Computer simulation of ci engine for diesel and biodisel blends

International Journal of Innovative Technology and Exploring Engineering (IJITEE)
ISSN: 2278-3075, Volume-3, Issue-2, July 2013
82
Computer Simulation of CI Engine for Diesel and
Biodiesel Blends
Laukik P. Raut
Abstract-Among the alternative fuels, biodiesel and its blends
are considered suitable and the most promising fuel for diesel
engine. The properties of biodiesel are found similar to that of
diesel. Many researchers have experimentally evaluated the
performance characteristics of conventional diesel engines
fuelled by biodiesel and its blends. However, experiments require
enormous effort, money and time. Hence, a cycle simulation
model incorporating a thermodynamic based single zone
combustion model is developed to predict the performance of
diesel engine. A comprehensive computer code using “C”
language was developed for compression ignition (C.I) engine.
Combustion characteristics such as cylinder pressure, heat
release, heat transfer and performance characteristics such as
work done, brake power and brake thermal efficiency (BTE) were
analyzed. On the basis of first law of thermodynamics the
properties at each degree crank angle was calculated. The
simulated combustion and performance characteristics are found
satisfactory with the experimental results.
Keywords: - Biodiesel, Numerical modeling, simulation.
I. INTRODUCTION
Modeling compression ignition engine depends on
characteristics of fuel. It is a process of designing a model of
real system and conducting experiment with it for the
purpose of understanding the behavior of the system. The
Numerical Model of a diesel engine can be regarded as an
explanation of real engine operation, which combines
mathematical relation between the relative components, can
be used to simulate the dynamic process of diesel engine. A
clear overview of engine operation is helpful to understand
the modeling of a real diesel engine. It serves as a tool for
better understanding of combustion and its effect on engine,
so as to build up more strong real systems.
Computer simulation has contributed enormously towards
new evaluation in the field of internal combustion engines.
Mathematical tools have become very popular in recent
years owing to the continuously increasing improvement in
computational power. Diesel engines occupy a prominent
role in the present transportation and power generation
sectors. There have been many methods tried and are in use
to reduce pollutant emissions from a diesel engine. The
main options to reduce pollutants are the usage of bio-fuels
and adopting some modifications to the combustion process.
Diesel engine simulation models can be used to understand
the combustion performance; these models can reduce the
number of experiments.
From the point of view of protecting the global environment
and the concern for long-term supplies of conventional
diesel fuel, it becomes necessary to develop alternative fuels
that give engine performance at par with diesel. Among the
alternative fuels, biodiesel holds good promises as an eco-
friendly alternative fuel [1].
Manuscript received on July, 2013.
Laukik P. Raut, Assistant Professor G. H. Raisoni College of
Engineering Nagpur, India.
Vegetable oil obtained from non edible sources are
considered promising alternate fuel for compression ignition
(CI) engine compared to their edible counterpart due to the
food vs. fuel controversy. Engine performances using
various sources of biodiesel viz., (a) salmon oil [2]; (b)
rapeseed oil [3–5] ; (c) rubber seed oil [6]; (d) tobacco seed
oil [7] ; (e) sunflower seed oil [8]; and; (f) soybean oil [9];
(g) jatropha curcus oil [10]; (h) karanja oil [11] were
studied.
As stated above, researchers have experimentally evaluated
the performance characteristics of conventional diesel
engines fuelled by biodiesel and its blends. However,
experiments require enormous effort, money and time. A
realistic numerical simulation model could reduce such
effort. Numerical simulation based on mathematical
modeling of diesel engine processes have long been used as
an aid by design engineers to develop new design concepts.
The present study describes a cycle simulation model. This
thermodynamic based model follows the changing
thermodynamic state of the working fluid through the engine
intake, compression, combustion, expansion and exhaust
processes for predicting the performance of a diesel engine
fuelled by diesel and also the different blends of diesel and
biodiesel. The model predicts the performance of a CI
engine in terms of brake power and brake thermal efficiency
for all the fuels considered for the present study. Fuel
properties [11] and the engine design and operating
parameters are specified as inputs to the model.
The purpose of this project i.e. Numerical Modeling of CI
Engine is to determine the effects of fuelling a diesel engine
with diesel and bio-diesel fuel blends. The investigation has
been done on 100% diesel fuel and 20% bio-diesel blend
with diesel. The results are the compared with the results get
from experimentations.
Some specific objects are to evaluate the performance of,
1. Engine output.
2. Numerical Modeling results.
3. To predict the net heat release for B20.
4. To investigate the output parameters such as temperature,
pressure, heat release etc.
II. BIODIESEL CHARACTERISTICS
2.1 Transesterification of Vegetable Oil
The vegetable oil is transesterified using methanol in the
presence of sodium hydroxide (NaOH) as a catalyst (Figure
1 and 2). The parameter involved in the processing such as
catalyst amount, molar ratio of alcohol to oil, reaction
temperature and reaction time are optimized.
Figure 1: - Transesterification chemistry of vegetable oil

Computer Simulation of CI Engine for Diesel and Biodiesel Blends
83
Figure 2: - Transesterification process of Jatropha seed oil
Known quantity of vegetable oil is taken in a biodiesel
reactor. A water-cooled condenser and a thermometer with
cork are connected to the side openings. The required
amount of catalyst (NaOH) is weighed and dissolved
completely in the required amount of methanol by using a
stirrer to form sodium methoxide solution. The oil is then
warmed by placing the reactor in water bath maintained at
the selected temperature. The sodium methoxide solution
then added into the oil and stirred vigorously by means of a
mechanical stirrer. The required temperature is maintained
throughout the reaction time and the reacted mixture is kept
in the separating drum. The mixture is then allowed to
separate and settled down by gravity settling into a clear,
golden liquid biodiesel on the top with the light brown
glycerol at the bottom. The glycerol was drained off from
the separating drum leaving the biodiesel at the top. This
pure biodiesel was measured on weight basis and the
important fuel and chemical properties were determined
(Table 1).
In this study, diesel and biodiesel was used as a fuel for
conventional engine. Biodiesel and diesel with 20% and
80% by volume was mixed thoroughly and thus a stable
mixture (hereafter referred as biodiesel) was prepared.
Table1: Properties of diesel fuel, B100 and B20
Properties Diesel
Fuel
(DF)
Biodiesel
(B100)
20%DF/80
%B100
(B20)
Density @15°C
(kg/m3
)
830 880 840
Viscosity
@40°C (cSt)
2.8 4.6 3.15
Flash point (°C) 55 170 80
Cetane number 45 50 46
Lower Heating
Value
42 36 40.5
III. EXECUTION OF PROGRAM AND VARIOUS
EXPRESSIONS USED FOR MODEL
3.1 Basic Input Data
The program developed here predicts the combustion
characteristics like pressure, temperature, heat release and
performance characteristics such as brake thermal efficiency
and brake power. Thus the basic input for the program is the
value of initial pressure, temperature corresponding to the
crank angle, for a selected range of combustion cycle.
The range chosen here is from 250
BTDC to 25O
ATDC.
Provision is made in the program, to read pressure-crank
angle data, at an interval of 10
crank angles. Other data
supplied initially in the program, is regarding engine
dimensions, properties of fuel and properties fluid in the
combustion chamber. These values are as follows:
B Cylinder bore = 0.0875 m
S Stroke = 0.110 m
CR Compression ratio = 18
RPM Rotations per minute = 1500 rpm
L Connecting rod length = 0.2 m
HV heating value of fuel = 10,500 Kcal/kg
= 44100 kJ//Kg.
An estimate of temperature of piston, cylinder-wall and
cylinder head is made. These values are given in the
program as below:
Ti: - Initial temperature = 311K
Tw: - Cylinder wall temperature = 900K
3.2 Calculation of Cylinder Volume at Various Crank
Angle
Four stroke internal combustion engines are currently
produced in two configurations reciprocating piston and
rotary.
Figure 3: - Geometry of reciprocating piston engine
The basic geometry of reciprocating piston engine is shown
in figure 3. It is describe in terms of cylinder bore B, length
of stroke S, length of connecting rod L and compression
ratio r,. The displacement volume Vdisp is swept out as the
piston move from bottom dead centre to top dead centre.
Now,
Since
we may write
With θ denoting the angular displacement of the crank from
BDC, the volume V(θ) at any crank angle is represented by

84
3.3 Wiebe Heat Release Model
The Wiebe heat release pattern is based on the exponential
rate of the chemical reactions. In this model; it is assumed
that all the fuel is injected before the end of ignition delay
period itself.
The fraction of heat-released pattern is expressed by non-
dimensional equations
By differentiating above equation, the rate of heat release
can be expressed as
The above equation can be expressed in terms of KJ/θ
CA as
follows
Where
Δθc duration of combustion in θ
CA.
θ crank angle at any instant.
θi crank angle at the start of combustion.
Qav heat release per cycle in KJ.
a This is the parameter which characterizes the
completeness of combustion. Wiebe assume
Xmax=0.990 and hence, a = 6.908m
It is also a parameter characterizing the rate of combustion.
The small value of m means a high rate at the beginning of
the combustion, while large value of m m means high rate
by the end of the combustion,
3.4 Heat Transfer Process
Heat transfer is must in IC engine to maintain cylinder
walls, cylinder heads and piston faces at safe operating
temperature. Heat is transfer from or to the working fluid
during every part of each cycle, and the net work done by
the working fluid in one complete cycle is given by
Wnet =
Where Δp is the pressure change inside the cylinder as a
result of piston motion, combustion, flow into or out of the
cylinder and heat transfer.
The pressure change Δp due to heat transfer is given by
Where
A interior surface area of engine volume.
M mass of working fluid.
.
T working fluid temperature
The heat transfer between the working fluid and the interior
surface is by forced convection, and the value of depends
on the gas velocity at the surfaces. As little is known about
the gas motion inside; it is common to use some empirical
formulae for calculating . The formula of Pflaum is
widely used.
Pflaum equation
Where
The positive sign is used if
And the negative sign is used if,
3.5 Friction Calculations
Frictional losses affect the maximum brake torque and the
minimum brake speciﬁc fuel consumption directly and are
often a criterion of good engine design. These losses not
only reduce the power but also inﬂuences the size of the
coolant systems. The mean effective losses of power due to
friction in different moving parts are calculated by using the
following empirical relations.
(i) Mean effective pressure (MEP) lost to overcome friction
due to gas pressure behind the rings.
Where,
)
(ii) Mean effective pressure absorbed in friction due to wall
tension of rings
where
(iii) MEP absorbed in friction due to piston and rings
where
(iv) Blow-by loss
where
N piston speed in rpm
(v) MEP lost in overcoming inlet and throttling losses
where,

85
(vi) MEP absorbed to overcome friction due to the valve
gear
where
G number of intake valve/cylinder
H intake valve diameter
(vii) MEP lost in pumping
(viii) MEP absorbed in bearing friction
(ix) MEP absorbed in overcoming the combustion chamber
and wall pumping losses
Total MEP lost in friction,
Net brake MEP = Indicated MEP – Friction MEP
3.6 Theoretical Considerations
In this analysis the molecular formula for diesel and
biodiesel are approximated, as C10H22 and C19H34O2 . The
combustion model is developed for the C.I engine and
suitable for any hydrocarbon fuel and their blends.
(i) Calculation of Number of Moles of Reactants and
Products
In this simulation during the start of combustion, the moles
of different species are considered includes O2, N2 from
intake air and CO2, H2O, N2 and O2 from the residual
gases. The overall combustion equation considered for the
fuel with C-H-O-N is
Stochiometric AFR
Total number of reactants and products during the start of
combustion as well every degree crank angle was calculated
from the equations.
(ii) Calculation of Specific Heat
Specific heat at constant volume and constant pressure for
each species is calculated using the expression given below.
where A, B and C are the coefficients of the polynomial
equation.
(iii) Initial Pressure and Temperature at the Start of
Compression
Initial pressure and temperature at the beginning of the
compression process is calculated as follows
and
(iv) Calculation of Enthalpy and Internal Energy
Enthalpy of each species is calculated from the expression
given below which is used to calculate the peak flame
temperature of the cyclic process.
The internal energy for each species and overall internal
energy are calculated from the expressions given below
where A, B and C are the coefficients of the polynomial
equation.
(v) Work Done
Work done in each crank angle is calculated from
IV. RESULTS AND DISCUSSION
In this study combustion parameters like cylinder pressure,
peak cylinder pressure and peak temperature are discussed.
Performance parameters like brake power is also discussed.
The results are compared with the experimental results.
4.1. Cylinder pressure
In a CI engine the cylinder pressure is depends on the fuel-
burning rate during the premixed burning phase. The high
cylinder pressure ensures the better combustion and heat
release.
Simulated Result Diesel
Actual Results Diesel
0 20 40 60 80 100120140160180200220240260280300320340360
0
10
20
30
40
50
60
70
Crank Angle
Pressure (bar)
Figure 4: - Comparison of simulated and experimental
pressure with crank angle

86
The Figure 4 shows the typical pressure variation with
respect to crank angle. It has been observed that the peak
pressure obtained through experimentation is 64.30 bar and
the pressure obtained through simulation is 63.65 bar.
Diesel
Jatropha (B20)
170 175 180 185 190 195 200 205 210 215 220 225
0
10
20
30
40
50
60
70
CrankAngle (Degree)
Pressure (bar)
Figure 5: - Pressure variation with crank angle for diesel
and biodiesel blend during combustion
Figure 5 shows the pressure variation with crank angle
during combustion for diesel and bio-diesel blends. The
peak pressure observed for jatropha B20 and diesel is 64.39
bar and 63.65 bar respectively. Hence we say that the
internal pressure increases which ultimately increases the
stress on the piston and cylinder walls.
4.2. Cylinder temperature
High pressure of compressed mixture increases its burning
rate. This increases the peak pressure inside the combustion
chamber. The comparisons of peak temperatures inside the
cylinder for diesel and bio-diesel is shown in figure 6. The
presence of oxygen in the biodiesel makes complete
combustion of fuel thereby producing more CO and hence
more heat is released from the gases. Thus, the peak
temperature of biodiesel-fueled engine is higher than that of
diesel fueled engine. The peak temperature is observed for
B20 and diesel is 2780 K and 2610 K respectively.
Diesel
Jatropha B20
0 20 40 60 80 100120140160180200220240260280300320340
0
500
1000
1500
2000
2500
3000
Crank Angle (Degree)
Temperature(Kelvin)
Figure 6: - Temperature variation with crank angle for
diesel and biodiesel blend
4.3 Effect of CR on Brake Power
Figure 7 summarize the predicted effect of CR on engine
brake power at 1500 rpm. With increasing CR, the brake
power increases for all the fuels. With the change in CR,
engine processes that inﬂuence its performance and
efficiency, namely, combustion rate, heat transfer and
friction, also vary. As the CR is increased, the heat loss to
the combustion chamber wall and frictional losses decrease;
hence, there is an improved performance at higher CR.
However, there is a limit at which further increase in CR
would not be beneﬁcial as it may lead to increasing surface
to volume ratio and slower combustion; because at higher
CR, the height of the combustion chamber becomes very
small. The brake power results predicted by the present
model also show an increasing trend with CR for all the
fuels.
Diesel
Jatropha (B20)
10 11 12 13 14 15 16 17 18 19 20 21
9
10
11
12
13
14
CR
Brake Power (KW)
Figure 7: - Variation of Brake power with compression
ratio
At 1500 rpm as shown in figure 7, the brake power values
for diesel fuel varied from a minimum of 12.89 kW (at CR
12) to a maximum of 13.47 kW (at CR 20). The
corresponding minimum and maximum values for B20 is
10.34kW and 11.12 kW respectively.
4.4 Effect of Peak Pressure and Temperature on Engine
Components
4.4.1 Stresses Acting Due to Peak Pressure
Figure 8: - Stresses acting due to application of peak
pressure
From figure 8 we can say that the maximum stress acting on
the piston head and it is 165.55 MPa which is less than the
ultimate tensile strength (245 MPa) of the material.

87
4.4.2 Temperature Distribution
Figure 9:- Heat distribution along the assembly
Figure 9 shows the heat distribution along the assembly. The
maximum temperature (2727°C) is inside the combustion
chamber and at the cylinder block wall it is found 35 °C.
V. CONCLUSION
A diesel engine cycle simulation model is developed for
predicting the performance of a single cylinder four stroke
diesel engine fuelled by diesel and various blends of diesel
and biodiesel. The model has been developed in such way
that it can be used for characterizing any hydrocarbon fuels
and their blends.
The model predicts a higher rate of pressure and
temperature rise for the blend during combustion as
compared to diesel.
It is observed that with the blend B20 the peak pressure
and temperature increases and hence we can say that the
resultant stresses will also increase.
It is also observed that with the increase in compression
ratio the brake power also increases.
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engine fueled with crude and reﬁned biodiesel from Salmon oil”.
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