30120130405031 2

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME

AND TECHNOLOGY (IJMET)

ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 4, Issue 5, September - October (2013), pp. 266-278
© IAEME: www.iaeme.com/ijmet.asp
Journal Impact Factor (2013): 5.7731 (Calculated by GISI)
www.jifactor.com

IJMET
©IAEME

A SIMULATE MODEL FOR ANALYZING THE EFFECT OF ENGINE
DESIGN PARAMETERS ON THE PERFORMANCE AND EMISSIONS OF
SPARK IGNITION ENGINES
BARHM-AB-MOHAMAD
B. Tech. KIRKUK TECHNICAL COLLEGE
M. Tech. SHEPHERD SCHOOL OF ENGINEERING AND TECHNOLOGY

ABSTRACT
A mathematical and simulation model has been developed to simulate a spark ignition engine
operation cycle. The programme written from this simulation model and modified so can be used to
assist in the design of a spark ignition engine for alternative fuels as well as to study many design
parameters such as the effect of engine design parameter like stroke and diameter of the cylinder on
the performance and exhaust emissions of spark ignition engines. In this paper, the description of
three type of engines design parameters according to (stroke/diameter) which are called under
square, square and over square engines using three type of fuel (gasoline, LPG, CNG) singly have
been taken. The variations of power output, thermal efficiency, specific fuel consumption, ignition
delay, temperature of exhaust gases, heat loss and the exhaust emissions (CO2, CO, NO, O2) by
volume, were calculated for each type of engine and then comparing the results to investigate how to
increase engine efficiency and reduce exhaust emissions. The accuracy of the present model is
confirmed by comparison with experimental result that have established by previous literatures and
the results were agreement with literatures. The main results obtained from the present study shows
that, the square engines (S/D=1) can be considered as most efficient, modern and suitable design for
engines running by gasoline and alternative fuels like LPG and CNG, because of higher power
output due to the suitable piston area for pressure distribution. The area of flame front which may
create higher combustion qualities and higher thermal efficiency through faster burning and lower
overall chamber heat loss, also, the potential of the square engines (S/D=1) for indicate specific fuel
consumption was 4% improved.
Keywords: Two-zone combustion, Combustion simulation, Percentage heat loss, Spark ignition
engine.

266


INTRODUCTION
Considering the energy crises and pollution problems today, investigations have concentrated
on decreasing fuel consumption by using alternative fuels and on lowering the concentration of toxic
components in combustion products, there are so many different engine manufacturers, past, present,
and future, that produce and have produced engines which differ in size, geometry, style, and
operating characteristics that no absolute limit can be stated for any range of engine characteristics
(i.e., size, number of cylinders, strokes in a cycle, etc.
Combustion is an important subject of internal combustion engine studies, to reduce the air
pollution from internal combustion engines and to increase the engine performance; it is required to
increase combustion efficiency. In this study, two basic types of models have been developed. They
can be categorized as thermodynamic and fluid dynamic in nature, depending on whether the
equations, which give the model its predominant structure are name given to thermodynamic energy
conservation based models are : zero-dimensional phenomenological and quasi-dimensional.
Fluid dynamic based models are often called multidimensional models due to their inherent
ability to provide geometric information on the flow field, based on the solution of governing flow
equations.
Many mathematical models have been developed to help understand, correlate, and analyze
the operation of engine cycles. These include combustion models, models of physical properties, and
models of flow into, through, and out of the cylinders. Even though models often cannot represent
processes and properties to the finest detail, they are a powerful tool in the understanding and
development of engines and engine cycles. With the use of models and computers in the design of
new engines and components, great savings are made in time and cost. Historically, new design was
a costly, time-consuming practice of trial and error, requiring new part construction and testing for
each change. Now engine changes and new designs are first developed on the computer using the
many models which exist. Often, only after a component is optimized on the computer is a part
actually constructed and tested.
Generally, only minor modifications must then be made to the actual component. Models
range from simple and easy to use, to very complex and requiring major computer usage. In general,
the more useful and accurate models are quite complex. Models to be used in engine analysis are
developed using empirical relationships and approximations, and often treat cycles as quasi-steady
state processes, Normal fluid flow equations are often used [8].
Some models will treat the entire flow through the engine as one unit, some will divide the engine
into sections, and some will subdivide each section (e.g., divide the combustion chamber into several
zones-burned and unburned, boundary layer near the wall, etc.). Most models deal only with one
cylinder, which eliminates any interaction from multi-cylinders that can occur, mainly in the exhaust
system.
Models for the combustion process address ignition, flame propagation, flame termination,
burn rate, burned and unburned zones, heat transfer, emissions generation, knock, and chemical
kinetics. They are available for spark ignition engines with either direct injection or indirect
injection. Values for properties are obtained from standard thermodynamic equations of state and
relationships for thermo-physical and transport properties.
Theoretical Analysis
The power cycle analysis in 4-stroke, spark ignition engine uses the first law of
thermodynamics by integrating various models for combustion, heat transfer, and the value of flow
rates, using integration methods from. Integration proceeds by crank angle position, allowing for
various fuels, air-fuel ratios, EGR or other inert gas for charge dilution, and/or valve-opening

267


profiles. The power cycle is divided into three principal sections: compression stroke, combustion
stages and expansion stroke.
Compression stroke: Its adiabatic processes in which the integration starts at the closing of
the intake valve and proceeds until the crank angle of ignition is reached. Residual gases from the
previous cycle are included in the cylinder gas mixture, and a number of iterations are performed
until the percentage and chemical content of the residual gases remain at a steady state value after
each cycle [10].
1. The total cylinder volume at each crank angle degrees can be written as [18]

V (θ) = Vc +

Vs 
2L
1 − Cos ( θ ) +
−
2 
S


2

 2L 

 − Sin
 S 

2


θ



(3.1)

The temperature of unburned mixture [T2] can be calculated from the following equation

T2

V 
= T1 *  1 
V 2 

k −1

V 
= T1 *  1 
V2 

C

v

Ro
( T1 )

(3.2)

The pressure of unburned mixture also can be calculated from the following equation:

 V 
T 
P 2 =  1  *  2  * P1
V2 
 T1 

(3.3)

2. Work can be calculated in compression stroke because of small variation of pressure and volume
inside the cylinder and the equation can be written as:
 P + P2 
dW = PdV =  1
 * (V 2 − V1 )
2



(3.4)

3. The first law of thermodynamic for checking values of (T2, P2), and the whole control volume
(two zones) can be written as:

dQ − dW = dE = E ( T2 ) − E ( T1 )

(3.5)

where dQconv is the rate of heat transfer by convection through the cylinder walls can be determine by
applying (Eichelberg Equation) which is written as

dQ

conv

= h * dA s * (T − T wall )

(3.6)

Where:
h = 2 . 466 * 10

-4

(U p

1
)3

( P)

1
2

−

(T )

1
2

268


A =  2A



p

+ 4*

T =  T1 + T

2


2

 P1 + P 2
2

2 *S *
Up = 

60


P= 

Vc

+ π de 
d









N 



4. The first law of thermodynamic can be written as[18] :

f(E) = E(T 2 ) − E(T 1 ) + dW − dQ

(3.7)

conv

The equation (3.7), can be solved numerically by Newton-Raphson method of iteration and
the equation (3.7) to be achieved when f (E) equal to zero.
By this method we can find (T2 ) n −1 which is more accurate:

(T 2 ) n = (T 2 ) n − 1 −

f(E) n − 1
f ′(E) n − 1

(3.8)

f ′(E ) its derivation of equation (3.7) for rate of (T) and for determine the value of f ′( E ) we can
consider ( dW = 0) because (dW) not affected by (T2):
dT

f ′( E ) =

dE ( T 2 )
dT

(3.9)

The rate of internal energy f ′( E ) at constant volume can be written as:

f ′ ( E ) = mC

v

(T 2 )

After substituting f ′( E ) in equation (3.8) finally it will become:
(T 2 ) n = (T 2 ) n −1 −

f(E) n −1
mC v (T 2 ) n −1

(3.10)

To find the value of pressure at combustion duration can be written as:

PV = mRT

(3.11)

269


By derivation of equation (3.11) with respect to (θ) can be written as:
P

dV
dP
dT
+ V
= mR
dθ
dθ
dθ

(3.12)

After substitute the value of (mR) from eq.(3.11) to eq.(3.12) and we now have :
P

dV
dP
PV dT
+ V
=
dθ
dθ
T dθ

(3.13)

By dividing eq.(3.13) on (PV) and rearrangement, the equation drive to :
1 dP
1 dV
1 dT
+
=
P dθ
V dθ
T dθ

(3.14)

The first law of thermodynamic incases of ideal gas and constant specific enthalpy can be written as:
mC

v

dT
dQ
dV
=
− P
dθ
dθ
dθ

(3.15)

After dividing left side by (mRT) and right side on (PV) of eq.(3.15) and become :
1 dT
1 dV 
 1 dQ
= (K − 1) 
−

T dθ
PV d θ
V dθ 


(3.16)

By summation two equations, eq. (3.14) and eq. (3.16) now we have:
dP
P dV
1 dQ
= −K
+ (K − 1)
dθ
V dθ
V dθ

(3.17)

The rate of dQ can be calculated from the following equation:
dθ
dQ
=
dθ

dQ
dθ

+ h * As( T

(3.18)

T wall )

app

To find the value of  dP  , we need to solve eq.(3.17) numerically using Runge-Kutta method, fourth
 
 dθ 

order.
The calculation start for the combustion products at every step of combustion duration using general
equation of combustion of hydrocarbon and air which is represent by :
a(C n H m O r ) +

i=q
1
m
r 
78
1

(n +
− )O 2 +
N2 +
Ar  → ∑ X i Z i
Φ
4
2 
21
21

i =1

(3.19)

From eq. (3.19) we can calculate amount of exhaust emissions for each compound like (CO, CO2,
NO, O2).
270


Expansion stroke : Two control masses are considered during this process, cylinder gases and
exhaust gases downstream of the exhaust valve, the method of calculations is same like compression
stroke, except the mixture include product compound and their concentrations will calculated till
exhaust valve opened.
Exhaust emission compound can be express by following chemical equations [18]:
1
H
2

→ H

(3.20)

1
O2 → O
2

(3.21)

1
N2 → N
2

(3.22)

2

2

+ O

→ 2H

H 2 O → OH +

1
H
2

(3.23)

2

2

2H

2O

CO

2

+ H

H 2O +

(3.24)
(3.25)

→ H 2 O + CO

2

1
N
2

2

→ H

(3.26)

+ NO

2

Generally, the chemical equilibrium constant (KP) of any chemical reaction (stoichiometric reaction)
for those element, A,B,C,D can be represent by the following chemical equation:
(3.27)

Va A + VbB ↔ VcC + Vd D

By rearrangement:
X
KP =  c
X a


Vc
Va

X
X

d
b

Vd
Vb






(3.36)

Where:
V = Stoichiometric coefficient, which is calculated from chemical equation.
X = Mole fraction, can be calculated from general equation of combustion of hydrocarbon and air.
Using chemical reaction equations from eq. (3.20) to eq. (3.26), and by applying reaction
equation (3.36), chemical equilibrium constants can be written as:

(

KP 1 = X 4

X2

)

(
X 10 )
KP 3 = (X 7
X5 )
KP 4 = (X 10 b 2 )
.P
KP 5 = (X 3 b X 2 )
KP

2

= X 11

(3.37)

P
P

(3.38)

P

(3.39)
(3.40)
(3.41)

P

271

KP

6

= (bX

KP

7

= X

(

6

b

8

5

(3.42)

)

X

X

9

)

(3.43)

P

Where, b = X 1
X

2

The chemical equilibrium constant (KP) for those reactions can be calculated from the
following relation equation:
LnKP

  vg(T) 
∆H o
 vg(T)  
= ∑ 
 − ∑
  −
RT
 RT  R
 RT  P 


(3.44)

Where,
∆H 0 is the enthalpy drop among the reactants and products at zero absolute (Kj).
g(T) is Gibbs Function and represent by following equation:

a
a
a
g(T)
= a 1 (1 − lnT) − a 2 T − 3 T 2 − 4 T 3 − 5 T 4 − a 6
RT
2
3
4

(3.45)

where a1 , a 2 , a 3 , a 4 , a 5 , a 6 are the constant values.
Now we have 7 reaction equations. 3 of them represent the reactants and 4 of them for
products, this equations are converted to computer language so that can be run by Quick Basic
program, some of input data are constant and others are variable.
50
Pressure 0.5
Pressure 1
Pressure 1.5

Pressure (Bar)

40

30

20

10

0
0

100

200

300

400

Crank Angle (Degree)

Fig. 3.1 Effect of variation (S/D) on pressure and crank angle curves using gasoline fuel (C8H18) at
speed (1500 rpm)
272


50

Press 0.5

+

Press 1

Press 1.5

Pressure (Bar)

40

30

20

10

0
0

100

200

300

400

Crank angle (Degree)

Fig.3.2 Effect of variation (S/D) on pressure and crank angle curves using LPG fuel (C3H8) at speed
(1500 rpm)

40
Press 0.5

+

Press 1
Press 1.5

Pressure (Bar)

30

20

10

0
0

100

200

300

400


Fig. 3.3 Effect of variation (S/D) on pressure and crank angle curves using CNG fuel (CH4) at speed
(1500 rpm)

273


Temp 0.5

3000

+

Temp 1
Temp 1.5

Temprature (K)

2000

1000

0
0

100

200

300

400


Fig. 3.4 Effect of variation (S/D) on temperature and crank angle curves using gasoline fuel (C8H18)
at speed (1500 rpm)

3000

Temp 0.5 +
Temp 1
Temp 1.5

Temperature (K)

2000

1000

0
0

100

200

300

400


Fig. 3.5 Effect of variation (S/D) on temperature and crank angle curves using LPG fuel (C3H8) at
speed (1500 rpm)

274


3000
Temp. 0.5
Temp. 1
Temp. 1.5

Temperature (K)

2000

1000

0
0

100

200

300

400

Crank Angle (Degree)

Fig. 3.6 Effect of variation (S/D) on temperature and crank angle curves using CNG fuel (CH4) at
speed (1500 rpm)

RESULTS AND DISCUSSION
4.1 The Effect of Engine Design Parameters on the Performance
The data results from computer programme were converted to graphs, so that to be easy to
the reader shown in figures below. The important parameters will discuss in this chapter according to
the results from programme which is include, power output, indicate specific fuel consumption,
pressure mean effective, emissions, thermal efficiency and heat loss.
4.2 The Effect of Engine Design Parameters on the Power Output
According to the data from the programme, exactly when the engines fueled by gasoline the
maximum indicate power or power output from the cylinder was obtained from square engine, then
50% of power output decrease when engine size changed to over square, also for under square
engine, the power output decrease about 60% as shown in fig.4.1.
For the engines running by LPG, the maximum power output obtained from square engine,
but to compare it with square engine running by gasoline is lesser because of the amount of air
injected to cylinder is less, so that reduce volumetric efficiency.
The power output decrease about 55% from maximum power output for over square engines
and then 60% decrease when engine size is under square as shown in fig.4.2.
Finally, for the engines using CNG as fuel, the maximum power output achieved from square
engine, but to compare it with square engine running by gasoline and LPG is lesser for the same
reason, also the power output decrease about 60% for over square and decrease 65% for under square
as shown in fig.4.3.

275


4.0

Power (KW)

3.0

2.0

1.0

0.0

0.5

1.0

1.5

2.0

S/D

Fig.4. 1 Effect of S/D on Power using gasoline fuel (C8H18)

2.0

Power (KW)

1.6

1.2

0.8

0.4

0.0
0.0

0.5

1.0

1.5

2.0

S/D

Fig.4.2 Effect of variation S/D on Power using LPG fuel (C3H8)

276

2.0

Power (KW)

1.6

1.2

0.8

0.0

0.5

1.0

1.5

2.0

S/D

Fig.4.3 Effect of variation S/D on Power using CNG fuel (CH4)

CONCLUSIONS
1- The results show that, the (S/D) ratio has a significant effect on both turbulence levels and
geometric interaction of the flame front with the combustion chamber walls.
2- In general, a square engines (S/D=1) leads to higher power output up to 50% improved.
3- Square engines (S/D=1) generate a higher thermal efficiency through faster burning and lower
overall chamber heat loss.
4- The potential of the square engine (S/D=1) for indicate specific fuel consumption was 4%
improved, according to output data from the programme the minimum ISFC was for the square
engine running by gasoline fuel.
5- The effect of (S/D) on pressure indicate mean effective also limit but vary with type of fuel used,
maximum PIME was calculated from gasoline engine then the value 8-10% decrease when
engine running by LPG and CNG fuels.
6- The (S/D) ratio has a significant effect on exhaust emission characteristics, exactly on (NO) and
(CO) emissions, for (S/D=1) the amount of (NO) 92% decrease when compared with amount of
(NO) emission from (S/D=0.5)and (S/D=1.5).
7- The amount of (CO) emission by volume, 10-15% increased slightly when (S/D=1), the amount
can be control by install thermal converter in exhaust manifold provides significant reduction in
(CO) concentrations on contrast temperature of exhaust increases due to more heat release for
(S/D=1) engines.

277


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