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SAE TECHNICAL
PAPER SERIES 2006-01-0237

Studies on Dual Fuel Operation of Karanja Oil

and Its Bio-Diesel with LPG as the Inducted Fuel
J. Nazar, A. Ramesh and B. Nagalingam
Indian Institute of Technology Madras

Reprinted from: Emission: New Diesel Engines and Components and CI

Engine Performance for Use with Alternative Fuels (SP-2014)

2006 World Congress

Detroit, Michigan
April 3-6, 2006

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2006-01-0237

Studies on Dual Fuel Operation of Karanja Oil and Its Bio-

Diesel with LPG as the Inducted Fuel
J. Nazar, A. Ramesh and B. Nagalingam
Indian Institute of Technology Madras

Copyright © 2006 SAE International

ABSTRACT However, preparation of biodiesel needs the use of

alcohols, catalysts etc. Vellguth [4] studied the
A diesel engine was operated with karanja oil, bio-diesel performance of a direct injection diesel engine on
obtained from karanja oil (BDK) and diesel as pilot fuels vegetable oil. He conducted variable load tests on the
while LPG was used as primary fuel. LPG supply was engine with rapeseed, peanut and soybean oils as fuels.
varied from zero to the maximum value that the engine He reported performance comparable to diesel values
could tolerate. The engine output was kept at different with a slightly reduced thermal efficiency and concluded
constant levels of 25%, 50%, 75% and 100% of full load. that vegetable oils could be directly used as fuels in
The thermal efficiency improved at high loads. Smoke diesel engines. However, research findings also
level was reduced drastically at all loads. CO and HC revealed that engine durability is adversely affected by
levels were reduced at full load. There was a slight the use of vegetable oils in the long-term [5]. This is due
increase in the NO level. Combustion parameters to the high viscosity and low volatility of vegetable oils.
indicated an increase in the ignition delay. Peak Table 1 gives the properties of Diesel, Liquid Petroleum
pressure and rate of pressure rise were not unfavorably Gas (LPG), Karanja oil (KO) and Bio-Diesel of Karanja
affected. There was an increase in the peak heat oil (BDK).
release rate with LPG induction. The amount of LPG that
could be tolerated with out knock at full load was 49%, Table 1 Properties of fuels [15]
53% and 61% on energy basis with karanja oil, BDK and
diesel as pilots. On the whole it is concluded that LPG Property Diesel LPG KO KBD
can be inducted along with air in order to reduce smoke
levels and improve thermal efficiency of vegetable oil Cetane number 47 NA 40 49
and bio-diesel fuelled diesel engines. LCV (kJ/kg) 42850* 47730 38865* 37913*

INTRODUCTION Density (kg/m3) 835* 2.26 928* 866

The world, at present is heavily dependent on petroleum Pour point (°C) -5 NA 6* -1*
fuels. Due to the fast depletion of petroleum reserves, Flash point (°C) 45-60** NA 248* 187*
the importance of alternate fuel research for internal
combustion engines needs no emphasis. Diesel engines Viscosity (cSt) 3.01* NA 46.48* 6.87*
are the main prime movers for public transportation at (38°C)
vehicles, stationary power generation units and for
agricultural applications. In developing countries much of Carbon residue 0.02* NA 0.64* 0.05*
the population is in rural areas and small diesel engines * indicates measured values
are used in a highly decentralized manner for pumping,
electricity generation and operating other agricultural The high viscosity and low volatility of vegetable oils
machinery. These engines can be powered by vegetable leads to poor mixture formation. This results in slightly
oils, which are readily available in rural areas. The level lower thermal efficiency than that of the diesel engine
of emissions that can be tolerated is much higher in rural and also high smoke levels. These problems of
areas as the population density of engines is not very vegetable oils can be overcome by properly modifying
much. the fuel. The methods employed include blending,
heating, thermal cracking and transesterification of
Vegetable oils can be directly used in diesel engines vegetable oils to convert them to biodiesel. Many
with out any modifications [1-3]. Many of their properties investigators reported better performance and lower
are close to diesel and they are miscible with diesel in all emissions by adopting the above methods [6,7].
proportions. Vegetable oils have also been converted to Senthilkumar et al. [8] investigated the performance and
their ethyl or methyl esters (Biodiesel) and used in diesel combustion characteristics of Jatropha oil and its methyl
engines. Biodiesels are much better fuels than raw ester in a single cylinder naturally aspirated direct
vegetable oils. Their properties are very close to diesel.
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injection diesel engine and compared the results with operated at a constant speed of 1500 rpm. The
conventional diesel fuel. They reported that the overall experimental setup is shown in Fig.1 and the
performance, emissions and combustion characteristics specifications of the engine are given in Table.2. The
of the methyl ester of jatropha oil are comparable to engine was modified to work on the dual fuel mode by
diesel. attaching a venturi type of gas carburetor in the intake
line. An LPG line was connected to the venturi through a
Gaseous fuels are clean burning. Hence, they have flame trap. The flame trap was used to suppress the
attracted worldwide attention. Many of the gaseous fuels flash back, if any from the intake manifold. A polythene
can be obtained from renewable sources. They have a diaphragm was fitted on the wall of the flame trap as a
high self-ignition temperature and hence are excellent safe guard. In the event of any severe flashback, this
spark ignition (SI) engine fuels. However, they cannot be diaphragm would burst and prevent any pressure build
used directly in diesel engines. But diesel engines can up leading to an explosion. The LPG from the cylinder
be made to use a considerable amount of gaseous fuels was allowed to flow through a regulator in order to bring
in the dual fuel mode. In the dual fuel engine a gaseous the pressure to atmospheric value. The flow rate of LPG
fuel called the primary fuel is either inducted along with was controlled manually and measured by using a wet
intake air or injected directly in to the cylinder and is type of flow meter. The maximum amount of LPG was
compressed like in a conventional diesel engine. The limited by unstable operation at low outputs and audible
mixture is then ignited by a small amount of diesel, knock at high outputs. The pilot fuel flow was varied by
called the pilot fuel and combustion of the gaseous fuel the governor of the engine and was measured using an
starts. The major advantages of the dual fuel engines electronic precision weighing machine on the mass
are their ability to use a wide range of gaseous fuels and basis. The engine was coupled to an eddy current
also to produce smoke levels lower than that of swinging field dynamometer. The engine output was
conventional diesel engines. Karim [9] has done varied by controlling the field current. The dynamometer
extensive work on dual fuel engines with different fuels, was periodically calibrated by applying known torques.
even water diesel emulsion and vegetable oils have Torque was measured by the dynamometer with the
been used as pilot fuels [10,11]. help of a strain gauge type of load cell mounted between
the stator and the base frame of the engine. Speed was
LPG has many advantages as a fuel for internal measured with the help of an inductive transducer. Air
combustion engines. It is comparatively cheap, easy to flow was measured by using a turbine type flow meter.
store, distribute and available in many parts of the world.
It has high energy density and a high-octane value. A 12 bit simultaneous sampling high-speed digital data
Hence, it is suitable for high compression ratio engines. acquisition system in conjunction with a piezoelectric
It mixes uniformly with air and results in good pressure transducer was used for the measurement of
combustion with reduced emissions. Poonia [12,13] has the cylinder pressure history. Average pressure data of
reported extensively on the performance of a dual fuel 100 consecutive engine cycles was used to calculate
engine with LPG as the primary fuel and diesel as the combustion parameters.
pilot fuel and the influence of different variables. He
reported that the performance is better than diesel at
high loads but at lower loads the brake thermal
efficiency is always lower than that of diesel values.
Nwafor [14] demonstrated the use of rapeseed oil and its
methyl ester as a pilot fuel in a natural gas dual fueled
engine. The overall test results indicate that the engine
performance with vegetable oil pilot injection was
satisfactory and comparable with the diesel fuel pilot
operation.

In the present work an attempt has been made to

investigate the effect of substituting renewable
alternative fuels like karanja oil (KO) and biodiesel of
karanja oil (BDK) for conventional diesel as pilot fuels in
a LPG inducted dual fuel engine. Karanja oil is available
in rural areas and the distribution network for LPG is
fairly well established in India even in the rural areas.

EXPERIMENTAL SETUP AND EXPERIMENTS

Tests were done on a stationary agricultural type of

diesel engine (Kirloskar TAF1, four stroke, single
cylinder, air cooled, direct injection.) using vegetable oils Fig.1 Experimental set-up
and their methyl esters along with LPG. The rated power
of the engine is 4.4 kW with diesel. The engine was
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A Bosch smoke meter was used for the measurement of Though tests were done with all the three fuels namely
smoke. A volume of 330ml of exhaust gas was drawn karanja oil, BDK and Diesel as the pilots and LPG as the
though a filter paper using a standard Bosch smoke inducted fuel, graphs relating to neat karanja oil-LPG
pump. The filter paper was later analyzed using an dual fuel mode alone are presented to indicate the effect
electronic Bosch smoke meter. A chemiluminescent of load and LPG fraction. However, the three pilot fuels
analyzer was used for the measurement of NO level. have been compared in a later graph at full load. Figure
NOx was not measured due to the lack of 2 shows the variation of brake thermal efficiency at
instrumentation. A Flame Ionization Detector was different outputs with percentage of LPG energy. There
employed for the measurement of hydrocarbon is a noticeable rise in the brake thermal efficiency at high
emissions (HC). An infrared analyzer was used to loads, namely 75% and 100% with LPG induction. At
measure carbon monoxide (CO) emissions. The sample high outputs the inducted LPG air mixture is reasonably
was passed through a cold trap to prevent water vapor rich which will lead to a high flame speed. Further, the
interference with functioning of the analyzer. 1000 cc of amount of pilot fuel injected is also high at these
exhaust gas at atmospheric pressure was passed conditions, which will lead to a strong ignition source.
through a preconditioned glass fiber filter paper using a These factors result in fast burning of the fuel air mixture
water displacement based system. The paper was once with high thermal efficiency. In fact at very high LPG flow
again conditioned and the particulate mass was rates the combustion becomes too rapid particularly
obtained based on weight difference. All tests were when the load is high so that the brake thermal
conducted at the rated engine speed of 1500 rpm. Rated efficiency decreases. Retarding the injection timing at
injector opening pressure of 200 bar was used these conditions will reduce the combustion rate due to
throughout. In a separate test, optimum injection timings a reduction in the ignition delay of the pilot fuel and this
were determined. The optimum static injection timings may improve thermal efficiency. However, this will lead
determined in the single fuel mode were 27°bTDC, to decreased brake thermal efficiency with neat karanja
29°bTDC and 29°bTDC with diesel, karanja oil and BDK oil and in the dual fuel mode at low output. This is seen
respectively. These were maintained in the dual fuel in the case of 100% load where the brake thermal
mode also. The engine was run at different constant efficiency drops after a LPG percentage of about 45.
outputs namely 25%, 50%, 75% and 100% of full load. Audiable knock was observed at these conditions.
At each output the amount of LPG inducted was varied. Knock in the dual fuel engine is because of the rapid
The pilot fuel was automatically changed by the speed combustion of the gaseous fuel along with the injected
governor. The methyl ester of karanja oil was prepared pilot. At full load, the maximum brake thermal efficiency
in the laboratory in the batch mode. The process occurs at a LPG percentage of 26 and it is 31.5% where
involves the reaction of methyl alcohol and vegetable oil as in the neat karanja oil mode the maximum thermal
in the presence of a catalyst (NaOH). During the efficiency is 30%. There is no drop in brake thermal
chemical reaction the glycerol of the triglyceride is efficiency at 50% output. At low outputs the brake
substituted by three molecules of methyl alcohol and thermal efficiency reduces with increase in the LPG
thereby forms three molecules of methyl ester of substitution as the quantity of karanja oil injected in to
vegetable oil and one molecule of glycerol. the cylinder is less and the induced LPG air mixture is
also lean. This is a drawback of dual fuel operation.
Table 2 Engine specifications Similar results were seen with BDK and diesel as pilot
fuels. On the whole dual fuel operation with LPG has
Make Kirloskar helped to enhance engine operation at medium and high
outputs with karanja oil and BDK. At high loads the
Type of engine Single cylinder, amount of LPG inducted has to be carefully controlled.
CI, 4-stroke, air cooled 40
Brake power 6 HP @1500 rpm 35
Compression ratio 17.5:1
Thermal efficiency (%)

30
Bore/Stroke 87.5 / 110mm
25
Injector opening pressure 200 bar
20

15
The engine was initially run in the neat diesel, karanja oil 25% load
and karanja oil methyl ester (Biodiesel of karanja oil- 10
50% load
BDK) modes. Then the amount of LPG admitted was
5 75% load
gradually increased till the engine either misfires or
Full load
knocks. The results have been plotted based on the 0
percentage of total energy obtained from LPG. Thus 0%
0 20 40 60 80 100
on the x-axis indicates neat pilot fuel mode.
Percentage of LPG

TEST RESULTS AND DISCUSSION Fig. 2 Variation of brake thermal efficiency of karanja oil
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The variation of volumetric efficiency is shown in Fig.3. It 0.4

is found to be higher at low loads and to decrease with
0.35
increase in LPG flow rate. The most dominant reason is
that LPG being a gas displaces some of the air that 0.3

Equivalance ratio
would otherwise be inducted. However, there is still
sufficient excess air for proper combustion. As would be 0.25
shown in a later graph the inducted LPG air mixture has 0.2
very low equivalence ratios (the maximum being 0.4).
Figure 4 represents the exhaust temperature at various 0.15
operating conditions. The exhaust gas temperature 0.1 25% load
increases with LPG admission in the case of 100% load 50% load
due to the increase in the combustion rate and peak gas 0.05
100% load
temperature. In other cases, it decreases with LPG
0
induction at low loads due to sluggish combustion as a
0 20 40 60 80 100
result of low pilot quantities. The variation of the
equivalence ratio with LPG percentage is seen in Fig.5. Percentage of LPG
At any given LPG share there is a considerable
difference between low and high load conditions. The
Fig. 5 Variation of equivalence ratio
lean mixtures at low loads lead to poor combustion of
the LPG air mixture. The larger equivalence ratios at
At low loads, CO levels increase with increase in LPG
high outputs lead to rapid combustion and knock.
rate as seen in Fig.6. This is due to incomplete
combustion of LPG due to fewer ignition centers. This is
expected because of the lower amount of pilot fuel. At
high loads combustion becomes better and CO emission
100
reduces with increase in the rate of LPG. At 75% load
we find that at low LPG flow rates, due to incomplete
95
combustion of the lean LPG air mixture that is inducted,
Volumetric efficiency (%)

the CO level initially rises. It falls there after when

90 combustion improves. Thus, at high loads dual fuel
operation has the advantage of lowering CO levels. It is
85 seen in Fig.7 that in the single fuel mode (0% LPG) the
HC level increases with power output as it depends on
80 25% load the amount of fuel injected. At 100 % load the
50% load introduction of LPG lowers HC levels. And at 75% load it
75 75% load does not affect it adversely. This is due to improved
Full load combustion and reduction in the amount of pilot fuel that
70 becomes the main source of HC at these conditions.
0 20 40 60 80 100 However, at 25% and 50% of full load, hydrocarbon
Percentage of LPG
emissions increase considerably with increase in LPG
admission. This is due to the incomplete combustion of
Fig. 3 Variation of volumetric efficiency the LPG air mixture due to the reasons discussed
with karanja oil earlier.
600
25% load As seen in Fig.8 at full load, NO level increases with
50% load percentage of LPG input due to the higher temperatures
500
Exhaust temperature (°C)

75% load
on account of the rise in the combustion rate. At lower
Full load
loads, LPG induction leads to a reduction in the NO
400
level. At 75% of full load; it is found that the NO level
falls with LPG input due to moderate rate of combustion.
300 Here a decrease in the pilot fuel quantity seems to have
a direct effect on the NO level. At very low loads the NO
200 level falls due to sluggish combustion in the dual fuel
mode. Dual fuel engines are expected to produce low
100 smoke as some of the energy release is due to
combustion of the homogeneous fuel air mixture. A
0 drastic reduction in smoke level is noticed in Fig.9. At full
0 20 40 60 80 100 load the smoke level is reduced from 4.2 BSU to 2.9
Percentage of LPG BSU at the highest possible energy share with karanja
oil. Similar trends were found with its BDK and diesel.
Fig. 4 Variation of exhaust temperature This is one of the greatest advantages with the dual fuel
with karanja oil
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mode of operation. A similar reduction in the particulate 12

levels can be expected.
25% load
10 50% load
At full load the peak pressure increases with increase in
the amount of LPG inducted (Fig.10) indicating 75% load

NO (gm/kW-hr)
8
increased combustion rate. Other researchers have Full load
observed similar trends in the case of diesel based dual
fuel engines. The combustion of the entrained LPG 6
along with the pilot fuel at high loads is the reason for
the high combustion rate particularly at the beginning of 4
the combustion process. At loads below 100 % the
induction of LPG reduces the initial combustion rate and 2
lowers the peak pressure. The peak heat release rate
also occurs later in the cycle as the LPG admission 0
increases at low loads. Similar trends have been 0 20 40 60 80 100
observed in rate of pressure rise also as seen in Fig.11. Percentage of LPG
Similar trends were also seen when BDK and diesel
were used as the pilot fuels. The reduced pilot quantity Fig. 8 Variation of NO with karanja oil
and lean LPG air mixtures are the reasons for the
reduced peak pressure and rate of pressure rise at low
loads. At 100% load the maximum rate of pressure rise 4.5
soars to very high values indicating rough combustion. 25% load
4
50% load
3.5
250 75% load
25% load 3

Smoke (BSU)
Full load
50% load 2.5
200
75% load
2
CO (gm/kW-hr)

Full load
150 1.5

1
100
0.5

0
50 0 20 40 60 80 100
Percentage of LPG
0
Fig. 9 Variation of smoke with karanja oil
0 20 40 60 80 100
Percentage of LPG

Fig. 6 Variation of CO with karanja oil 90

80
200
70
Peak pressure (Bar)

180 25% load

60
160 50% load
75% load 50
140
HC (gm/kW-hr)

Full load 40
120
30 25% load
100 50% load
20
80 75% load
10
60 Full load
40 0
0 20 40 60 80 100
20
Percentage of LPG
0
0 20 40 60 80 100
Fig. 10 Variation of peak pressure with karanja oil
Percentage of LPG

Fig. 7 Variation of HC with karanja oil

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12 COMPARISON OF KARANJA OIL, BIO-DIESEL

Rate of pressure rise (bar/°CA) FROM KARANJA OIL AND DIESEL AS PILOT
25% load
10 FUELS
50% load
75% load
8 This comparison has been made at full load under
Full load different LPG flow rates. Figure 16 indicates that the
6 brake thermal efficiency increases with all the three pilot
fuels as the LPG fraction increases due to enhanced
4 combustion rate. The maximum brake thermal efficiency
occurs with diesel followed by BDK and karanja oil in
2 both the single fuel and dual fuel modes. At full load the
brake thermal efficiency with karanja oil increases from
0 30% to 31.5% at an energy share of 26% from LPG and
0 20 40 60 80 100 for BDK it rise from 32.2% to 33.2% at 33 % of energy
share from LPG. The (maximum) audiable knock limited
Percentage of LPG
LPG fractions are 49% with Karanji oil, 53% with karanja
ester and 61% with diesel at 100% load. The exhaust
Fig. 11 Variation of rate of pressure raise
gas temperature as seen in Fig.17 is highest with
with karanja oil
karanja oil due to slower combustion on account of its
higher viscosity and poor mixture formation. With LPG it
increases marginally when karanja oil and BDK are used
It rises from a value of about 4 bar/°CA (Crank Angle)
as pilots.
with neat fuel to about 10 bar/°CA in the dual fuel mode
at full load and maximum LPG flow rate. In the case of
neat diesel operation it was about 6 bar/degree at 100% 30
load. Thus the dual fuel operation at full load increases
the noise levels. We may have to limit the amount of 25
LPG that can be used based on this limitation at full
Ignition delay (°CA)

load. Probably about 40% of the energy can be from 20

LPG as the maximum rate of pressure rise at this
condition at full load is near neat diesel values. 15

Ignition delay always rises in the dual fuel mode as the 25% load
10
inducted LPG affects the ignition of the pilot fuel by 50% load
changing the oxygen availability and physical 75% load
5
characteristics of the charge. The variation of ignition Full load
delay is seen in Figs.12. At full load, ignition delay
0
increases from 16°CA to 17.5°CA at about 50% of
0 20 40 60 80 100
energy substitution from LPG with karanja oil as the pilot
fuel. Results of karanja ester and diesel were also Percentage of LPG
similar. The increase in ignition delay and the Fig. 12 Variation of Ignition delay with karanja oil
accumulation of the pilot fuel is responsible for the
sharper heat release rate at high outputs in the dual fuel
mode as noted earlier. At 75% and 100% loads the 100
combustion duration decreases with introduction of LPG 90
Combustion duration (°CA)

indicating a rise in the overall combustion rate. At low 80

loads the combustion duration is almost unaffected by
70
LPG introduction (Fig.13).
60
The heat release rates shown in Figs.14 and 15 indicate 50
a significant difference between the neat karanja oil 40 25% load
mode and the karanja oil–LPG mode. A sharp rise in the
30 50% load
initial heat release, which is due to the combustion of the
20 75% load
accumulated pilot and the entrained LPG, is seen at high
outputs. This is the reason for the high NO, peak 10 Full load
pressure and maximum rate of pressure rise. At low 0
loads and low gas substitutions the initial combustion 0 20 40 60 80 100
rate is not so sharp as the entrained LPG is less.
Percentage of LPG

Fig. 13 Variation of Combustion duration

with karanja oil
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80 550
Karanja 500
70
Karanja+50%LPG 450

Exhaust temperature (°C)

60 Karanja+78%LPG 400
Heat release rate (kJ/°CA)

50 350
300
40
250 diesel
30
200
20 150 karanja
100
10 BDK
50
0 0
300 360 420 480 0 20 40 60 80
-10
Percentage of LPG
-20
Crank angle (deg) Fig.17 Comparison of exhaust temperature at full load

Fig. 14 Variation of heat release at half load The CO level (Fig.18) decreases with introduction of
LPG with all the pilot fuels due to improved combustion.
However, the values are much higher with karanja oil.
160 This indicates the dominating effect of the pilot fuel. HC
karanja emissions also show similar trends (Fig.19). The HC
140 emission is not affected much with the amount of LPG
Karanja+25%LPG
admitted. However, at low outputs it was found to
Heat release rate (kJ/°CA)

120
karanja+49%LPG increase. The HC level with karanja oil, as the pilot fuel
100 is about 14.4 gm/kW-hr where as with diesel and BDK
80 as pilot fuel it is 5.9 gm/kW-hr and 4.8 gm/kW-hr
respectively due to better combustion at maximum
60 substitution of LPG. Again the influence of the pilot fuel
40
is significant on the HC level. In the single fuel mode the
NO level is highest with BDK (Fig.20). It increases with
20 LPG induction in all cases as the combustion rate gets
0 increased resulting in higher combustion temperature. In
300 360 420 480
the case of diesel the levels are lower. This is probably
-20 due to the higher viscosity of karanja oil and BDK, which
Crank angle (deg) result in localized sources of ignition. We find higher
peak heat release rates with karanja oil and BDK as
Fig.15 Variation of heat release at full load compared to diesel in the dual fuel mode at almost
similar LPG input as will be seen later (Fig.27).
40
35
Brake thermal efficiency (%)

diesel
30
30
karanja
25
CO (gm/kW-hr)

BDK
20 20

diesel 15

10 karanja 10

BDK 5

0 0
0 20 40 60 80 0 20 40 60 80
Percentage of LPG Percentage of LPG

Fig.16 Comparison of brake thermal

efficiency at full load Fig.18 Comparison of CO at full load
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18 500
16 diesel 450
14 karanja

PM (mg/m3 of exhaust gases)

400
BDK kara
HC (gm/kW-hr)

12
350 nja
10
300
8 LPG
250
die
6 BDK +
sel
LPG kara
4 200 LPG+
+ nja
BDK
2 150 dies
0 el
100
0 20 40 60 80
50
Percentage of LPG
0
Fig.19 Comparison of HC at full load 1
14
Fig. 22 Comparison of particulate emissions at full load
12
90
10
NO (gm/kW-hr)

80
8
70

Peak pressure (bar)

6 60
diesel
4 50
karanja
40
2 BDK diesel
30
0
20 karanja
0 20 40 60 80
Percentage of LPG 10 BDK
0
Fig.20 Comparison of NO at full load 0 20 40 60 80
4.5 Percentage of LPG
4 diesel
Fig.23 Comparison of peak pressure at full load
3.5 karanja
14
3 BDK
Smoke (BSU)

Rate of pressure rise (bar/°CA)

2.5 12

2 10
1.5
8
1
0.5 6
diesel
0 4
0 20 40 60 80 karanja
2
Percentage of LPG BDK
0
Fig.21 Comparison of smoke at full load
0 20 40 60 80
Percentage of LPG

Fig.24 Comparison of rate of pressure raise at full load

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The smoke emission shown in Fig.21 indicates a drastic

25
reduction in the dual fuel mode. Smoke levels are lowest
with the BDK as pilot fuel on account of the oxygen in its
20 molecule and also because its viscosity is comparable to
diesel which leads to good mixture formation. The drop
Ignition delay (°CA)

in smoke is more prominent with diesel and BDK. It may

15 be noted that the pilot fuel quantity at any given LPG
percentage highest with karanja oil on account of the
lower thermal efficiency and calorific value. We find that
10 in the single fuel mode the particulates are the lowest
diesel with BDK as seen in Fig. 22. There is a reduction of
about 60mg/m3 with the dual fuel mode with BDK and
5 karanja
diesel on an average. In all cases the peak pressure and
BDK rate of pressure raise increase with LPG addition (Figs.
23, 24). It is also seen that at high LPG flow rates the
0
maximum rate of pressure rise is higher with karanja oil
0 20 40 60 80 and BDK as compared to diesel. This is the reason why
Percentage of LPG the maximum amount of LPG that can be used is lesser
when karanja oil and BDK are used as pilot fuels. The
Fig.25 Comparison of ignition delay at full load ignition delay increases with LPG flow rates and is
slightly lower for karanja and BDK than that of diesel
(Fig. 25). Figure 26 indicates the combustion duration. In
general the combustion duration falls with an increase in
100
the LPG flow indicating a rise in the combustion rate.
90 The heat release rate with different pilot fuels is seen in
Combustion duration (°CA)

80 Fig .27. We find that the peak heat release rates are
high with BDK and karanja oil as compared to diesel in
70
the dual fuel mode at almost similar LPG input. In the
60 case of karanja oil the latter part of the heat release
50 dominates probably due to the high amount of the pilot
fuel.
40 diesel
30
karanja CONCLUSIONS
20
10 BDK Induction of LPG was found to enhance the performance
with Karanja oil (KO) and bio-diesel obtained from
0
Karanja oil (BDK) at medium and high outputs in a
0 20 40 60 80 compression ignition engine. The maximum amount of
Percentage of LPG LPG that can be inducted is limited by knock at high
outputs. The peak heat release rate increases with LPG
Fig.26 Comparison of combustion duration at full load induction. The maximum amount of LPG that can be
180
inducted with KO is 49%, 53% and 61% on the energy
diesel+LPG 51% basis at full output. At part loads the HC and CO levels
160 rise with LPG induction where as this is not the case at
karanja+LPG 49%
high outputs.
Heat release rate (kJ/°CA)

140
KBD+LPG 52%
120
An increase in brake thermal efficiency and a drastic
100 reduction in smoke from 4.2 BSU to 2.9 BSU with KO
80 and from 2.7 BSU to 1.4 BSU with BDKO was observed
60
at full output. A significant drop in particulate levels was
also observed with LPG induction along with KO and
40 BDK. NO emissions were elevated however. Thus this
20 method will allow the use of vegetable oils and bio-
0
diesels in CI engines with low smoke levels. The long
term effects are to be evaluated.
-20300 360 420 480

Crank angle (deg) ACKNOWLEDGEMENT

Fig.27 Comparison of heat release rate at full load The third author acknowledges All India Council for
Technical Education for providing funds for this research
work.
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