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This article was downloaded by: [University of Auckland Library]On: 05 November 2014, At: 15:11Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK
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MODELING AND SIMULATION OF COMPRESSION IGNITIONENGINESYousef S.H. Najjar a & Abdullah M. Alturki aa Mechanical Engineering Department(Thermal) , King Abdulaziz University , Jeddah , S.APublished online: 25 Apr 2007.
To cite this article: Yousef S.H. Najjar & Abdullah M. Alturki (1996) MODELING AND SIMULATION OF COMPRESSION IGNITIONENGINES, Fuel Science and Technology International, 14:8, 1019-1035, DOI: 10.1080/08843759608947626
To link to this article: http://dx.doi.org/10.1080/08843759608947626
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FUEL SCIENCE & TECHNOLOGY INT'L., 14(8), 1019-1035 (1996)
MODELING AND SIMULATION OF COMPRESSION IGNITION
ENGINES
rouser S.H. Najjar and Abdullah M. Alturki
Mechanical Engineering Department (Thermal)
King Abdulaziz University-Jeddah -SA
ABSTRACT
Modeling of a compression ignition engine was carried out coveringlosses
emanent from imperfect construction of real engines such as progressive
combustion, valve timing, and heat transfer. Furthermore, friction was
included to obtain brake performance. Simulation of engine performance
was tackled by varying engine speed, compression ratio and injection
timing over wide range. The results were compared with those obtained
from the experiemntal facility.
Predictions by the model compare favourably with experiment within
(n~ and <j.n for power and stc respectively. The losses considered in
1019
Copyright C 1996 by Marcel Dekker, Inc.
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1020 NAJJAR AND ALTURKI
this work amount to about 30% of the fuel energy input at the design
point.
INTRODUCTION
This paper is a continuation for the previous one on modeling of spark
ignition engine [II. Hence, the detailed background on engine losses in
the introduction; and the nomenclature are almost similar for the two
papers. Further consideration of losses could be found in [2-61. As far as
the experimental facility is concerned, the same test facility and
procedure, previously mentioned, have been used with the same engine
converted to a compression ignition engine after some modifications such
as using fuel injection system instead of the carburetor. The fuel used is
light diesel Which has the properties shown in Table 1.
MODELING AND SIMULATION
The ideal model used in this work is based on that of campen [7].
However, for the purpose of this work some modifications were made
namely; fuel, compression ratio, injection timing, air mass flow rate and
heat of combustion.
In this ideal gas model, variation of thermodynamic properties with
temperature is assmed for both reactants and products. Approximations
are assumed to fit limited equilibrium products. Furthermore,
compression and expansion processes are isentropic as snown in fig. 1.
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COMPRESSION IGNITION ENGINES
Table 1. Properties of diesel fuel
1021
Property Gasoline
Formula CH 1.75
Relative molecular mass 220
Carbon/hydrogen mass ratio 6.857
Carbon, %by wt 87.3
Hydrogen, %by wt 12.7
Density, kg/ I 0.850
Netheat of combustion, II.]/kg. 42,517
Stoichiometric A/F mass ratio 14-53
Formula C16 H28
Distillation
Initial boiling point, 'C
10% recovery by Vol., 'C
50% recovery by Vol., 'C
90% recovery by vet, 'C
162
208
285
350
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1022
VTDe
VCYI
NAJJAR AND ALTURKI
41
VBoe
Fig. 1 Fuel _ air cycle of C. 1. engin e
Then, the compression work is
WCOMP = (NA + NX) CVR (T2-T1)
where NA and NX are the moles of air and residual gas , CVR is the
constant volume heat capacity of the mixture, while T I and T2 are the
temperatures at the start and end of the compression stroke.
In the following, losses due to imperfect construction of the engine
namely progressive combustion, valve timing and heat transfer are
considered in addition to friction. Hence the fuel-air cycle is converted to
brake performance.
Progressive Combustion
If mass fraction DN. of the fuel burns while the piston moves through a
volume change amounting to tN, the resulting change in pressure, is
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COMPRESSION IGNITION ENGINES
DV VTOCDP = - P K- + (P3 -P2)- DN
V V
where k = CplCv
1023
(2 )
P2 = pressure at TDC at end of the compression stroke.
P3 = the pressure that would be reached if all the fuel burned
instantaneously at TDC
The volume V3can be found by
V3 = VTOC [ I + P_3;.,..-_P_2 ]K P2
(3)
Now examine the time rate of burning, represented by the ratio DN/dt.
Writing the equation in the following form:
DN = I F(Z) DZdt V3 - VIDe dt
where
Z= crank angle at start of combustion
DZ = crank angle incrementstep in combustion process.
This equation can be used when ZIl = 0.0, but when ZIb: 0.0, then
DN = F(Z-ZII) *D2I(V 3-VTDC)dt
where
ZI I = crank angle at start of injection before TOe, radians.
The combustion processmust be followed in stepwise fashion:
DV = F(Z) DZ
(4)
(6)
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Table 2. Range ot operating variables Cor the c.1. Engine
CR 14.00 16.00 18.00 20.00
21ID 000 10.00 20.0 30.00
N,rpm 1250 1500 2000 2250
Table 3. Experimental data Cor the single cylinder C.1. engine
engine speedlrpm) 1250 1500 2000 2250
C.IE. power (kW) 3.30 4.30 5.90 6.20
SFC(g/kW h) 313.0 309.0 3250 355.0
16.00
12.00
V 8.000<o
CL
4.00
0.00100000 1500.00 2000.00
Engine speed. rpm2500.00
Fig.2: Variation of power with engine speedfor different modifications
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COMPRESSION IGNITION ENGINES 1025
.---.--------. ideal
experiment
•_____.~~ friction
,---;~.
____...----. heat transfer
--~'----'.---' • valve timing,-'
• .---. progressive
--- cornbustlon
2500.001500.00 2000.00Engine speed. rpm
100.00
50.001000.00
150.00
400.00
300.00
350.00
U 200.001.L
'Jl
s:~
<,250.00C1'
Fig.3: Variation of SFC with engine speedfor different modifications
Where F(Z): the derivative of engine volume, m3, When the burning rate
reaches the maximum allowable value
DN = DNmaxDT
The expansion work is found by
WEXP = L [p + DP l"v + U (T3) - U (T4)2 f p p
(3)
Where the summation applies for the entire combustion process, and T3
is the temperature at the end of combustion [71.
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1026 NAJJAR AND ALTURKI
'=f=====-=i friction----==. experiment
'-_______ idee!-----.---.tc__ progressive
• • * combustion
---,,___ valve timing
"-------.----=::---.==--- heat tronsfer
2500.001500.00 2000.00Engine speed, rpm
20.00
60.00
10.001000.00
L50.00
70.00
~ 30.00~
<l)
s:I-
>u
.~ 40.00
.~
Fig.4: Variation of therm.ol efficiency with enginespeed for different modifications
Table 4. Variation in power, stc and efficiency due to ideal
engine modifications at the design point
(Qin,i =22.521 kW; SFCi = 152.92 g/kWh)
Engine with Power, kW S.F.C. g/kWh 1],%
ideal cycle 12.47 152.92 55.37
p.c 913 20881 4054
'{.t 8.06 236.52 35.79
h.t 779 244.82 3459
friction 5.35 330 2376
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COMPRESSION IGNITION ENGINES
1400 -
--' ideal
12.00 »->:.i->:
10.00progressive
:: -' combustion.:< --'.-----' -
verve timing
L 8.00 -------.::::::: '::::::::====: heat transfer<V~ :::::::---.0CL
6.00friction--',--'4.00
2.00 -n-rTTlTTTTTTTTrrTTlCTTTTTTTl"TrTTlTTTTTTTTTlrTTlTTTTTl
12.00
1027
Fig.5: Variation of power with compression ratiofor different modifications
Valve Timing and Heat Transfer
Tile procedure is similar to that followed in the spark ignition engine,
because the same engine is used in both modes.
FRICTION
Friction MEP increases as engine size decreases [3.9],
FMEP = CI + 48 (N/lOOO)+ 0.4 S2p
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1028 NAJJAR AND ALTURKI
friction
heot tr onster
votve liming
progressivecombustion'-._------• idee!
:~:_-==='-. ====
400.00
0.00 ~
12.00 14.00 16.00 18.00 20.00 22.00Compression rolio, CR
500.00
10000
uu: 200.00(f)
.c~ 30000<,0'
Fig.6: Variation of specific fuel consumption withcompression ratio for different modifications
where C1 = 144 kPa. Then friction power is calculated from
FMEP VDISP NFRP=----
120
DISCUSSION OF RESULTS
Engine performance has been parametrically studied using experimental
work and modeling. The range of operating conditions is shown in table
2. The design point comprises N=2000 rpm, CR = 18, and fuel injection
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2.00 IIII1 Iii II III iii l i I II1I1 I Iii i I I' I til i i II I0.00 10.00 20.00 30.00 40.00
Injection timing. (degree)
COMPRESSION IGNITION ENGINES 1029
14.00
idealI12.00 <.10.00 .~:~
~.x: ~.-: 8.00 .~ ~ progressive<ll combustion30
Q.. valve timing
6.00 <. heal transfer
4.00 <.friction
Fig.7: Variation of power with injection timingfor different modifications
timing ZII = 20"BTC. Experimental results obtained by varying N are
shown in table 3. Performance in general, is graphically represented.
Figure 2 shows the variation of power with engine speed N ior diiierent
modifications of the ideal engine namely progressive combustion, valve
timing and heat transfer to get the indicated power ior the real engine.
Friction is then subtracted to produce the brake power which is
compared vvttn the experimental results.
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1030 NAJJAR AND ALTURKI
valve timing
progressivecombustion
ideo!
friction
heat transfer
0.00 II iii 1111'lll III II I Iii., l j I II I II' i 1111111
0.00 10.00 20.00 30.00 40.00Injection liming. (degree)
500.00
400.00
100.00
uu.: 200.00if)
s:
~ 300.00<,en
Fig.8: Variation of specific fuel consumption withinjection timing for different modifications
Figures 3 and 4 show the variation of src and T] with N for similar
modifications as those with power. Table 4 shows the variation in
efficiency along with power and sfc due to these modifications at the
design point.
Figures 5 and 6 show the variation of power and sfc respectively with
compression ratio CR, whereas, figures 7 and a show the variation with
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COMPRESSION IGNITION ENGINES
1.60
1.40
1.20
~
~ 1.00oa.
00.80z
0.60
0.40
0.20
N
1031
0.00 0.50 1.00 1.50 2.00Non-dimentional variables (N, CR, ZII)
Fig.9: Relative effect of operating variableson power
injection timing ZII. Figures 9 and 10 show the relative effect of the
operating variables namely N, CR and ZII on power and '1 respectively.
The highestenect is seen to be for Nthen ZI I followed by CR.
Figures I I and 12 compare the model predictions with the experimental
results for power and sfc. It is noticed that the percentage deviation
from experiment,at the design point, is about 9.3% in power, and 9.7% in
SFe.
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1032 NAJJAR AND ALTURKI
1.40
1.20
>. 1.00ucQ)
.«W
0.80
0.00 0.50 100 1.50 2.00Non-dimentional voriobles (N, CR, ZII)
Fig,10: Relative effect of operating variableson efficiency
CONCLUSIONS
1- Modeling effort comprised engine losses ernanent from imperfect
construction such as progressive combustion, valve timing and heat
transfer. By adding engine friction, brake performance results.
2- Engine performance was simulated by varying, widely, engine
speed N, compression ratio CR, and injection timing21 I.
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COMPRESSION IGNITION ENGINES 1033
7.00
600
~ 5.00
LQ)
~e 4.00
300
/ model
2500.001500.00 2000.00Engine speed. rpm
2.00 --hrr-rrr-rTTTT..-r-.--r-,--,-,-,rrrrr-rTTTT"--"1000.00
Fig.l1: Comparison of model with experimentversus engine speed
3- A modified single cylinder compression ignition engine was used as
experimental facility with the potential of varying the above-
mentioned variables.
4- The model compares favourably with experiment within 9.3% and
9.7% for power and SFC respectively.
5- The relative effect of the losses on performance is generally in this
sequence: progressive combustion, friction, valve timing and heat
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1034 NAJJAR AND ALTURKI
360.00
350.00
340.00
L3:<,330.000'
U 320.001.L
(f)
310.00
300.00
290.001000.00
-:.i->
'----.
1500.00 2000.00Engine speed, rpm
• experiment
model
2500.00
Fig.12: Comparison of SFC from model withexperiment versus engine speed
transfer. These losses amount to about 30% of the fuel energy
input at the design point.
ACKNOWLEDGEMENTS
Assistance received from Mr. O. Bashir and Mr. H. Abu Kayyas is
gratefully acknowledged. Thanks are extended to Dr. M. Zaamout for
producing most of the graphs.
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COMPRESSION IGNITION ENGINES 1035
REFERENCES
1- Najjar Y.SH. and Alturl<i, A.M., "Mo<Ieling and simulation or spark
ignition engines", submitted for publication.
2- Ferguson, CR. "Internal Combustion Engines", john Wiley, New
Yorl<, 1986.
3- Taylor, C.F., "Internal Combustion Engines in Theory and Practice",
The MIT Press,Cambridge, 1966.
4- Lichty, L.C., "Combustion Engine Processes·, McGraw-Hill, New Yorl<,
1967.
5- Mathur, M.L. and Sharma, R.P., "A course in Internal Combustion
Engines", DhanpatRai, Delhi, 1990.
6- Ballaney, P.L., "Internal Combustion Engine", Khanna Publishers,
Delhi, 1980.
7- Campell, A.s., ""Thermodynamic Analysis of Combustion Engines",
John Whiley & Sons, New Yor1<., 1979.
8- Millington, B.W., and Hartles, ER., "Friction losses in diesel engines",
Paper 680590, SAE Trans., Vol. 77, 1968.
9- Heywood. J.B., "Internal Combustion Engine Fundamentals",
McGraw Hill, NewYorl<, 1988.
RECEIVED: June IS, 1995
ACCEPTED: September 23, 1995
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