1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 171-179, © IAEME
171
PERFORMANCE EVALUATION OF A LOW HEAT REJECTION DIESEL
ENGINE WITH COTTON SEED BIODIESEL
Dr. V. NAGA PRASAD NAIDU1
, Prof. V. PANDU RANGADU2
1
(Principal,Intellectual Institute of Technology,Ananthapuramu, A.P,ndia,nagveluri@gmail.com)
2
(Prof. in Mech Engg., JNTUCEA, Ananthapuramu, A.P, India, pandurangaduv@yahoo.com)
ABSTRACT
In recent years the search for alternative fuels has become inevitable due to fast depletion of
fuels and huge demand for diesel in transport, power and agricultural sectors. One of the best
alternatives is Biodiesels obtained from Vegetable oils. Due to the lower temperatures and pressures
in the normal diesel engines, the burning of the vegetable oils is not complete, the low heating value
and high viscosity of Biodiesels causes to reduce efficiency of the engine. The low heat rejection
(LHR) diesel engine is only solution to overcome these problems. In the present work Investigations
are carried out to evaluate the performance and emissions characteristics of a low heat rejection
(LHR) diesel engine consisting of an air gap insulated piston with Cotton seed biodiesel. The air gap
between the piston crown and piston skirt is varied from 1mm to 2.5mm to find best one at which the
performance and emission characteristics are good. An increase in engine power, decrease in
specific fuel consumption and significant improvements in exhaust emissions were found at 2mm air
gap in the piston as compared with other air gaps.
Keywords: Cotton Seed Bio Diesel, Low Heat Rejection Engine, Emissions, Hydro Carbons,
Air Gap Piston.
I. INTRODUCTION
In the scenario of increasing energy demand, the escalating petroleum prices and depleting of
fossil fuel reserves has triggered to search for an alternative fuels. Vegetable oils can be an important
alternative to the diesel oil, since they are renewable and can be produced in rural areas1
. The
inventor of diesel engine Rudolpf diesel predicted that the plant based oils are widely used to operate
diesel engine. The bio diesel has great potentials as alternative diesel fuel2
. But use of pure bio diesel
can cause numerous engine related problem such as injector choking, piston deposit formation and
piston ring sticking due to higher viscosity and low volatility of bio diesel3
. Transesterification4
of
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ISSN 0976 – 6340 (Print)
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Volume 5, Issue 2, February (2014), pp. 171-179
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2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 171-179, © IAEME
172
bio diesel provides a significant reduction in viscosity, thereby enhancing their physical and
chemical properties and improve the engine performance. Due to the lower temperatures and
pressures in the normal diesel engines, the burning of the vegetable oils is not complete. The drop in
efficiency is due to its low heating value and high viscosity.
It is well known fact that about 35% of heat generated5
is lost in to the surroundings of the
combustion chamber, most heat transfer happens through the piston. If these losses be controlled, the
thermal potency of the engine may be more increased. Hence in order to reduce the heat transfer
through the piston in the present experimental work an air gap insulated engine (AGIE) is developed
which cut back the heat losses from the piston crown to the piston skirt. This increases the heat in the
chamber and heats the incoming fresh charge. So that combustion is complete and thermal potency is
improved.
In the present work Investigations are carried out to evaluate the performance and emissions
characteristics of a low heat rejection (LHR) diesel engine consisting of an air gap insulated piston
with Cotton seed Biodiesel. The air gap between the piston crown and piston skirt is varied from
1mm to 2.5mm to find best one at which the performance and emission characteristics are good.
II. DEVELOPMENT OF AIR GAP INSULATED PISTON
The aim of insulating the piston is to reduce the rate of heat transfer from the crown to skirt
as much as possible. Further, the insulated piston is to be similar to the original piston with respect to
dimensions and the shape of combustion chamber. So in the present work the piston with air-gap
insulation is used.
III. TECHNICAL SPECIFICATIONS OF THE ENGINE
In this work experiments were conducted on 4 stroke, single cylinder, C.I engine (Kirloskar
Oil Engineers Ltd., India) of maximum power-3.68 KW with AVL smoke meter and Delta 1600 S
gas analyser.
Air-Gap Insulated Piston

3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 171-179, © IAEME
173
IV. MATERIAL & METHODS
In the present work tests were conducted on LHR diesel engine consisting of air gap insulated
piston with cotton seed Bio Diesel to evaluate performance and emission characteristics. Cotton has
long been known as nature's unique food and fiber plant. It produces both food for man and feed for
animals in addition to a highly versatile fiber for clothing, home furnishings and industrial uses.
Cottonseed oil has a ratio of 2: 1 of poly n saturated to saturated fatty acids and generally consists of
65-70% unsaturated fatty acids including 18-24% monounsaturated (ole ic) and 42-52%
polyunsaturated (linoleic) and 26-35% saturated (palmitic and stearic)6
. The various properties of the
cotton seed bio diesel7
is presented in table 1.
TABLE I
PROPERTIES OF FUEL USED
Properties Cotton seed Diesel
Density (kg/m3) 874 830
Calorific Value (kJ/Kg) 40000.32 43000
Viscosity @400C(cSt) 4 2.75
Cetan Number 51.2-55 45
Flash Point (o
C) 70-110 74
V. RESULTS AND DISCUSSIONS
1. BRAKE THERMAL EFFICIENCY
The brake thermal efficiency variation with power output for different amount of air gaps
between crown and skirt is illustrated in figure 1. The thermal efficiency depends on the amount of
heat produced in the combustion chamber. It further depends upon the amount of fuel present in the
chamber, mixture strength and amount of heat given to the charge before combustion. If the charge is
preheated before the combustion, fuel vaporization is faster; the fuel will undergo complete
combustion and hence increase in the thermal efficiency.
Figure1. Variation of Brake thermal Efficiency with power output
0
5
10
15
20
25
30
35
0 1 2 3 4
Brakethermalefficiency(%)
Brake Power (kW)
1mm air gap
1.5 mm air gap
2 mm air gap
2.5 mm air gap

4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 171-179, © IAEME
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The air gap between crown and skirt acts as an insulator to the heat and that will be given the
incoming charge for the combustion. This heat transfer increases with the amount of air gap up to
2mm and thereafter it will decrease. This is because of reduction in the material thickness between
crown center and skirt. The brake thermal potency increases with the load. The efficiency of cotton
seed oil at 2 mm air gap is 30.5% and for at 1 mm air gap it is 28.8%. The thermal efficiencies at 1.5
mm and 2.5 mm are in between the efficiencies of 1 mm and 2 mm.
2. BRAKE SPECIFIC FUEL CONSUMPTION
The figure 2 illustrates the variation of brake specific fuel consumption (BSFC) with power
output. The BSFC mainly depends upon the homogeneous mixture formation and complete
combustion of the fuel. Due to the cotton seed oil’s higher viscosity it requires higher temperatures
for the fuel evaporation in the chamber. With the vaporization of the fuel, the charge becomes
homogeneous and further the combustion will complete. Because of the air insulation between crown
and skirt the temperature in the combustion chamber increases up to 2 mm air gap and after that it
decreases due to the reduction in the material thickness which allows the heat to the skirt.
Figure 2: Variation of brake specific fuel consumption with power output
At the rated load the BSFC for 1 mm air gap is 0.32 kg/kW.hr. At 1.5 mm and 2 mm air gap
it is 14% and 18.75% higher and at 2.5 mm air gap it is 3.12% less than that.
3. EXHAUST GAS TEMPERATURE
The variation of exhaust gas temperatures with power output is illustrated in the figure 3. The
exhaust gas temperature in the combustion chamber depends on the combustion quality and viscosity
of the fuel injected. Further the combustion efficiency depends on the mixture strength in turn the
evaporation rate of the fuel. Due to the higher viscosity the vegetable oil evaporation increases with
the temperature availability in the chamber and further the combustion. In the LHR diesel engine the
air acts as an insulator for the heat transfer and retains the heat in the combustion chamber and
further aids for the combustion. The exhaust gas temperature of cotton seed oil for the 1mm air gap
at rated load is 2650C and at 2mm air gap it is 9.43% higher than that. The exhaust temperatures at
the remaining air gaps are in between these two.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 1 2 3 4
BrakeSpecificFuel
Consumption(kg/kW-hr)
Brake Power (kW)
1 mm air gap
1.5 mm air gap
2 mm air gap
2.5 mm air gap

5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
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Figure 3: Variation of Exhaust gas temperatures with power output
4. VOLUMETRIC EFFICIENCY
The variation of volumetric efficiency with power output is illustrated in figure 4. The
volumetric efficiency of the engine mainly depends on the combustion chamber temperatures. With
the increase in the chamber temperatures the charge temperature increases and this reduces the mass
of air and thus less amount of air enters the engine. This reduces the power output. At the rated load
for 1 mm air gap the volumetric efficiency is 80.5% and this is dropped by 2% with 2 mm air gap.
The efficiency at the remaining air gaps are in between 1 mm air gap and 2 mm air gap. As the
temperatures in the chamber increases with the air gap, the volumetric efficiency dropped
.
Figure 4: Variation of the volumetric efficiency with power output
74
76
78
80
82
84
86
0 1 2 3 4
VolumetricEfficiency(%)
Brake Power (kW)
1 mmair gap
1.5 mm air gap
2 mm air gap
2.5 mm air gap
0
100
200
300
400
0 1 2 3 4
ExhaustGasTemperture(0C)
Brake Power (kW)
1 mm air gap
1.5 mm air gap
2 mm air gap
2.5 mm air gap

6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 171-179, © IAEME
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5. SMOKE DENSITY
Figure 5 shows the variation of smoke densities with the power output. The mixing of the
fuel with the air in the diesel engine is varied from region to region of the combustion chamber. The
smoke in the diesel engine is due to the unburnt liquid particles of fuel or lubricating oil and further
it creates partial combustion. The smoke and soot form on the chamber walls due to the incomplete
burning of the fuel droplets in the chamber. With the increase in the load more amount of fuel is
injected in to the combustion chamber and increases the unburned fuel droplets on the chamber
walls. This is more in the rich regions of the combustion chamber. As the cotton seed oil consists of
inherent oxygen, it is distributed during the combustion process and enhances the combustion
efficiency and reduces the smoke formation. Though more oxygen is presented at higher loads the
time available for the atomization is less, further the fuel droplets are larger in size and increase the
smoke densities. This formation can be reduced with the complete combustion of the fuel i.e with the
higher temperatures in the chamber. In the LHR diesel engine the temperatures in the chamber
increases with the air gap and the drops the smoke emissions. The smoke emission for 1 mm air gap
at the rated load is 0.52 bosch. Similarly the smoke emissions at the remaining air gaps are 3.85%,
7.69%, and 5.77% lesser than 1 mm air gap.
Figure 5: Variation of smoke density with power output
6. HYDROCARBON EMISSIONS (HC EMISSIONS)
The hydrocarbon emissions variation with power output is illustrated in figure 6. The HC
emissions mainly depend on the fuel atomization and presence of oxygen for the combustion.
0
0.2
0.4
0.6
0.8
0 1 2 3 4
Smokedensity(bosch)
Brake Power (kW)
1 mm air gap
1.5 mm air gap
2 mm air gap
2.5 mm air gap

7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 171-179, © IAEME
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Figure 6: variation of hydrocarbon emissions with power output
Further the improper burning of the fuel and lubricating oil are the other main sources for the
emissions. It is observed that at lesser loads less fuel will be injected and the available higher oxygen
makes the charge rich and further enhances the combustion and reduces the emissions. These
emissions reduce with the higher temperatures in the chamber. This combustion chamber
temperature increases with the air insulation between crown and skirt of the piston. The hydrocarbon
emissions for 1 mm air gap at the rated load are 645 ppm. The emissions for the remaining air gaps
are 1.24%, 2.95% and 1.70% lesser than 1 mm air gap. This is attributed to the higher temperatures
in the combustion chamber.
7. CARBON MONOXIDE EMISSIONS (CO EMISSIONS)
The figure 7 shows the variation of carbon monoxide emissions with power output. With the
higher temperatures in the Air gap insulated engine the combustion improves and further the
oxidation of carbon monoxide is also improved. Hence the CO emission in the
Figure 7: Variation of CO Emissions with Power output
300
400
500
600
700
800
900
0 1 2 3 4
HydroCarbonEmissions(ppm)
Brake Power (kW)
1mm air gap
1.5 mm air gap
2mm air gap
2.5 mm air gap
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 1 2 3 4
COemissions(%volume)
Brake Power (kW)
1 mm air gap
1.5 mm air gap
2 mm air gap
2.5 mm air gap

8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 2, February (2014), pp. 171-179, © IAEME
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Exhaust drops drastically. At the lower loads due to the rich mixture formation more oxygen
will be present and hence the CO converts into CO2 and thus CO emissions plunged. As the load is
increased fuel injected increases and consequently CO emissions are also increased. These emissions
are remunerated with the higher temperatures in the chamber and inherent oxygen in the cotton seed
oil. At the rated load the emissions for the 1 mm air gap is 0.55 % vol. Similarly the emissions for
1.5 mm, 2 mm and 2.5 mm air gap are 5.45%, 9.09% and 3.64% lesser than that.
8. NITROGENOXIDE EMISSIONS
The variation of NOx emissions with power output is illustrated in figure 8. In general the
nitrogen gas is dormant at the inferior temperature and is dynamic at the elevated temperatures of the
combustion chamber. This is further responsive to the oxygen content and reacts with that at higher
temperature and forms NOx emissions. At lower loads more oxygen will be available for the
combustion and emissions will be increased but it is compensated by lower temperatures in the
chamber.
Figure 9: Variation of NOx emissions with power output
Further as the load Increases in the LHR diesel engine the combustion chamber temperature
will also increase and the formation of NOx emissions will also increase. This is further enhanced by
the inherent oxygen present in the cotton seed oil. The NOx emission for cotton seed oil at rated load
for 1 mm air gap is 630 ppm. The emissions are 1.6%, 3.97% and 2.38% higher at 1.5 mm, 2 mm
and 2.5 mm air gap than 1mm air gap.
400
450
500
550
600
650
700
750
0 1 2 3 4
NOxEmissions(ppm)
Brake Power (kW)
1 mm air gap
1.5 mm air gap
2 mm air gap
2.5 mm air gap

9. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
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VI. CONCLUSIONS
The following conclusions are drawn based on the experimental results of the above work:
With the air insulation between piston crown and skirt the temperature in the combustion
chamber increases. This further enhances the brake thermal efficiency .
The air insulation reduces the heat transfer through the piston and in turn in the increases
exhaust gas temperature.
The volumetric efficiency dropped in the engine and is attributed to the higher temperature in
the combustion chamber. This can be further compensated by the turbo charging of the engine
The Hydrocarbon emissions and CO emissions are less with the air gap insulated engine due
to the complete combustion of the fuel with elevated temperature in the chamber
With the higher temperatures in the chamber and inherent oxygen in the cotton seed oil the
NOx emissions is increased.
It is concluded that out of the four different air gaps between piston crown and skirt tested in
LHR diesel engine, 2 mm air gap is best for the cotton seed oil which illustrated the best in terms of
efficiency and emissions.
VII. ACKNOWLEDGMENT
Authors thank authorities of Intellectual Institute of Technology and Intell Engineering
College Anantapuramu, AP, India for providing facilities for carrying out research work.
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