“Numerical Investigation of Combustion Process in a 4-Stroke Gasoline Direct Injection (GDI) Sing

7/25/2019 Numerical Investigation of Combustion Process in a 4-Stroke Gasoline Direct Injection (GDI) Sing

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Submitted by : Mr. Chetan .G. DathSupervisors : Dr .S. N. Sridhara

AndProf Ashok .C. Meti

M.Sc (Engg) Dissertation in Automotive Engineering

M.S. Ramaiah School of Advanced Studies

Coventry University (UK) Postgraduate Engineering Degree

Programme

Gnanagangothri Campus, New BE Road, MSR Nagar,

Bangalore!"#$ $"%

&el'(a)* +#$""+'+#$-+/ we0site* http*''www.msrsas.org

1$$%!1$$"

Numerical 2nvestigation of Com0ustion 3rocess in a %!stro4e

Gasoline 5irect 2n6ection 7G528 Single C9linder Engine!

7(lat :ead 3iston8


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M.S. Ramaiah School of Advanced Studies

Coventry University (UK) Postgraduate Engineering Degree

Programme

Bangalore

Certifcate

This is to certiy that the M!c (Engg)

Pro"ect Dissertation titled Numerical

Investigation of Combustion Process in a 4-

stroke Gasoline Direct Injection (GDI) Single

Cyliner !ngine- ("lat #ea Piston)$ is a

#onafde record o the Pro"ect $or% carried out

#y Mr Chetan & Dath in 'artial ulflment o

reuirements or the a$ard o M!c (Engg)

Degree in utomotive Engineering during the

academic year *++,- *++.

Dr ! / !ridhara and Pro sho% C Meti

cademic !u'ervisors

Project Title: Fluid Flow Visualization during Expansion Stroke of a Four-stroke S. I. Engine using F! ii


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Dr !0 !han%a'al Pro sho%

C Meti Dean1 PEP2! Programme

Manager

Dr !0 !han%a'al

Director

5ECARA&2;N

Project Title: %Numerical Investigation of

Combustion Process in a 4-stroke Gasoline

Direct Injection (GDI) Single Cyliner !ngine-

("lat #ea Piston)$

The Project Dissertation is submitted in partial fulfilment of academic requirements for

M.Sc (En! in Automotive Enineerin. This dissertation is a result of m" o#n

investiation. All sections of the te$t and results% #hich been obtained from other sources%

are full" referenced. & understand that cheatin and plaiarism constitute a breach of

'niversit" reulations and #ill be dealt #ith accordinl".

Name of the student* C:E&AN .G. 5A&:Name of the student* C:E&AN .G. 5A&:

Project Title: Fluid Flow Visualization during Expansion Stroke of a Four-stroke S. I. Engine using F! iii


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SignatureSignature**

5ate* 15ate* 1ththSep 1$$"Sep 1$$"

Project Title: Fluid Flow Visualization during Expansion Stroke of a Four-stroke S. I. Engine using F! i"


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M.S Ramaiah School of Advanced Studies Postgraduate Engineering Programmes (PEPs)

Ac4nowledgement

& am ver" rateful to !r. S.#. Srid$arafor havin been iven an opportunit" to

carr" out a project under his e$pert uidance. & #ould lie to e$press m" ratitude to him%

#ithout #hose support and e$pertise% this project #ouldn)t have been accomplished. &n

spite of his ver" bus" schedule% he #as ind enouh to uide and help me brin this

project to consummation. *is classes not onl" helped me to build a stron foundation for

this project% but also have helped me in man" other fields. & #ill al#a"s be rateful to him

for that.

This project #ould never taen form #ithout the un#averin support of Prof

%s$ok .. &eti for his constant support. & also than him for providin the resources

required for the project riht in time% #hich helped me to complete this project #ithin

time.

M" special thans to our director !r. S.'. S$ankapal% #hose emphasis for e$cellenceept me focused on to m" project and helped me complete it on time.

& am reatl" indebted to all the facult" members% #ho have helped me immensel"%

especiall"&r. ()es$* &r. $etan and &r. +ris$na

iii

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,ast but not the least% & #ould lie to e$press m" sincere thans to each one of m"

friends and m" famil" members% #ho ave continuous support throuhout the project.

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A0stract

-Necessit9 is the mother of invention is a reat sa"in. The entire

automobile #orld is po#ered b" this necessit" for po#er% comfort% fuel efficienc"%

pollution control etc. Riht from the first automobile to the present da" there have been

constant and po#erful chanes. The technoloical advancements never stop leadin place

to ne#er chanes. ,!I Tec$nolog is the latest in the Automobile Development. The

project is a humble contribution to#ards the development of this Technolo". The project

deals #ith the numerical anal"sis of an enine of no#n specifications b" incorporatin

this technolo".

T$e first part projectinvolves /D cold flo# anal"sis of an e$istin commercial 01

stroe S.&. enine)s #orin c"cle.

T$e second partof the project involves includin injections b" main use of the

discrete phase models.

T$e t$ird partof the project involved combustion anal"sis for the same eometr".

A number of soft#are tools #ere used for the purpose of 2luid 2lo# Anal"sis. The" #ere

'apid For)for obtainin the cloud point data% %TI% V ' // and (,for 3eometricModellin% ,%&0IT 1.1for rid eneration%PreP!F 2./ for4ombustion Modellin and

F3(E#T 4.1./4 for the Anal"sis of the 3D& Enine (the continuit"% momentum and

ener" equations #ere solved b" appropriatel" settin the boundar" conditions!

The main conclusion dra#n #as the fluid flo# visuali5ation for evaluatin flo#

characteristics #ithin ports and in c"linder. 2luid flo# #as visuali5ed b" settin up the

"

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required animations and also b" e$tractin raphs of various variables lie pressure%

velocit" etc #it respect to the cran anle. 4ontours of different variables #ere also

obtained at required cran anles to anal"se the combustion process.

Contents

DE4,ARAT&67............................................................................................iv

Acno#ledement...........................................................................................v

Abstract...........................................................................................................vi

4ontents.........................................................................................................vii

,ist of Tables...................................................................................................$

,ist of 2iures.................................................................................................$i

,ist of 3raphs...............................................................................................$iv

,ist of S"mbols..............................................................................................$v

4hapter 81 &ntroduction...................................................................................8

8.8 A t"pical &4 Enine....................................................................................................8

8./ The 01stroe S& Petrol Enine..................................................................................../

8.9 Motivation..................................................................................................................9

8.0 Present #or...............................................................................................................:

4hapter1 / ,iterature Revie#..........................................................................;

/.8 *istorical Development..............................................................................................;

/./ Technoloical developments in petrol enines..........................................................

2iure /.9. / *emispherical 4hamber.................................................................................>

2iure /.9. 9 A crescent combustion chamber...................................................................8@

2iure /.9. 0 Co#l1in1piston combustion chamber..........................................................8@

2iure /.0. 8 4arburettor....................................................................................................8/

2iure /.0. / MP2&.............................................................................................................89

2iure /.0. 9 Direct injection s"stem.................................................................................8:

2iure /.:. 8 3D& Enine...................................................................................................8;

2iure /.;. 8 'priht Straiht &ntae Ports in 3D& Enine...............................................8;

2iure /.;. / 4urved1Top Piston in 3D& Enine ...............................................................8;

2iure /.;. 9 2uel Spra" ,ocus (Cottom ie#! ................................................................8@s.

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&n the ;@s% hemispheric combustion chamber and overhead camshaft started to be

popular in sports cars% no# the" are standards in ever" car.

Turbocharer appeared for the first time in 4hevrolet 4orvair of the ;@s% #hich

enabled /./ litres output 8:@ hp. *o#ever% the first one used this technolo"

maturel" #as Porsche >88 turbo 9.@ of 8>@@@ further incorporated it in

a multi1valve enine% thus successfull" applied it to mass production sedans.

0 valves per c"linder technolo" appeared as earl" as 8>8/ in Peueot 3P racer%

but until the =9. A fe# "ears later% 01valve enine became standard in the

mass production 4orolla and *onda 4ivic% then spreaded to other carmaers in the

ne$t decade. &n 8>


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&n the late >@s% most development budet #as spent to emission control and fuel

efficienc" enhancement 1 direct injection petrol and common1rail direct injection

diesel are the latest hihliht.

1.+ 5evelopments in design of com0ustion cham0ers

Several basic combustion chamber shapes are used in spar inition

enines toda". The four most commonl" used shapes are the #ede% the crescent% the

hemispherical% and the bo#l1in1piston chambers.

edge Cham0er

The #ede chamber shape #as an as"mmetrical desin. The #ede #as called

an open chamber head since the c"linder head #as concave. The valves #ere not placed

in the center of the chamber. Rather% the valves #ere inclined in an off1center position.

(igure 1.+. - edge cham0er with uench and suish area ?1@

:emispherical Cham0er

The hemispherical combustion chamber until date is a ver" popular desin.

This chamber #as a s"mmetrical desin. &t #as also an open chamber due to the

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concavit" of the c"linder head. The valves #ere placed on an arc1shaped head. The hemi

(abridement of hemispherical! chamber #as ver" popular in hih performance

automobiles. A hih performance enine no#n as the -0/; *emi used this t"pe of

combustion chamber.

(igure 1.+. 1 :emispherical Cham0er ?1@

Crescent 73ent!Roof8 Cham0er

The crescent combustion chamber #as ver" similar to the hemi chamber. The main

difference bet#een the t#o chambers #as that in the crescent chamber the valves are

placed on a trape5oidal1shaped head instead of an arc1shaped head. The valves of a

crescent shaped chamber #ere placed at an anle on flat on the head. The crescent

chamber #as also called -pent1roof combustion chamber.

(igure 1.+. + A crescent com0ustion cham0er ?1@

Cup 7Bowl8 Cham0er

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Some chambers #ere called closed rather than open. &n closed chambers% the

c"linder head #as virtuall" flat. *o#ever% the piston #as dished. The dish in the piston

simpl" created concavit" in the piston. A bo#l1in1piston chamber #as an e$ample of a

closed chamber. &n this chamber% the valves #ere placed perpendicular to the head.

(igure 1.+. % Bowl!in!piston com0ustion cham0er ?1@

ide Spacing &echnolog9

The above mentioned combustion chamber shapes are bein interated #ith this

revolutionar" technolo". The 3D& enineNs abilit" to precisel" control the mi$in of the

air and fuel is due to this ne# concept called #ide spacin% #hereb" injection of the fuel

spra" occurs further a#a" from the spar plu than in a conventional petrol enine%

creatin a #ide space that enables optimum mi$in of aseous fuel and air. This

technolo" can be used #ith an" of the combustion shapes e$plained especiall"

hemispherical and #ede. This technolo" maes use of both the features of S& and 4&

enines. The piston has a comple$ shape% as it required for mi$ture preparation. &n

stratified combustion ('ltra1,ean Mode!% fuel is injected to#ards the curved top of the

piston cro#n rather than to#ards the spar plu% durin the latter stae of the

compression stroe. The movement of the fuel spra"% the piston headNs deflection of the

spra" and the flo# of air #ithin the c"linder cause the spra" to vapori5e and disperse. The

resultin mi$ture of aseous fuel and air is then carried up to the spar plu for inition.

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The biest advantae of this s"stem is that it enables precise control over the air1to1fuel

ratio at the spar plu at the point of inition.

1.% &echnological developments in the fuel suppl9 s9stems

Car0uretted fuel suppl9 s9stem

4arburettor is a device used for atomisin and vapori5in the fuel and mi$in it

#ith air in var"in proportions to suit the chanin conditions and to suppl" for

combustion in the enine c"linder. This process of breain up and mi$in fuel #ith air is

called carburetion. The carburettors #ere in practice from 8>/@ to 8>>@. The main

reasons% #hich led to the fall of the carburettor% are iven belo#.

Refrieration t"pe icin occurs in a carburettor venturi #hen fuel vapori5es in

moist air

2uel distribution characteristics #ere bad (one c"linder operatin at a ver" lean

airHfuel mi$ture #hile another ma" be operatin near the rich end of the mi$ture

scale!

The carburettor #as a meterin device% #hich just told the amount of fuel that had

to be supplied in different situations. (That is more or less!. *o#ever% it did not

suppl" the e$act amount of mi$ture that #as needed. &t had a number of additional circuits for different situations lie acceleration%

idlin% altitude etc that made its manufacturin quiet difficult.

A float t"pe carburettor can onl" operate in an upriht position.

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(igure 1.%. - Car0urettor?+@

Multipoint fuel in6ection s9stem

MP2& stands for Nmulti point (electronic! fuel injectionN. This s"stem injects

fuel into individual c"linders% based on commands from the Oon board enine

manaement s"stem computer) B popularl" no#n as the Enine 4ontrol 'nitHE4'.Mpfi

S"stems can either be+ a! OSequential) i.e. direct injection into individual c"linders aainst

their suction stroes% or b! OSimultaneous) i.e. toether for all the four or #hatever the

number of c"linders. The O2uel &njectors) are precision built OSolenoid alves)% somethin

lie ?ashin Machine ?ater inlet alves. These have either sinle or multiple O6rifices)

#hich Ospra") fuel into the 2uel inlet manifold of a 4"linder upon actuation% from a

common RailH*eader pressuri5ed to around 9 bar% fed b" a hih pressure electricall" drive

fuel pump inside the Petrol tan of the 4ar. The Oon1board) E4' primaril" controls the

&nition Timin and quantit" of fuel to be injected. &n eneral% an E4' in turn is

controlled b" the Odata input) from a set of OSE7S6RS) located all over the Enine and its

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Au$iliaries. These detect the various Ooperatin states) of the Enine and the performance

desired out of it. Such Sensors constantl" monitor+

8! Ambient Temperature /! Enine 4oolant Temperature 9! E$haustHmanifold

temperature 0! E$haust O6/) content% :! &nlet manifold vacuum% ;! Throttle position% etc.

Cased on a Oprorammed) interpretation of all this input data% the E4' ives

the various Ocommands) to the Enine)s fuel intae and spar inition timin s"stems% to

deliver an overall satisfactor" performance of the Enine from start to shut do#n%

includin Oemission control).

(igure 1.%. 1 M3(2 ?+@

Advantages of M. 3. (. 2.

More uniform AH2 mi$ture #as supplied to each c"linder and hence% the

difference in po#er developed in each c"linder #as minimum. ibration from the

enine equipped #ith this s"stem #as less. Due to this% the life of enine

components improved.

There #as no need to cran the enine t#ice or thrice in case of cold startin as it

happens in the carburettor s"stem.

&mmediate response% in the case of sudden acceleration H deceleration.

Since the enine #as controlled b" E4M (Enine 4ontrol Module!% more accurate

amount of AH2 mi$ture #ill be supplied and as a result% complete combustion too

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place. This led to effective utili5ation of fuel supplied and hence lo# emission

level.

The fuel efficienc" #as improved.

5isadvantages

&f E4M fails to send control sinal to all actuators then the enine #onNt et

started.

&f E4M fails to service from all sensors then also the enine #onNt et started.

?astae of fuel in different load conditions as the fuel is mi$ed #ith air outside

the c"linder.

Emissions are hiher than Direct &njection s"stems.

5irect in6ection s9stem

This is the ne# revolution in fuel injection s"stems. Even thouh MP2&

proved to be better than the carburetted enines% the main problem #as at part loads. &n

this s"stem% the E4' had loo up tables embedded in it. These loo up tables had

different Rpm)s and the required amount of fuel that has to be supplied #ritten in them.

The main disadvantae of this is that the injector injects more than necessar" amount of

fuel into the combustion chamber. 2or e$ample% consider the situation #here the enine is

runnin at /9@@ rpm. &n the loo up table% the amount of fuel that has to be supplied at

/@@@ rpm and /:@@ rpm has been embedded but not the amount that has to be supplied at

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/9@@ rpm. Since /9@@ rpm is closer to /:@@rpm% it supplies the amount of fuel at /:@@

rpm. This e$tra fuel is supplied #hich #ill result in incomplete combustion and more

e$haust products. This can be avoided b" follo#in the s"stem similar to diesel injection

s"stem #here a metered amount of fuel is injected into the chamber. The desired

stratified chare effect is obtained in this #a"+ The cloud of air containin sufficient

fuel to form an initable mi$ture is ept to a confined volume and surrounds the spar

plu at the moment of inition. Since the fuel is delivered at a shallo# anle b" the

injector% the cloud of fuel maes scarcel" an" contact #ith the piston cro#n+ a so1called

air1uided process. After combustion% a la"er of insulatin air remains bet#een the

inited mi$ture and the c"linder #all. This cuts the amount of heat lost to the enine

bloc and increases the enineNs operatin efficienc".

(igure 1.%. + 5irect in6ection s9stem?+@

This has the advantaes of reducin the tendenc" to noc because of direct fuel

injection into the combustion chamber and the resultin internal coolin effect. &n

addition% the enine is capable of operatin at a hiher compression ratio .

The technoloical developments e$plained above have finall" led to the birth of the

3D& technolo". 2or "ears% enineers have no#n that if the" could build a petrol enine

that #ored lie a diesel enine1in other #ords% one in #hich fuel is directl" injected into

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the c"linder and then the stratified% rich mi$ture riht near the spar plu is inited% then

the" #ould have an enine that achieved both the fuel efficienc" of a diesel enine and

attained the hih output of a conventional petrol enine

1." Gasoline 5irect 2n6ection 7G528

&n these enines% petrol is directl" injected into the c"linder% eliminatin man" of the

restrictions on combustion control% such as the impossibilit" of addin fuel after the

induction valves #ere closed. C" achievin precise combustion control that is free of

restrictions% the 3D& delivers a previousl" unseen combination of fuel econom" and

po#er. er" efficient intae and relativel" hih compression ratio unique to the 3D&

enine deliver both hih performance and response.

(igure 1.". - G52 Engine ?%@

1.# &echnical features of G52 engine

'priht straiht intae ports for optimal airflo# control in the c"linder

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(igure 1.#. - >pright Straight 2nta4e 3orts in G52 Engine ?"@

4urved1top pistons for aidin s#irl and tumble.

(igure 1.#. 1 Curved!&op 3iston in G52 Engine ?"@

*ih1pressure s#irl injectors for optimum air1fuel mi$ture

(igure 1.#. + (uel Spra9 ocus 7Bottom iew8 ?"@

*ih1pressure fuel pump to feed pressuri5ed fuel (o)pact Spraor the one Spra!

into the injectors

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(igure 1.#. % &9pes of (uel Spra9 in G52 Engine ?"@

1.D G52 Engine and its main characteristics

>ltra!lean Com0ustion Mode for ower (uel Consumption Mode

'nder most normal drivin conditions% up to speeds of 8/@mHh% 3D& enineoperates in ultra1lean combustion mode for less fuel consu)ption. &n this mode% fuel

injection occurs at the latter stae of the compression stroe and inition occurs at an

ultra1lean air1fuel ratio of 9@ to 0@ (9: to ::% included E3R!.

Realiation of lower fuel consumption

The 3D& enineNs abilit" to precisel" control the mi$in of the air and fuel is due

to a ne# concept called #ide spacin% #hereb" injection of the fuel spra" occurs further

a#a" from the spar plu than in a conventional petrol enine% creatin a #ide space that

enables optimum mi$in of aseous fuel and air. &n stratified combustion ('ltra1,ean

Mode!% fuel is injected to#ards the curved top of the piston cro#n rather than to#ards the

spar plu% durin the latter stae of the compression stroe. The movement of the fuel

spra"% the piston headNs deflection of the spra" and the flo# of air #ithin the c"linder

cause the spra" to vapori5e and disperse.

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The resultin mi$ture of aseous fuel and air is then carried up to the spar plu for

inition. The biest advantae of this s"stem is that it enables precise control over the

air1to1fuel ratio at the spar plu at the point of inition. As a result% e$tremel" stable

combustion of ultra1lean mi$ture #ith an air1fuel ratio of 0@ (::% E$haust 3as

Recirculation included {EGR}! is achieved.

(igure 1.D. - >ltra!lean Com0ustion Mode ?"@

Graphbelo# sho#s the 2uel consumption durin ruising

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Graph 1.D. - (uel consumption during Cruising at %$ 4m'h ?"@

Superior ;utput Mode

?hen the 3D& enine is operatin #ith hiher loads or at hiher speeds% fuel

injection taes place durin the intae stroe. This optimises combustion b" ensurin a

homoeneous% cooler air1fuel mi$ture that minimi5es the possibilit" of enine nocin.

Realiation of Superior ;utput

To achieve po#er superior to conventional MP& enines% the 3D& enine has a $ig$

co)pression ratio and a$ig$l efficient air intake sste)% #hich result in improved

volumetric efficienc" and hence hiher po#er output. Graph 1.D.1 sho#n belo#

represents the increase in "olu)etric efficiencin a 3D& enine.

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Graph 1.D. 1 olumetric Efficienc9 versus Engine Speed in a G52 Engine ?"@

Emission Control

Previous efforts to burn a lean air1fuel mi$ture have resulted in difficult" to control

76$ emission. *o#ever% in the case of 3D& enine% >


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1. Review of 3revious or4 in G52 &echnological 5evelopment

This section contains e$cerpts from technical papers and other literature. This #as

found useful for arrivin at the present #or. &t has also helped in solvin the problems

related to the present #or and bottlenecs.

The 3D& development started in the earl" >@)s.As the fuel prices started soarin and

the environmental reulations re# stricter this technolo" ained momentum. 3D&

enines have brouht about a revolution in the enine technolo" of the present da" cars.

&n the past ten "ears% a lot of #or has been carried out reardin this technolo".

Mitsubishi released the first protot"pe in 8>>;. *o#ever% the technolo" #as refined

further b" others in the subsequent "ears.

&n 8>>>% Edward S. Suh and hristopher !. Rutland ?#@ carried out the numerical

simulations on the airHfuel mi$in preparation in a asoline direct injection (3D&! enine.A t#o1valve% 6verhead alve Mechanism Enine #ith #ede combustion chamber #as

investiated since automobiles equipped #ith this t"pe of enine #ere readil" available. A

pressure1s#irl injector and #ide spacin injection la"out #ere adapted to enhance

mi$ture preparation. &t #as concluded that modif"in and retrofittin these enines for

3D& operation could become a viable scenario for some enine manufactures. 6ther

conclusions dra#n #ere that the fuel injection and inition point #ere also important for

the mi$ture preparation.

&n /@@/". P. #an$ieleghe% et al?D@carried out 3asoline Direct &njection Modellin

and its alidation #ith Enine Planar ,aser &nduced 2luorescence E$periments. The

model considered the transient behaviour of the pre1s#irl spra" and the stead"1state

behaviour of the main spra". An e$tended 4oherent 2lame model% accordin to "aritaud

et al. #as also developed as part of this stud". Areement bet#een the model and the

e$perimental results #as sho#n to be e$cellent.

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&n /@@9 &. olin' (. "enkenida and . (ngel)erger ?@ carried out developments on

the 9D modellin of combustion in spar inition enines. &mprovements to the classical

coherent flame model (42M! #ere made to "ield the e$tended coherent flame model

(E42M!% specificall" adapted for simulatin the combustion process in direct injection1

spar inition (D&1S&! enines. The principal idea of e$tension of the model #as to locall"

describe the fuelHair (2HA! equivalence ratio in fresh ases composition (includin

residual ases! allo#in the improvement in the description of lare1scale stratification.

2inall"% a model to predict noc in S& enines #as developed. These developments #ere

then validated on t#o enine confiurations+ An ?ptical %ccess Engine% for #hich ,&2

(laser induced fluorescence! measurements #ere made and The ,asoline !irect

Injection &itsu7is$i Enginefor lobal validations.

&n /@@0*rit$ "ed+ord' ,iao u and lrich Sch%idt?@ studied a spar1inited enineand a direct injection diesel enine usin the 4omputational 2luid D"namics code Fluent

and validated aainst e$perimental data. The S& enine #as studied for improvin the

accurac" of the thermal stress anal"sis of the enine components. The D& enine #as

studied to validate an inition dela" model in 2luent ;./. A 4aterpillar 90@@ series heav"

dut" D& diesel enine #as simulated usin 2luent ;./ and compared #ith published

e$perimental data. The objective #as to validate an inition model in conjunction #ith

the e$istin d"namic mesh and spra" models aainst an established data set consistin of

si$ different load and speed conditions (modes! from a federal transient test procedure.

An additional focus of the #or #as the evaluation of the applicabilit" of the current

models for predictin production of nitroen o$ides at hih temperatures.

2rom the above revie#% it can be seen that there is a large scope for the

development of G52 technolog9 in the %!stro4e single c9linder engine for two

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wheelers especiall9 in the 2ndian Mar4et. The above papers reveal that there has been a

lot of development in the automobile sector #ith reard to the 3D& technolo". The

development has been carried out mainl" on the multi c"linder automobile enines.

*o#ever% it is the t#o1#heeler sement #here in this technolo" has a lot of scope for

improvement. &n the current &ndian Maret >:L of the t#o #heelers is main use of

carburetted s"stem. G52 technolog9 can therefore 0e used for the two!wheeler

segment increasing fuel efficienc9 and decreasing emissions.

1. -$ 2dentification of the pro0lem

The current thesis is based on the 7umerical &nvestiation of the combustion process in

a 01stroe sinle c"linder t#o1#heeler enine. 2or the purpose of the project a #ell

no#n carburetted t#o1#heeler enine #as modelled and the direct injection s"stem #asimplemented and anal"sed.

1. -- Solution Methodolog9

The entire problem #as numericall" investiated. The models used for the anal"sis

purpose are briefl" described belo#. The equations and the basics behind these models

are described in 4hapter B;.

2inite volume method #as used for conductin the different t"pes of anal"sis on

the /D model of the enine. 2,'E7T based on this numerical method #as used

for this purpose.

The solver used #as a Sereated% 'nstead"% and 2irst 6rder &mplicit.

The flo# #as assumed hihl" turbulent and a Turbulence model #as used. The

model used #as k-&odel.

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The problem involved a movin piston and valves. 2or this purpose% the rid had

to chane d"namicall".!na)ic &es$ &odel#as used for this purpose.

2or conductin the 4old 2lo# anal"sis% the above models #ere used. Providin

appropriate boundar" conditions solved the ener"% continuit" and momentum

equations.

2or anal"sin the combustion process% a combustion model #as included named

#on- Pre)ixed o)7ustion &odel. This model #as used to define the required

species involved in combustion. The calculations #ere carried out inPreP!F.

2or includin the &njections% the !iscrete P$ase &odels#ere used. A number of

options under this model lie Droplet breaup% Droplet collision and Droplet dra

#ere enabled.

The required Discreti5ation schemes for different variables lie pressure%

Pressure1velocit" couplin% momentum etc #ere selected.

1. -1 alidation 3rocedure

The procedure follo#ed for the numerical anal"sis has been validated #ith the Fluent

Tutorials. An attempt has also been made to validate the results #ith technical papers and

other boos.

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Chapter + F 3ro0lem 5efinition

+.- 3ro6ect Aim


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The entire project has a revolutionar" impact on the automobile technolo" in the

near future. The main aim of arrivin at vehicles% #hich provide e$cellent fuel efficienc"

and superb performance #hile maintainin cleaner emissions and drivin comfort is near

possibilit" b" incorporatin this technolo".

+.+ &ools >sed

'apid For)for obtainin the cloud point data

%TI% V ' // and (,for 3eometric Modellin

,%&0IT 1.1for rid eneration

PreP!F 2./ for4ombustion Modellin

F3(E#T 4.1./4 for the Anal"sis of the 3D& Enine.

+.% ;06ective of the 3ro6ect

7umerical investiation of cold flo# anal"sis on the 1! )odel of engine

&ncludin &njections (considerin a particular &njection Pressure! at a particular

instant of time.

Anal"sin the 4ombustion Process for the enine modelled.

+." 3ro6ect 3rocedure

The procedure adopted for the project is described in brief here.

The first step as alread" e$plained #as literature sur"e and analsing the

problem on hand.

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The ne$t step #as settingup the o7jecti"esof the project.

The third step #asprocuringthe required software toolsandpara)eters of t$e

enginethat #ere required for the successful completion of the project.

The Engine #as then )odelled (dependin on the parameters collected! usin

'e"erse Engineering Tec$ni@ueand also b" main use of a suitable software

tool.

The ,rid #as enerated for the 1! )odel of t$e engineusin suitable Soft#are

tool% #hich #as compatible #ith 42D pacae bein used. The rid #as

enerated eepin in mind the anal"sis that had to be carried out.

7e$t the 3rid #as imported into a suitable 42D pacae. The models that #ere

required for anal"sis #ere chosen carefull".

6nce the anal"sis #as completed the results #ere checed. The" #ere validated

#ith no#n benchmars

2inall" conclusions #ere dra#n based on the results.

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+.# ;0servations and alidation

The main observations of the anal"sis #ere the raphs of different variables #ith

respect to the cran anle. The pressure% velocit"% turbulence intensit"% temperature and

mass flo# rates at inlet and outlet raphs #ere obtained from 2,'E7T. These raphs

#ere then validated #ith the technical papers and reno#ned &4 Enine boos. Also

contours of the above mentioned variables #ere e$tracted at different cran anles ivin

an insiht into the anal"sis of the combustion process. The "alidations and o7ser"ations

are e$plained in detail in $apter- > and$apter-;respectivel".

(igure +.". -belo# sho#s the Schematic Representation of the Procedure adopted for

achievin the project objectives.

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(igure +.". -Schematic Representation of the 3ro6ect 3rocedure

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Chapter % F Geometric Modelling of the Engine

%.- 2ntroduction

A eometric model describes the shape of a ph"sical or mathematical object b" means

of eometric concepts. 3eometric modellin is the construction or use of eometric

models. ,eo)etric )odelsare used in computer raphics% computer1aided desin and

manufacturin 9%!*2inite Element Anal"sis 9FE&*4omputational 2luid D"namics

9F!and man" other applied fields. A 3eometric model has to be created before an"

anal"sis. This model acts as the bacbone of the entire anal"sis. The discreti5ation of this

model and the element choosin techniques are ver" important

,eo)etric )odellingis thePre-processing stepin an" anal"sis as e$plained

earlier in the Project Methodolo". &n this chapter the eometric modellin of the enine

has been e$plained in brief.

TheSoftware Toolsused for creatin the 3eometric Model #ere %TI% V

'// and (,. These tools #ere chosen% as the" #ere user friendl" and ver" efficient.

4AT&A #as specificall" chosen for its surface modellin capabilities

%.1 3arameters of the Engine selected

7umber of c"linders 1 -

7umber of stroes per c"cle 1 %

4oolin t"pe B Air Cooled

Core diameter 1 "$ mm

Stroe lenth B"D mm

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4onnectin rod lenth B-$$ mm

Piston shape1 flat head

4learance volumeF -# cc

Stroe volumeF --1 cc

%.+ Steps involved in the Geometric Modelling of the Engine

Reverse enineerin of the enine selected.

Surface creation usin the enerate cloud point data.

Modellin different parts of the enine lie the c"linder% c"linder head% ports%

valves and the piston.

Surface e$traction and assembl" creation as required b" the anal"sis.

2ile conversion as required b" the rid eneration soft#are.

%.% Reverse Engineering of the selected Engine

The process of eneratin enineerin desin data from e$istin components is called

Reverse Enineerin (RE!.

&n reverse enineerin% a point cloud t"picall" acquired usin scannin techniques is

used as a basis for constructin 9D 4AD surface data from a ph"sical model.

This enables a considerable speed1up of the desin and construction process as #ell as

an earl" qualit" control of the ph"sical model throuh comparison of ph"sical object data

#ith 4AD surface data.

Steps involved in the RE of the Engine

The selected enine #as reverse enineered usin 8! 3aser Scanner to et the

required cloud point data of the inner surface of the c"linder head and the piston

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top. The enine #as positioned in the 9D laser scanner and the required eometr"

#as scanned.

The cloud point data #as obtained from the 'apid For) Software.The cloud

point data obtained #as smoothened and then modified to et the required

#ireframe surface of the c"linder head and the piston top.

#ote:The inner surface of c"linder head and the piston top #ere the t#o main parts of the

enine that #ere scanned% as it #as ver" difficult to measure the dimensions of these parts

usin the measurin instruments. All the other parts of the enine c"linder% ports% valves

and the piston #ere measured usin tools lie ernier caliper% *eiht aue% Dial aue

and bevel protractor.

(igure %.%. - 3h9sical Model of the C9linder :ead

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(igure %.%. 1 Scanned ire (rame 2nner Surface of the C9linder :ead and the 3iston &op.

%." Surface Creation using CA&2A " R--

The #ireframe surface obtained from the Rapid 2orm Soft#are #as converted

into igesformat% as it #as compatible #ith 4AT&A.

Theigesfile #as further used to develop the surfaces usin the ,enerati"e S$ape

!esign &odule. 6ptions lie e$trude% join% translate% spilt and others #ere used in

obtainin the surface of the c"linder head)s inner surface and the piston top. The

surface so obtained #as checed for connectivit" and smoothened to et the

required accurac".

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(igure %.". - 5eveloped Surfaces of the 2nner Surface of the C9linder :ead and the 3iston &op

%.# Modelling different parts of the engine

6nce the c"linder head)s inner surface and the piston top surface #ere created the

different parts of the Enine #ere modelled. The parts that #ere modelled #ere c"linder%

ports% valves and the piston. As e$plained earlier these parts #ere measured from the

ph"sical model and #ere modelled accordin to the dimension. The different parts #ere

modelled in '3.

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alves

The required dimensions of the valves lie the lenth of the stem% #idth% stub radius%

seat anle etc #ere obtained b" accurate measurements. The main parameter #as the

anle at #hich the inlet and the e$haust valves #ere seated on the c"linder head in their

closed positions. &t #as // derees for the inlet valve and /@ derees for the e$haust

valve. (igure %.#. -belo# sho#s the valves modelled on the c"linder head.

(igure %.#. -alves Modelled on the C9linder :ead

3orts

The inlet and the e$haust ports #ere modelled b" measurin the radius of the ports in

the ph"sical model at different points. The fiure belo# sho#s the ports that #ere

modelled. The ports #ere connected to the c"linder head.

2nner Surface of the C9linder head

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As e$plained earlier the surface #as developed in %TI%. The developed surface #as

further modified in (,. The surface #as provided #ith valve seats and the #hole surface

#as smoothened. (igure %.#. 1belo# sho#s the final surface of the c"linder head.

(igure %.#. 1 2nner Surface of the C9linder

3iston

7e$t the flat piston #as modelled b" matchin the scanned piston top surface in '3

the entire piston #as developed accordin to the oriinal dimensions as in the ph"sicalmodel.

(igure %.#. + Modelled (lat 3iston

%.D Surface e)traction and assem0l9 creation

6nce all the required parts #ere modelled the assembl" #as created as required

b" the anal"sis. The analsis re@uiredthe "al"es to 7e in t$eir closed positions and t$e

piston in T!(Top Dead 4entre! position. 2or the purpose of the anal"sis onl" the top

surface of the flat the piston #as taen. Also since the %nalsis#as 1!onl" the surfaces

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#ere required. The c"linder #all thicness #as inored and onl" the inner surface of the

c"linder #alls #as taen. Similarl" onl" the outer surfaces of t$e "al"e* inner surface of

t$e ports and inner surface of t$e clinder $ead#ere taen. (igure %.D. -belo# sho#s

the assembl" as required b" the anal"sis.

(igure %.D. - Modelled Engine Assem0l9

%. (ile Conversion

The 1! sketc$of the assembl" sho#n in the above fiure #as e$tracted usin the

setcher mode. 6nl" the lines of the setch #ere selected. The lines of the setch

represented the inner surfaces of the different parts of the enine as described earlier.

6nl" the lines of the valve represent the outer surfaces. T$e 1! sketc$e$tracted #as later

converted into iges format and #as then taen to the rid eneration soft#are 3AMC&T.

This format #as selected% as it #as compatible #ith 3AMC&T.

(igure %.. -belo# sho#s the /D setch that #as e$tracted from 9D assembl"

model and #as converted into iges format

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(igure %.. - 15 S4etch of the Engine Assem0l9 E)tracted for Anal9sis

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Chapter " ! Grid Generation using GAMB2&

".- 2ntroduction

Discreti5ation of the domain under anal"sis is a ver" important pre1processin step.

&n this step the domain is discreti5ed into a number of small elements. Anal"sis is further

carried out for each of these elements. The process of rid eneration refers to the

discreti5ation the domain% #hich is under anal"sis. The rid eneration #as carried out in

,%&0IT 1.1.This soft#are #as selected mainl" because of its compatibilit" #ith the

F!pacae that #as used later for the purpose of anal"sis.

".1 Steps 2nvolved in Grid Generation

The /D model of the enine in igesformat #as imported into ,%&0IT.

The required eometr" cleanup #as done.

Surfaces #ere created #herever necessar".

7e$t the meshin of the model #as carried out. &t involved comple$ process as the

mesh consisted of $7rid ele)ents(Trianular and Guadrilateral!.

The meshed model #as assined proper 7oundar zones and fluid zones b"

loadin the required solver. &nterfaces #ere provided #herever there #as no connectivit" bet#een the

trianular and quadrilateral elements

The mesh #as tested for its size independence. The anal"sis #as carried out #ith

=.1)) and=. ))cells. The final parameters remained the same #ith both the

si5es.

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*ence the si5e of the elements chosen for the final meshed model #as =.1 )).

2inall" an element qualit" chec #as conducted.

The rid that #as enerated #ith all the boundar" and fluid 5ones #as converted

into a format that #as compatible #ith the F! packagebein used.

".+ Grid Generation

The rid that #as enerated #as not stationar". &t #as a d"namicall" chanin one. As

the piston moved from the T! to 0!the rid had to ro# and collapse and vice versa.

Also the inlet and the e$haust valves moved in and out durin the four stroes that #ere

simulated. ?henever the valve lift #as provided the rid had to aain ro#. As the valves

closed the rid had to collapse. This t"pe of rid #as needed for the purpose of anal"sis.

59namic la9ering

&n order to meet the requirements of d"namic la"erin concept% the meshin 5one #as

divided into t#o different sub15ones.

All cells adjacent to the movin face 5one #ere quadrilaterals even thouh the cell

5one ma" contain mi$ed cell shapes.

The cell la"ers #ere completel" bounded b" one1sided face 5ones.

(ace Creation

2irst the required faces #ere created. The faces #ere created eepin in mind the

d"namic la"erin concept. Around the movin part of the valve a face #as created. This

face #as further meshed #ith quadrilaterals% as it #as a movin part. The valve #as

moved in and out onl" from the stem portion. The stub of the valve #as ept stationar".

Also the faces #ere spilt #henever necessar".

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(igure ".+. -sho#s the faces created on the /D model of the enine. &t can be

clearl" seen that the valves are in closed position and the piston is in TD4 position. The

5oomed vie#s sho# ho# the surfaces #ere spilt above the movin parts as these faces

#ere meshed #ith quadrilaterals. Just above the piston and all alon the valve the faces

#ere spilt.

(igure ".+. - (aces created in GAMB2& on the 15 Model

Meshing the faces

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As e$plained earlier the mesh #as h"brid in nature. &t #as seen to it that the

connectivit" bet#een the trianular and the quadrilateral elements #as not provided at

appropriate places. This #as aain determined on the 42D pacae used. ?henever there

#as no connectivit" bet#een the h"brid elements the 42D pacae handled it #ith the

help of interfaces.

&riangular Meshing

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(igure ".+. 1&riangular Mesh created on the Reuired (aces of the 15 Model

(igure ".+.1 sho#n above represents the faces that #ere meshed #ith trianular

elements. &t can be seen from the above fiure that the inner surface of the c"linder is

meshed #ith trianular elements until the top of the piston. *o#ever the mesh is biased

to#ards the top of the c"linder inner surface as a spar #as provided at this point in the

anal"sis. Also it can be seen that around the valves the faces are not meshed. This #as

because these #ere movin faces and had to be meshed #ith quadrilaterals

uad Meshing

6nce the trianular meshin #as finished the remainin faces #ere meshed #ith

quadrilaterals. *o#ever connectivit" bet#een the t#o different t"pes of cells #as not

provided ever"#here. The line separatin the t#o meshes bet#een #hich there #as no

connectivit" #as defined as interface.

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(igure ".+. +uad Mesh created on the Reuired (aces of the 15 Model

(igure ".+. + sho#s onl" those faces that #ere meshed #ith quadrilaterals. &t can be

seen that the faces just above the movin boundaries are all meshed #ith quadrilaterals as

required b" d"namic la"erin.

Entire Grid Representation

(igure ".+. %Entire Grid Representation.

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(igure ".+. % sho#s the entire rid. &t consists of both trianular and quadrilateral

elements. This #as the final rid that #as taen to the */pacae for Anal"sis. The

mared circles on the fiure represent the 5oomed imaes% #hich are sho#n belo#.

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(igure ".+. " Hoomed 2mages of the Grid at Specific ocations

".% Assigning Boundar9 and (luid Hones

6nce the rid eneration #as complete the boundar" 5ones #ere assined. This

formed a ver" important part of pre1processin step% as there #ere 0@ 5ones in total. 7e$t

the fluid 5ones #ere assined. There #ere a number of fluid 5ones correspondin to the

boundar" 5ones assined.

Steps 2nvolved in Assigning Boundar9 Hones

The solver F3(E#T A4#as first loaded. This #as because the 42D pacae in

#hich the anal"sis #as carried out #as 2,'E7T ;./.8;.

6nce the solver #as defined all the terms reardin the boundar" conditions #ere

as represented in 2,'E7T.

&ndividual edes #ere selected and the boundar" conditions #ere assined. This

#as because the model #as /D. &f it #as 9D then faces had to be selected.

Same procedure #as applied to all the edes.

Similarl" all the interfaces #ere defined. ?henever there #as an interface there

#ere overlappin edes. These overlappin edes #ere present in order to avoid

connectivit".

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(igure ".%. - Boundar9 Hones Assigned

(igure ".%. - represents a fe# of the boundar" conditions specified. The inlet for

e$ample #as desinated as pressure inlet. The term pressure inlet is related to the 42D

pacae used (2,'E7T ;./.8;!. Selectin the required ede desinated inlet.*o#ever

under Coundar" T"pe menu pressure inlet #as chosen. The Same procedure has been

follo#ed for all the boundar" 5ones.

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(igure ".%. 1 Menu used for Assigning Boundar9 Hones

(igure ".%.1sho#s the menu bein used for assinin the boundar" 5ones in3AMC&T. &t can be seen that the 2,'E7T :H; solver has been loaded.

Steps involved in Assigning (luid Hones

The fluid 5ones #ere assined in the same #a" as the boundar" 5ones.

The onl" difference #as that the 5ones #ere assined b" selectin the surfaces.

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The fluid #as air and all the boundar" faces #here there #as airflo# #ere

selected.

(igure ".%. + (luid Hones Assigned

(igure ".%.+ sho#s a fe# of the fluid 5ones specified. &n the same #a"% all the faces

#herever there #as fluid flo# #ere assined b" ivin different names. These names

#ere iven so that the 5ones could be easil" distinuished in 2,'E7T.

"." (ile Conversion

6nce the rid #as enerated and all the boundar" and fluid 5ones #ere assined the

meshed model #as converted into a 2,'E7T compatible format. The format selected

#as.)s$. The converted file #as then imported to the 42D pacae. All the boundar"

and fluid 5ones #ere related to 2,'E7T as the" #ere assined b" loadin 2,'E7T :H;

solver in 3AMC&T.

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Chapter # F 15 Anal9sis of the Engine

#.- 2ntroduction

&n the present da" scenario computational fluid d"namics pla"s a ver" importantrole in various #als of life. 4omputational 2luid D"namics (42D! has ro#n from a

mathematical curiosit" to become an essential tool in almost ever" branch of fluid

d"namics% from aerospace propulsion to #eather prediction. 42D is commonl" accepted

as referrin to the broad topic encompassin the numerical solution% b" computational

methods% of the overnin equations #hich describe fluid flo#% the set of the 7avier1

Stoes equations% continuit" and an" additional conservation equations% for e$ample

ener" or species concentrations.

2or the purpose of project the 42D pacae used #as F3(E#T 4.1./4.This soft#are

#as chosen because of its user1friendl" environment% compatibilit" #ith the pre

processin soft#are and accurac".

#.1 (acts a0out the Anal9sis

/. The solution #as carried out in 2,'E7T ;./.8;

1. The solution simulated all the four stroes of the &4 enine.

8. The solution period #as $.$ secat -"$$ rpm.

2. The solution too about 1$ hrson a -GBs"stem and a 3%processor.

. The simulation carried out #as a direct injection s"stem #ith the spar provided at

8@ derees before the compression stroe.

4. Thefuelused #asPentane.

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#.+ Models used for Anal9sis

4! epsilon model

(Turbulence Iinetic Ener"% k% and the Turbulence Dissipation Rate% !

The si)plestBco)pletemodels of turbulence are t#o1equation models in #hich the

solution of t#o separate transport equations allo#s the turbulent velocit" and

lenth scales to be independentl" determined.

The standard 1 epsilon model in 2,'E7T falls #ithin this class of turbulence

model and has become the #orhorse of practical enineerin calculations in the

time since ,aunder and Spaldin proposed it.

Robustness% econom"% and reasonable accurac" for a #ide rane of turbulent

flo#s e$plain its popularit" in industrial flo# and heat transfer simulations.

&n the derivation of the 1 epsilon model% it #as assumed that the flo# is full"

turbulent% and the effects of molecular viscosit" are neliible. The standard 1

epsilon model is therefore valid onl" for full" turbulent flo#s.

&ransport Euations for the Standard 4!epsilon Model

2or k C/=D

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2or C/=D

&ur0ulent iscosit9 ?-$@

The turbulence viscosit" depends on both k and .6nce the transportation equations

are solved the values are substituted in the above equation to obtain Turbulent iscosit".

59namic Mesh Model

The d"namic mesh model in 2,'E7T can be used to model flo#s #here the

shape of the domain is chanin #ith time

The integral form of the conservation euation for a general scalar,,on an

arbitrar" control volume% % #hose boundar" is movin can be #ritten as/F

?here

is the fluid densit"

u is the flo# velocit" vector

gu is the rid velocit" of the movin mesh

is the diffusion coefficient

Sis the source term of

Reions that are deformin due to motion on their adjacent reions are rouped

into separate 5ones in the startin mesh.

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The non1conformal or slidin interface capabilit" in 2,'E7T can be used to

connect the various 5ones in the final model.

Three mesh motion methods are available in 2,'E7T to update the mesh in the

deformin reions subject to the motion defined at the boundaries+

-. Spring!0ased Smoothing

1. 59namic a9ering

+. ocal Remeshing

2or the 1! engine )odelthe d"namic mesh model #as used for specif"in the

valve and piston movements. The three methods of d"namic meshin mentioned

above #ere used.

Apart from this theIn-linder options* !na)ic ones and In-linder e"ents

#ere used for specif"in various parameters lie movements and valve openins

Non!premi)ed com0ustion model

&n non1premi$ed combustion% fuel and o$idi5er enter the reaction 5one in distinct

streams. This #as the case in ,!I engine#here onl" air is taen in throuh the inlet and

at a specified cran anle fuel #as injected

. This is in contrast to premi$ed s"stems% in #hich reactants are mi$ed at the molecular

level before burnin. E$amples of non1premi$ed combustion include methanecombustion% pulveri5ed coal furnaces% and diesel (compression! internal1combustion

enines. 'nder certain assumptions% the thermo chemistr" can be reduced to a sinle

parameter i.e. the mi)ture fraction. The )ixture fraction% denoted b" f% is the mass

fraction that oriinated from the fuel stream. &n other #ords% it is the local mass fraction

of burnt and unburnt fuel stream elements (4% *% etc.! in all the species (46 /% */6% 6/%

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etc.!. The approach is eleant because atomic elements are conserved in chemical

reactions. &n turn% the mi$ture fraction is a conserved scalar quantit"% and therefore its

overnin transport equation does not have a source term. 4ombustion is simplified to a

mi$in problem% and the difficulties associated #ith closin non1linear mean reaction

rates are avoided. 6nce mi$ed% the chemistr" can be modelled as in chemical equilibrium%

or near chemical equilibrium #ith the laminar flamelet model. (or the pro6ect, the

euili0rium approach has 0een used

Mi)ture (raction

The basis of the non-pre)ixed )odellingapproach is that under a certain set of

simplif"in assumptions% the instantaneous thermo chemical state of the fluid is related to

a conserved scalar quantit" no#n as the )ixture fraction 6 f 5 C/=D

?here iis the elemental mass fraction for some element% i.

&ransport Euations for the Mean Mi)ture (raction ?-$@

Mean Mi)ture (raction ariance

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Relationship of


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bubbles! dispersed in the continuous phase. 2,'E7T computes the trajectories of these

discrete phase entities% as #ell as heat and mass transfer toHfrom them. The couplin

bet#een the phases and its impact on both the discrete phase trajectories and the

continuous phase flo# can also be included.

2,'E7T provides the user follo#in discrete phase modellin options+

4alculation of the discrete phase trajector" usin a ,aranian formulation that

includes the discrete phase inertia% h"drod"namic dra% and the force of ravit"%

for both stead" and unstead" flo#s

Prediction of the effects of turbulence on the dispersion of particles due to

turbulent eddies present in the continuous phase

*eatinHcoolin of the discrete phase

apori5ation and boilin of liquid droplets

4ombustin particles% includin volatile evolution and char combustion to

simulate coal combustion

6ptional couplin of the continuous phase flo# field prediction to the discrete

phase calculations

Droplet breaup and coalescence

Solver

Segregated Solver ?-$@

'sin this approach% the overnin equations are solved sequentiall" (i.e.%

sereated from one another!. Cecause the overnin equations are non1linear (and

coupled!% several iterations of the solution loop must be performed before a convered

solution is obtained. Each iteration consists of the follo#in steps.

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2luid properties are updated% based on the current solution. (&f the calculation has

just beun% the fluid properties #ill be updated based on the initiali5ed solution.!

The u% v% and # momentum equations are each solved in turn usin current values

for pressure and face mass flu$es% in order to update the velocit" field.

?hen interphase couplin is to be included% the source terms in the appropriate

continuous phase equations ma" be updated #ith a discrete phase trajector"

calculation.

A chec for converence of the equation set is made.

2mplicit (ormulation

&n both the sereated and coupled solution% methods the discrete% non1linear overnin

equations are lineari5ed to produce a s"stem of equations for the dependent variables in

ever" computational cell. The resultant linear s"stem is then solved to "ield an updated

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2lo# field solution. The manner in #hich the overnin equations are lineari5ed ma" tae

an i)plicit or explicitform #ith respect to the dependent variable (or set of variables! of

interest.

I)plicit: 2or a iven variable% the unno#n value in each cell is computed usin a

relation that includes both e$istin and unno#n values from neihborin cells.

Therefore% each unno#n #ill appear in more than one equation in the s"stem% and these

equations must be solved simultaneousl" to ive the unno#n quantities.

>nstead9 State

&n unstead"1state% the process variables chane #ith time. (6ne class of unstead"1

state processes are oscillator"% #here the" process variables chane #ith time in a reular

#a". All other unstead" processes ma" be called Transient meanin that the process

variables continuousl" evolve over time!.

2or the iven problem unstead state#as selected as all the variables lie pressure%

densit"% velocit"% turbulence chaned #ith respect to time. As the piston from T! to

0!to complete the four stroes the variables chaned #ith time.

#.% Steps 2nvolved in Anal9sis of the 15 model of the engine

&he entire anal9sis was grouped into two stages.

&n the First Stage the non-pre)ixed co)7ustion )odel #as used. The

calculations #ere carried out inPreP!F 2./. Coth%dia7atic and #on-%dia7atic

calculations #ere carried out. The loos up tables created #ere #ritten into a pdf

file and #as finall" read into F3(E#T.

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&n The Second Stae all the models described lie dna)ic )es$* tur7ulenceand

others #ere used for the purpose of analsis in F3(E#T. The loo table

obtained from PrePD2 #as also read into 2,'E7T. The final results #ere

obtained from 2,'E7T.

Non!3remi)ed Com0ustion Model Solution using pre35( %.-

3ro0lem 5escription*

The liquid fuel combustion s"stem considered here consisted of a liquid spra" of

pentane fuel enterin the combustion chamber in #hich air #as flo#in at +$+I. The

c"linder #alls #ere held at a constant temperature of 9@9I. The model considered

included an &4 enine of 0orediameter "$ mmand a stro4eof "D mm. The Re9nolds

num0er% based on inlet conditions% #as rouhl" -,$$,$$$and the flo# #as turbulent. As

the pentane evaporated% it entered the as phase and reacted. The com0ustion #as

modeled usin the mi)ture!fraction'35( approach% #ith the equilibrium mi$ture

consistin of 88 chemical species 9/1* 2* ?* ?1* 1* 1? 9g* 1? 9l* ?1* ?*

9s and #1. The spra" #as assumed to consist of 8@@1micron diameter liuid droplets

in6ectedat +$$ Iover a filled spra" half1anle of #$ degreeson the duct centerline. The

mass flow rateof liquid fuel #as $.$$ 4g's% correspondin to fuel1lean conditions in the

flo#.

;utline of pre35(

The mi$ture1fractionHPD2 model #as used% b" preparin a PD2 file #ith the

preprocessor% prePD2. The PD2 file contained looup tables relatin species

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concentrations and temperatures to the mi$ture fraction. The loo1up tables #ere used b"

2,'E7T to obtain these scalars durin the solution procedure. After creatin the PD2

file% the PD2 modelin option in 2,'E7T #as activated and boundar" conditions for the

mi$ture fraction and its variance #ere defined. The problem #as then solved in the usual

manner% usin the PD2 file to describe the s"stem chemistr"

Steps 2nvolved in 3re35( %.-

7onadiabatic calculations #ere more time1consumin than those for adiabatic

s"stems #ere% hence the PD2 model #as started b" considerin the results of an adiabatic

s"stem. C" computin the PD2Hequilibrium chemistr" results for the adiabatic s"stem%

appropriate s"stem parameters #ere determined that made the nonadiabatic calculation

more efficient. Specificall"% the adiabatic calculation provided information on the peak

9adia7atic fla)e te)perature* on t$e stoic$io)etric )ixture fraction% and on the

importance of individual components to the chemical s"stem.

%d ia7atic calculation Steps

Selectin the adia7atic )odeinitiall" set up the case.

All the inputs required for the adiabatic calculations #ere iven.

The species involved in the calculations #ere set up

2inall" the PD2 table #as computed

The results #ere studied to obtain information on the pea adiabatic flame

temperature and the stoichiometric mi$ture fraction #hich #ere further used as

inputs for the 7onadiabatic calculations

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Inputs for t$e %d ia7atic alculations

Total numbers of chemical species defined #ere 88.

9/1* 2* ?* ?1* 1* 1? 9g* 1? 9l* ?1* ?* 9s and #1

?perating onditions: The li@uid fuel inlet te)perature (and the vapori5ation

temperature! #as 4= +and the oxidizer inlet te)perature was 8=8+. The sste)

pressure was / at)osp$ere.

Mole fraction for /1 #as entered as 8. The mole fraction for o$idi5er (#1 and

;1! #as entered as =.1< and =.>/respectivel"

'esults for %d ia7atic alculations

(igure #.%. - &emperature'mi)ture!fraction relationship for the Adia0atic Case in 3re35(

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The temperatureHmi$ture1fraction relationship displa"ed in (igure #.%.-revealed

that the peak fla)e te)perature was a7out 11>= + and occurred at a )ixture

fraction of approxi)atel =./.

(igure #.%. 1 Species Concentration (or the Adia0atic Case

(igure #.%. 1 sho#s that all species% e$cept 6* and */6 (,!% appeared in sinificant

mole fractions in the equilibrium s"stem. This information #as used to eliminate these

species from the s"stem chemistr". *o#ever% all the 88 species #ere retained here.

#onadia7atic alculation steps

The simple adiabatic calculation considered above provided useful input to the

nonadiabatic calculation required for the liquid fuel simulation considered. The current

prePD2 inputs #ere altered to those% #hich #ere used for the final calculation.

The s"stem description #as redefined as nonadiabatic.

The pea temperature #as defined based on the adiabatic results.

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After these alterations% the s"stem chemistr" #as recomputed and saved

Inputs for #onadia7atic alculation

*ere% vapori5ation beins at rouhl" ;:@ I and the o$idi5er enters the combustion

chamber at 9@9I. *ence% the )ini)u) te)perature #as set as 1;= +. The

ma$imum temperature must have been at least 8@@ I hiher than the pea flame

temperature found in the preliminar" adiabatic calculation. *ere% the )axi)u)

te)perature#as taen as 1;== +% sinificantl" above the pea adiabatic s"stem

temperature of //


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'esults for #onadia7atic alculations

(igure #.%. + +5 oo4 >p ta0le for the Non Adia0atic case in 3re35(

(igure #.%. + represents the loo1up tables containin time1averaed scalar values at

discrete matri$ points. 2or nonadiabatic cases% these loo1up tables #ere three1

dimensional and could be plotted in a slice1b"1slice fashion.

C" default% the displa" of temperature #as on a slice of the 9D loo1up table

correspondin to adiabatic enthalp". This displa" looed ver" similar to the loo1up table

created durin the adiabatic calculation.The pea temperature (/9:@ I! #as hiher than that predicted in the adiabatic

calculation. This #as because the nonadiabatic s"stem% #ith a Distribution 4enter Point

of @./% included better resolution around the stoichiometric mi$ture fraction

Suc$ looks up ta7les at different points were sa"ed into a P!F file and t$en were

read into F3(E#T w$ile doing t$e final %nalsis.

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(igure #.%. % Species Concentration (or the Non Adia0atic Case

The partial equilibrium calculation% considered here% resulted in an equilibrium

s"stem description onl" up to the rich limit mi$ture fraction of =.8. Ce"ond this value of

mi$ture fraction% prePD2 computed the composition b" mi$in pure fuel #ith theequilibrium composition found at the rich limit. This treatment of the s"stem is reflected

in (igure #.%. %

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Solution Set >p in (>EN& #.1.-#

6nce the loos up tables #ere enerated in PrePD2 0.8 the .)s$ 91! )odel of t$e

engine file #as imported into 2,'E7T. >ltra lean mode or econom9 mode #as

anal"sed. The ultra lean mode has been e$plained in the first chapter. 2or the sae of

anal"sis various models available in 2luent #ere used. The" are listed belo#

/. Viscous )odelB (I1 epsilon model!.

1. !na)ic )es$ )odel

8. #on-pre)ixed co)7ustion )odelusin Pre pdf 0.8.

2. !iscrete p$ase )odels.

. Sol"er 1 'nstead" State% Sereated Solver% 2irst 6rder &mplicit

The file imported #as saved as .casfile. 2urther the case file #as set up for anal"sis.

The steps are sho#n belo#.

A rid chec #as conducted on the imported file. &t #as seen that there #ere no

neative volumes. The rid #as further scaled to the required dimensions.

7e$t the solver t"pe #as selected. &t #as 'nstead" state% sereated% implicit

solver.

The different models required for anal"sis #ere selected. 2irst the k- Tur7ulence

)odel #as selected. The default parameters associated #ith this model #ere

retained.

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7e$t the Species Transport &odel#as selected and the P!F fileenerated in

prePD2 0.8 #as read in. 4are #as taen to include the compressibilit" effects.

The Val"e 3ift Profile#as read into 2luent usin the profile menu. The valve lift

profile consisted of data correspondin to "al"e )o"e)ent at a particular crank

angle degree. The valve lift for both the valves #as measured from the ph"sical

model. The valve lift file #as created in notepad and #as saved in .cformat. The

inlet 1valve and e$haust1 valve openin and closin periods #ere decided b"

referrin to the Val"e-Ti)ing diagra). T$e inlet "al"ewas openfor a period of

18< degreesand the ex$aust "al"e was openfor a period of 12= degrees. This

included the valve overlap period also. (igure #.%." represents a part of the

profile file and the fields associated #ith it. The entire period correspondin to theopenin of inlet and e$haust valve #as divided into cran anle steps of 8.;

derees and at each step the valve lift #as provided. &n all there #ere 8:/ points

#here the valve lift #as provided.

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(igure #.%. " alve 3rofile (ile

2urther the !na)ic &es$ &odel #as selected. All the three mesh update

methods Sprinin% Remeshin and ,a"erin #ere selected. Even theIn-linder

)odel #as selected. The &nputs iven are sho#n belo#

&a0le #.%. - 2nputs for the 59namic Mesh Model

4ran shaft Speed (rpm! -"$$

Startin cran Anle (derees! $

4ran Period (derees! D1$

4ran Anle Step Si5e (derees! $.1"

Piston stroe (mm! "D

4onnectin Rod ,enth (mm! -$$

Piston Stroe 4ut1off (mm! -$

Minimum alve ,ift (mm! $.-

The d"namic mesh model #as further set up b" definin the !na)ic ones.

The" #ere of three t"pes Stationar* !efor)ing* and 'igid. All three t"pes

#ere used as required to set up the piston and the valve motion. All parameters

lie the 4ell 3ro#th factorK Remeshin factors etc #ere input in this step.

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The In-linder e"ents #ere defined ne$t. The inlet valve openin and

closin anles #ere defined. Durin this period the Slidin &nterfaces #ere

created. Similarl" e$haust valve openin and closin cran anles #ere also

defined. (igure #.%. # represents the events that #ere defined.

(igure #.%. # 59namic Mesh Events

(igure #.%.D represents t$e !na)ic &es$ )o"e)ent throuhout the 2our

stoes. &t can be seen ho# the valves are closin and openin and ho# the piston

is movin from T! to 0!

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(igure #.%. D 59namic Mesh Grid Movement

The!iscrete P$ase &odels#ere primaril" included to define injections. The

6ptions under discrete Phase Models and the &njections chosen are e$plained

belo#. These models #ere also included to trac the particles injected% to

stud" the !roplet ollision 9unstead case* !roplet 0reak (p* eat and

&ass Transfer calculations.

8. The &a9lor Analog9 Brea4up7&AB8spra" brea up model #as used

to estimate the spra" brea up.

/. The 59namic 5rag Model#as used to determine the droplet dra co1

efficient d"namicall"% accountin for variations in the droplet shape.

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9. The t"pe of injection used #as Group 2n6ection. The point properties

and the t"pe of particle bein injected #ere mentioned. -$ streams of

fuel inlet#ere defined in all.

0. ar"in the J and K velocitiesvaried the injection cone anle and

pressure% as it #as a /D setup. A cone anle of #$ degrees #as

maintained b" var"in the J velocit9 #hile K velocit9 #as ept

constant.

:. The particle t"pe selected #as !roplet% #hich made use of particular

heat transfer la#s.

;. The volatile species #as selected as -$$L pentane as input in thePrePD2

;>

Q1elocit" (mHs! 1:


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Diameter (m! @.@8 @.@8

Temperature (I! 9@9 9@9

2lo# Rate (Hs! @.@@@= @.@@@=

Start time injection (sec! @.@0

End time injection (sec! @.@08:

The &aterial &odels #ere ne$t set up. The )aterial )odels for both

continuous and discrete p$ases#ere set up.

8. ontinuous P$ase+ All thermod"namic data% includin densit"% specific

heat% and formation enthalpies% #ere e$tracted from the prePD2 chemical

database #hen the PD2 model #as used (e$plained in the previous

chapter!. These properties #ere

“Numerical Investigation of Combustion Process in a 4-Stroke Gasoline Direct Injection (GDI) Sing

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Transcript of “Numerical Investigation of Combustion Process in a 4-Stroke Gasoline Direct Injection (GDI) Sing