Direct injection system for a two stroke...

Direct injection system for a

two stroke engine

Master’s Thesis in the Automotive Engineering Master's programme

JOSE RODOLFO I. CERVANTES TREJO

Department of Applied Mechanics

Division of Combustion

CHALMERS UNIVERSITY OF TECHNOLOGY

Göteborg, Sweden 2011

Master’s Thesis 2011:42

MASTER’S THESIS 2011:42

Direct injection system for a two stroke engine





CHALMERS UNIVERSITY OF TECHNOLOGY





© JOSE RODOLFO I. CERVANTES TREJO, 2011

Master’s Thesis 2011:42

ISSN 1652-8557



Chalmers University of Technology

SE-412 96 Göteborg

Sweden

Telephone: + 46 (0)31-772 1000

Cover:

Figure text for the cover picture (if applicable), possibly with reference to more

extensive information in the report.

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I






Chalmers University of Technology

ABSTRACT

Direct injection is becoming an important option to further optimize internal

combustion engines. In the case of two stroke engines, the opportunity of dramatically

reducing the HC emissions by almost eliminating short circuit while scavenging,

makes this system even more attractive. For small two stroke engines, like the ones

used to power chain saw tools, the need of a high pressure fuel pump (its size and

electricity needs) makes that the use of direct injection becomes not feasible.

By using a self pressurized (boosted) direct injector, the opportunity of using direct

injection opens for these small engines since a high pressure pump is not needed. The

Evinrude E-TEC™ outboard engine uses a direct injection system which makes use of

this kind of injectors. The Evinrude E-TEC™ outboard engine is analyzed in a test

rig to find out the characteristics of the injector and the combustion modes the engine

runs at different speeds and loads. The emissions of the engine are measured, along

with the power, speed, combustion chamber pressure trace, bsfc, and voltage and

current developed by the injector.

Key words:

Direct injection, boosted injector, self pressurized injector, E-TEC, Evinrude, test rig.

Contents

1 INTRODUCTION 1

1.1 Purpose 1

1.2 Background 1

1.3 Objectives 1

1.4 Approach 2

2 TWO STROKE ENGINES 3

2.1 Two and Four Stroke Engines 3

2.2 Two-stroke scavenging process 5

3 DIRECT INJECTION 10

3.1 Injection types 10

3.2 Fuel Injectors 12

4 THE EVINRUDE E-TEC™ OUTBOARD ENGINE AND ITS INJECTOR'S

CHARACTERISTICS 13

5 METHODOLOGY 15

5.1 Parameters selection 15

5.2 Test Rig Set Up 17

5.3 Experimental Setup 20

5.4 Data Structure 25

6 RESULTS 30

6.1 Torque-Speed curve 30

6.2 Injector parameters 33

6.3 Injection Timing 36

6.4 Specific Fuel Consumption and Emissions 46

6.5 Spray Characterization 50

7 DISCUSSIONS AND CONCLUSIONS 54

7.1 Injection mode 54 7.1.1 Conclusion 1 60

7.2 Influence of Back Pressures 60 7.2.1 Conclusion 2 61

II

8 APPENDIXES 63

9 REFERENCES 67

10 ACKNOWLEDGEMENTS 68

Figure Index

Figure 2-1 The two stroke engine .................................................................................. 4

Figure 2-2 The four stroke engine ................................................................................. 5

Figure 2-3 Scavenging process in the two stroke engine ............................................... 6

Figure 2-4 Mixing process during scavenging ............................................................... 7

Figure 2-5 Short circuit during scavenging ................................................................... 8

Figure 2-6. Different arrangements of scavenging ports. a) Cross scavenge. b) Loop

scavenge. c) Uniflow. .................................................................................................... 9

Figure 3-1. Indirect injection, or port injection. ........................................................... 10

Figure 3-2. Direct injection. ......................................................................................... 11

Figure 4-1 The Evinrude E-TEC™ Engine ............................................................... 13

Figure 4-2 Injector size ................................................................................................ 14

Figure 4-3 Injector Construction .................................................................................. 14

Figure 5-1 Engine on rig .............................................................................................. 17

Figure 5-2 Gearbox and brake ..................................................................................... 18

Figure 5-3 Cooling and exhaust separation ................................................................. 18

Figure 5-4 Cooling of gearbox ..................................................................................... 19

Figure 5-5 Exhaust container ....................................................................................... 19

Figure 5-6 Pressure sensor setup .................................................................................. 20

Figure 5-7 Torque curve approximation ...................................................................... 21

Figure 5-8 Measurement points ................................................................................... 21

Figure 5-9 Throttle opening points .............................................................................. 22

Figure 5-10 Propeller's torque curve ............................................................................ 23

Figure 5-11 Full set of measurement points ................................................................ 24

Figure 6-1 Torque-Speed curve ................................................................................... 30

Figure 6-2 Real set of measurement points .................................................................. 31

Figure 6-3 Power-Speed curve ..................................................................................... 32

Figure 6-4 Electrical measurements at 5 Nm and 3000 rpm ....................................... 33

Figure 6-5 Electrical measurements at 46Nm and 3000 rpm ...................................... 34

Figure 6-6 Injector electrical measurements at 3000 rpm ........................................... 35

Figure 6-7 Injector electrical measurements at 20 Nm ................................................ 36

Figure 6-8 Ignition and Injection timing at 3000 rpm ................................................. 37

Figure 6-9 Time between injection and ignition at a constant speed of 3000 rpm ...... 37

Figure 6-10 Injection time in mSec at 3000 rpm ......................................................... 38

Figure 6-11 Injection time in CAD at 3000 rpm .......................................................... 38

Figure 6-12 Ignition and Injection timing at 30 Nm .................................................... 39

Figure 6-13 Time between injection and ignition at a constant load of 30 Nm ........... 40

Figure 6-14 Injection time in mSec at 30 Nm .............................................................. 40

Figure 6-15 Injection time in CAD at 30 Nm .............................................................. 41

Figure 6-16 Ignition and Injection timing along propeller curve ................................ 41

Figure 6-17 Time between injection and ignition along the propeller curve ............... 42

Figure 6-18 Injection time in mSec along propeller curve .......................................... 42

Figure 6-19 Injection time in CAD along propeller curve ........................................... 43

Figure 6-20 Injection timing map. The values in each area of the contour plot show

the range in CAD the injector is injecting at when the engine is operating inside such

area. .............................................................................................................................. 44

Figure 6-21 Ignition timing map. The values in each area of the contour plot show the

range in CAD the spark plug is igniting at when the engine is operating inside such

area. .............................................................................................................................. 45

Figure 6-22 Throttle angle map. The values in each area of the contour plot show the

range in degrees the throttle is positioned at when the engine is operating inside such

area. .............................................................................................................................. 45

Figure 6-23 bsfc map ................................................................................................... 46

Figure 6-24 HC map .................................................................................................... 47

Figure 6-25 NO map .................................................................................................... 47

Figure 6-26 NO2 map .................................................................................................. 48

Figure 6-27 NOx map .................................................................................................. 48

Figure 6-28 CO map .................................................................................................... 49

Figure 6-29 CO2 map .................................................................................................. 49

Figure 6-30 Cone diameter and spray penetration ....................................................... 50

Figure 6-31 Comparison of sprays at different back pressures .................................... 50

Figure 6-32 Drop speed and diameter histogram for .5 bar back pressure and 2.3 mSec

injection ........................................................................................................................ 52

Figure 6-33 Comparison of sprays at different driving pressures ................................ 53

Figure 7-1 Lambda-Emissions plot .............................................................................. 55

Figure 7-2 Lambda calculation from CO values .......................................................... 56

IV

Figure 7-3 Lambda calculated from CO/CO2 ratio ..................................................... 57

Figure 7-4 Injection map - lambda values superimposition ......................................... 58

Figure 7-5 Ignition map - lambda values superimposition .......................................... 59

Figure 7-6 Stratified area delimitation ......................................................................... 60

Figure 7-7 Fuel injected - back pressure comparison for propeller curve ................... 62

Figure 8-1 Injector Current .......................................................................................... 63

Figure 8-2 Injector Power ........................................................................................... 63

Figure 8-3 Engine Power ............................................................................................ 64

Figure 8-4 Pinj / Peng Ratio ........................................................................................... 64

Figure 8-5 Fuel Consumption ..................................................................................... 65

Figure 8-6 Injection Time ........................................................................................... 65

Figure 8-7 Back Pressure ............................................................................................ 66

Figure 8-8 Fuel Injected .............................................................................................. 66

Table Index

Table 1. Parameters measured from the engine ........................................................... 15

Table 2 Predicted measurement points ........................................................................ 24

Table 3 Data structure as stored in Matlab .................................................................. 26

Table 4 Naming of measured points also used in Matlab ............................................ 32

Table 5 Injector events at different back pressures ...................................................... 51

Table 6 Injector events at different back pressures (continued) .................................. 52

CHALMERS, Applied Mechanics, Master’s Thesis 2011:42 1

1 Introduction

1.1 Purpose

This thesis is based on the interest of an outdoor power products company in

implementing a direct injection system in the two stroke engine of a chainsaw

product. The present thesis work aims to the first steps in the process of this

implementation.

1.2 Background

The possibility of direct injecting a two stroke engine, as it is going to be seen later,

represents many advantages in fuel consumption and emissions, being an important

opportunity for a chainsaw application. As the space in such application is limited,

direct injection has the important disadvantage of needing more space compared to

indirect injection and to carburetor systems. The need for a high pressure pump which

is big in size, and the requirement of this pump for a high electric energy supply,

which forces to equip the engine with a big generator and a big battery; seriously

compromises packaging, cost and weight.

In the beginning of 1990´s Ficht GmbH developed a boosted direct injector for use

with two stroke engines. This injector was unique in that it did not required a high

pressure pump but was still capable of generating enough pressure to inject into a

closed combustion chamber. The way this injector works is described in chapter 4.. In

1995 Outboard Marine Corporation (OMC) licensed Ficht technology and introduced

it on a production outboard engine in 1996. The engine manufacturing portion and

brands (Evinrude Outboard Motors and Johnson Outboards), including the Ficht

technology, were purchased by BRP in 2001.

In 2003, Evinrude introduced the E-TEC™ system, an improvement to the Ficht fuel

injection1. In 2004, Evinrude received the EPA Clean Air Excellence Award for their

outboards utilizing the E-TEC™ system. The E-TEC™ system has recently also been

adapted for use in performance two-stroke snowmobiles.

1.3 Objectives

To obtain operation information of the Evinrude E-TEC™ outboard engine’s injection

system on a dynamometer test rig under idle, medium and heavy load conditions.

Execute a spray characterization on the Evinrude direct injector to find out its main

characteristics as size of the cone, penetration, speed and diameter of the drops.

1 Strauss Sebastian, Zeng Yangbing and Montgomery David. Optimization of the E-TEC™ Combustion

System for Direct-Injected Two-Stroke Engines Toward 3-Star Emissions. SAE 2003-32-0007.

http://en.wikipedia.org/wiki/Outboard_Marine_Corporation

http://en.wikipedia.org/wiki/Evinrude_Outboard_Motors

http://en.wikipedia.org/wiki/Johnson_Outboards


1.4 Approach

Operation parameters are going to be measured in the Evinrude engine in a test rig.

Among this parameters are the operational requirements of the injector (current and

voltage supplied). The spray characterization phase involves using the operational

characteristics of the injector gathered during rig testing.


2 Two stroke engines

In order to put in context the relevance of the work done in the thesis, a brief

description and further comparison of the two and four stroke engine is developed in

the first part of this chapter, and then a higher detailed description of the two stroke

engine over its most relevant details is presented.

An internal combustion engine (ICE) is a kind of engine which produces work by a

combustion process of a fuel-air mixture which takes place inside the body of the

engine itself. Other types of engines are electrical, steam, or exothermal.

There are different architectures of internal combustion engines. The type of engine

which is the main focus of this work is the reciprocating engine, and it is widely used

in many applications, as automotive, marine, tool driving, or electrical power

generation. Those with a rotative architecture, which are a different type of ICE, are

out of the scope. Two fuels used in the reciprocating engine are mainly used, and

define the thermodynamic characteristics that the engine is going to have. The diesel

engine injects diesel fuel in a mass of air which is at high pressure and temperature;

this inflame the fuel injected, increasing the pressure in the engine. The gasoline

engine uses a mixture of fuel and air which is detonated with a spark to increase

pressure and obtain work from it. The former is the engine referred to in this work.

In the reciprocating engine there is a rotating crank shaft which delivers the power to

a driveline. This crank shaft is connected to a reciprocating piston via a connection

rod. The piston is moving inside a cylindrical chamber where the combustion process

takes place. The high pressure developed by the combustion process pushes the piston

in the direction of the crank shaft transforming the linear force of the piston to an

angular force on the crank shaft. The piston moves linearly back and forth along the

space available in the cylinder as the crank shaft rotates in one direction. The position

when the piston is furthest from the crank shaft is called Top-dead-centre (TDC). The

position when the piston is nearest the crank shaft is called Bottom-dead-center

(BDC). The furthest part of the cylinder is closed to prevent pressure leakages which

may reduce the force that the pressure puts in the surface of the piston.

2.1 Two and Four Stroke Engines

The reciprocating engine is divided in two types: Two-stroke and Four-stroke. In the

two-stroke the combustion of the fuel-air mixture takes place every stroke the piston

travels towards the crank shaft, from the TDC to the BDC; this is called a power

stroke. When the piston approaches the BDC position, ports which are originally

blocked by the piston, unblock to allow the change of burned gases with fresh air-fuel

mixture in a process called scavenging. See Figure 2-1.

One of the ports has the mission of letting the burned gases to go away from the

combustion chamber to the atmosphere, it is called exhaust port. The other one, called

scavenging port, has the task of letting in the fresh fuel-air mixture in to the

combustion chamber. The change of gases takes place at the same time, while the

piston is in the BDC. Once the piston goes to the TDC back again, the ports are

covered and the fresh fuel-air mixture is compressed towards the closed combustion

chamber. When the piston reaches the TDC, the spark detonates the air-fuel mixture

increasing the pressure in the combustion chamber and forcing the piston again in the

BDC direction.


Figure 2-1 The two stroke engine

The four-stroke engine has one power stroke every two turns of the crank shaft. This

engine has one stroke dedicated to the exhaust of the burned gases out of the

combustion chamber, and another stroke dedicated to the admission of the fresh fuel-

air mixture in to the cylinder. The ports through which the gases flow are not covered

and uncovered by the piston. Instead, two valves, generally at the top of the cylinder,

open and close accordingly to the admission and exhaust strokes. See Figure 2-2. In

the first stroke of the cycle, when the piston is approaching the BDC, the admission

valve opens to allow fresh air-fuel mixture go into the cylinder. In the second stroke,

when the piston has reached BDC and changes direction to TDC once again, the

admission valve closes to allow for the compression of the mixture. Once the piston

has reached TDC, the mixture is inflamed and the pressure of the burning gases

pushes the piston in the direction of the BDC. When the piston reaches the BDC for

the second time the exhaust valve opens to let the burned gasses escape from the

cylinder, allowing the piston to eliminate it almost completely when the piston is at

the TDC back again.


Figure 2-2 The four stroke engine

There are two main differences between the two types of engines. The first one is that,

since the two-stroke has a power stroke every turn of the crank shaft and the four-

stroke has it every two turns of the crank shaft, the overall power developed by the

two-stroke is the double than the power of the four-stroke engine. It also means that a

two-stroke engine needs half of the size than a four-stroke to have the same power.

The second one is that the gas interchange in the two-stroke is less efficient that the

one in the four-stroke. Since the four-stroke does admission in one stroke and exhaust

in another, the gases doesn´t mix and there is no way that fresh fuel-air mixture goes

out unburned through the exhaust valve. This makes that the four-stroke has more

control over the combustion, being smoother when running and having a better

efficiency than the two-stroke. Thus, the advantage of having the double of the power

than the four-stroke is only theoretical. Also the problem of the fresh mixture going

out through the exhaust valve increases dramatically the emissions of the two-stroke

engine, taking it out from the possibilities of being used in applications such as

automotive, where these engines have very high emission restrictions.

2.2 Two-stroke scavenging process

As it’s been said, the two-stroke engine changes gases at the same time, in a process

called scavenging. In an ideal scavenging process, the fresh fuel-air mixture going in

to the combustion chamber should push away the burned gases through the exhaust

port whit out mixing with them and whit out letting any particle of fresh mixture to go

out as well, filling completely the combustion chamber in which no particles of

exhaust gas should remain at all. The real scavenging process is different.

A difference in pressure is needed to be able to move the gases inside the combustion

chamber, which means that the pressure in the scavenging port have to be increased in

order for the fresh fuel-air mixture to displace the burned gases out of the combustion

chamber. In the most simple configuration, the face of the piston which looks to the


crank shaft forms a pump with the crankcase. Air is introduced through a manifold in

the crankcase by means of the vacuum produced by the piston when increasing the

volume inside the crankcase. When the piston reduces the volume, a Check or a Reed

valve, or a similar component, blocks the flow of the air back to the manifold,

increasing the pressure of the gas inside the crankcase. See Figure 2-3. When the

piston unblocks the scavenging port, the pressurized gas in the crankcase flows to the

combustion chamber at the other side of the piston, which has a lower pressure. It has

to be noticed that, since the exhaust port opens before the scavenging port, the

remaining pressure of the combustion is lost, and ideally the chamber is at

atmospheric pressure, being the pressure in the crankcase higher and thus flowing the

fresh fuel-air mixture to the combustion chamber. In more complex designs, the

difference in pressure is achieved by different devices, as stepped pistons, scavenging

pumps or external compressors such as turbo chargers and super chargers.

Figure 2-3 Scavenging process in the two stroke engine

The mission of the fresh air-fuel mixture is to replace the burned gases which are

spread over all the volume of the chamber. Both, the scavenging and exhaust ports are

located at the bottom side of the combustion chamber, as them have to be unblocked

by the piston near the BDC and blocked again on the cylinders way to the TDC. See

Figure 2-4. On entrance to the combustion chamber, the fuel-air mixture has to travel

to the top of the cylinder and back again to displace the burned gases. In such a

complex move, mixing between burned and fresh gases happen, depending on the

amount of turbulence generated in this movement. There may be also places of the

chamber which the fresh gases cannot access in the time available before the closing

of the exhaust port. This makes that some burned gases remain in the cylinder to face

the next combustion process, lowering the efficiency of it.


Figure 2-4 Mixing process during scavenging

Also, if the scavenging and exhaust ports are facing one each other at opposite sides

of the combustion chamber, the fresh gases will tend to cross the cylinder straight to

the exhaust port, going out from the combustion chamber unburned; as the natural

tendency of the pressurized gases is to keep going in a straight path. See Figure 2-5.

This problem leads to high fuel consumption and high HC emissions.


Figure 2-5 Short circuit during scavenging

The efficiency of the scavenging process depends mainly on the design of the

combustion chamber. Different locations of the ports can force the path of the fresh

gases in a way which reduces mixing and prevents them to go straight to the exhaust

port. See Figure 2-6. Cross scavenge is the simplest arrangement of the ports, in

which fresh gases go in at one side of the cylinder, and burned go out at the opposite

one. The design of the top of the cylinder must be done in a way that it blocks the

gases from short circuiting to the exhaust port, and to force them to the top of the

cylinder. This arrangement has good scavenging at medium and low speeds, but high

fuel consumption at high speeds2. In Loop Scavenge, both ports are in the same side

of the cylinder, the exhaust above the scavenging one. This arrangement avoids the

fresh gases to go straight to the exhaust port, and makes that the fresh gases reach it

only after having travelled through all the combustion chamber. This arrangement has

good scavenging at wide open throttle but low scavenging and high fuel consumption

at part throttle operation3. In Uniflow arrangement, instead of using ports at the

bottom of the cylinder, the exhaust is relocated to the top of the combustion chamber

behind valves like the ones used in the four-stroke engines. This makes that the fresh

gases doesn’t have to change direction in order to clean up the cylinder from burned

gases, they only travel through the cylinder from the bottom to the top. This

arrangement can produce an annular shaped area of burned gases unscavenged, but

this problem can be overcome by producing a swirling motion in the incoming gases.

This arrangement produces a very good scavenging at wide open throttle4, but it loses

2 John B. Heywood, Eran Sher. The Two-Stroke Cycle Engine. Society of Automotive Engineers. 1999.

Pag 52, Table 2-1. 3 John B. Heywood, Eran Sher. The Two-Stroke Cycle Engine. Society of Automotive Engineers. 1999.

Pag 52, Table 2-1. 4 John B. Heywood, Eran Sher. The Two-Stroke Cycle Engine. Society of Automotive Engineers. 1999.

Pag 52, Table 2-1.


the simplicity of the conventional two-stroke engines because it needs complex

mechanisms to operate the valves.

Figure 2-6. Different arrangements of scavenging ports. a) Cross scavenge. b) Loop scavenge. c) Uniflow.


3 Direct Injection

3.1 Injection types

The gasoline spark ignited engine has two types of injection system.

Indirect injection or port injection

Direct injection

The indirect injection system places the fuel in the air manifold, outside the

combustion chamber. See Figure 3-1. This arrangement produces a premixed fuel-air

mixture, which means that the fuel and the air are already mixed when they enter the

cylinder. This has as consequence that, in normal conditions, the flame originated by

the ignition of the spark plug will grow from the center (position of the spark plug) to

the walls. When the flame collides with the walls, it transfers an important amount of

heat to them; this heat cannot be converted to pressure and will go away as waste

through the cooling system.

In abnormal conditions an auto ignition phenomenon, known as Knock, may occur.

While the flame develops, the burned gasses behind it increase their pressure,

compressing the unburned gasses in front of the flame and increasing their

temperature, pressure and density. If the temperature is high enough, it will cause a

detonation of these gasses, which release the major part of its energy, if not all, faster

than the gases being ignited by the flame. This phenomenon can cause a serious

damage to the engine.

For the two stroke engine specifically, it will cause the problem of short circuiting

described in the previous chapter, in which an unburned amount of fuel-air mixture

goes straight to the exhaust port, increasing emissions and fuel consumption, reducing

the efficiency of the engine.

Figure 3-1. Indirect injection, or port injection.

The direct injection system introduces the fuel directly in the combustion chamber,

which means that only air enters the cylinder through the manifold and the mixture of

air and fuel takes place inside the combustion chamber. See Figure 3-2. This system

has the possibility of running in the premixed mode previously described if the

injection of the fuel is done during the admission stroke, and in a mode called

stratified if the fuel is injected at the end of the compression stroke which means that

the fuel burns while being injected.

Stratified combustion has the advantage of avoiding knock, since there is no air-fuel

mixture in the front of the flame. Gasoline needs to have a special property of anti


ignition to avoid knocking when the pressure inside an engine's combustion chamber

is very high, but in the case of stratified combustion it is not needed; even more,

different kinds of fuels can be used by the same engine.

A second advantage of stratified combustion is that, since the front of the flame

doesn't reach the cylinder wall, less amount of heat is transferred to them, increasing

the work transferred to the piston. The third advantage of this type of injection is that

the combustion can be controlled by the amount of fuel being injected, living the

opportunity of not using a throttle valve at all and to reduce significantly pump losses.

This also gives better control of the flame in the combustion chamber than premixed

mode, as in premixed mode the flame propagation depends heavily on the air

movement inside the combustion chamber which is not always the same, and in

stratified mode the flame is always near the injector and controlled by the injection of

the fuel and the shape of the piston.

As for the two stroke engine the big advantage is that, since the fuel is being injected

when the exhaust port is closed, the short circuit problem is totally overcome. This

characteristic is very important since this problem has not permitted the two stroke

engine to be further used in the automotive industry due to the high emissions it

produces.

Figure 3-2. Direct injection.

Another big and important difference between both combustion modes is that flame

propagation is faster in premixed mode than in stratified. This makes that premixed

mode can reach higher engine speeds, developing higher power than stratified mode.

This difference makes that, in practical applications, an engine needs to use both

combustion modes. Stratifying at low and mid revs makes that the operation of the

engine is smoother and the fuel consumption is improved. Premixing at high revs will

develop a higher power

The final difference to be mentioned in this work is the fuel pressure the injector

needs to have on each injection type. Indirect injection runs on premixed mode, and in

this mode the gasoline have time enough to mix with the air. Direct injection runs also

in stratified mode, in which the gasoline has to mix with the air very fast to be able to

ignite when going out from the injector. This requires the direct injector to produce a

thinner spray than the indirect injector (smaller drops of fuel in the jet spray). To

achieve this, the direct injection system needs a higher pressure in the fuel rail, and

thus a high pressure fuel pump, which increases energy consumption, weight and cost.

There are some other strategies to implement a direct injection system, like a dual

fluid injector, or a hammer type of injector. An example of the last one is going to be

presented in section 4.


3.2 Fuel Injectors

Attending to the injection mechanism, the injectors can be divided in two types.

Solenoid actuated

Piezoelectrically actuated.

The solenoid actuated injectors use a solenoid to actuate the needle which allows the

fuel to be injected in to the combustion chamber. The piezoelectric actuated injector

uses an arrangement of piezoelectric crystals to operate the needle. This crystals

change their dimensions when an electric voltage is applied to them. The main

difference between them is that piezoelectric injectors have a higher actuation speed

than solenoid ones. This speed increment can be used to produce two injections

during the same stroke, as to change from stratified to premixed mode in a softer way.

It is also possible for them to vary the needle lift, changing the flow of the fuel.


4 The Evinrude E-TEC™ Outboard Engine and its

Injector's Characteristics

The factor which makes the engine being

analyzed so interesting is the fuel injector

it has. The engine is direct injected,

having all the characteristics described in

the previous chapter. But this injector is

different from the common direct

injectors described.

This injector is solenoid activated, but it is

able to develop the fuel pressure needed

for the injection by itself: it doesn't need a

high pressure pump like the common

direct injection systems. The E-TEC™

injector is based in the FICHT™

development of self pressurized injector

(boosted). The system needs a low-

pressure fuel pump providing 2.5 bar5.

"To actuate the injector, an

electromagnetic field accelerates a steel

armature through a short free stroke until

it impacts a fuel column, thus generating

fuel pressure which opens a spring loaded

outwardly opening nozzle. During the first

part of the injection event, the fuel

pressure is increased due to the additional

conversion of the initial armature kinetic

energy into pressure. The fuel pressure

during the second stage of the injection

process is solely driven by the

electromagnetic force."6

The limit of pressure the injector can create is 50 bar. The driving voltage of the

injector is 40 V. The time that the injector is fed with this voltage determines the time

of the injection. The injector develops a current of up to 10 amperes, depending of the

time that the injector is fed with voltage. The coil of the injector reaches its current

limit at 1.5 mSec. An image from the injector is shown in Figure 4-2. Figure 4-3

shows an image of the injector with the main case disassembled.


System for Direct-Injected Two-Stroke Engines Toward 3-Star Emissions. SAE 2003-32-0007. 6 Strauss Sebastian, Zeng Yangbing and Montgomery David. Optimization of the E-TEC™ Combustion


Figure 4-1 The Evinrude E-TEC™ Engine


Figure 4-2 Injector size

Figure 4-3 Injector Construction


5 Methodology

As it has been mentioned in chapter 1, the main objective of this thesis work is to

obtain information of the engine's operation and to characterize the injector's spray.

The steps taken to achieve these objectives are shown in the following list.

1. Selection of the parameters to be measured during the normal operation of the

engine.

2. Installation of the engine in the test cell. This step involved hard work, as some

adaptations to the engine had to be done. Also the sensors to be used to measure

the parameters were installed during this step. The biggest issue with the sensors

was the set up of the data acquisition system. The pressure sensor and the angle

encoder gave many problems.

3. Setting up of the experiments. This means to decide the points at which the

measurements are going to be taken. Points determined by different loads (torque)

at different speeds.

4. Design of the data structure. As many points were to be measured, and there were

to be many parameters by each point, a data structure had to be decided in order to

access the information fast and in an ordered way during the data manipulation.

5. Performing of the measurements in the test rig.

6. Setting up of the injector in the spray characterization chamber, in order to

characterize the injector's spray.

7. Performing of the spray characterization.

8. Analysis of the information (results, analysis and conclusions).

5.1 Parameters selection

The information to be gathered from the engine was mainly defined by the thesis

sponsor, and it was mainly the combustion modes the engine runs at. Other aspects of

the engine's operation the sponsor was interested in, were the pressure inside the

combustion chamber, the power and the torque developed by the engine. As the

combustion mode the engine is running at does not comes straight forward from a

sensor, but from an analysis that has to be done from other parameters, this ones were

specified as a first step. The parameters to be measured are shown in Table 1.

Table 1. Parameters measured from the engine

Crank angle

position.

This is determined by an angle encoder. The signal is fed

directly in to a computer.

Combustion

chamber's pressure

trace.

This measurement comes from a pressure sensor installed on

the engine's head and which is in direct contact with the

gasses inside the combustion chamber. The signal is

continuously fed in to a computer, and matched with the

angle encoder signal.


Injection timing. The current going in to the injector is continuously

monitored and matched with the angle encoder signal. Then,

the pulse of current shown in a plot reveals the injection

timing.

Ignition timing. This is analog to what is done with the injection timing, but

monitoring the current being fed in to the coil.

Fuel consumption. An instrument is used which weights the amount of fuel

used along a determined period of time. From here, the fuel

consumption in g/sec is straight forwardly obtained. Also,

the bsfc is calculated using the measured mass over the

average power delivered by the engine during that same

period of time.

Exhaust gasses'

lambda value.

It is measured using a lambda sensor very common in the

automotive industry. However, it is not useful when

measuring this engine, since as it is a two stroke engine, the

short circuit phenomena modifies the properties of the

exhaust gases. For the specific case of the Evinrude engine,

as it is short circuiting only air, the lambda value goes very

lean (up to 4 when idling).

Throttle's angle. A sensor locating the position of the throttle was not used.

Instead, since the throttle is controlled using a servo and thus

the position of the throttle is directly related to the dial

controlling the servo, it was calculated from the dial

position. The angle of the throttle when full closed and full

open was measured and related to the position of the dial at

the same points. From there, the angle of the throttle is

derived.

Emissions They were measured using an emissions measuring

instrument. There were measurements for HC, NOx, NO,

NO2, CO and CO2.

Engine speed This was provided by the brake's instruments. Since the

brake was connected to the engine's gearbox, as it is going to

be described in section 5.2, it has to be converted to the real

engine's speed using the gear ratio of the gear box.

Engine torque This was provided by the brake's instruments. The case is

analog to the engine speed. It had to be converted to the real

engine's torque using the gear ratio of the gear box.

Engine power This was derived from the speed and torque information.

Engine bmep This was derived from the power, using the formula

P=power, V=engine's displacement, n=engine's speed.


Also, in order to control the injector in the spray characterization rig, the injector's

electrical parameters had to be measured first during the normal operation of the

engine.

5.2 Test Rig Set Up

Figure 5-1 Engine on rig

The outboard engine was connected to the measuring brake through the propeller

shaft. It was decided to mount the engine complete, to try to preserve as much

conditions the engine was designed to as possible. For this reason, all the brake

measurements such as brake power and bmep have the gear box included, in other

words, the losses of the gear box have not been calculated.


Figure 5-2 Gearbox and brake

The first challenge with the engine was to split the cooling water from the exhaust

gasses. The engine is designed to use water from the sea, or the lake it is being used

at, and use it as a cooling fluid. Once the water has been used, it is mixed with the

exhaust gases in a chamber between the gearbox and the engine, and they are disposed

from the engine thru the center of the propeller. As the emissions measurement

equipment does not admit any particle of water, the engine had to be dismantled and

modified to split water from exhaust gases.

Figure 5-3 Cooling and exhaust separation

The gearbox temperature was a concern. I is normally cooled down by the water it is

immersed in. The complexity of needing a container for the cooling water and a shaft

going out from it through a sealed hole motivated for a different solution. It was

decided to circulate the oil from the gear box in to a heat exchanger. This was not

enough when speeding up the engine at high loads, being one of the biggest obstacles

when measuring those points. A fast and simple fixture was conducted using a simple

bucket, a hose and aluminium paper for the most demanding points. Even though this

fixture was not able to maintain the temperature for a long time, it gave enough time

to record the data point by point.


Figure 5-4 Cooling of gearbox

The exhaust pipe ends in an open container full of water. This arrangement tries to

replicate the counter pressure of the water of the sea. In the beginning, the exhaust

pipe was connected to the exhaust system of the test cell. This system sucks the gasses

from the engine with a light vacuum. This vacuum pulled more oil from the oil

container in the engine, damaging the spark plugs. For this reason, the option of the

container full of water was adopted.

Figure 5-5 Exhaust container

The engine had holes aside of the spark plugs blocked by a screw. May be this holes

are used in some way in larger engines, but they are not in this engine. A pressure

sensor was adapted to fit this hole. The model of pressure sensor couldn't stand the

temperature (AVL GM12D), and in a preliminary measurement it stopped operating.

A second sensor was installed, with the provision this time of air cooling. A

thermocouple was also installed to monitor the effectiveness of the cooling system.

The temperature was maintained around 200 C.


Figure 5-6 Pressure sensor setup

The engine was connected to an AVL Dynamic Fuel Balance to perform fuel

consumption measurements.

The ignition and injector timings were measured with a Fluke AC current clamp. The

intention with those was only to track the timings, as they are not precise enough as to

measure the current of the injector. With this purpose a simple circuit was built to

measure current and voltage. It made the current to run through resistors of known

values and the voltage on those resistors was measured. Using a differential amplifier

the current and voltage was captured in the computer using LabView express. As the

differential amplifier was not available all the time for being in use in another project,

only selected points were measured with it.

5.3 Experimental Setup

Relevant points for measurement must be selected which represent some interest for

the engine analysis. In the beginning it is difficult to select those points as there is not

knowledge about the engine’s characteristics. For such reasons, some predictions have

to be done in order to plan ahead the points to measure.

As a start point, it is possible to calculate the torque at the peak power point by using

the technical information of the engine, in which is stated that:

From there, a torque of 30 Nm is calculated for that point.

In a preliminary test, by using the dyno's analogical equipment (speed and torque

meter), two measurements of the torque at WOT where taken, being 41.86 Nm@2150

rpm and 46.51 Nm@3225 rpm. 3000 rpm is assumed to have the highest torque,

and a torque of 15Nm@900 rpm is also assumed. From this information it is possible

to build an approximated torque curve, which is shown in Figure 5-7.


Figure 5-7 Torque curve approximation

As the time needed to take the measurements from each point is not known, a set of

priority points is selected; this in the case that it becomes not possible to measure all

the points. It was decided to measure all the points in the case that time would be

available.

In general it is possible to say that the points of interest are those of low load in a low

speed area and those with a high load in the high speed area. Those points are shown

in Figure 5-8.

Figure 5-8 Measurement points

0

5

10

15

20

25

30

35

40

45

50

900 1500 2000 3000 4000 5000 5800

Engi

ne

to

rqu

e (

Nm

)

Engine speed (rpm)

Torque Curve Aproximation

WOT

0

5

10

15

20

25

30

35

40

45

50

900 1500 2000 3000 4000 5000 5800

Engi

ne

to

rqu

e (

Nm

)

Engine speed (rpm)

Measurement Points

WOT


During preliminary tests, it has been identified that the engine runs lean in the low

revs area having a lambda value is as high as 4, and it decreases as speed and load

increase. Further observation of the engine has shown that the throttle doesn’t open

until a certain load and speed has been reached. It has been observed that the speed of

the engine while the throttle is still closed can go as high as 8 Nm@3000 rpm, or 11

Nm@2500 rpm.

As this frontier where the throttle starts opening is interesting also to analyze, some

measurements have been done to include it in the predicted torque curve. This line is

added to the curve in Figure 5-9.

It is also needed to say that the lambda values seen on the lambda measurement

device are not real. It will always show lean values because a two stroke engine short

circuits clean air in to the exhaust port. This will make that the amount of air will

increase in relation to the fuel burned, making the reading something different from

what is going on in the combustion chamber. The real lambda values are calculated

from the CO and CO2 measurements. This is explained later.

Figure 5-9 Throttle opening points

In this plot the throttle opening curve is showing the frontier at which the engine starts

working at lambdas near to 1, while the area below the curve is an area in which the

engine runs lean, driven only by the changes of mass of fuel and injector and ignition

timings.

There is one more curve that has to be considered. Since this engine has been

conceived for a marine application, attention has to be put in the power consumed by

0

5

10

15

20

25

30

35

40

45

50

900 1500 2000 3000 4000 5000 5800

Engi

ne

to

rqu

e (

Nm

)

Engine speed (rpm)

Throttle Oppening Points

WOTThrottle Opening


the propeller. This curve can be approximated as well. From the Propeller Handbook7

there comes the relation:

n = 2.7 for average boats

PHP = Propeller horse power

RPM = Engine speed

C1 = Constant

From here, the torque relation can be found:

The engine's operation manual mentions that "the correct propeller for your boat,

under normal load conditions, will allow the engine to run near the midpoint of the

RPM operating range at full throttle"8. Considering 3000 rpm as the middle of the

operating range, and using τ=45 Nm, C1 is found to be 55.22x10-6

. In this way, the

propeller's torque curve is approximated to Figure 5-10.

Figure 5-10 Propeller's torque curve

The propeller's torque is then added to the torque map. The complete set of points

resulting from the addition of all this curves becomes the Engine Map, which

organizes all the measurements that have to be done to the engine; it is shown in

Figure 5-11.

7 Dave Gerr. Propeller Handbook. International Marine. 2001. Pag. 4 @ Google Books.

8 BRP Us Inc. Evinrude Etec Outboard Operator's Guide. 2010. Pag. 65.

0.00

10.00

20.00

30.00

40.00

50.00

900 1500 2000 3000

Torq

ue

_Nm

Speed_rpm

Propeller's Torque


Figure 5-11 Full set of measurement points

Each point is named using a number, in order to easily identify it during the analysis

of the data. The numbers assigned to the points are shown in the following Table 2.

Table 2 Predicted measurement points

load

speed 0 5 10 15 20 25 30 35 40 45 wot Throttle op Propeller

900 1 2 3 4 5 45

1500 6 7 8 9 10 11 12 13 46

2000 14 15 16 17 18 19 20 21 22 23 24 47

3000 49 50 51 52 53 54 25 26 27 28 29 48

4000 30 31 32 33 34

5000 35 36 37 38 39

5800 55 56 57 40 41 42 43 44

Measurement points

The consecution of numbers is related to the progression of the load in a single engine

speed. The points for the WOT, Throttle opening and Propeller's curve are identified

separately in the same table.

0

5

10

15

20

25

30

35

40

45

50

900 1500 2000 3000 4000 5000 5800

Engi

ne

to

rqu

e (

Nm

)

Engine speed (rpm)

Engine Map

WOT Throttle Opening Propeller consumed torque


5.4 Data Structure

Information from 50 cycles will be stored for each measurement point. This is with

the intention of averaging the information from those 50 cycles, and being more

precise with the measurements. Each cycle will have 15 parameters measured and 5

more parameters calculated from the first ones.

The pressure trace, the spark timing, the injector timing, the speed and the load are

refreshed cycle by cycle, while the rest of the data, as emissions of fuel consumption,

are captured only one time and being stored the same for all the cycles. The structure

of the data is shown in Table 3.

Once there is a data average for each point, the bmep, torque and power curves can be

built. Also, from the injector and spark timing information, the injector's operation

characteristics can be gathered in order to analyze the mode it is running at (premixed

or stratified). The values that are going to be considered for this are the following:

Spark timing in CAD.

Injection timing in CAD.

Injection time in seconds.

Important information is also the current and voltage used by the injector. For this

purpose, and for them to be accurately measured, a circuit was built which sent the

information to a differential amplifier which allowed the signals to be fed in to the

logging computer. The differential amplifier is not available in the lab all the time, so

special measurements will be performed for this purposes, gathering the current and

the voltage signals for all the loads in steps of 5 Nm for the constant speed of 3000

rpm, and for all the speeds planned for the engine map at a constant load of 20 Nm.

For the points considered in the engine map, the current to the injector will be

measured using a magnetic clamp with the purpose of detecting when the injection is

taking place, as the current reading of this device can be not as precise as the

differential amplifier one.


Table 3 Data structure as stored in Matlab

Evinrude Point Cycle Data

PresTrace

injCurrent

sparkTim

fuelConsm

lambda

dialPos

bsfc

HC

NO

a01 NO2

NOx

CO

CO2

speed

torque

throtAng

massInjected

airMass

point01 bmep

power

a02

a03

.

.

.

a50

Data average

Evinrude point02

point03

.

.

.

point48

bmepTrace

torqueTrace

powerTrace

injParameters

injMap

ca

lcu

late

d

me

asu

red


5.5 Spray Characterization Setup

The spray characterization task was performed using a spray characterization chamber

which consists of a sealed volume in which the injector discharges fuel in to a

pressurized volume representing the back pressure of the cylinder. The chamber has

windows thru which the injector's spray is measured. The spray characterization

chamber is shown in Figure 5-12.

Figure 5-12 Spray Characterization Chamber

As the Evinrude injector has a different volume and shape from the common gasoline

indirect and diesel injectors for which the chamber was designed, it was needed to

modify the support to which the injector was attached to the chamber. A cut view of

the spray characterization chamber is shown in Figure 5-13. There it is possible to see

the position the injector has in the chamber.

Figure 5-13 Spray Characterization Chamber Section View


The control of the injector was an important issue at this stage of the project. At the

combustion lab there is a set of standard injector controllers, but at the beginning it

was not sure how to set tem up in order to produce a useful signal. During the first

measurements of the current driving the injector, it became clear that those standard

controllers were useless as the current they produced didn't match the current required

by the Evinrude injector. See section 6.2 for details on the current used by the

injector. For this reason, it was needed to build a controller specially designed to drive

this injector. It was a main issue as it took long time until the controller was ready to

be used.

High speed imaging was used to capture images of the injector's spray. The images

were used to measure the penetration and the diameter of the spray's cone. It also

allows seeing the spray's behaviour against different back pressures. Also, it is known

that the injector is capable of generating its own pressure to inject the fuel in to the

combustion chamber, but it is interesting also to find out if the pressure of the pump

feeding the fuel in to the injector makes a difference in the spray This was possible to

see using high speed imaging as well. The arrangement is shown in Figure 5-14.

Cam era

Flash

Spray Cham ber

Figure 5-14 High Speed Imaging Setup

To measure the speed and diameter of the drops in to the injector's spray, a phase

doppler laser was used. Usually, when performing this kind of measuring, a complete

mesh of the spray is measured, but as the intention in this work is to have an

estimation of the speed and diameter of the drops, only one point was taken. Figure

5-15 represents the spray in to the combustion chamber. It is clearly visible the source

of the spray, the needle, which is set to be the origin to start measuring the spray size.


Figure 5-15 Spray in to the combustion chamber

The point selected to measure drop speed and diameter was at 53.5 mm below the

surface of the needle, and 17.5 mm out its center. As the spray has a conic shape, it is

useless to measure in the center, so the measuring point has to be set on the face of the

cone. The representation of the measured point is also shown in Figure 5-15.This

point was selected because it is considered that there the spray is completely

developed.

The arrangement of the phase doppler instrument is shown in Figure 5-16. The

receiver related to the beam has to be at 60º in order to properly work.

Transm itter

Receiver

Spray Cham ber

Figure 5-16 Phase Doppler set up

Measured point

60º


6 Results

This chapter presents the results obtained from the engine characterization in the test

rig. The first result is to obtain the real torque-speed curve and to compare it to the

curve estimated in the methodology section. The power-speed curve and the imep-

speed curve are also presented in this section.

The second section presents the electrical measurements from the injector. As it's

been said in the previous chapter, the current and voltage of the injector have been

measured in a way which assures high precision, and they are presented compared to

the injection time.

In the third section the map of the injector is presented, in which the injection timing

is deployed along spark timing and injection time. This is with the purpose of

identifying the combustion mode in which the engine is running at (homogeneous or

stratified).

The fourth result presented is composed by the plots for the specific fuel consumption

and the emissions, as to identify the consumption and emissions performance of the

engine through its normal use along the propeller curve.

6.1 Torque-Speed curve

In the approximated torque curve described in chapter 5, Figure 5-7, the maximum

torque was assumed to be 45 Nm@3000 rpm. According to it the propeller curve was

set to have its peak at the same point. In the real curve the maximum torques in every

speed were found to be higher than expected, and the maximum engine torque was

found to be 52.5 Nm@4000 rpm (among the speeds that were measured). The torque-

speed curve is shown in Figure 6-1.

Figure 6-1 Torque-Speed curve

9.6

15.4

30.3

15.3

14.1 9.6

8.0 5.8

34.6

43.9

50.3 52.5

42.9

35.2

0.0

10.0

20.0

30.0

40.0

50.0

60.0

1500

2000

3000

4000

5000

5800

Engi

ne

To

rqu

e _

Nm

Engine Speed _rpm

Torque-Speed Curve

Propeller

Throttle

Torque


The max torque curve is represented in thick blue. The torque of each point is shown

near the corresponding point, and they are shown in Nm. It can be seen that the speed

of 900 rpm was removed from the planned engine map. During the measuring it was

noticed that the engine was so unstable at this speed that it was hard to set the precise

load in the screen, making the reading not very trustable. Even though points of 0 Nm,

5 Nm and 10 Nm @900 rpm were measured, they will not be used.

It also can be seen how the peak torque is at 4000 rpm. The propeller curve was

modified as to match it with this point, adding one additional point to the measuring

map. As it has been described in chapter 5.3, the constant C1 is now found to be

3.988x10-5.

As it was established in chapter 5, the red curve stands for the point at which the

throttle starts to open. Below that curve the engine works as a diesel engine, in the

sense that the increment in speed and/or load is achieved by the injection timing and

mass of fuel injected.

The rest of measuring points are shown in Figure 6-2.

Figure 6-2 Real set of measurement points

Comparing this figure to Figure 5-8, it can be seen that some points have been added.

In order to have a complete set of measurements for the peak torque and peak power

speeds, measurements were taken to all the loads for 3000 rpm and 5800 rpm. After

the measurements were finished, it was found that the peak torque point is at 4000

rpm. Due to temperature problems in the gear box at high speeds, it was decided not

to perform the missing measurements at 4000 rpm.

The description of the complete set of points measured is shown in Table 4.

30 30

40 40

45 45 34.6

43.9

50.3 52.5

42.9

35.2

0.0

10.0

20.0

30.0

40.0

50.0

60.0

1500

2000

3000

4000

5000

5800

Engi

ne

To

rqu

e _

Nm

Engine Speed _rpm

Torque-Speed Curve

Torque


Table 4 Naming of measured points also used in Matlab

load

speed 0 5 10 15 20 25 30 35 40 45 wot Throttle op Propeller

900 1 2 3 45

1500 6 7 8 9 10 11 58 12 13 46

2000 14 15 16 17 18 19 20 21 22 23 24 47

3000 49 50 51 52 53 54 25 26 27 59 28 29 48

4000 30 31 32 60 33 34 63

5000 35 36 37 61 38

5800 55 56 57 40 41 42 62 43

Measurement points

A total of 59 points were measured, as points 4, 5, 39 and 44 were decided not to be

done. The order of the numbering of the points is not completely in order because it

was more flexible in that way during the measurement process. This was useful to

face unexpected situations very fast, as it was sometimes needed due to the problems

in the temperature of the gearbox, the temperature of the pressure sensor and some

others. The first step during the processing of the data in Matlab was to order all the

information according to the structure described in chapter number 5.4, and Table 4 is

used to identify any point needed.

The calculation of the power is simply done by multiplying the speed and the torque.

The curve obtained is shown in Figure 6-3.

Figure 6-3 Power-Speed curve

As it has been seen that all the torque values where higher than expected, it is easy to

think that the power curve will hold higher values also. Of course, the max power

5.3

9.3

16.1

22.4 23.2 22.6 21.3

0.0

5.0

10.0

15.0

20.0

25.0

1500

2000

3000

4000

5000

5800

Engi

ne

Po

we

r_kW

Engine Speed _rpm

Power-Speed Curve


@5800 rpm is higher than the reported in the technical specifications; from 18 kW to

21.3 kW. But also it is seen that the maximum power is somewhere between 4000

rpm and 5000 rpm as the spline interpolation is showing.

6.2 Injector parameters

One of the main objectives of the present work is to measure the electrical parameters

of the injector in order to find out how to control it. It wasn't needed to measure both,

current and voltage thru all the points in the engine's map. The objective was to

identify the changes in the current and in the voltage when the engine is increasing

speed at a constant load, and when the engine is developing more torque at a constant

speed.

Figure 6-4 and Figure 6-5 show the measurements of the driving voltage and current

on the injector when the engine is developing 5 Nm and 46 Nm at 3000 rpm

respectively. In them it is possible to see that the driving voltage is constant at 40 V

during the time desired for the injection event. The current increases from cero to a

maximum value. As the injector is a coil, it takes time for it to fully charge of energy.

When that happens, the current shows a constant value as well. This event happens at

around 1.5 mSec.

Figure 6-4 Electrical measurements at 5 Nm and 3000 rpm

0.00

2.00

4.00

6.00

8.00

10.00

12.00

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

50.00

-0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Cu

rre

nt_

A

Vo

ltag

e_V

Injector Current and Voltage 5 Nm at 3000 rpm

Voltage

Current


Figure 6-5 Electrical measurements at 46Nm and 3000 rpm

The injector is basically an electro magnet driving a piston which, when pushing the

fluid, has to overcome the force of a spring which maintain the needle closed (see

chapter 4). This means that the needle will open at the same pressure. Doesn't matter

how much more voltage is fed in to the coil, the pressure of the fluid going through

the needle is always going to be the same. For this reason there were suspicion that

the voltage fed in to the injector had always the same magnitude, and that the current

would follow the function of the coil when charging energy. Being this right, it would

then mean that the only parameter which has to change in order to operate the injector

is the time during which the voltage is being fed.

Figure 6-6 shows the measurements of the injector parameters along different loads at

a constant speed of 3000 rpm.

0.00

2.00

4.00

6.00

8.00

10.00

12.00

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

50.00

-0.2 0

0.2

0.4

0.6

0.8 1

1.2

1.4

1.6

1.8 2

2.2

2.4

2.6

2.8 3

3.2

Cu

rre

nt_

A

Vo

ltag

e_V

Injector Current and Voltage 46 Nm at 3000 rpm

Voltage

Current


Figure 6-6 Injector electrical measurements at 3000 rpm

The plot clearly shows that the voltage is constant through all the load increment at a

certain speed. The numbers in the table at the bottom of the plot confirm that there is

no difference among them. The red curve, which represent the amount of current

flowing in to the injector's coil, reveals the time that it takes for the coil to complete

charge energy. The blue curve, representing the time of injection, shows the steady

increment of mass of fuel injected.

Figure 6-7 shows the measurement of injector parameters performed at constant load.

0 5 10 14 18 23 28 33 37 41 46

Voltage_V 39.98 39.98 39.98 39.98 39.98 39.98 39.98 39.98 39.98 39.98 39.98

Time_mSec 1.13 1.25 1.30 1.43 1.51 1.63 1.70 1.75 1.86 1.98 2.21

Current_A 9.185 9.589 9.694 9.971 9.995 9.995 9.995 9.995 9.995 9.995 9.995

0.00

2.00

4.00

6.00

8.00

10.00

12.00

0.000

5.000

10.000

15.000

20.000

25.000

30.000

35.000

40.000

45.000

Tim

e_m

Sec

C

urr

en

t_A

Vo

ltag

e_V

Load_Nm

Injector Parameters Load at 3000 rpm


Figure 6-7 Injector electrical measurements at 20 Nm

This plot reveals again that the voltage has the same magnitude. Now the injection

time is erratic, even it tends to be reduced as the speed increases. It looks strange

since the higher the power in the engine, the higher the demand for energy from the

fuel. But we have to keep in mind that the timings for the injector and for the spark

plug are changing. As for the current, the value at 1.5 mSec seems not to make

completely sense with the others. The other values completely make sense, even if

they are crossed with the values of Figure 6-6. From there, a conclusion can be drawn

that the injector's coil charges completely at 1.45 msec. Also, from Figure 6-5 it can

be said that the span of injection time is 1.1 mSec.

6.3 Injection Timing

Going further in the injector analysis, attention now has to be put in the injection and

spark timings, along with the injection time. Figure 6-8 shows the progression of the

injection and ignition along different loads at 3000 rpm. This figure expands the

contents of Figure 6-6, which shows the same information but for the injector current

and voltage. Figure 6-9 shows the time between the injection event and the ignition

event in mSec, which reflects the mixing time that the fuel has with the air in the

combustion chamber. Also, Figure 6-10 and Figure 6-11 show the time plots of

injection in mSec and CAD.

1500 2000 3000 4000 5000

Voltage_V 39.980 39.980 39.980 39.980 39.980

Current_A 9.995 9.985 9.995 9.995 9.987

Time_mSec 1.63 1.50 1.60 1.45 1.44

1.30

1.35

1.40

1.45

1.50

1.55

1.60

1.65

0.000

5.000

10.000

15.000

20.000

25.000

30.000

35.000

40.000

45.000

Tim

e_m

Sec

Cu

rre

nt_

A

V

olt

age

_V

Speed_rpm

Injector Parameters Speed at 20 Nm


Figure 6-8 Ignition and Injection timing at 3000 rpm

Figure 6-9 Time between injection and ignition at a constant speed of 3000 rpm

-57.6

-111.72

-250

-200

-150

-100

-50

0

0 10 20 30 40 50

CA

D

Load _ Nm

Injection Timing Load at 3000 rpm

Spark Timing Injection Timing

3.01

0.00

2.00

4.00

6.00

8.00

10.00

12.00

0 10 20 30 40 50

Tim

e m

Sec

Load_Nm

Mixing Time Load at 3000 rpm


Figure 6-10 Injection time in mSec at 3000 rpm

Figure 6-11 Injection time in CAD at 3000 rpm

0.00

2.00

4.00

6.00

8.00

10.00

12.00

0 10 20 30 40 50

Tim

e_m

Sec

Load_Nm

Injection Time mSec Load at 3000 rpm

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

50.00

0 10 20 30 40 50

CA

D

Load_Nm

Injection Time CAD Load at 3000 rpm


The red curve in Figure 6-8 reflects the spark plug timing, which moves between -20

and -60 CAD, as it is possible to see in the axis to the left. The blue curve reflects the

injector timing. It is clearly visible that the injector time increases while the injection

timing advances more and more. The points on the curves show the moment at which

the throttle starts opening.

In Figure 6-7 it was shown that the injection time reduce while the speed increase at a

constant load of 20 Nm. Figure 6-15 represents the injection time for a constant load

of 30 Nm and confirms the observation. Also Figure 6-12 reveals that at low speed the

injector changes its timing, but at high 4000 rpm it stays in the same value.

Figure 6-12 Ignition and Injection timing at 30 Nm

-250

-200

-150

-100

-50

0

1500 2500 3500 4500 5500

CA

D

Speed_rpm

Injection Timing Speed at 30 Nm



Figure 6-13 Time between injection and ignition at a constant load of 30 Nm

Figure 6-14 Injection time in mSec at 30 Nm

4.15

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

1500 2000 2500 3000 3500 4000 4500 5000 5500

Tim

e m

Sec

Speed_rpm

Mixing Time Speed at 30 Nm

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

1500 2000 2500 3000 3500 4000 4500 5000 5500

Tim

e_m

Sec

Speed_rpm

Injection Time mSec Speed at 30 Nm


Figure 6-15 Injection time in CAD at 30 Nm

Figure 6-16 shows the injector timing data for the propeller curve. In this case the

engine is increasing both, speed and load, and as a consequence the plot seems to be

more complex.

Figure 6-16 Ignition and Injection timing along propeller curve

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

1500 2000 2500 3000 3500 4000 4500 5000 5500

CA

D

Speed_rpm

Injection Time CAD Speed at 30 Nm

-51.3

-82.56

-250

-200

-150

-100

-50

0

1500 2000 2500 3000 3500 4000

Tim

e_m

Sec

Speed_rpm

Injection & Ignition Timing Propeller curve



Figure 6-17 Time between injection and ignition along the propeller curve

Figure 6-18 Injection time in mSec along propeller curve

2.60

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

1500 2000 2500 3000 3500 4000

Tim

e_m

Sec

Speed_rpm

Mixing Time Propeller curve

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

1500 2000 2500 3000 3500 4000

Tim

e_m

Sec

Speed_rpm

Injection Time mSec Propeller curve


Figure 6-19 Injection time in CAD along propeller curve

One of the most important features that this engine has is the flexibility (being direct

injected) of changing the time of injection in a very wide area, and making the engine

to run over different injection modes. Figure 6-20 shows a contour plot over the bmep

curve showing the variations in injection timing. It can be observed that the latest

injections are in the low load - low speed areas, and the earliest ones are mainly where

the highest energy is being produced. The curve at which the throttle starts opening is

shown in bright green. Also the zone for which no measurements were taken, or

shadow, is shown in gray line.

0.00

10.00

20.00

30.00

40.00

50.00

60.00

1500 2000 2500 3000 3500 4000

Tim

e_m

Sec

Speed_rpm

Injection Time CAD Propeller curve


Figure 6-20 Injection timing map. The values in each area of the contour plot show the range in CAD the

injector is injecting at when the engine is operating inside such area.

Figure 6-21 shows a contour plot of the ignition timing against a bmep curve. The

most advanced times are in the lower center of the plot. It shows no significant change

across the speeds which can explain the increase of speed with a reduction of injected

mass when in constant load.

0

1

2

3

4

5

6

7

1500 2000 2500 3000 3500 4000 4500 5000 5500

bm

ep

_bar

Engine Speed _rpm

Injection Map

shadow Throttle bmep

-20 / -60 -60 / -80 -80 / -100

-100 / -140

-140 / -160

-160 / -180 -180/ -200

-200/-220

-180/ -200

-100 / -140


Figure 6-21 Ignition timing map. The values in each area of the contour plot show the range in CAD the

spark plug is igniting at when the engine is operating inside such area.

The throttle angle may be also interesting when trying to figure out the injection mode

of the engine. The contour plot for the throttle angle is shown in Figure 6-22.

Figure 6-22 Throttle angle map. The values in each area of the contour plot show the range in degrees the

throttle is positioned at when the engine is operating inside such area.

0

1

2

3

4

5

6

7

1500 2000 2500 3000 3500 4000 4500 5000 5500

bm

ep

_bar

Engine Speed _rpm

Ignition Map

shadow Throttle bmep propeller

0

1

2

3

4

5

6

7

1500 2000 2500 3000 3500 4000 4500 5000 5500

bm

ep

_bar

Engine Speed _rpm

Throttle Angle


-20 / -40

-30 / -40

-40 / -50

-40 / -50

-50 / -60

-50 / -60

20

20 / 30

30 / 40

40 / 90


6.4 Specific Fuel Consumption and Emissions

Figure 6-23 shows a superimposed plot of the bmep, propeller and throttle curves over

a colored plot of the specific fuel consumption of each measured point. The colour of

the background in each cell indicates the value of the sfc, being red the higher and

green the lowest.

What is interesting to see in this figure is that the optimum fuel consumption is not in

the low speed high load region as in automotive engines is. In this case the optimum

point is near the center of the bmep curve in the high loads. When compared to the

propeller curve, it can be seen that this curve is near to that area, which seems logical

as this engine is projected to be running along the propeller curve, and the optimum

point being at the highest speed along this curve. SFC values in the plot are given in

g/kWh.

368 307.7

300.0 333.7 280.1 328.5

333.7 314.5 285.9 298.9

526.4 410 337.2 298.9 314.1 347.5

401.3 310 291.8 307.5 321.9 330.6

399 395.9 377.7 320.2 357.1

417.1 362.1 396.4 334.6

445.5 488.8 311.3 357.6

364.8 264.6 355.8 430.9

723.1 901.8 987.3 362.5

2746.6 1477.7 740.6 862.4

0

1

2

3

4

5

6

7

1500 2000 3000 4000 5000 5800

bm

ep

_bar

Engine Speed (rpm)

bsfc_g/kWh

propeller throttle bmep

Figure 6-23 bsfc map


The superimposed plots for emissions are shown in the following figures.

4920 2060

3060 2880 1590 1750

2280 1850 1660 1630

4730 1980 1860 1700 1530 1380

2830 2040 1956 1600 1480 1380

2710 1820 2010

1400 1760

2010 1610 1090

1720

1170 990 920

1920

770 2280 570

580

960 1000 770

320

1530 1670 1980

1070

536 516

361 730 644 362

591 844 427 407

378 633 607 360 301 205

385 421 454 312 207 205

368 366 356 133 190

65 206 526 104

92 64 173 56

40 65 46 79

26 16 27 38

4 3 4 18

0

1

2

3

4

5

6

7

1500 2000 3000 4000 5000 5800

bm

ep

_bar

Engine Speed (rpm)

HC_ppm


Figure 6-24 HC map

0

1

2

3

4

5

6

7

1500 2000 3000 4000 5000 5800

bm

ep

_bar

Engine Speed (rpm)

NO_ppm


Figure 6-25 NO map


32 25

29 41 8 19

47 47 16 6

30 48 36 15 18 12

37 23 29 18 13 12

35 22 18

11 12

35 23 19

8

49 40 26

7

45 35 43

3

453 42 25

3

24 24 16

5

569 534

397 778 652 379

630 892 434 420

405 684 648 374 321 213

422 443 470 331 223 213

400 381 377

147 202

100 228 551

115

141 104 201

64

85 100 89

83

70 57 52

41

27 27 21

26

0

1

2

3

4

5

6

7

1500 2000 3000 4000 5000 5800

bm

ep

_bar

Engine Speed (rpm)

NO2_ppm


Figure 6-26 NO2 map

0

1

2

3

4

5

6

7

1500 2000 3000 4000 5000 5800

bm

ep

_bar

Engine Speed (rpm)

NOx_ppm


Figure 6-27 NOx map


2.19 2.446

2.975 1.31 0.986 2.3

1.56 0.96 2.13 1.865

3.768 1.14 1.075 2.078 1.604 2.398

1.526 1.267 1.269 1.355 1.13 1.86

1.565 1.467 1.216

1.143 1.721

0.161 1.31 0.968

1.38

0.07 0.0585 0.693

1.816

0.175 0.194 0.376

0.806

0.13 0.138 0.251

0.264

0.092 0.107 0.15

0.342

6.52 7.61

5.82 7.4 7.99 7.6

6.58 7.7 8.6 7.6

5.21 6.98 7.77 8.86 8.07 8.63

6.19 7.31 8.15 9.03 8.35 8.63

6.03 7.15 7.81

8.56 8.54

5.75 7.18 7.65

8.98

6.65 7.8 8.01

9.37

4.73 5.75 8.14

9.56

3.52 3.78 5.96

9.14

2.36 2.58 3.25

6.7

0

1

2

3

4

5

6

7

1500 2000 3000 4000 5000 5800

bm

ep

_bar

Engine Speed (rpm)

CO_ppm


Figure 6-28 CO map

0

1

2

3

4

5

6

7

1500 2000 3000 4000 5000 5800

bm

ep

_bar

Engine Speed (rpm)

CO2_ppm


Figure 6-29 CO2 map


6.5 Spray Characterization

As part of the project a spray characterization of the Evinrude injector was done.

Some results were obtained, as more time is needed to do a complete set of spray

characterization, being subject of a different project.

Figure 6-30 shows a measurement in millimetres of the injector's spray at .5 bar back

pressure and 2.3 mSec of injection time.

Figure 6-30 Cone diameter and spray penetration

From this figure it can be seen that the penetration of the injection reaches up to 60

mm. The diameter of the hollow cone is around 12 mm.

Figure 6-31 Comparison of sprays at different back pressures


In this image is possible to see how the pressure affects the shape of the spray. In

chapter 7.2 it was presented the way that the mass of injected fuel changes with

different back pressures along the propeller's curve.

Table 5 and Table 6 show in detail the response of different events of the injector

along different back pressures. There is possible to see in detail how the injection time

(considering the time during which fuel is going through the needle, instead of the

time while the injector is being feed with voltage which is the one used in previous

chapters) changes with the back pressure, and also the lag of the injector between the

time when it is feed with voltage and when it shows a response.

Table 5 Injector events at different back pressures

Back Pressures

Needle Open

Start of Injection

End of Injection

Injection Time

6

1.490 1.520 3.200 1.71

1.490 1.520 3.180 1.69

1.480 1.520 3.180 1.70

1.480 1.510 3.190 1.71

1.490 1.520 3.200 1.71

1.490 1.520 3.190 1.70

1.487 1.518 3.190 1.70

4.5

1.480 1.510 3.160 1.68

1.470 1.510 3.190 1.72

1.480 1.500 3.180 1.70

1.470 1.500 3.190 1.72

1.470 1.510 3.190 1.72

1.480 1.510 3.190 1.71

1.475 1.507 3.183 1.71

3

1.480 1.500 3.180 1.70

1.470 1.500 3.180 1.71

1.480 1.510 3.200 1.72

1.480 1.510 3.180 1.70

1.480 1.510 3.180 1.70

1.480 1.510 3.190 1.71

1.478 1.507 3.185 1.71

2.5

1.470 1.500 3.190 1.72

1.470 1.510 3.210 1.74

1.470 1.500 3.210 1.74

1.480 1.510 3.200 1.72

1.470 1.500 3.190 1.72

1.480 1.510 3.190 1.71

1.473 1.505 3.198 1.73

2

1.460 1.500 3.220 1.76

1.470 1.510 3.190 1.72

1.472 1.506 3.198 1.73

1.5 1.460 1.500 3.220 1.76

1.470 1.500 3.210 1.74


1.468 1.503 3.206 1.74

Table 6 Injector events at different back pressures (continued)

Back Pressures

Needle Open

Start of Injection

End of Injection

Injection Time

1

1.490 1.490 3.210 1.72

1.490 1.490 3.250 1.76

1.475 1.498 3.216 1.74

0.8

1.460 1.490 3.250 1.79

1.470 1.490 3.200 1.73

1.475 1.494 3.222 1.75

0.5

1.460 1.480 3.230 1.77

1.460 1.500 3.240 1.78

1.467 1.492 3.226 1.76

0.3

1.460 1.480 3.240 1.78

1.460 1.480 3.240 1.78

1.464 1.488 3.233 1.77

0.2

1.450 1.480 3.270 1.82

1.450 1.490 3.260 1.81

1.458 1.485 3.245 1.79

0.1

1.450 1.480 3.240 1.79

1.460 1.490 3.240 1.78

1.455 1.485 3.248 1.79

Figure 6-32 Drop speed and diameter histogram for .5 bar back pressure and 2.3 mSec injection


Figure 6-32 shows information about the speed and the diameter of the drops in the

spray of the injector. From there it is seen that the average speed is at 15 m/sec, and

the average diameter is around 19.87 µm.

Figure 6-33 shows the change in spray when the driving pressure (fuel pump) is

changed. The specified working pressure is 2.5 bar (35 psi)9. The changes considered

from 5 bar to 0.1 bar. No change was noticed. Even it was noticed that the injector can

run if no pressure is given by the pump at all. The injector seems to have a reservoir

of fuel when the main frame is full of fuel, and being small the amount of fuel

injected in relation to the reservoir of fuel, it takes some time until this reservoir gets

empty. And as Figure 6-33 is showing, the driving pressure makes no difference in the

injector behaviour, then the only thing that the injector needs to operate is to have fuel

in it reservoir.

Figure 6-33 Comparison of sprays at different driving pressures




7 Discussions and Conclusions

Being a direct injected engine, there is the advantage of having the possibility of

running over both, stratified and homogeneous modes. One of the biggest interests in

this work is to find out in which points does the engine runs at each mode, and it can

be done by using the results presented in the previous chapter. This discussion is the

first section of this chapter.

The second section contains the discussion over the phenomena of the engine

speeding up at a constant load while the injection time reduces.

7.1 Injection mode

The lambda value is related to the injection mode, in the sense that stratified injection

runs with lean mixtures and homogeneous mode uses richer mixtures. It's important

to mention that the lambda value being referred to is the lambda value of the exhaust

gases. During the combustion, due to the non uniform spread of the fuel when fuel

injecting on stratified mode, there are areas of the combustion chamber which are

burning rich mixtures, even though the overall mixture is lean. This makes that the

lambda value during the combustion is different than the lambda value from the

combustion gases. The same could happen in homogeneous mode, but is less likely. A

good signal that the engine is running whether at homogeneous or stratified is the

exhaust lambda value, and a plot of the lambda values measured from the engine

would be useful.

The problem is that the measured lambda values are not trustable. Since the engine

being measured is a two stroke engine which doesn't have valves (uniflow) then some

part (about 20%) of the fresh air coming in to the combustion chamber short circuits

to the exhaust port, altering the readings of the lambda sensor.

An alternative to the lambda value is the CO value, which increases when the mixture

becomes rich, and decreases when it becomes lean. Figure 7-1 illustrates this.


Figure 7-1 Lambda-Emissions plot

The grey line in the middle represents the stoichiometric point. On the right is the lean

area, and on the left the rich one. It is shown how CO has a big change in the rich area

and under the stoichiometric point. In the lean area the change is not very high. This

means that deducting the lambda value from the CO information is practical only in

the rich area, as the errors in the CO measurements could be bigger than the change of

CO in the lean area.

Figure 6-28, shown in section 6.4, displays a color plot of the CO values measured in

the engine. Figure 7-2, shown below, converts those CO values to lambda values.10

10

This process of converting the CO and CO/CO2 values to lambda was provided by the thesis sponsor, and is protected under secrecy agreement.


1.0462 0.9051

0.8844 0.9608 0.9805 0.9114

0.9471 0.9884 0.9191 0.9316

0.8530 0.9708 0.9748 0.9215 0.9448 0.9071

0.9489 0.9633 0.9662 0.9582 0.9714 0.9071

0.9468 0.9520 0.9662

0.9706 0.9388

1.0504 0.9608 0.9817

0.9568

Lean Lean 1.0013

0.9340

1.0530 1.0504 1.0291

0.9929

1.0598 1.0585 1.0431

1.0415

Lean Lean 1.0567

1.0327

Values in green reading "Lean" are values which are beyond the frontier of the

confidence of the calculation, so they are the leaner.

Another way to calculate lambda from exhaust emissions is by using the relation

CO/CO2. The values of the conversion are presented in Figure 7-3.

0

1

2

3

4

5

6

7

1500

2000

3000

4000

5000

5800

bm

ep

_bar

Engine Speed (rpm)

Lambda CO values


Figure 7-2 Lambda calculation from CO values


1.027 0.883

0.843 0.934 0.962 0.889

0.910 0.969 0.906 0.907

0.801 0.941 0.954 0.911 0.925 0.896

0.906 0.936 0.945 0.948 0.955 0.896

0.902 0.922 0.945

0.957 0.923

1.027 0.932 0.960

0.946

1.049 1.052 0.986

0.927

1.025 1.027 1.017

0.988

1.025 1.025 1.020

1.032

1.059 1.021 1.017

1.013

Looking at both plots, it can be seen that they keep a good correlation between them.

Even though the values obtained are not as lean as expected, having this correlation

points out that the conversion procedure is trustable enough. The first glance over

these graphs allows us to identify the green (lean) area in the low load and low speed

area, and also in the low speed area at 5800 rpm. There is a lean point at the

maximum bmep at 3000 rpm in both plots. As it is one of the points with highest

bmep, the only possible reason is that there were some errors while taking that

measurement.

To dig a little bit more in to this matter, Figure 7-4 shows a superimposition of the

injector timing contour plot over Lambda CO.

0

1

2

3

4

5

6

7

1500

2000

3000

4000

5000

5800

bm

ep

_bar

Engine Speed (rpm)

Lambda CO/CO2 values


Figure 7-3 Lambda calculated from CO/CO2 ratio


There is a strong change from green to yellow at 1500 and 2500 rpm in the color plot

(lambda values). That change happens in the -80/-100 area. After that, at 3000 rpm,

the color change is not so hard, and the transition part goes in to the -100/-140 area.

At 5800, the change also happens in the -100/-140 area. In a stratified combustion, the

ignition timing follows the injection timing, with enough time between them as to let

the fuel to mix a little bit with the air, but not letting the cloud of fuel to spread too

much, as to avoid having more than one flame in the combustion chamber.

Figure 7-5 shows the superimposition of the ignition contour plot over the CO color

map.

0

1

2

3

4

5

6

7

1000 1500 2000 2500 3000 3500 4000 4500 5000 5500

bm

ep

_bar

Engine Speed _rpm

Injector Map


-20 / -60

-60 / -80

-80 / -100

-100 / -140

-140 / -160

-160 / -180 -180/ -

200

-200/ -220

-180/ -200

-100 / -140

Figure 7-4 Injection map - lambda values superimposition


1.0462 0.9051

0.8844 0.9608 0.9805 0.9114

0.9471 0.9884 0.9191 0.9316

0.8530 0.9708 0.9748 0.9215 0.9448 0.9071

0.9489 0.9633 0.9662 0.9582 0.9714 0.9071

0.9468 0.9520 0.9662

0.9706 0.9388

1.0504 0.9608 0.9817

0.9568

0.0000 0.0000 1.0013

0.9340

1.0530 1.0504 1.0291

0.9929

1.0598 1.0585 1.0431

1.0415

0.0000 0.0000 1.0567

1.0327

In this plot it is possible to see that the ignition timing starts also very early in the

leanest corner, and it keeps advancing until the change of color from green to yellow

happens. From there, once the ignition angle is at -50/-60, it goes back again reducing

the advance of ignition. Figure 7-4 states that the injection timing keeps advancing

and advancing in the direction of the richest lambda values. Looking at Figure 7-5

again, we see that the ignition advances until the lambda color plot changes from

green to yellow and it goes back again, letting the injector to keep advancing alone.

This point where the ignition timing goes back indicates the area when the engine

changes from stratified to homogeneous mode.

Attending to Figure 6-8 in section number 6.3, it can be easily seen how the ignition

timing follows the injection timing when the engine increases its load at a constant

speed of 3000 rpm. The CAD at which they completely split is near to -57.6 degrees

for the ignition and -111.72 degrees for the injection when there is a difference of

54.12 degrees. This happens at 20 Nm, which corresponds to 2.1 bar. Looking back at

Figure 7-5 it is possible to see that they match the areas where the change from

stratified to homogeneous is suspected to happen.

Going to Figure 6-12, which represents the engine increasing its speed at a constant

load of 30 Nm, it is not possible to see a clear relation between the ignition and

0

1

2

3

4

5

6

7

1000 1500 2000 2500 3000 3500 4000 4500 5000 5500

bm

ep

_bar

Engine Speed _rpm

Spark Map

shadow Throttle bmep propeller

-20 / -40

-30 / -40

-40 / -50 -40 /

-50

-50 / -60

-50 / -60

Figure 7-5 Ignition map - lambda values superimposition

Ignition Map


injection timings. Also, the smallest difference among them is bigger than the

difference they had when they split in Figure 6-8. Now, all the points at 30 Nm, which

corresponds to 3.3 bar, if we look at the lambda color plot, are deep in to the

suspected lean area, meaning that the combustion mode is homogeneous.

Finally, in Figure 6-16 the data for the propeller curve is shown. The point at which

they seem to split is located at 2000 rpm. When locating this point along the propeller

curve in figure Figure 7-5 it is seen that it is near to the frontier established between

stratified and homogeneous modes.

7.1.1 Conclusion 1

Figure 7-6 Stratified area delimitation

Figure 7-6 shows in red line the stratification frontier. Below it the engine is

considered to operate in stratified mode; above it the engine is considered to operate

at homogeneous mode.

7.2 Influence of Back Pressures

In chapter 6.3 Figure 6-18 was presented. It showed the injection time over the

propeller curve, and it was observed that the injection time varied too little, and near

to 1500 it even decreased while the speed increased.

At this point, back pressure is a parameter which becomes important. Back pressure is the pressure in the

the pressure in the combustion chamber, which depends on the compression stroke. At the beginning of it,

Stratified Area


the beginning of it, the pressure in the cylinder is relatively low, and at the end of the compression stroke the

compression stroke the pressure is high. As the injection timing is changing, the back pressure is changing

pressure is changing as well. This means that the amount of fuel injected will change if the back pressure

if the back pressure changes even though the injection time remains the same, as the injector has to

injector has to overcome more or less force to inject the fuel. This variation is clearly visible in

visible in

Figure 6-31.

7.2.1 Conclusion 2

Figure 7-7 shows the plot of the back pressure and the fuel injected in the combustion

chamber when following the propeller's curve.


Figure 7-7 Fuel injected - back pressure comparison for propeller curve

In this plot is easy to see that the amount of fuel is increasing while the back pressure

decreases, even though in Figure 6-18 it's seen that the injection time decreases or

almost remains steady.

7.3 Influence of pressure pump in the injector's spray.

The injector produces its own pressure to inject fuel in the combustion chamber. But it

was not sure if the pressure of the fuel pump feeding fuel in to the injector had any

impact in the spray characteristics. It was even noticed that the injector was able to

run with no pressure in the fuel pump at all. This information can be important when

choosing a fuel pump for a different application.

7.3.1 Conclusion 3

It is clearly visible in Figure 6-33 that the spray characteristics of the injector do not

change among different fuel pump pressures.

0.000

2.000

4.000

6.000

8.000

10.000

12.000

14.000

16.000

0.000

0.500

1.000

1.500

2.000

2.500

3.000

1500 2000 2500 3000 3500 4000

Mas

s_m

g

Bac

k P

ress

ure

_bar

Speed_rpm

Injector Map Propeller Curve

Back Pressure Fuel Injected


8 Appendixes

In this chapter figures which were not directly involved in the discussions, but still are

interesting to know, are shown.

9.995 9.995

9.995 9.995 9.995 9.995

9.995 9.995 9.995 9.995

9.995 9.995 9.995 9.995 9.995 9.995

9.995 9.995 9.995 9.995 9.995 9.995

9.995 9.995 9.995

9.995 9.995

9.995 9.995 9.995

9.995

9.995 9.995 9.995

9.967

9.995 9.995 9.995

9.783

9.995 9.995 9.995

9.542

9.995 9.995 9.175

9.467

0.3996 0.3996

0.3996 0.3996 0.3996 0.3996

0.3996 0.3996 0.3996 0.3996

0.3996 0.3996 0.3996 0.3996 0.3996 0.3996

0.3996 0.3996 0.3996 0.3996 0.3996 0.3996

0.3996 0.3996 0.3996

0.3996 0.3996

0.3996 0.3996 0.3996

0.3996

0.3996 0.3996 0.3996

0.3985

0.3996 0.3996 0.3996

0.3911

0.3996 0.3996 0.3996

0.3815

0.3996 0.3996 0.3668

0.3785

0

1

2

3

4

5

6

7

1500 2000 2500 3000 3500 4000 4500 5000 5500

bm

ep

_bar

Engine Speed _rpm

Injector Current _amp

shadow Throttle bmep propeller Stratification frontier

0

1

2

3

4

5

6

7

1500 2000 2500 3000 3500 4000 4500 5000 5500

bm

ep

_bar

Engine Speed _rpm

Injector Power_kW


Figure 8-1 Injector Current

Figure 8-2 Injector Power


16.0699 22.3903

9.3465 14.5909 18.6088 22.6203

8.4375 12.6131 17.7084 21.6006

5.3365 7.5909 11.0555 14.8166 18.7853 21.2645

4.7738 6.2427 9.5920 12.9303 15.5116 17.5362

3.9725 5.3173 8.1424

13.2025 15.0750

3.2628 4.2884 6.4921

11.5314

2.4082 3.2740 4.9810

9.1639

1.5145 2.1513 2.9759

5.8561

0.7831 1.2326 1.6350

3.5731

0.2312 0.3501 0.2505

1.8022

0.0249 0.0178

0.0428 0.0274 0.0215 0.0177

0.0474 0.0317 0.0226 0.0185

0.0749 0.0526 0.0361 0.0270 0.0213 0.0188

0.0837 0.0640 0.0417 0.0309 0.0258 0.0228

0.1006 0.0752 0.0491

0.0303 0.0265

0.1225 0.0932 0.0616

0.0347

0.1659 0.1221 0.0802

0.0435

0.2639 0.1857 0.1343

0.0668

0.5103 0.3242 0.2444

0.1068

1.7283 1.1415 1.4642

0.2100

0

1

2

3

4

5

6

7

1500 2000 2500 3000 3500 4000 4500 5000 5500

bm

ep

_bar

Engine Speed _rpm

Engine Power_kW


0

1

2

3

4

5

6

7

1500 2000 2500 3000 3500 4000 4500 5000 5500

bm

ep

_bar

Engine Speed _rpm

Pinj / Peng Ratio


Figure 8-3 Engine Power

Figure 8-4 Pinj / Peng Ratio


1.6 1.87

NaN 1.33 1.46 2.02

0.82 1.11 1.44 1.8

0.77 0.85 1.03 1.24 1.63 2.05

0.54 0.54 0.77 1.1 1.45 1.68

0.44 0.57 0.86

1.22 1.48

0.41 0.44 0.71

1.11

0.31 0.43 0.42

0.88

0.15 0.15 0.29

0.73

0.15 0.29 0.43

0.45

0.15 0.15 0.13

0.42

2.389 2.204

2.091 2.232 2.001 2.040

2.332 2.074 1.936 1.965

2.849 2.275 2.014 1.882 1.861 1.917

2.508 2.204 1.943 1.798 1.762 1.821

2.472 2.172 1.919

1.667 1.584

2.323 2.078 1.833

1.527

2.151 1.903 1.716

1.474

1.973 1.799 1.611

1.404

1.918 1.672 1.531

1.273

1.985 1.593 1.410

1.239

0

1

2

3

4

5

6

7

1500 2000 2500 3000 3500 4000 4500 5000 5500

bm

ep

_bar

Engine Speed _rpm

Fuel Consumption_g/s


0

1

2

3

4

5

6

7

1500 2000 2500 3000 3500 4000 4500 5000 5500

bm

ep

_bar

Engine Speed _rpm

Injection Time_mSec


Figure 8-5 Fuel Consumption

Figure 8-6 Injection Time


0.5561 0.3590

0.7008 0.0682 0.6494 0.4735

0.4913 1.3292 0.7868 0.9596

0.6644 0.4522 0.6392 0.7312 1.1341 -0.0733

0.4632 0.3601 0.4631 0.2835 1.1287 1.1195

0.7992 0.5514 0.4800

0.9678 0.8033

0.8550 0.9643 0.5443

0.8915

1.2568 1.3609 0.5783

0.2695

2.5361 1.1818 0.6584

0.3044

2.9235 1.6338 0.6805

0.2783

4.5443 2.3023 1.6509

0.3012

15.741E-3 13.783E-3

NaN 13.159E-3 10.922E-3 12.030E-3

12.055E-3 11.106E-3 10.497E-3 10.613E-3

15.693E-3 12.570E-3 10.274E-3 9.231E-3 9.609E-3 10.653E-3

10.603E-3 8.033E-3 7.652E-3 8.181E-3 8.682E-3 9.025E-3

8.725E-3 8.556E-3 8.545E-3

7.277E-3 7.707E-3

8.023E-3 6.658E-3 7.070E-3

5.738E-3

6.204E-3 6.343E-3 4.157E-3

4.574E-3

2.993E-3 2.222E-3 2.938E-3

3.748E-3

2.972E-3 4.304E-3 4.294E-3

2.308E-3

3.557E-3 2.259E-3 1.301E-3

2.169E-3

0

1

2

3

4

5

6

7

1500 2000 2500 3000 3500 4000 4500 5000 5500

bm

ep

_bar

Engine Speed _rpm

Back Pressure_bar


0

1

2

3

4

5

6

7

1500 2000 2500 3000 3500 4000 4500 5000 5500

bm

ep

_bar

Engine Speed _rpm

Fuel Injected_g


Figure 8-7 Back Pressure

Figure 8-8 Fuel Injected


9 References

Strauss Sebastian, Zeng Yangbing and Montgomery David. Optimization of the E-

TEC™ Combustion System for Direct-Injected Two-Stroke Engines Toward 3-Star

Emissions. SAE 2003-32-0007.

John B. Heywood, Eran Sher. The Two-Stroke Cycle Engine. Society of Automotive

Engineers. 1999.

John B. Heywood, Internal Combustion Engine Fundamentals. McGraw Hill. 1988.

Dave Gerr. Propeller Handbook. International Marine. 2001. Pag. 4 @ Google Books.

BRP Us Inc. Evinrude Etec Outboard Operator's Guide. 2010. Pag. 65.


10 Acknowledgements

This work is the product of the effort of many people. Without them the objectives of

this work would have never been reached.

Anders Mattsson Solving the water cooling of the engine, fitting sensors on the engine, solving the exhaust issues of the engine, and in general fitting the engine on the test rig.

Daniel Härensten Solving issues with pressure sensor and crank angle sensor, and in general programming the data acquisition system.

Alf Magnusson Installation of emissions measurement equipment, support on spray characterization chamber and support and advice in general during the development of the project.

Allan Sognell Support on installation and maintenance of the test rig.

Lars Jernqvist Design and construction of the injector controller and injector's current and voltage measurement equipment.

Eugenio De Benito Installation of the spray characterization equipment (Visioscope). Support on spray characterization chamber installation. Spray characterization expertise. Support during spray characterization execution.

Petter Dahlander Supervision. Support on data manipulation. Support on spray characterization equipment installation.

Mats Lavenius Industrial contact. Advice on project presentation, and link with the sponsor of the project.

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