em usingrtment ofogy, Ma-

,

Inrecentyears, the reduction of exhaust emissions hasbeenthe main concern of automotive engineers eversincethe hazards of automobile pollution were recog-nized.Efforts are on by the automobile manufacturerstoreduce these emissions. The present stringent emis-sionnorms are difficult to be met with carburetors.Thishas lead the automotive industry to look for fuelinjection system with the help of electronics. Onemore problem, in using carburetor, is the mal-distributionof mixture in multi-cylinder engines. Byadoptingthe fuel injection system, which has got in-dividual injector for each cylinder, the mal-distributionbetween the cylinders can be avoided. Inthecarburetor version of the engine, it is very difficulttooptimize the air-fuel ratio over the entire operatingrangeof the engine. Since the fuel injection systemcanbe controlled through the Electronic Control Unit(EeU), it is possible to optimize the air- fuel ratiothroughoutthe engine operating range.

Now the challenge will be to design the intakesystemthat will create the minimum restriction in theintakepath. It has become necessary for the intakesystem designer to understand the function of eachcomponent of the intake system so that he achievesthebest performance. The layout of air intake system

IndianJournal of Engineering & Materials SciencesVoLII, April 2004, pp. 93-99

Flow through S.l. engine air intake system using CFD at part throttleand full throttle

J Suresh Kumar & V Ganesan

Internal Combustion Engines Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Madras,Chennai 600 036, India I

Received 3 February 2003; accepted J March 2004

The objective of present study is to predict and analyze the flow through the SI engine air intake system using Com-putational Fluid Dynamics (CFD) and to validate the prediction by experimental data. Three-dimensional model of air in-take system was analyzed by using the commercially available FLUENT software. The mesh was generated using the Tet-hybrid scheme which includes primarily of tetrahedral mesh elements but may include hexahedral, pyramidal and wedgeelements. The pressure boundary conditions were used to define the fluid pressure at the inlet and outlet of Air Intake Sys-tem. In the present study, the CFD code was validated by the experimental work. Experimental data was generated at onebar outlet pressure for the part throttle and full throttle conditions. The CFD plots give informative pictures of the flow field,which will help the designer to understand the effect of various components of Air Intake System. The predicted airflowrate shows good agreement with the experimental results. The results indicate that the CFD model can be used as a tool tounderstand the effect of various parts of air intake system for optimization. This in effect will reduce the number of experi- •ments to be carried out for arriving at final optimized system.

IPC Code: Int. Cl.7 F 02B 29102; F 1SD 1100

under consideration is shown in Fig. 1. The air intakesystem consists of throttle body assembly, which in-cludes the key parts such as throttle plate and throttleshaft. Manifold consists of plenum chamber andmanifold runners. Cylinder head intake path and in-take valves also form part of air intake system.

CFD is the analysis of systems involving fluidflow, heat transfer and associated phenomena such aschemical reactions by means of computer-basedsimulation. CFD can be described as the use of com-puters to produce information about the ways in

~ AIr flow direction

Fig. 1 - Layout of air intake system

94 INDIAN J. ENG. MATER. set, APRIL 2004

which fluid flows through a given system under agiven condition.

The fundamentals of CPO have been clearly ex-plained by Versteeg and Malalasekera' and Shaw2

.

. Winterbone and Pearson' have explained the intakemanifold tuning, which has been described with refer-ence to an engine filled with individual intake pipes ofuniform cross-sectional areas. After the intake valvehas opened, the descent of the piston during the in-duction stroke reduces the pressure in the cylinder andcauses a rarefaction wave to be propagated into theintake pipe. This rarefaction wave travels to the endof intake pipe where it is reflected as a compressionwave. The arrival of the peak of this compressionwave in the critical period defined above which aug-ments the filling of the cylinder with air.

'Experiments conducted by Livergood et al.4 showthat at low lifts, the flow remains attached to the valvehead and seat, giving high values of discharge coeffi-cient. At intermediate lifts, the flow separates fromthe valve head at the inner edge of the valve seat. Anabrupt decrease of discharge coefficient occurs at thispoint. The discharge coefficient increases with in-crease in lift thereafter. This is because the size of theseparated region remains approximately constantwhile the flow area increases. At high lifts, flow sepa-rates from the inner edge of the valve seat.

Ohata and Ishida5 studied the basic mechanism ofintake manifold tuning to provide a high pressure atthe intake valve so that the mass flow into the cylin-der is boosted at a given engine speed. In particular, itis vital that a high pressure is maintained at the intakevalve in a period between bottom dead center (BOC)of the induction stroke and a point just before theclosing of the valve.

The objective of present study is to analyze theflow through the air intake system by CPO at partthrottle (50%) and full throttle and to validate the pre-diction by using the experimental data. The air intakesystem selected for this study is being currently usedin a popular automobile.

Numerical ProcedureThe numerical simulation of the flow region of in-

terest requires: (a) Modelling and formulating theproblem in mathematical form; (b) Choice of numeri-cal method; (c) Programming; (d) Execution for ob-taining results; and (e) Interpretation of the results.

The flow problem is solved by continuity and mo-mentum equation in a given domain of interest. The

velocity component is governed by momentum equa- ,tions. However, the real difficulty in the calculation ofthe velocity field lies in the unknown pressure field.The pressure gradient forms a part of the source termfor the momentum equation. The difficulty associatedwith the determination of pressure has led to severalmethods in solving pressure from the governingequation. One such procedure, which is widelyadopted, is called SIMPLE, which stands for Semi-Implicit Method for Pressure Linked Equations.

Continuity equation

The mass balance for the fluid element is that, therate of increase of mass in fluid element is equal tothe net rate of flow of mass into fluid element. Sincethe fluid is assumed to be incompressible, and thedensity (p) is constant, we get:

Momentum equation

According to Newton's law the rate of change ofmomentum of a fluid particle equals the sum of theforces on the particle. Based on this,

X-component of momentum equation is,

Du o(-p+rxx) oryx orz.x Sp-= +--+--+ Mx

Dt ox oy oz

Y-component of momentum equation is,

Dv orxy o(-p+ryy) orZY Sp-=--+ +--+ MyDt ox oy oz

Z-component of momentum equation is,

Dw OTxz oryz o(-p+r"zz) sp--=--+--+ + Mz

Dt ox oy oz

SM(x,y,z) is source momentum per unit volume perunit time in x, y, z directions respectively. The reasonfor using the term SM(x,y,z) is to have the overall effectof momentum in x, y and z directions without consid-ering the body forces.

Turbulence model equation

In the present study, two-equation (k- E) turbu-lence model has been used for physical modelling.This model uses two partial differential equations to

estimate the v(commonly kr»lence.

o(pk) di (at+ IV c

O(pE) di (at+ IVP

The standaconstants thatfitting for a ~are,

CIl = O.09;O'k :

where eddy"

multiplied wit!of production I

Calculation of ec

Par .one-diikinematic turbm2/s can be e)city scale L (rrvelocity scalethe effects of t

Vt = C.L.1

where C is a I

ity. For dynarr

III = Cp.L.1

For standarscale which aturbulence are

L= k 1/2

1= e12/£

It is permitthe large eddythe rate at wlthe mean flo,

,transfh of ersmall, dissipat

rrn equa-ilation ofure field.irce termssociatedo severaloverning, widelyor Semi-1S.

that, theequal tont. Sinceand the

hange ofm of the

ume pere reasonill effectt consid-

) turbu-xlelling.itions to

KUMAR & GANES AN: FLOW THROUGH 5.1. ENGINE AIR INTAKE SYSTEM

estimatethe velocity and length scales and hence it iscommonlyknown as two-equation model of turbu-lence.

a(pk) + div(pkU) = div[~gradkl + 2f.1tEu.Eij - peat (J k

a(pE). . [f.1 1--+dzv(p£Ut=dzv _t gradeat . (JE

£ £2+CIE k2f.1tEij.Eij - C2EPT

The standard k-s: model employs values for theconstantsthat are arrived at by comprehensive datafittingfor a wide range of turbulent flows and theyare,

Cp=O.09;(Jk =1.00;(JE =1.30;CIE =1.44;C2E =1.92'

whereeddy viscosity (f.1t) = pC).l ~, The term Eije

multipliedwith eddy viscosity will determine the rateof production or dissipation of k or E respectively.

Calculationof eddy viscosity

For 'one-dimensional flows we assume that thekinematicturbulent viscosity Vt, which has dimensionsm2/scan be expressed as a product of turbulent velo-cityscale L (m/s) and a length scale' I' (m). When onevelocityscale and one length scale suffice to describetheeffects of turbulence, dimensional analysis yields:

"vt=C.L.I

whereC is a dimensionless constant of proportional-ity.For dynamic turbulent velocity,

~t = Cp.L.I

For standard k-e model velocity scale and lengthscalewhich are the representative of the large-scaleturbulenceare defined as:

L = k 112

1= k312/£

It is permitted to use the 'small eddy' E to definethelarge eddy 'I' because at high Reynolds numberstherate at which large eddies extract energies fromthe mean flow is precisely matched to the rate oftransfer of energy across the energy spectrum tosmall,dissipating eddies.

Details of geometry and mesh generationThe three-dimensional model of air intake system

was created using the software SOLID WORKS. Inorder to numerically solve the governing partial dif-ferential equations, approximations to the partial dif-ferential need to be introduced. The mesh was gener-ated using Tet-hybrid scheme, which includes pri-marily of tetrahedral mesh elements but may includehexahedral, pyramidal, and wedge elements. For meshgeneration GAMBIT software was used.

Boundary conditionsThe present problem has three types of boundaries.

They are inlet, outlet and wall boundary. The waythese boundary condition are prescribed are:

Inlet - Pressure boundary conditions are used todefine the fluid pressure at the flow inlet. This condi-tion is used when the inlet pressure is known but theflow rate or velocity is not known.

Outlet - Pressure outlet boundary conditions re-quire the specification of static pressure at the outletboundary.

Wall - In the present case walls are assumed to beadiabatic with no slip condition. Standard wall func-tions are used to calculate the variables at near wall-cells.

Convergence criteriaFinal convergence is decided by way of residual-

source criterion. The convergence criteria in the pres-ent study are set as 10-3

, i.e., the sum of residualsource term in the entire domain becomes less than111000 for all the variables viz. u, v, W, k and E.

Numerical prediction matrixFor the numerical predictions, valve lift of 8 mm

was considered to be maximum and the inlet pressureis considered as 1.013 bar. Predictions have been car-ried out for all the three runners for 50% and wideopen throttle (WOT) position. For the outlet, six dif-ferent cylinder pressures have been considered from0.7 to 1.2 bar in steps of 0.1 bar.

Experimental Set-upThe details of the experimental set-up are shown in

Fig. 2. The flow bench consists of air pump, with aflow control knob. It has got a set of orifice plates tomeasure the air-flow. To maintain the test pressureacross the valve, it has got a test pressure meter with acontrol knob. The desired pressure across the inletvalve can be maintained by adjusting the knob. It has

95

INDIAN J. ENG. MATER. SCI., APRIL 200496

Table 1 - Validation of CFD resultsINCLINED MANOMETER FLOWMETER 1.50e .•.Oi

1.350+01 -~;;-~1.20e+01 ~~

~ ..1.05k01 .~.-~9.008 .•.00 .'':'~'..7.50e+OO

~:~:t'lJ7~:'!}

S.OOe+OO ~.-~.•. ' ..4.508+00 '-'::;

..•--.z: ~3.00e.OO Ji-"''''_

.zJ ..•-'1.508+00

..~ •.

3.96e-04

TEST PRESSURE METER

Manifold Throttle opening Outlet pressure (bar)

50%WOT

50%WOT

50%WOT

1.01.01.0

Runner no. 1

Runner no. 2

Runner no: 3FLOWSCALE%

DIAL INDICATOR ANDDOLT TO OPEN THE VALVE

Results and DiscussionIn order to understand the flow through the intake

system, the flow regions are divided into three sec-tions. These are marked in Fig. 1 as 1, 2 and 3. Wewill discuss the flow through these sections in greaterdetail in the following paragraphs.

Flow through throttle body assembly - Throttlebody controls the airflow to the cylinder as per theengine demand. The throttle plate, which is shown inFig. 1 performs this function. To analyse the flowfield, a section is taken at the throttle body assemblysuch that it passes through the centre of throttle as-sembly as shown in Fig. l.

From Fig. 3a, it could be seen that at 50% throttleopening, re-circulation zone is formed around thethrottle plate. The maximum velocity occurs at theouter portion of the re-circulation zone near the wall.Air rushes to the plenum entry through this throttleopening and fills the plenum chamber. The reason forthis re-circulation could be attributed to the' throttleplate which restricts and obstructs the flow.

At wide open throttle position, by observing theFig. 3b, two re-circulation zones could be seen aroundthe throttle plate. One re-circulation zone is creatednear the throttle plate area one at upstream and otherat downstream. One more observation that can bemade from the figure is that at the throttle plate edgeand at the bottom of upstream re-circulation zone, thevelocity values are high.

Flow in plenum chamber - The function of ple-num chamber is to distribute the airflow to variousmanifold runners and also to dampen the pressurepulses, which are created because of valve events.Fig. 1 shows the section at the plenum vhamber takenfor analysis when the air enters the plenum chamberand moves towards the runners.

Fig. 4a shows the velocity plot at 50% throttleopening. Two re-circulation zones could be seen veryclose to the runner outlet. When the throttle is opened,air rushes into the plenum chamber and leavesthrough the runner outlet to the individual cylinders.Maximum velocity occurs inside the plenum andclose to the walls of the plenum.

CYLINDERADAPTER

Fig. 3a - Velocity \part throttle (m/s)FLOW CONTROL KNOB

Fig. 2 - Experimental set-up

got an inclined manometer, which measures the pres-sure across the orifice plate. This is fed to the digitalflow meter, which will indicate the flow rate. Top ofthe bench has got an adapter for mounting the cylin-der head.

Working Principle" - The cylinder head is mountedon the cylinder head adapter, which is normally madeof acrylic sheet. The bolt is fixed on the top of 'theinlet valve along with the dial indicator. When theblower is switched on, air flows through the intakepath and it goes outside the test bench through theorifice plate.

The test pressure is adjusted by using the controlknob, and the reading can be seen in the manometercolumn. By selecting the appropriate orifice plate, andby adjusting the flow control knob, flow through thepart under test can be varied. If the reading in the in-clined manometer is above 100% the next orifice plateis switched on. The reading in the inclined manometeris noted which gives the airflow across the orificeplate in terms of percentage (%). Using the chartgiven by the flow bench manufacturer, one can get theairflow through the intake system for the selected ori-fice plate and the percentage flow given by the in-clined manometer. If the inclined manometer readingis fed to the digital flow meter, it automatically dis-plays the mass flow rate.

8288-04

Fig. 3b - Velocity vfull throttle (in rnIs)

Fig. 4b showthrottle. There istern at increased tthere are two SIT

rushing into thenear the re-circul:

Flow in plenusection (3 in Fig.flow filed when iSa shows the velNumber of smallthe runner outlet:mum velocity oee

Fig. 5b shows 1

tion. The flow 1=throttle. Here alcloser to the walls

CFD validationCFD predicted Airfk

Figs 6 and 7 shthe three manifoleyll, cyl2 and cy

To validate the CFD result, valve lift (8 mm) andinlet pressure (1.013 bar) were used. The details aregiven in Table 1.

ure (bar)

ie intakeiree see-rd 3. Wen greater

Throttle; per the.hown inthe flowissembly'ottle as-

) throttle.und the.s at thethe wall.; throttle-ason for: throttle

ving then around: creatednd othercan be

ate edge.one, the

1 of ple-various

pressure: events.ier takenchamber

throttleeen veryopened,I leavesylinders.urn and

KUMAR & GANESAN: FLOW THROUGH S.1. ENGINE AIR INTAKE SYSTEM

150e .•.Ol

1.359+01

1.20e+Ol

1.05e .•.Ol

9.006+00

7.50e.00

6.00e+00

4.50e .•.OO

l.OO..oO

1.508-+-00 2]3.969--04

"'~~:r •.•..._~ ~.. -, •..~""-.~ • .:-:_ ..,......~_-:-:?:~:':'::~:;."~':;.:.:~~~~..: \": ~.'" : ~t ,~;;;r.'?,II' _ . _.;..~_:--: ~ _ .::.:...:..-~'~'£·~,~f,\:.··,J/~-;:~!.-::_ 4" '"...~*-~""~~...."\ \'.I I: f/'.t..f/ ~:>A{;-"""'~~ :.._.- •.~ •••~~~'tf •.•'I r"r~"~-~"o.C--"''>':-:',/\'•.f,~'\.Y \.'".l;/'.I{' ,'!,t'. '(I.",tl, ~~":(;;~~-i; ~ ;',~.'p:.r, ~• ,Ill' 'l'ti~I \ ~ I t 1I:'d1,~t;:;: p,••• , lqn';C~'l!';~~}if1Jlk,\lt'~~~\W':'~~"::.-.:F:t.~'t!'~;-]~. -Y/}.,;~~.It{'i •.II\\~ ~~~ _~, ~ J\.:I

.• ~ ", 'f., f h. ~~- ~-. 'l't-•• : ·';-,f ,6,Lj \l'~~~'~'.,- ---::~ '/;r'l,,,-- -";"'-,~ ~#~ ~,,)..' ~~ ••~- --,--:::..-;:;.:---~. - ~ 1O'J,; ..~~ ~",r.••JI"f'\ .•t..~":---- _-:::..~~ -_:. .,,.. ';~f"\" ,_ ~_~.~,-::~:Z~:.~-'~:,~,~.-~~,--.-

Fig.3a - Velocity vectors at throttle body (section 1 in Fig. 1) atpartthrottle (m/s)

2,80e .•.01 ~ ••. ,~._. ;

2.52e+01 .• ...f '" ~- -_;'. .., .,,- " " ".,.... ,,:.-:;..._,.,:.....-..:.7C:-;:... '::' • "", - - ,--..- '.'.224e+01 .<:f;. .,~-"':,.:..,. ~~~ ...• "" "".s--- ~ ~ "-'~ .

tI! - ....."' ~..-- -........,- ,"" _ .•....::::..- - -~~~)'...........-- - ~•.196e~1 _ --__ .., - -,.:;: -~ ..•• ~ \ If -rr /::.-: "£'" ~.<'.. ._# '/r-::'''- .•...'.••.~''', II. ". ,;N:'':;:-~ ..,.. ,\,\\_..,' l"" C ,,-

168.+01 -_::"",,'1 :;;-~~' '. .~.1~~.,(t;{.Q:·/-''- .~~ ,- f~;",y· s:-:= ".\\. l-rm- .JV'~, .• "' .. '"__ ". ~_, •. if.. ;:- ~,\- l " < ' 1." • I' r".

140"01 ;..•••..;.-1". Itf· • ~ r.. ,.'.' II, ,1i\ /I .-I. . ...•.. }( ~ :"','1_/.., yl~'I".,·...-. .Ii"!!"! I. • ..••. )<',#.'1- .U2e+Ol :y),,. . ~..<r : J '"f I.".trtt .•• ,:. _"::;;t"1/840

.•••:_ •• f:4i.'> ,," 'il/'JT~·· "~;;;~:"~''';'. ..00 ~" -- 'I' ",.~., ' -s-"",(:I",~" ~~.,..r' ..•,,,-.", . --- ~:.,...-""'-'"

'~ '.,. ..• : ~ "'- r " .J" 4-'" ~""': - ~ .5.&Oe+oO _, •••._--.....-....--~ ••.... - i ,. I ~~~•• ~,.~~ _ ...•.....:::~_~... - •• :- .': ~--c.Z:2.80e+oO~" ~-~ ~ ••• -- - --=-=--~-i""828e-04

Fig.3b - Velocity vectors at throttle body (section 1 in Fig. 1) atfull throttle (in m/s)

Fig. 4b shows the velocity, plot at wide-openthrottle.There is considerable change in the flow pat-ternat increased throttle opening. It could be seenthatthereare two small re-circulation zones and, the airrushinginto the plenum. Maximum velocity occursnearthe re-circulation zone

Flow in plenum and manifold runner path - Asection(3 in Fig. 1) has been taken to understand theflowfiled when it branches to different runners. Fig.Sa shows the velocity plot at 50% throttle opening.~umberof small re-circulation zones could be seen attherunner outlets from the plenum chamber. Maxi-mumvelocity occurs near the wall.

Fig. 5b shows the velocity plot at full throttle posi-tion.The flow pattern is quite different from partthrottle. Here also the maximum velocity occurscloserto the walls.

CFDpredicted Airflow

Figs 6 and 7 show the CFD predicted airflow in allthe three manifold runners, which are specified ascyll, cyl2 and cyl3 for part throttle opening and full

2.000+01

1.80e+01-. ----~. ~- ..•••..-... ~ -; ....;!--~ ---~

"':.j..1'3~~-~.~;'''l''.;::.~~~",,,, ",- . ,,<"',)C., .<></ •• , " , ~ '~'"'/1:( '·r:·· 1 •• -: •• I{ _ • .: ••• ~~ ~...,.}\

III j ld..,.f,,~t'~.•'.- '2"..r~·~ '!f I "i\\~ Io~ ~\ ~ _ '\\tI. ~\ ~'\. .•••,\ '::".- 'l r -." ~ ~~' . .I~~·~\'~~~....:.;.-;:t'.:,~..,~::}~tetf'. ~\' ~~~~ --'£~~:'/";z'-<;;;;- ~=:~,. " , ~}'\.~~-, '-, ••. ~ "0~~ •.• ~~~~

'~:~~' " •..;" '~---. ~~~t\';;--;t$~~' jII\ •••~,,,,,,~~- ~'~".... .• .....-~_YI'~- . /'i 1 ..,... ~.. -~ ••.)1(;.,/,.~ '~1t,.:\,~'i.,~ .~,~ .•.~., .410'-«:: :'~~.tlt.(;I.•.t!-f ~:'~\~~t ~.~t..~"..:,' ~.~~¥.~ .•..•...~ So ••. · ••• -e , -.J' ••.•. ~ _~ .•..••..•...•.~ .,.;-':~~---~;. <"",~•.~ - - .••.•••.• ~ .•.•-:-..;'~ -.- ;~-.::::,-.:..-

1.S0e+01

1.40..01

1.20e+01

1.00e+01

8.008+00

6.00e.oO

4.00e+OO

2.00e+OO

3.96e--04

Fig. 4a - Velocity vectors at plenum chamber (section 2 inFig. 1) at part throttle (m/s)

2.50u01

2.25e .•.01

2.00e+01

1.750+01

1500+01

1.25e..ol

1.009+01

7.50e+OO

5.00e+OO

2.50e+00

8.2Be-04

Fig: 4b - Velocity vectors at plenum chamber (section 2 inFig. 1) at full throttle (m/s)

throttle respectively. As it is evident from the figures,flow through the various runners is almost the samethough there is a marginal difference. This marginaldifference is bound to occur because of the differencein lengths of the various runners. This indicates thatthe design of the air intake system is quite satisfac-tory. For CFD analysis, different outlet pressures wereconsidered. The outlet pressure is varied from 0.7 barto 1.2 bar in steps of 0.1 bar. The range 0.7 to 1.2 baris the normal expected range in the S.I.engine cylin-der pressure during the intake stroke.

For CFD prediction the maximum valve lift of 8mm is selected. As mentioned earlier at part throttleand, full throttle mass flow rate are quite the same inall the three-manifold runners. It can also be seen thatthe airflow rate reduces with increase ill outlet pres-sure. This is expected since the reverse flow that oc-curs when the outlet pressure exceeds the inlet pres-sure. Because of this reverse flow, the incoming air-flow from the intake system is pushed back into theintake system. This happens when the inlet valve juststarts to open and at the same time cylinder pressures

97

~1

INDIAN J. ENG. MATER. SCI., APRIL 200498

2.00,

1.80,

1.S0,

1.40,

1.20,

1.00,

ROO,

S.OO,

4.00,

2.00,

3.9S, rFig. Sa - Velocity vectors at plenum and manifold runner path(section 3 in Fig. 1) at part throttle (m/s)

2.50e.01

2.25e+01

2.00e+Oi

1.75e.Oi

1.50.+01

1.25e+01

1.00e+o1

5.00e-+OO

2.50e+OO

8.280-04

Fig. Sb - Velocity vectors at plenum and manifold runner path(section 3 in Fig. 1) at full throttle (m/s)

are higher than the inlet pressure. This is the mainreason for poor part load economy of S.1. engines.When the outlet pressure is above the inlet pressure,reverse flow was found to occur when the pressuredrop across the throttle plate is high; the airflow to thecylinder is also high. This holds good for all throttleopenings. This happens when the piston is closer tothe bottom dead center position drawing the freshcharge with the exhaust valve closed.

Comparison of predicted flow and experimental data

Fig. 8 compares the CFD prediction and experi-mental data at 1.0 bar outlet pressure. It can be seenthat, for all the three runners, named as 1, 2 and 3 re-spectively, the CFD predicted results are found to bequite close to experimental data. This. figure alsoshows the comparison of predicted and experimental

34,-------------,32~~----------~~30+--~~--------_1.:!!~28+----~~-------1o~26+_----~~~----~~<24+_-------3~~--~22+_---------~~~

-CYL1

-CYL2

-CYL3

0.8 0.9 1 1.1 1.2OUTLET PRESSURE (bar)

Fig. 6 - CFD predicted flow for various cylinders at part throttle

20~-----------_._18~~~---------~.!!1to~16+----~~~~-----~o~14+_---------~~~~-_1a:<12+_-------------------~~

-CYL1

-CYL2

-CVL3

10+_--~---~__~--~--_10.7 0.8 0.9 1 1.1

OUTLET PRESSURE (bar)1.2

Fig. 7 - CFD predicted flow for various cylinders at full throttle

~"•..•C".LIIE.m.J30 I25 ,

2 3

I

I-;II

Iii 20 .•:§~ 15 ....JU.~< 10 r

5To I

1 2 3

PART THROTTLE FULL THROTTLE

Fig. 8 - Comparison of CFD and experimental data

results for the part throttle and full throttle. The per-centage deviation between the predicted and experi-mental data is found to be less than 5% in all thecases. As could be seen from the figure, CFD predic-tion is always higher than the experimental values.This is to be expected since in the analysis the rough-ness of pipe, boundary layer development and coeffi-cient of discharge of the valve are not taken into ac-count.

As regards to the difference in flow between run-ners, it could be attributed to geometry of the runners.Since the runner lengths are different which basicallydepend on the vehicle layout there are differences inthe airflow rate. Bends in the runner path will reducethe velocity of airflow considerably, Particularly, it is

a challengebest judgrne

The impcduce the nuan insight rtake systenvalidates ththe agreemeresults regafar as air imately imp I

and mass flstant. This (

Conclusion1. CFD vecthe flow fietion and des

CYL1

CYl2

CYlJ

art throttle

CYLl

CYl2

CVl3

III throttle

'.rso' I.~ I

Iata

The per-I experi-1 all the) predic-t values.e rough-d coeffi-into ac-

een run-runners.basically'ences inII reducearly, it is

KUMAR & GANESAN: FLOW THROUGH S.l. ENGINE AIR INTAKE SYSTEM

achallenge for the intake system designer to make thebestjudgment for optimum performance.

The importance of CFD prediction is that it can re-ducethe number of experiments. Further, it also givesan insight regarding the flow field through the air in-take system. Confidence can be gained when onevalidates the predicted results. As could be seen thattheagreement between the predicted and experimentalresults regarding the mass flow rate is quite good. Asfar as air intake system is concerned what is ulti-mately important is that proper air motion takes placeand mass flow through each manifold is almost con-stant.This could be seen in the present study.

Conclusions1. CFD vector plots gives good informative picture oftheflow field which can help in the proper configura-tionand design of the intake system.

2. Experiment values are closer to the CFD predictedresults. The deviation between prediction and experi-mental data is within 5%.3. From this study it can be concluded that CFD canbe used a tool for optimization in order to reduce thenumber of experimental iterations.

ReferencesVersteeg H K & Malalasekara W, An introduction to compu-tational fluid dynamics: The finite volume method (LongmanGroup Limited, London, UK), 1995.

2 Shaw C T, Using computational dynamics (Prentice Hall,Indiana, USA), 1992.

3 Desmond E Winterbone & Richard J Pearson, Theory ofmanifold design: Wave action methods for l C engines (Pro-fessional Engineering Publishing Limited, London, UK),1999.

4 Livengood J C, Rogowski A R & Taylor C F, SAE, 6(4)(1952).

5 Ohata A & Ishida Y, SAE-820407, 1982.6 Super flow: Operator's manual, London, UK, 1982.

.J

99