1. INTERNATIONALMechanical Engineering and Technology (IJMET), ISSN 0976 –
International Journal of JOURNAL OF MECHANICAL ENGINEERING
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME
AND TECHNOLOGY (IJMET)
ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online) IJMET
Volume 4, Issue 2, March - April (2013), pp. 209-216
© IAEME: www.iaeme.com/ijmet.asp
Journal Impact Factor (2013): 5.7731 (Calculated by GISI) ©IAEME
www.jifactor.com
THEORITICAL INVESTIGATIONS OF INJECTION PRESSURE IN A
FOUR STROKE DI DIESEL ENGINE WITH ALCOHOL AS FUEL
S.Sunil Kumar Reddy1 and Dr. V. Pandurangadu2
1
Associate Professor, Mechanical Department, N.B.K.R.I.S.T, Vidyanagar, Nellore, A.P
2
Professor, Mechanical Department, Jawaharlal Nehru Technological University, Anantapur.
A.P
ABSTRACT
An intensive search for alternate fuels is going on due to the stringent emission
legislation all over the world for diesel engines which produce more environmental pollution.
The major pollutants from these engines are oxides of nitrogen (NOx), smoke and particulate
matter. The difficulty in meeting the increasingly stringent limitations on emissions has
stimulated interest in alcohol -fueled diesel engines because it is a renewable bio-based
resource and it is oxygenated, thereby providing the potential to reduce particulate emissions
in compression–ignition engines and ethanol diffusion flames produce virtually no soot. With
the high latent heat of vaporization, alcohol absorbs heat from the combustion chamber and
makes it cools. This reduces the efficiency of the engine. So, more amount of fuel cannot be
injected in to combustion chamber. But due to the low viscosity of alcohol more fuel will be
injected in to the combustion chamber with the available fuel injection pump, which normally
operates at 180 bar pressure. This makes the starting of the engine difficult.
In order to compensate this, the fuel injection pressure is to be reduced. So an attempt is
made to find an injection pressure for the suitability of using alcohol in diesel engines. In the
present theoretical investigation, the performance parameters for normal diesel engines are
obtained by using a computer program. Then the performance of the diesel engine is compared
with alcohol at different injection pressures. The injection pressure of alcohol fuel is selected
for the further experimental work in such a way that the injection pressure at which the
performance of alcohol and diesel fuel are in close agreement. So to study the effect of
injector opening pressures, five injector opening pressures (180, 175, 170, 165 and 160 bar)
are considered. From the theoretical results, it is observed that the injector opening pressure
of 165 bar results in higher brake thermal efficiency and is in close agreement with diesel
fuel.
209

2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME
KeyWords: alcohols, fuel pump, injection pressures and emissions
INTRODUCTION
During recent years INDIA imported 75% of crude oil from other countries to meet
energy requirements. This intensified the research for discovering the new type of engine
design and alternative fuels for better control over pollution, and further leads to the stringent
emission norms. Alcohols are being considered to be supplementary fuels to the petroleum
fuels in India because these are derived from indigenous sources and are renewable. Due to
the high self-ignition temperature and latent heat of alcohols, it requires abnormally high
compression ratios to use them in conventional diesel engines [2].
J P Subrahmanyam [6] developed a computer simulation model for the single cylinder
DI diesel engine with diesel and alcohol as fuel. This model illustrates the simulation of
overall cycle consisting of compression, combustion, expansion and exhaust processes and
predicts various combustion and performance parameters. Further, this model is validated
with available experimental results. Nadir Yilmaz et al [3] identified some of the practical
problems encountered during the usage of alcohol in the diesel engines due to its
characteristics (high latent heat of vaporization, high auto ignition temperature) in which the
reaction transport mechanism is absent. He developed a model which measures the chemical
reactions in the combustion, which further models cylinder pressure and attendant extent of
reaction. Saeed et al [5] conducted experiments with alcohol in single cylinder diesel engine
to find effect of alcohol to diesel fuel on the ignition delay period and concluded that with
increasing the alcohol content ignition delays are prolonged and this can be reduced by air
preheating and/or supercharging.
For the complete combustion in the diesel engine very short time is available. So the
liquid fuel should be injected in droplets of smallest size to obtain largest surface-volume
ratio. But the rate of burning depends primarily upon the rate at which the products of
combustion can be removed from the combustion chamber and replaced by fresh oxygen. So
in diesel engines for the efficient combustion, fuel injection pump plays an important role [7].
An attempt is made for theoretical investigations with different injection pressures for
suitability of using alcohol in diesel engines.
The diesel engine performance is obtained with a computer programming. In such
analysis, if all the variables are taken into account, the computer capability and time required
will be beyond those available for this work. Hence the aim of this theoretical analysis is
restricted only to identify the important variables affecting the performance of the insulated
engine and to know the trends.
The general assumptions that are made in developing this model for the diesel engines
are as follows [4]:
(a) The charge inside the cylinder at any instant consists of a non-reacting mixture
of air and residual gases.
(b) The fuel is assumed to mix homogeneously with air.
(c) The pressure and temperature are spatially uniform.
The performance equations used for the development of computer program for the
diesel engine at various stages is explained below briefly
210

3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME
COMPRESSION PERIOD
During the compression period the charge consists of air and residual gas.
The general equation for the work can be written as follows
WCOMP = NA CVR (T2-T 1)
Assumed wall temperature is the temperature at the end of the compression stroke.
With this value of P ( θ +d θ ) and knowing the value of index and pressure P ( θ ) and the
temperature T ( θ +d θ ) can be computed.
T ( θ +d θ ) = [ P(θ + dθ ) ]( r − 1 / r ) * T ( θ )
P (θ )
COMBUSTION PERIOD
The combustion model for the simulation is based on the following assumptions and
simplifications.
i) The ideal gas law is applicable.
ii) The cylinder content consists of a homogeneous mixture of air and combustion
products at all times.
Work done is calculated using the equation.
WCOMB = Σ ((P + ∆P)/2) ∆V
EXPANSION PERIOD
During this process the computations carried out are all similar to the computations
carried out earlier during the compression period.
HEAT TRANSFER MODEL
The heat transfer (hc) in the engine can be calculated with the HOHENBERG RELATION
hc = 0.13 * V-0.06 * [P(W+1.4)]0.8 T-0.4 ( KW / m2 K)
HEAT RELEASE MODEL
The rate of heat release (Hr) is calculated using an empirical relation
Hr = WC * C1 (m+1) exp (-WC ( θ / θ C) m
IGNITION DELAY MODEL
Ignition delay is understood as being the period of time elapsing between the start of
injection nozzle needle lift and the rise in cylinder pressure which is indicated by a marked
deviation of the cylinder pressure from the compression pressure.
ID (CA) = [0.044 exp (45 / T) / P 1.1] * RPM
211

4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME
FRICTION MODEL
Because of various parameters like gas pressure, wall tension of rings, blow by loss,
pumping losses, throttling loss etc;, the frictional mean effective pressure varies in the
combustion chamber and is given by the GOSCH equation.
FMEP = 0.6 (CR-4) + RPM / 200 +1.1x10 6 V2
COMPUTER PROGRAM
The computer program for this model is written in C language. The computer
Graphics has been developed to plot various output parameters on the monitor theoretically
[1]. The various engine geometry parameters such as bore, stroke, connecting rod length and
combustion chamber geometry are given as inputs to the program. The engine variables such
as compression ratio, intake temperature, intake pressure, injection advance, calorific value
and combustion duration are also given as inputs.
For the practical results experiments are conducted on 4-stroke 3.68 KW Kirloskar
water cooled DI Diesel engine at various loads with an injection pressure of 180 bar. Air
suction rate and exhaust air flow rates were measured with the help of an air box method.
Temperatures at the inlet and exhaust valves are monitored using Nickel-Nickel Chromium
thermocouple thermocouples. Time taken to consume 20 cc of fuel was noted using a digital
stop watch.
Figure1. Experimental set up of Engine Test Rig
Engine RPM is measured using an electro-magnetic pick up in conjunction with a digital
indicator of AQUTAH make. The experimental set up used is as shown the following
Figure.1.
212

5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME
RESULTS
Pressure
The computed values of the engine parameters for the normal engine are evaluated. The
computed values of pressure during compression and expansion at various crank angles for
120
100 Practi…
Theo…
80
Pressure (bar)
60
40
20
0
-120 -60 0 60 120
Crank Angle (degree)
Exhibit 1 Variation of Pressure with Crank angle
theoretical and practical normal engine are shown in Exhibit 1 and are observed that the peak
pressure is higher for the theoretical engine than for the practical normal engine and increases
substantially with increase of crank angle. The cycle peak pressure for a normal practical
engine is 72.76 bar and for theoretical engine it is 79.34 bar.
Temperature
Exhibit 2 shows the cycle peak temperature for theoretical and practical normal
engines. The cycle peak temperature for a normal practical engine is 1156 K and for
theoretical engine it is 1375 K. The rise is about 219K at the peak value. At the end of the
expansion the cycle temperature for the practical engine is 719 K and for theoretical engine it
is 790 K. The rise is about 69 K for the theoretical engine.
1600
Practic
al
1200
Temperature (K)
800
400
0
-120 -60 0 60 120
Crank Angle (degree)
Exhibit 2 Variation of Temperature with Crank angle
213

6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME
This concludes that both the theoretical and experimental values are in close
agreement. So this program can be used to verify at which injection pressure the diesel engine
has better performance characteristics when Alcohol is used as fuel. In the computer program
instead of diesel fuel properties, alcohol properties are introduced with different injection
pressures to know at which injection pressure the alcohol performance will be in close
agreement with diesel fuel. Injection pressures are varied from 180 bar to 160 bar to test the
performance of
the engine. The optimum alcohol pressure obtained is used in diesel engines for the further
experimental investigations.
Brake Thermal Efficiency
The variation of Brake Thermal Efficiency with power output using alcohol as fuel is
shown in exhibit.3 with different injection pressures and the same is compared with diesel
fuel performance. It is evident from the graph that diesel has the highest Brake Thermal
Efficiency. Brake Thermal Efficiency depends on combustion process which is very complex
phenomenon that depends on chamber design, viscosity of the fuel, latent heat of
vaporization and the fuel injection pressure. It is observed that at 165 bar injection pressure,
the brake thermal efficiency is slightly better than the other and is in close agreement with
35
Brake Thermal Efficiency (%)
30 Pure diesel
25 Alcohol-180
20 Alcohol-175
Alcohol-170
15
Alcohol-165
10
Alcohol-160
5
0
0 1 2 3 4
Power (KW)
Exhibit 3 Comparison of Brake Thermal Efficiency with Power
Output with Different Injection Pressures
diesel fuel. The remaining values of Brake Thermal Efficiency of alcohol are in between 180
bar and 165 bar pressure.
Indicated Thermal Efficiency
It is evident from the graph that diesel has the highest Indicated Thermal efficiency.
From the graph shown in exhibit 4, it is observed that at 165 bar injection pressure, the
indicated thermal efficiency is maximum compared to other injection pressures. This is due to
the amount of alcohol entered in to the combustion chamber is reduced with the reduction of
214

7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME
fuel injection pressure. This further reduces the amount of heat absorbed by the alcohol for
the evaporation from the combustion chamber. At 160 bar fuel injection pressure, the amount
of alcohol injected is less and this reduces the power output. So at 165 bar fuel injection
pressure, optimum amount of fuel is injected in such way that the indicated thermal
45
40
Indicated Thermal Efficiency (%)
Pure diesel
35
Alcohol-180
30
Alcohol-175
25
20 Alcohol-170
15 Alcohol-165
10 Alcohol-160
5
0
0 1 2 3 4
Power (KW)
Exhibit 4 Comparison of Indicated Thermal Efficiency with Power
Output with Different Injection Pressures
efficiency is higher. The remaining values of Indicated Thermal Efficiency of alcohol are in
between 180 bar and 165 bar pressure.
CONCLUSIONS
• The pure Alcohol at 165 bar pressure has higher Brake Thermal Efficiency and
indicated thermal efficiency than all other. This is due to the entering of optimum
amount of alcohol in to the combustion chamber and at the remaining pressures more
amount of alcohol is entered and made the combustion chamber cool.
• It is concluded that Alcohol can be used in diesel engines with 165 bar pressure at
which the performance of alcohol is in close agreement with diesel fuel. At this
pressure the low viscosity of the alcohol is compensated. So the same fuel injection
pump can be used for the experiments by reducing the injection pressure to 165 bar.
REFERENCES
1. Y.Miyairi,” Computer Simulation of an LHR DI diesel engine”, SAE Paper No.880187.
2. Dr.V.Ganesan., “Internal Combustion Engines”
3. Nadir Yilmaz, A. Burl Donaldson “Modeling of Chemical Processes in a Diesel Engine
with Alcohol Fuels”, Journal of Energy Resources Technology, December 2007,
Volume 129, Issue 4, pp 355-359.
4. Dr.V. Ganeshan, “ C.I. Engine Simulation”
5. Saee, M.N, Henein, N.A “Combustion phenomenon of alcohols in C.I. Engines”,
Journal of Engineering for Gas Turbines and Power, Vol/Issue 111:3, 1999.
215

8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME
6. J P Subrahmanyam, Rafiqul Islam “ computer simulation studies of an alcohol-fueled,
Low hear Rejection, Direct- Injection diesel engine”, SAE 972976
7. Roy Kamo, Nagesh S “ Injection characteristics that improve performance of ceramic
coated diesel engines”, SAE 1999-01-0972
8. Ram Chandra, T.K. Bhattachary, “Performance Characteristics of a Stationary Constant
Speed Compression Ignition Engine on Alcohol-diesel Micro emulsions”, Agricultural
Engineering International: the CIGR E Journal, Vol VIII, June 2006.
9. Shri. N.V. Hargude and Dr. S.M. Sawant, “Experimental Investigation of Four Stroke
S.I. Engine Using Fuel Energizer for Improved Performance and Reduced Emissions”,
International Journal of Mechanical Engineering & Technology (IJMET), Volume 3,
Issue 1, 2012, pp. 244 – 257, ISSN Print : 0976 – 6340, ISSN Online: 0976 - 6359.
10. A. P. Patil and H.M.Dange, “Experimental Investigations of Performance Evaluation of
Single Cylinder, Four Stroke, Diesel Engine, using Diesel, Blended with Maize Oil”,
International Journal of Mechanical Engineering & Technology (IJMET), Volume 3,
Issue 2, 2012, pp. 653 - 664, ISSN Print : 0976 – 6340, ISSN Online: 0976 - 6359.
11. N.V. Hargude, “An Experimental Investigation for Performance Analysis of Four
Stroke S.I. Engine using Oxyrich Air”, International Journal of Mechanical Engineering
& Technology (IJMET), Volume 3, Issue 2, 2012, pp. 532 - 542, ISSN Print : 0976 -
6340, ISSN Online: 0976 - 6359.
NOMENCLATURE
V = Cylinder volume, m3
P = Cylinder pressure, atm.
W = Mean piston speed, ms-1
T = Cylinder temperature, K
WC = Wibe’s constant (6.908)
m = constant (0-2)
θ = crank angle under consideration (CAD)
θ C = combustion duration (CAD)
C1 = FKG* HV/COMDUR
CA = Crank angle
T = Temperature in the combustion chamber
P = Pressure in the combustion chamber
RPM = Speed of the engine
FMEP = frictional Mean Effective pressure
CR = Compression ratio
216