will be significantly altered, re-ordered etc. Sketches offer a

MUCH more robust method of controlling linked features or shared geometry.

RULE #5: Learn which are the most robust relationship types. Sadly, not all rel-

ationships are created equal (pun intended!). Symmetric relationships are

probably the most 'fragile' and easily broken, whereas 'connect' and 'align'

relationships are nearly bullet-proof. Where symmetry is required, it may be

preferable to use equality / alignment relationships or else Construction

elements in lieu of the actual symmetry function. In case you haven't yet

discovered Construction Elements, they are ordinary profile entities which are

'toggled' as Construction elements which withdraws them from the Profile but

leaves them as 'scaffolding'. Take the case of a rectangular pattern of holes

placed as a User Defined Pattern, where the centre-point of the pattern must

be controlled by a driving dimension. A line can be drawn between diagonally-

opposite hole centres, then the Driving Dimension applied to the mid-point of

this Construction line (lines & arcs drawn whilst in the Hole Step are

automatically identified as Construction Elements although they initially display

as solid not chained).


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For any given profile, there may be many different ways of applying relationships

(and in different order) which achieve the same end result, but some will be more

robust than others. Most of us have had the experience of a Profile turning it-

self 'inside out' or going feral - often it is simply the ORDER of construction or of

applying relationships which determines how robust the construction will be. It

is good practice to try several different configurations for a profile (by varying the

value of Driving Dimensions etc.) to verify that the geometry behaves as you

expect. There's always the 'Undo' icon ......

RULE #6: Utilise the power of Open Profiles. Solid Edge has an extraordinary ability

to interpret Open Profiles. As long as the 'projected' envelope properly intersects

the parent solid, open profiles can be used for Ribs, Bosses, Webs, Gussets,

Fins, Cutouts, Section cuts, Grooves, Notches ...... and in many cases, smart

selection of both the Profile Plane and orientation will result in the Open Profiled

feature being completely independent of the topography of the parent solid. This

means that the feature will regenerate successfully even if significant changes

are made to the parent - a great 'robustness' attribute.

Unfortunately, Open Profiles cannot be used for swept or lofted features as far as

I am aware.

RULE #7: Use Feature Pathfinder to advantage. Solid Edge's Feature Pathfinder has

a few tricks up its sleeve which even experienced users sometimes overlook. The

Playback feature functions like a VCR, allowing you to 'replay' the construction of

the model. Features can be renamed to have more meaningful descriptions (a

great habit to get into!) so that "UserDefinedPattern_23" becomes something like

"Attch_Holes_M8" for example. This is particularly useful when interpreting some-

one else's work or in the case of the dreaded 'Back Burner Syndrome' where a job

suddenly gets resurrected after weeks or months of delay.

Individual features, planes, sketches & surfaces can be selected with the RMB

(Right Mouse Button) to show/hide them, suppress/un-suppress, edit/change

dimensions etc. (Try RMB with the cursor in the graphics screen, toolbars, over

highlighted entities, etc. etc .......)

When selecting a feature from the graphics screen is difficult, it can be selected

with precision from Pathfinder. Re-ordering of features and insertion of features in

the tree can also be done from Pathfinder, both of which are vitally important tools


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in a robust model. Single-stepping through the construction of a part in Playback

mode is a tool I use often while reviewing other peoples' work. Often while I'm

doing this I learn something new from another user's approach to their task.

RULE #8: Apply dimensions with care. Well-applied Driving Dimensions make for a

robust model. Indiscriminately applied dimensions or dimensions applied

using the wrong Mode or settings can lead to disaster. When dimensioning the

profile of a rotated protrusion or cutout, find and use the Diametral dimension;

when dimensioning to small elements, zoom to ensure the correct attachment-

point. Understand the difference between Horizontal/Vertical, 2-Points and Axis-

Aligned dimensions. Remember always when placing Driving Dimensions that the

base Reference Planes are the ONLY indestructible features in your part - attach

dimensions to them whenever possible.

Learn ALL the functions of the Smart Dimension tool - it is surprisingly powerful,

yet many users have never investigated its options on the Ribbon Bar. Don't

think that because you have used Driving Dimensions to fully control a Profile,

non-driving dimensions have no place: they are often useful as reference or as

checking dimensions, to save having to perform a calculation etc.

RULE #9: Capture as much DESIGN INTENT as possible in your Part. Get into some

good habits when commencing a Solid Edge part. As soon as you rename the part

to save it, open the File Properties notebook and fill in the relevant details. I have

my Normal.par file saved with Prompts in the Properties fields, so users have a

guide as to what information should be entered. Don't overlook the Comments field

as a handy note-pad for 'To Do' items, checking notes etc.

While applying dimensions in the Profile Step, use all the facilities at your disposal

to add tolerances, prefixes / suffixes etc. to your dimensions. This is even handy

for noting changes or comments (eg add dimension suffix "was 22.873mm" or

"must not exceed 37.4° " etc.) - just a little bit of extra information can avoid costly

errors or time-wasting misunderstandings. The Dimension Type icon is active in the

Profile Step as well as in Draft, remember - you can place Toleranced, Reference,

Basic, Inspectable etc. dimensions on a Profile sketch (but NEVER out-of-scale!).

RULE #10: Be adventurous. Solid Edge has more features and options than any single

User can possibly commit to memory. Investigate the function of infrequently-used

Icons, Menu options etc. Leave "Tip of the Day" turned on - often it provides a


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little memory-jog about a forgotten function or workflow (and Dental Hygiene).

Compare notes with colleagues, or (better yet) TEACH Solid Edge to a colleague,

student or friend - it doesn't matter that you are an inexperienced User, you will

become a better user (and gain some valuable insights) by helping someone else

discover the power of Solid Edge, and by practising Robust techniques. Use ALL

the available Tools (and this includes the excellent context-sensitive Help found

in Solid Edge) to add the highest possible value to your Part Models - it's the

way 'professionals' work!

Prepared by: R.H. (Rick) Mason

MASCO Design Services Pty. Ltd.

Solid Edge Support (Australia)

Sydney, Australia.

Queensland University Research

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Transcript of Queensland University Research