Effect of injection timing and mixing rate of water in jatropha emulsion on combustion and performance of DI diesel engine
Effect of Injection Timing and Mixing Rate of Water in Jatropha Emulsion
on Combustion and Performance of DI Diesel Engine
Nguyen Kim Bao1
1. Vietnam Maritime University; E-mail: nguyenkimbao@vimaru.edu.vn
Address: 484 Lach tray street, Hai phong City, Vietnam
Abstract The current paper studies the effect of the injection timing and Jatropha water emulsion (JWE)
with different mixing ratios on the combustion and performance characteristics of a direct injection
diesel engine. The experimental study was carried out using a four-stroke, high speed, small capacity,
direct-injection diesel engine. The engine ran on the Light oil (LO) and neat Jatropha oil (JO) for
baseline data. In this study, Jatropha emulsion was made by mixing mass ratios of 10% and 20% of
water so called JWE10%, and JWE20%, respectively. While changing fuels from LO to JO, JWE10%,
and JWE20%, we tested the engine with various injection timings of 17, 20, and 23 degree crank angle
before top dead center (o BTDC). The acquired data was analyzed for various combustion parameters
such as in-cylinder pressure, heat release rate (HRR), ignition delay (ID); for performance parameters
such as exhaust gas temperature and brake thermal efficiency (BTE). At the original injection timing,
the peak of in-cylinder pressure, and the HRR reduced, and they marginally increased when advancing
the injection timing in comparison with those of the Jatropha oil at original injection timing. Ignition
delay increased with an increase of the injection timing for both emulsion fuels. When advancing the
injection timing to 23o BTDC, the emulsion fuels reduced exhaust gas temperature. BTE increased when
using emulsion fuels, particularly the JWE10%. Overall, the optimum water mixing rate was 10%, while
the optimum injection timing was 20o BTDC.
Keywords: Jatropha water emulsion, mixing rate, injection timing, combustion, performance.
1. Introduction
Diesel engines have been faced with problems like the fossil fuel crisis, and the more stringent criteria
regulated by governments the world over attempting to protect the air quality. The main harmful
pollutants, namely NOx and particulates, which are trade-offs in using diesel engines, have been closely
watched. Additionally, the production of global warming gas (CO2) is unavoidable whatever the fuel
when using diesel engines. To allay these concerns, vegetable oils have recently gained attention as a
promising alternative fuel for a greener future. Short-term tests have revealed that most vegetable oils
are capable of being used directly in existing diesel engines with little or no modification. However,
long-term test has reported some operational problem such as piston ring sticking, injector and engine
deposits, gum formation and oil thickening [1]. Physical properties of the vegetable oils such as high
viscosity, poor volatility, and bulky molecules result in an increase in CO, HC and PM, but lower NOx
emissions compared to those of diesel oil alone [2-4]. Among vegetable oils, Jatropha has been of
interest because it is not a food source [3]. Jatropha oil was identified as a leading candidate for an
alternative fuel among various non-edible vegetable oils [5] since the plant does not suffer excessively
from droughts, or need concentrated irrigation. Higher smoke, HC, CO have been observed [3, 7, 8],
while NOx emissions have also been reported lower when engines run on Jatropha oil [3, 8]. In the
performance aspect, the brake thermal efficiencies of engines fueled with Jatropha have been generally
lower in comparison with those using diesel oil [3, 6-9]. This is attributed to the physical-chemical-
properties of Jatropha oil such as high viscosity, poor volatility, bulky molecular structure, and low
cetane number. The drawbacks of Jatropha oil may be overcome by preheating [7, 8], and/or blending
with diesel [10, 11].
The usage of water emulsion fuel is a well-known way to significantly reduce NOx emissions due to
the cooling effect of the vaporization of water in the emulsion fuel [12-16]; while the reduction of soot
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is seen as a consequence of the micro-explosion [13, 15], or the presence of OH radicals releasing during
the combustion process [13, 15], or more air entrainment [16].
From this one might surmise that a combination of a change in injection timing with Jatropha water
emulsion may reduce both NOx emissions and soot in diesel engine. Moreover, it may improve
performance of the engine as a result the effect of micro-explosion. However, as yet this combination
has not been tried to the best of our knowledge.
Our current experimental research was conducted to remedy this situation. We investigated the effect
of injection timing and Jatropha water emulsion on the combustion, performance, and emissions
characteristics of a diesel engine. During the experiments, the engine were varied with different
injection timings of 17o (default value), 20o, and 23o BTDC, while we changed the test fuel from LO
and JO to the JWE with water mass mixing ratios of 10% and 20%.
2. Experimental setup and procedures
Figure 1 Diagram of experimental setup
Table 1 Specifications of test engine
Model
Engine type
YANMAR NFD 13-ME
Horizontal, 1-cylinder, 4-stroke
Direct injection
92 × 96 mm
0.638 liter
17.7
Combustion type
Bore × Stroke
Displacement
Compression ratio
Rated output
8.1 kW @ 2400 rpm
Injection nozzle
Nozzle opening pressure
4-hole nozzle
19MPa
Experiments were conducted on a single cylinder, four-stroke, high speed, direct injection diesel engine
(Yanmar Co., Ltd., Japan). The scheme of experimental setup is shown in Fig. 1 and the main
specifications of the test engine are given in Table 1. The fuel injection system of the engine was
modified to a common rail injection system. Main components of the common rail system include a
motor-driven-pump (radial piston pump), a common rail (high pressure tube), an electronic injector,
and an electronic control unit (ECU). The ECU was connected to a computer via a combustion analyzer
(Yokogawa) to record the data. The in-cylinder pressures were measured using a piezoelectric pressure
transducer (Kistler) fitted into the cylinder of the engine and connected to a charge amplifier. Load of
the engine was set through an electrical-dynamometer (Toyo Electric Co., Ltd.) coupled to the shaft of
the engine. A set of gas analyzers VIA-510, CLA-510SS (Horiba) was used to measure the emissions
of CO2, NOx, respectively, and along with MEXA-324J (Horiba) for measurement of CO, HC. Dust
matters were trapped on the ADVANTEC PG-60 paper filters (glass fiber Fluorine coated filter, Toyo
215
Roshi Kaisha, Ltd.) in 10 liters of exhaust gas at each step of the experiments with the help of a D-25UP
gas sampler (OCT science, Ltd.). In each experiment step, we collected the dust on 4 paper filter sheets.
Afterward, soluble organic fraction in the dust trapped filters was dissolved by dichloromethane and
was calculated by balancing the mass of the filters before and after extraction (average value). In-soluble
organic fraction was calculated by subtraction of the paper filter mass after SOF dissolving and the
original filter. Measurements were carried out using LO, JO, JWE10%, and JWE 20%. To make the
emulsion fuel, a mixing system with a tank for JO; a tank for water; a circulating pump; and a static
mixer was used. The engine was fed with LO, and JO at the injection timings of 17, 20, and 23o BTDC
for baseline data. These timings were also set to investigate the effect of the Jatropha emulsion with
different water mass mixing rates. Water with 10% and 20% in mass was added to the Jatropha creating
emulsion fuels prior to the experiments. The experimental conditions (injection timing and test fuels)
of the experiments are provided in Table 2. All experimental steps were conducted at room temperature
and the results were recorded at steady operational conditions of the engine. During the experiments,
the engine load was set at different values of 3.0 kW, 4.5 kW, and 6.0 kW with a speed of 2000 rpm,
while the rail pressure was kept at 100 MPa. The gas emissions including CO, CO2, HC, smoke, and
NOx were read during each step of the experiments. While, the concentration of dust, in-soluble organic
fraction (ISF), and SOF were determined in experiments, as well.
Table 2 Experimental conditions
Test fuels
Engine
Speed
[rpm]
Injection
timing
Jatropha emulsion
10% 20%
LO-17 JO-17 JWE10%-17 JWE20%-17
Light Jatroha
[o BTDC]
oil
oil
2000
2000
2000
17
20
23
-
-
-
-
JWE10%-20 JWE20%-20
JWE10%-23 JWE20%-23
3. Results and discussions
3.1 Combustion characteristics
In this section, the combustion characteristics are demonstrated by a number of factors, namely
combustion pressure, heat release rate, and ignition delay. In-cylinder pressure of the engine is indicated
in Fig. 2. It is clear that the peak pressures of the engine depend on the injection pattern as well as the
fuel. Perhaps, for emulsion fuels, the development of the pressure in the cylinder depends on some
factor, such as the cooling effect; the combustion of cumulated fuel; and the help of second-atomization.
When compared with JO-17, the JWE10% reduced the peak pressures of 5%, 5.8%, and 4.5%, while
the JWE20% had a minor reduction of 0.1%, 0.9% and 0.2% at 3.0, 4.5 and 6.0 kW, respectively. At
this timing, it can be seen that for the emulsion fuels the developments of pressure were retarded when
compared with JO or LO. The reduction and retardation of peak pressures can be resulted from the
cooling effect and higher viscosity of the emulsion fuels. When advancing injection timing, most
emulsion fuel increased peak pressures in the cylinder, particularly for the 23o BTDC. At lower powers,
the JWE10% had a relative increment of peak pressure of 7.0% and 8.8%, while the JWE20% had peak
pressure of 7.0% and 5.5% higher in comparison with those of the JO-17. At 6.0 kW, the JWE20% had
an increment of 5.9%, while the JWE10% had 7.1% higher in comparison with peak pressure of the JO-
17. The increment of the peak pressure may result from either the combustion of the fuel cumulated in
the combustion chamber or the help of micro-explosion contributing to the better mixing of fuel and air
in the combustion chamber. At the 20o BTDC, for the JWE10%, the minor reductions are seen at lower
powers, while it had a marginal increase of 6.2% when compared with JO-17. These may result from
the cooling effect could over the other factors at lower loads, while at higher power the cumulated fuel
and second-atomization could enhanced the development of the in-cylinder pressure. At this timing,
and at lower power, the JWE20% had slight increment of 4.3% and 5.8%, while the pressure was
comparable with those of the JO-17 at 6.0 kW. This can be explained as the high enough water content
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in the JWE20% resulting in the dominant second- atomization at lower powers, and it would be enough
for cooling effect at high load, respectively.
Heat release rate (HRR) in the cylinder of the engine is presented in Fig. 3. The peak of HRR reduced
from 65.9, 66.2, and 64 J/deg. of the LO-17 to 62.5, 59, and 57 J/deg. of the JO-17 at 3.0, 4.5, and 6.0
kW, respectively. This is resulted from properties of the JO such as higher viscosity, lower volatility,
and lower cetane number. At the 17o BTDC, the HRR of the emulsion fuels had a relative reduction of
13.1%, 12.9%, and 11% for the JWE10%, and 3.1%, 8.1%, and -1.5% for the JWE20% in comparison
with those of the JO-17 at 3.0, 4.5, and 6.0 kW, respectively. The reduction of the HRR may attribute
to the cooling effect of the water in the emulsion fuels. However, less reduction of the HRR for the
JWE20% may result from the aid of dominant micro-explosion over the cooling effect. When advancing
the injection of the emulsion fuels the HRR start increasing in comparison with those of the JO-17,
particularly for the injection timing of 23o BTDC. At the 20o BTDC, the JWE10% reduced the HRR
6% at 3.0 kW, while it increased the HRR 10.6% and 19.7% at 4.5 and 6.0 kW. At this timing, the
JWE20% increased HRR 12.1% and 16.5% at 3.0 and 4.5 kW, and it had a reduction of 6.5% at 6.0
kW. At the 23o BTDC, for the JWE10%, the HRR of had an increment of 9.6%, 33.2% and 31.4%,
while for the JWE20%, the reduction was 14%, 13.6%, and 9.7% in comparison with those of the JO-
17 at 3.0, 4.5, and 6.0 kW. This may result from the dominant cooling effect of the JWE20% over the
JWE10%, especially for higher engine powers.
LO-17
7
6
5
(a)
JO-17
JWE10%-17
JWE10%-20
JWE10%-23
JWE20%-17
JWE20%-20
JWE20%-23
4
320
340
360
380
400
420
Crank angle [deg.]
(b)
7
6
5
LO-17
JO-17
JWE10%-17
JWE10%-20
JWE10%-23
JWE20%-17
JWE20%-20
JWE20%-23
4
320
340
360
380
400
420
Crank angle [deg.]
LO-17
JO-17
7
6
5
(c)
JWE10%-17
JWE10%-20
JWE10%-23
JWE20%-17
JWE20%-20
JWE20%-23
4
320
340
360
380
400
420
Crank angle [deg.]
Figure 2 In-cylinder pressures at (a) 3.0 kW, (b) 4.5 kW, and (c) 6.0 kW at a speed of 2000 rpm
217
Ignition delay is shown in Fig. 4. The ignition delay is the duration from the start of injection to the
start of combustion. The start of combustion is determined by the timing at which the HRR changes
from a negative to a positive value. The ignition delay was shorter for LO and JO, while the emulsion
fuel increased the ID and also increased with an increase of injection timing. At default timing, the
JWE10% increased the ID from 6.4% to 8.3%, while at the 23o BTDC the ID had an increment of 22.9%
to 29.9% when compared with those of the JO-17. For the JWE20%, at the 17o BTDC, the ID increased
4.0% to 6.4%, and it increased up to around 30% when timing advanced to the 23o BTDC in comparison
to those of the JO-17. The increment of the ID for the emulsion fuels and when advancing the injection
timing can be attributed to the cooling effect of water in the emulsion fuels and the worse combustion
conditions at advanced injection timing, respectively.
120
LO-17
(a)
JO-17
100
80
60
40
20
0
JWE10%-17
JWE10%-20
JWE10%-23
JWE20%-17
JWE20%-20
JWE20%-23
-15
-15
-15
0
15
Crank angle [deg.]
30
45
45
45
-20
120
100
80
60
40
20
0
LO-17
JO-17
(b)
JWE10%-17
JWE10%-20
JWE10%-23
JWE20%-17
JWE20%-20
JWE20%-23
0
15
30
-20
Crank angle [deg.]
120
100
80
60
40
20
0
LO-17
JO-17
(c)
JWE10%-17
JWE10%-20
JWE10%-23
JWE20%-17
JWE20%-20
JWE20%-23
0
15
30
-20
Crank angle [deg.]
Figure 3 Heat r elease rates at (a) 3.0 kW, (b) 4.5 kW, and (c) 6.0 kW at a speed of 2000 rpm
218
3.0
2.5
2.0
1.5
1.0
0.5
0.0
LO-17
JO-17
JWE10%-17
JWE10%-23
JWE20%-20
JWE10%-20
JWE20%-17
JWE20%-23
3.0
4.5
Engine power [kW]
6.0
Figure 4 Ignition delay at different powers and at a speed of 2000 rpm
3.2 Performance characteristics
The performance parameters of the engine, such as in-cylinder and exhaust gas temperatures, and brake
thermal efficiency will be introduced in this section.
Exhaust gas temperature is shown in Fig. 5. Exhaust gas temperatures increased with an increase in the
engine power. This is due to more fuel injected and combustion which generates more engine power.
At most injection timing, for JWE10%, the exhaust gas temperature reduced when compared with those
of the JO-17. At the 17o and 20o BTDC, the exhaust gas temperatures reduced from 2.1% to 3.1% when
compared with those of the JO-17. At the 23o BTDC, they had more relative reduction of 5.2%, 5.9%,
and 2.0% at 3.0, 4.5, and 6.0 kW, respectively in comparison with those of the JO-17. This may result
from the cooling effect of the water in the emulsion fuel, also when advancing the injection timing, the
heat released more early resulting in early combustion in the combustion chamber. For the JWE20%,
at the original timing, the exhaust gas temperature had a relative reduction of 2.6% to 3.4%, while at
the 23o BTDC the reduction was 3.9%, 2.8%, and 0.6% at 3.0, 4.5, and 6.0 kW, respectively. At the 20o
BTDC, the exhaust gas temperature was comparable with those of the JO-17.
800
LO-17
JO-17
JWE10%-17
JWE10%-23
JWE20%-20
JWE10%-20
JWE20%-17
JWE20%-23
600
400
200
0
3.0
4.5
6.0
Engine power [kW]
Figure 5 Exhaust gas temperatures at different powers and at a speed of 2000 rpm
Brake thermal efficiency of the engine is indicated in Fig. 6. The emulsion fuel significantly increased
the BTE, especially for the advancing timing, when compared with those of the neat Jatropha oil at the
original timing. At the default timing, at higher engine powers, the JWE10% had a relative increment
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of 3% to 6%, while the JWE20% had a relative increment of 8% to 10.7% in comparison with those of
the JO-17.
50
LO-17
JO-17
45
40
35
30
25
20
15
10
5
JWE10%-17
JWE10%-23
JWE20%-20
JWE10%-20
JWE20%-17
JWE20%-23
0
3.0
4.5
Engine power [kW]
6.0
Figure 6 Brake thermal efficiencies at different powers and at a speed of 2000 rpm
At 20o BTDC, the JWE10% increased from 13.6% to 21%, while the JWE20% increased around 12.5%
when compared with those of the JO-17. The relative increment was 17% to 23.5% of the JWE10% and
10.9% to 14.9% of the JWE20% at 23o BTDC. At medium power, and at the 23o BTDC, the JWE10%
had optimum BTE up to 31.8% that overs the BTE of the LO-17 of 30.7%. The increment of the BTE
of the emulsion fuels may attribute to the effect of micro-explosion resulting to the better mixing of fuel
and air in the combustion chamber.
3.3 Emissions characteristics
1000
900
800
700
600
500
400
300
200
100
0
0.3
0.25
0.2
LO-17
JO-17
JWE10%-17
JWE10%-20
JWE10%-23
LO-17
JO-17
(a
(c)
JWE10%-17
JWE10%-23
JWE20%-20
JWE10%-20
JWE20%-17
JWE20%-23
0.15
0.1
0.05
0
3.0
4.5
6.0
3.0
4.5
6.0
Engine power [kW]
Engine power [kW]
14
12
10
8
14
12
10
8
LO-17
JO-17
JWE10%-17
JWE10%-20
JWE10%-23
LO-17
JO-17
JWE10%-17
JWE10%-20
JWE10%-23
(d
(b
6
6
4
4
2
2
0
0
3.0
4.5
Engine power [kW]
6.0
3.0
4.5
6.0
Engine power [kW]
Figure 7 Exhaust gas emissions at different powers and at a speed of 2000 rpm
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The gas emissions of the engine such as CO2, CO, HC, and NOx are indicated in Fig. 7a-d. Emission
of CO2 is presented in Fig. 7a. It is clear that the emissions of CO2 were higher for JO when compared
with LO at the original timing. When using emulsion fuels, the emissions of CO2 reduced when
compared with JO-17. When advancing the injection timing, the emulsion fuels reduced CO2. At the
original injection timing, the JWE10% reduced 3.6%, 2.9%, and 4.5%, while the JWE20% reduced
6.3%, 0.6%, and 0.1% when compared with those of the JO-17 at 3.0, 4.5, and 6.0 kW, respectively. At
the 23o BTDC, the JWE10% had a reduction of 11.8%, 7.2%, and 5.5%, while the JWE20% had a
reduction of 12.6%, 9.5%, and 10.2% when compared with those of the JO-17 at 3.0, 4.5, and 6.0 kW,
respectively. The reduction of CO2 may result from the better mixing between fuel and air, especially,
when advancing the injection timing. The better BTE also means the less fuel consumption and the less
emission of the CO2.
Emission of CO is shown in Fig. 7b. The emulsion increased emission of CO with an increase of the
water in the emulsion fuel. When advancing the injection timing of the emulsion fuel, the emission of
CO dramatically reduced. For the JWE10%, at 3.0 kW, increaments of the CO were 28.6%, 16.4% at
17 and 20o BTDC, respectively, while for the 23o BTDC, the reduction of the CO was 6.8% when
compared with the JO-17. At 4.5 kW, the emissions of CO were comparable with the JO-17. At 6.0
kW, a much increment of 70% was at the original injection timing, and when injection was advanced
to 20 and 23o BTDC, the emission of CO increased 11% and 20%, respectively. For the JWE20%, at
the original timing, CO emission increased 89%, 33%, and up to 110% at 3.0, 4.5, and 6.0 kW,
respectively. When timing was advanced to 20o BTDC, the increment of emission of CO was 64%,
35%, 16%, while at 23o BTDC, it was 24%, -5.3%, and 22% at 3.0, 4.5, and 6.0 kW. The higher emission
of CO for the emulsion fuel can be attributed to the cooling effect of water, and the higher viscosity of
the emulsion fuels. The reduction of the CO when advancing injection timing may result from more
available time for oxidation of CO to CO2, the less fuel consumption, the higher BTE as seen previously.
HC emission is indicated in Fig. 7c. The emission of HC depends on the power of the engine, the
injection timing, and the fuel. The emissions of HC decreased with an increase in the engine power.
This is due to the higher combustion temperatures at higher engine powers. At lower power, for the
JWE10%, HC decreased 16.6% for the 20o BTDC and 4% for the 23o BTDC when compared with those
of the JO-17. This can be explained by the more available time for fuel oxidation. While, for the
JWE20%, HC increased 20.8% up to 58% when compared with the JO-17. This could result from more
water in the emulsion fuels, thus the higher viscosity and density, therefore more fuel droplets got into
the crevice clearance. In the other hand, the combustion conditions were inferior in lower power, thus
increased the HC. At medium power, due to the better combustion conditions, thus the JWE10% at
moderate advancing injection timing marginally reduced HC with 12.7% in reduction compared with
the JO-17. At higher power, the JWE10% slightly increased HC. While, for the JWE20% at medium or
higher powers, the HC emissions were higher than those of the JO-17. These could attribute to the
higher viscosity and density of the emulsion fuels when compared with those of neat Jatropha oil.
Fig. 7d displays NOx emissions of the engine. The emissions of NOx had a strong correlation to the
fuel and injection timing. It is clear that combustion of the emulsion fuels released less NOx than the
JO and LO at the original injection timing. When compared to those of the JO-17, for the JWE10%, the
reductions were 21.3%, 11.2%, and 25.8%, while for the JWE20%, the reductions were 37.1%, 22.4%,
and 29.9% at 3.0, 4.5, and 6.0 kW. This is due to the cooling effect and the dilution of the water in the
emulsion fuel. NOx emissions increased with an increase of the injection timing. This is due to more
fuel cumulated in the combustion chamber when advancing the timing. However, at the 20o BTDC, for
the emulsion fuel, particularly the JWE20%, NOx were 10% to 12% less than or comparable to those
of the JO-17.
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600
500
400
300
200
100
0
LO-17
JO-17
(a)
JWE10%-17
JWE10%-23
JWE20%-20
JWE10%-20
JWE20%-17
JWE20%-23
3.0
4.5
6.0
Engine power [kW]
600
500
400
300
200
100
0
LO-17
JO-17
(b)
JWE10%-17
JWE10%-23
JWE20%-20
JWE10%-20
JWE20%-17
JWE20%-23
3.0
4.5
6.0
Engine power [kW]
600
500
400
300
200
100
0
LO-17
JO-17
JWE10%-20
JWE20%-17
JWE20%-23
(c)
JWE10%-17
JWE10%-23
JWE20%-20
3.0
4.5
Engine power [kW]
6.0
Figure 8 Concentrations of (a) dust, (b) ISF, and (c) SOF at different powers
and at a speed of 2000 rpm
Concentration of dust, in-soluble organic fraction (ISF), and soluble organic fraction (SOF) are
displayed in Fig. 8a-c. This shows that the dust emissions were higher for emulsion fuels when
compared with those of the LO and JO at the original injection timing. In comparison with JO-17, dust
increased 87.7%, 30.5%, and 50.4% for the JWE10%, while it increased 109%, 13.5%, and 29% for the
JWE20% at 3.0, 4.5, and 6.0 kW, respectively. When advancing the timing to the 20o BTDC, at higher
powers, the dust reduced around 28% for the JWE10%, and decreased 5.8% to 31.6% for the JWE20%.
For the 23o BTDC, the reductions of dust were 19.1% and 28.3% for the JWE10% and were 3.1% and
31.1% for the JWE20%. The reductions of dust when advancing injection timing can be attributed to
the dilution of the fuel by the water, the aid of micro-explosion, and the longer time for more complete
combustion. Fig. 8b shows the reduction of the ISF when advancing the injection timing. When
compared with JO-17, the highest reduction of the ISF was 31.3% at 20o BTDC for the JWE10%, while
it was 37.7% for the JWE20% at the same timing. At low power, due to the combustion conditions were
inferior, thus the SOF were higher for the emulsion fuels. At medium power, and at the advanced
injection timing, the SOF reduced 25.9% and 17.7% for the JWE10% at the 20o and 23o BTDC, while
for the JWE20%, SOF slightly increased when compared with the JO-17. At 6.0 kW, the reductions of
the SOF were 23%, and 33.7% for the JWE10%, while for the JWE20%, the reductions were 13.1%,
222
and 21.2%. At higher power, the combustion temperature is higher resulting in better micro-explosion;
and the longer available time for combustion thus reducing the SOF.
4. Conclusions
A direct injection diesel engine was used to investigate the effects of injection timing and Jatropha water
emulsion fuels with a mixing rate of 10% and 20% on the combustion, performance, and emissions of
the engine. In summary, the main features are as follows.
1- The peak of in-cylinder pressure reduced when the emulsion fuels were used at the original
injection timing. When advancing the injection timing, it marginally increased when compared
with those of neat Jatropha oil at the original timing. The increment was from 7% to 8.8% for the
JWE10%, and from 5.5% to 13.1% for the JWE20% at 23o BTDC in comparison with those of the
JO-17. The HRR slightly reduced at the original injection timing when using the JWE10%, while
for the JWE20%, the marginal increment has seen at lower power, and the reduction has observed
at high power. When advancing injection timing, heat released more early and higher than those
of the JO-17. The ignition delay increased with an increase of injection timing, and up to 30%
when compared with those of the JO-17 for both emulsion fuels.
2- Emulsion fuel reduced the exhaust gas temperature at lower engine powers. When advancing
injection timing to 23o BTDC, both emulsion fuels reduced exhaust gas temperature. BTE of the
engine using emulsion fuels was higher than that of the neat Jatropha oil fueled engine. When
advancing injection timing, emulsion fuels increased the BTE, particularly for the JWE10% with
a maximum relative increment of 23.5% when compared with that of the JO-17 fueled engine.
3- When advancing the injection timing to a reasonable timing, the emulsion fuel reduced or kept the
comparable emission of CO2, CO, HC, and NOx. For emulsion fuels, the dust, ISF, and SOF
concentration dramatically reduced when injection timing advanced to 20o or 23o BTDC, especially
for the JWE10%.
4- Overall, the optimum mixing rate of water for Jatropha emulsion fuel was 10%, while the optimum
injection timing was at 20o BTDC for combustion, performance, and emissions of the engine.
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