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Renewable Energy 32 (2007) 1136–1154
Use of HOT EGR for NOx
control in a compression
ignition engine fuelled with bio-diesel from
Jatropha oil
V. Pradeep, R.P. SharmaÃ
Internal Combustion Engines Laboratory, Department of Mechanical Engineering,
Indian Institute of Technology Madras, Chennai 600036, India
Received 23 December 2005; accepted 30 April 2006
Available online 27 June 2006
Abstract
Environmental degradation and depleting oil reserves are matters of great concern round the
globe. Developing countries like India depend heavily on oil import. Diesel being the main transportfuel in India, finding a suitable alternative to diesel is an urgent need. Jatropha based bio-diesel
(JBD) is a non-edible, renewable fuel suitable for diesel engines and is receiving increasing attention
in India because of its potential to generate large-scale employment and relatively low environmental
degradation. Diesel engines running on JBD are found to emit higher oxides of nitrogen, NOx
. HOT
EGR, a low cost technique of exhaust gas recirculation, is effectively used in this work to overcome
this environmental penalty. Practical problems faced while using a COOLED EGR system are
avoided with HOT EGR. Results indicated higher nitric oxide (NO) emissions when a single cylinder
diesel engine was fuelled with JBD, without EGR. NO emissions were reduced when the engine was
operated under HOT EGR levels of 5–25%. However, EGR level was optimized as 15% based on
adequate reduction in NO emissions, minimum possible smoke, CO, HC emissions and reasonable
brake thermal efficiency. Smoke emissions of JBD in the higher load region were lower than diesel,irrespective of the EGR levels. However, smoke emission was higher in the lower load region. CO
and HC emissions were found to be lower for JBD irrespective of EGR levels. Combustion
parameters were found to be comparable for both fuels.
r 2006 Elsevier Ltd. All rights reserved.
Keywords: HOT EGR; Jatropha; NO (Nitric oxide)
ARTICLE IN PRESS
www.elsevier.com/locate/renene
0960-1481/$ - see front matterr 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.renene.2006.04.017
Ã
Corresponding author.E-mail addresses: [email protected], [email protected] (R.P. Sharma).
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1. Introduction
Use of efficient diesel engines need encouragement in the future since they consume less
fuel and significantly reduce potent green house gases like carbon dioxide. Ever increasing
diesel consumption, large outflow of foreign exchange and concern for environment haveprompted developing countries like India to search for a suitable environmental friendly
alternative to diesel fuel. The country has to simultaneously address the issues of energy
insecurity, increasing oil prices and large-scale unemployment. It is in this context that
development and use of bio-diesel from Straight vegetable oils (SVO) like Jatropha Curcas
may be looked at.
Straight vegetable oils even though projected as an engine friendly fuel by many
researchers have recently lost its attraction. Being highly viscous and less volatile, SVO’s
will result in poor spray atomization, vaporization, and pose serious threat to the engine
health in the long run. More over many SVO’s are edible oils whose continuous supply
cannot be ensured in India [1–4].
1.1. Features of Jatropha Curcas
The ‘Jatropha Curcas’ plant can grow in waste lands and consumes less water.
Its cultivation, seed collection, oil extraction, and bio-diesel production can generate
large-scale employment.
The by-products during bio-diesel production can be used in soap and fertilizer
industry.
Vegetable oils are triglycerides and as per ASTM, bio-diesels are mono alkyl esters of
long chain fatty acids derived from renewable fats such as oils and animal fats for use in
diesel engines. Transesterification is an effective process of bio-diesel production in which
straight vegetable oils are treated with methanol in the presence of catalyst. Catalysts like
sodium or potassium hydroxide are generally used [1–5]. Jatropha Curcas oil (SVO) is
chemically modified into bio-diesel through a transesterification process. Bio-diesel thus
obtained has properties close to diesel fuel and is found to be engine friendly [1,4].
In spite of several advantages, Jatropha based bio-diesel (JBD) is found to emit higher
NOx
compared to diesel fuel. Higher NOx
level in the JBD exhaust as reported by several
researchers [1,2], is a serious issue to be addressed before its wide spread implementation[1,2]. The authors also found higher NO emissions when the JBD was tested in the
laboratory. Higher NOx
emission from JBD is probably due to their higher bulk modulus
and boiling point. Inherent oxygen in its structure can also aggravate the situation [1,6].
1.2. Properties of JBD and their significance
Bio-diesel from Jatropha oil is free from sulfur and still exhibits excellent lubricity,
which is an indication of the amount of wear that occurs between two metal parts
covered with the fuel as they come in contact with each other [1].
It is a much safer fuel than diesel because of its higher flash and fire point. Presence of oxygen in the structure of JBD reduces the energy content of fuel and
significantly contributes to NOx
emissions. However, presence of oxygen facilitates
complete combustion and reduces CO and HC emissions.
ARTICLE IN PRESSV. Pradeep, R.P. Sharma / Renewable Energy 32 (2007) 1136–1154 1137
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Bulk modulus is another important property, which results in a dynamic advance of
injection timing in bio-diesel fuelled engine. Bulk modulus of JBD is higher than the
diesel fuel, which leads to a more rapid transfer of the pressure waves from fuel pump to
lift the needle of the injector much earlier. This advance results in more fuel
accumulation before the start of combustion leading to higher peak temperature andpressure in premixed phase and subsequently higher NO
x[6].
Boiling point of bio-diesel is higher than diesel fuel. Because of higher boiling point, bio-
diesel retains its liquid state for an increased duration, facilitating more droplet-
penetration into the engine cylinder. This feature can lead to increased fuel
consumption, peak temperature and higher NOx
[6].
An effective transesterification process is mainly aimed at bringing the viscosity and
density of JBD closer to that of diesel. Table 1 shows slightly higher viscosity and density
for JBD compared to diesel. Higher viscosity and density can lead to poor mixture
formation, poor spray atomization, higher smoke and increased pumping losses [1,3].
1.3. NOx
reduction strategies—a comparison
Even though some cetane improving additives are capable of reducing NOx
, the amount
of reduction is reported to be inadequate. Moreover, most of the additives are expensive
and can promote auto-oxidation in bio-diesel. Extensive studies have revealed that NOx
reduction by altering fuel properties is highly limited [6–8].
Retarded injection is an effective method employed in diesel engines for NOx
control.
However, this method leads to increased fuel consumption, reduced power, increased HCand excess smoke. Water injection on the other hand is prone to corrosion. In addition, it
adds to the weight of the engine system for maintaining a water storage tank. It is also
difficult to retain water at a desired value during cold climate.
Exhaust gas recirculation is an effective method for NOx
control. The exhaust gases
mainly consist of inert carbon dioxide, nitrogen and possess high specific heat. When
recirculated to engine inlet, it can reduce oxygen concentration and act as a heat sink. This
process reduces oxygen concentration and peak combustion temperature, which results in
reduced NOx
. EGR is not free from demerits. It can significantly increase smoke, fuel
consumption and reduce thermal efficiency unless suitably optimized.
Many researchers have used EGR after cooling to room temperature (COOLED EGR).This method even though effective, is expensive and difficult to implement. Exhaust gases
being at high temperature, a properly designed gas cooler is necessary for cooling exhaust
to room temperature. Many researchers have reported serious difficulties in maintaining
ARTICLE IN PRESS
Table 1
Properties of diesel and Jatropha based bio-diesel
Property Diesel Jatropha bio-diesel
Kinematic viscosity at 40 1C (mm2/s) 3.8 4.4Density (kg/m3) 840 878
Calorific value (MJ/kg) 42.5 38.5
Flash point (1C) 50 179
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such a system with respect to its cooling capacity, weight etc., especially in higher load
regions [9]. As a cost effective technique of exhaust gas recirculation, HOT EGR is
effectively used in this work to reduce NO emissions. Practical difficulties faced in a
COOLED EGR system viz. corrosion of gas cooler, cooling capacity at higher load, extra
weight are avoided with HOT EGR.
1.4. Effects of HOT EGR
Dilution effect refers to the reduction in oxygen supplied to the engine due to application
of EGR where as chemical effect is due to the participation of carbon dioxide, (present in
the EGR) in the combustion process. Thermal effect refers to the increase in inlet charge
thermal capacity due to the recirculation of exhaust gas [10].
2. Experimentation
The specifications of the engine used are given in Table 2 and the experimental set up
used is shown in Fig. 1.
2.1. EGR piping
Exhaust gases were tapped from exhaust pipe and connected to inlet airflow passage. An
EGR control valve was provided in this pipe for EGR control (Fig. 2). The exhaust gases
were regulated by this valve and directly send to the inlet manifold without a gas cooler.
Sufficient distance for thorough mixing of fresh air and exhaust gases were ensured.
Temperature of this exhaust gas-fresh air mixture was measured just before its entry into
the combustion chamber using a K type thermocouple (refer Table 3).
EGR amount was determined using the expression
% EGR ¼
Mass of air admitted without EGR ÀMass of air admitted with EGR
Mass of air admitted without EGR.
2.2. Instrumentation
Electrical dynamometer, wherein the generator output connected to a resistance load,
was used as loading device. Separate burettes and fuel piping were provided for both fuels
ARTICLE IN PRESS
Table 2
Engine specification
Make Kirloskar AV1
Details Single cylinder, DI, Four stroke, Water cooled
Bore and stroke 80Â 110 mm
Compression ratio 16.5:1Rated power 3.7 kW at 1500 rpm
Injector opening pressure 210 bar
Injection timing 27 deg bTDC static (diesel)
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and connected to a single fuel pump with change over provision. An AVL piezoelectric
pressure transducer in conjunction with a KISTLER charge amplifier and data acquisitionsystem were used to measure cylinder pressure. Before mounting on to the cylinder head,
the transducer–charge amplifier combination was statically calibrated using a dead weight
pressure tester. An optical encoder using photo emitter and detector was used to detect
TDC. A non-dispersive infrared analyzer (NDIR), HORIBA-MEXA-324 FB was used for
the measurement of CO and HC. CO was measured as percentage volume and HC was
measured as n-hexane equivalent, ppm. Smoke was measured as percentage opacity using
an AVL 437 Opacimeter. A chemiluminescent analyzer (Rosemount analytical—951 A)
was used for NO measurement. A turbine type air flow meter coupled to a counter was
used to measure the airflow rate. Temperatures were measured using K-type thermo-
couples (refer Table 3).All the experiments were conducted at a rated speed of 1500 rpm. Injection timing was
optimized w.r.t. brake thermal efficiency (BTE) for both diesel and JBD. An optimized
injection timing of 27 and 28 degree bTDC (static) was used for diesel and bio-diesel
ARTICLE IN PRESS
23 4
1
8 9
13 14 15
10 11 12
167
65
Exhaust
gas
1817
Fig. 1. Experimental setup. (1) Air flow meter; (2) air vessel; (3) engine; (4) dynamometer; (5) smoke meter; (6)CO, HC analyser; (7) NO analyser; (8) EGR valve; (9) thermocouples (inlet/exhaust); (10) exhaust temperature
indicator; (11) intake temperature indicator ; (12) inlet cooling water temperature indicator ; (13) outlet cooling
water temp. indicator; (14) stopwatch; (15) speed indicator; (16) data acquisition system; (17) fuel tank; and (18)
burette.
Air vessel
E
NG
I
N
E
EGR Valve
Exhaust Gas
Air flow
Meter
Fig. 2. EGR Piping.
V. Pradeep, R.P. Sharma / Renewable Energy 32 (2007) 1136–11541140
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respectively. The cooling water outlet temperature was maintained at 70 1C during all the
experiments. Since most of the modern diesel engines use EGR, JBD performance under
various EGR, levels were compared with corresponding diesel performance also.
3. Results and discussion
3.1. Performance
3.1.1. Brake thermal efficiency
Fig. 3 shows the comparison of BTE for JBD and diesel without EGR. Comparable
efficiency values were obtained for both fuels.Fig. 4 indicates variation of BTE at 5% EGR level. Both fuels have shown small
improvement in thermal efficiency probably due to the increased combustion velocity
because of higher intake charge temperature, with HOT EGR [11]. HOT EGR is believed
to have improved combustion due to higher inlet temperature. In addition, it is believed
that EGR being at slightly higher pressure than atmosphere might have reduced pumping
losses also. The chemical effect of EGR associated with dissociation of carbon dioxide to
form free radicals can also be attributed to this improvement in efficiency [11,12]. Fig. 5
indicates the variation of BTE at optimized EGR level of 15%. With 15% EGR, full load
BTE was found to be 30.1% and 32.4% for JBD and diesel, respectively. However due to
predominant dilution effects, BTE of JBD reduced to 29.6% and 29.4% for 20% and 25%EGR levels at peak power.
Beyond 15% EGR level, BTE also reduced significantly. Percentage reduction in BTE
over an EGR range of 0–25% was 6.6% for diesel whereas it was only 4.9% for JBD. The
drop in efficiency at higher levels viz. 20% and 25% of EGR is possibly due to
predominant dilution effect of EGR leaving more exhaust gases in combustion chamber.
3.1.2. Brake specific energy consumption (BSEC)
Brake specific energy consumption is more effective than brake specific fuel
consumption (BSFC) in comparing fuels of different calorific value. Fig. 6 indicates the
variation of full load BSEC with % EGR. BSEC can be obtained as the product of BSFCand calorific value of the fuel. BSEC of bio-diesel was slightly higher for all levels of EGR
compared to corresponding diesel values. This is presumably due to lower calorific value,
higher boiling point and viscosity [1,6].
ARTICLE IN PRESS
Table 3
Inlet charge temperatures at various EGR levels
%EGR Temperature (1C)
Diesel Bio-diesel
5 38 38
10 40 41
15 45 46
20 53 51
25 61 56
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3.2. Emission
3.2.1. Smoke emissionFig. 7 shows smoke variation with various EGR levels. Smoke emissions were found to
be lower for JBD compared to diesel at full load irrespective of EGR level. This is
presumably due to good mixture formation and presence of oxygen in bio-diesel. However,
ARTICLE IN PRESS
0
5
10
15
20
25
30
35
0 1 2 3 4
Brake Power (kW)
T h e r m a l e f f i c i e n c y ( % )
Diesel with 5% EGR
Bio-diesel with 5% EGR
Diesel without EGR
Bio-diesel wihout EGR
Fig. 4. Comparison of brake thermal efficiency(5% EGR).
0
5
10
15
20
25
30
35
0 1 2 3 4
Brake power (kW)
T h e r m a l e f f i c i e n c y ( % )
diesel bio-diesel
WITHOUT EGR
Fig. 3. Comparison of brake thermal efficiency (No EGR).
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higher smoke emissions were observed for JBD up to 60% load. Smoke emissions at no
load condition are also shown in Fig. 7. Bio-diesel with slightly higher viscosity and lower
volatility can result in poor mixture formation in lower load region were temperatures are
comparatively low. Water content if not removed properly during bio-diesel productioncan also result in higher smoke emission especially in the lower load region [2,3]. Smoke
opacity values higher than 60% were observed for EGR levels of 20 and 25% for both
fuels. However, it was still lower for bio-diesel at higher loads. Since opacity values
ARTICLE IN PRESS
10
11
12
13
0 5 10 15 20 25
% EGR
B S E C ( M J / k W - h r )
Diesel JBD
Fig. 6. Comparison of BSEC with EGR (full load).
0
5
10
15
20
25
30
35
0 1 2 3 4Brake power (kW)
T h e r m a l e f f i c i e n c y ( % )
Diesel with 15% EGR
Bio-diesel with 15% EGR
Diesel without EGR
Bio-diesel wihout EGR
Fig. 5. Effect of 15% EGR on brake thermal efficiency.
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higher than 60% were unacceptable, optimum EGR rate with respect to smoke was found
to be 15%.
3.2.2. Carbon monoxide emission
Fig. 8 indicates full load CO variation with various EGR levels. CO emissions were
found to be lower for bio-diesel compared to diesel with and without EGR. For both fuels,
CO levels increased as EGR rate was increased. However, CO emissions of JBD were
comparatively lower. Higher values of CO were observed at full load for both fuels beyond
15% EGR. Very high CO values for diesel under higher EGR are due to the oxygen
deficient operation. For bio-diesel, the excess oxygen content is believed to have partially
compensated for the oxygen deficient operation under EGR. Dissociation of CO2 to CO at
peak loads where high combustion temperatures and comparatively fuel rich operation
exists, can also contribute to higher CO emissions [12].
3.2.3. Hydrocarbon emission
Fig. 9 shows variation of full load HC emission with EGR rate. Increase in HC was not
significant as EGR level was increased for bio-diesel. This is probably due to oxygen
content in bio-diesel compensating for oxygen deficiency and facilitating complete
combustion. However, for diesel, full load HC increased from 20 ppm without EGR to
even 90 ppm at 25% EGR. The variation over this range was only 10–40 ppm for bio-
diesel. For 15% EGR, diesel and bio-diesel HC was comparable at full load.
3.2.4. Oxides of nitrogen emissionFig. 10 indicates the variation of NO emission with brake power. NO was found to be
1255 ppm for diesel and 1350 ppm for bio-diesel at full load and 0% EGR operation. NO
emissions were also higher at part loads for bio-diesel without EGR. This is probably due
ARTICLE IN PRESS
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25
% EGR
S m o k e o p a c i t y ( % )
Diesel (Full load)
JBD (Full load)
Diesel (No load)
JBD (NO load)
Fig. 7. Comparison of smoke with EGR (full load and no load).
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to higher bulk modulus of bio-diesel resulting in a dynamic injection advance apart from
static injection advance provided for optimum efficiency. Excess oxygen (10%) present in
the bio-diesel would have aggravated the situation. At higher loads, NO levels were higher
by 5–8% compared to diesel.
Figs. 11–13 indicate the variation of NO emissions with EGR rate for the entireload range. With 5% EGR, the NO level came down to 1105 ppm for bio-diesel and
900 ppm for diesel, at full load operation. However, for JBD, NO levels were found to
be increasing for load range of 0-40% under 5 and 10% EGR operation. These values
ARTICLE IN PRESS
0
20
40
60
80
100
0 5 10 15 20 25
% EGR
H C ( p p m )
Diesel
JBD
Fig. 9. Comparison of HC with EGR (full load).
0.0
0.5
1.0
1.5
2.0
0 5 10 15 20 25
% EGR
C O ( % V o l )
Diesel
JBD
Fig. 8. Comparison of CO with EGR (full load).
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were found to be higher compared to both diesel and bio-diesel, without EGR. This is
probably due to the increased inlet charge temperature because of HOT EGR [10,11].Dynamic injection advance of bio-diesel fuel can also assist the NO formation. However,
at higher loads NO levels reduced significantly presumably due to the dominant dilution
effect of EGR.
ARTICLE IN PRESS
100
300
500
700
900
1100
1300
1500
0 1 2 3 4
Brake power (kW)
N O ( p p m )
Diesel
JBD
WITHOUT EGR
Fig. 10. Comparison of NO with power (no EGR).
600
800
1000
1200
1400
0 5 10 15
% EGR
N O ( p p m )
Diesel (full load) JBD (full load)
Diesel (80% load) JBD (80% load)
Fig. 11. Variation of NO with EGR (full load and 80%).
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With 10% EGR, NO levels were 885 ppm for diesel and 910 ppm for bio-diesel. Since
many modern diesel vehicles run on EGR, experiments were continued for higher levels of
EGR to reduce NO levels significantly. With 15% EGR, NO levels were found to be
ARTICLE IN PRESS
300
400
500
600
700
800
0 5 10 15
% EGR
N O ( p p m
)
Diesel (60% load) JBD (60% load)
Diesel (40% loaad) JBD (40% load)
Fig. 12. Variation of NO with EGR (60% and 40% load).
0
50
100
150
200
250
300
0 5 10 15
% EGR
N O ( p p m
)
Diesel (20% load) JBD (20% load)
Diese l(No load) JBD (No load)
Fig. 13. Variation of NO with EGR (20% and no load).
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772 ppm for bio-diesel and 780 ppm for diesel at full load. NO emission from bio-diesel at
all loads, for this EGR rate, was lower compared to diesel under no EGR condition also.
Even though 20 and 25% EGR were able to reduce NO by a large amount, reduction in
BTE and large increase in smoke, CO and HC emissions were observed.
3.3. Combustion parameters
3.3.1. Cylinder pressure
Fig. 14 indicates the cylinder pressure data obtained. Cylinder pressure data obtained at
full load, no EGR condition was found to be comparable for diesel and bio-diesel. Peak
pressure was found to be 52.5 bars for diesel and 53.9 bars for bio-diesel under these
conditions. This is indicative of good mixture formation for bio-diesel at higher loads
where temperatures are high. Slightly higher values are probably due to static and dynamic
injection advance.
As shown in Fig. 15 no significant deterioration in cylinder pressure was observed for
JBD under smoke limited, optimized EGR of 15%. In this case, the peak cylinder pressure
was 53 bars.
3.3.2. Rate of heat release and cumulative heat release
A First law analysis was used for heat release calculations [13]. Rate of heat release
(HRR) and cumulative heat release are shown in Figs. 16–19. Slightly higher peak HRR of
51.7 J/deg. was obtained for bio-diesel under full load, no EGR condition. It was found to
be 48.4 J/deg. for diesel under similar conditions. Increase in heat release rate is indicative
of better-premixed combustion and is probably the reason for increased NO emission.With smoke limited EGR of 15%, HRR was found to be 47.7 J/deg. for bio-diesel. Higher
HRR for bio-diesel without EGR is probably due to excess oxygen present in its structure
and a dynamic injection advance apart from static injection advance. Higher boiling point
of bio-diesel can also result in higher HRR [6]. Cumulative heat release were found to be
ARTICLE IN PRESS
0
10
20
30
40
50
60
340 350 360 370 380 390
Crank angle (deg.)
C y l i n d e r P r e s s u r e ( b a r )
Diesel withoutEGR
Bio-diesel withoutEGR
Fig. 14. Comparison of cylinder pressure (full load, no EGR).
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comparable for both fuels without and with optimized EGR of 15% as shown in Figs. 18
and 19.
3.3.3. Rate of pressure rise
Figs. 20 and 21 show the variation of rate of pressure rise with crank angle. Higherrate of pressure rise is indicative of noisy operation of the engine. A value exceeding
8 bar/deg. CA is generally considered as unacceptable. Rate of pressure rise was found
to be comparable for both fuels without EGR and with optimized EGR level of 15%.
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0
10
20
30
40
50
60
340 350 360 370 380 390
Crank angle (deg.)
C y l i n d e r P r e s s u r e ( b a r )
Bio-diesel withoutEGR
Bio-diesel with
15% EGR
Fig. 15. Effect of 15% EGR on cylinder pressure (full load).
-10
0
10
20
30
40
50
60
340 350 360 370
Crank angle (deg.)
H e a t r e l e a s e r a t e ( J / d e g . )
Bio-diesel
without EGR
Diesel withoutEGR
Fig. 16. Comparison of rate of heat release (HRR) (full load, no EGR).
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Peak values at full load were found to be 5.8 bar/deg. for diesel and 6.2 bar/deg. for
JBD. With smoke limited EGR of 15%, the rate of pressure rise decreased slightly to5.7 bar/deg probably due to reduced peak heat release rates. Comparable rate of pressure
rise obtained is indicative of stable and noise free operation of compression ignition
engines with JBD.
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-10
0
10
20
30
40
50
60
340 350 360 370
Crank angle (deg.)
H e a t r e l e a s e r a t e ( J / d e g . )
Bio-dieselwithoutEGR
Bio-dieselwith 15%
EGR
Fig. 17. Effect of 15% EGR on HRR (full load).
-100
0
100
200
300
400
500
600
340 380 420 460 500
Crank angle (deg.)
C u m u l a t i v e h e a t r e l e a s e ( J )
Bio-diesel
without EGR
Diesel without
EGR
Fig. 18. Comparison of cumulative heat release (full load, no EGR).
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3.3.4. Combustion duration
Fig. 22 shows the comparison of combustion duration for both fuels at full load. Valuesobtained were 801 for diesel and 781 for JBD. As mentioned earlier, comparable peak
pressures, efficiency and heat release obtained for bio-diesel were indicative of good
mixture preparation at these conditions. Oxygen content in the bio-diesel is believed to
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-100
100
300
500
700
340 380 420 460 500
Crank angle (deg.)
C u m u
l a t i v e
h e a
t r e
l e a s e
( J )
Bio-diesel
without EGR
Bio-diesel with
15% EGR
Fig. 19. Effect of 15% EGR on cum. heat release (full load).
-2
0
2
4
6
8
300 350 400 450
Crank angle (deg.)
R
a t e o
f p r e s s u r e r i s e
( b a r
/ d e g . )
Diesel without
EGR
Bio-diesel
without EGR
Fig. 20. Comparison of rate of pressure rise (full load, no EGR).
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have enhanced flame velocity that resulted in small reduction in the combustion duration
[14]. However, Combustion duration for JBD with optimized value of 15% EGR,
increased by one degree than no EGR condition, probably due to the presence of exhaust
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-2
0
2
4
6
8
300 350 400 450
Crank angle (deg.)
R a
t e o
f p r e s s u r e r i s e
( b a r
/ d e g .
)
Bio-diesel
without EGR
Bio-diesel with15% EGR
Fig. 21. Effect of 15% EGR on rate of pressure rise (full load).
Diesel
without
EGR JBD
without
EGR
JBD with
15% EGR
70
75
80
85
C o m b
u s t i o n d u r a t i o n ( d e g . )
Fig. 22. Comparison of combustion duration (full load).
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gases in combustion chamber resulting in weak combustion. For JBD, the effect of excess
oxygen content might have been nullified under EGR operation (Table 4).
4. Conclusions
Following are our main conclusions based on the experimental work conducted with
diesel and Jatropha based bio-diesel with and without HOT EGR.
BTE with JBD was found to be comparable with diesel, at all loads with and withoutEGR.
NO emission from JBD was found to be comparatively higher than the diesel fuel.
HOT EGR of 15% effectively reduced NO emission without much adverse effects on
the performance, smoke and other emissions.
Higher EGR of 20 and 25% resulted in inferior performance and heavy smoke.
Because of the increased inlet charge temperature due to HOT EGR and dynamic
injection advance, 5 and 10% EGR levels were not sufficient to reduce NO emission at
all loads for JBD. However, these EGR levels significantly reduced NO at peak loads.
About 15% of EGR, on JBD was found to be effective in reducing NO emission to
values lower than that of diesel, without EGR, at all loads. Full load NO emission from JBD with 15% EGR, was found to be lower than that of
corresponding diesel NO emission.
Inherent oxygen present in the bio-diesel structure is believed to have played a
significant role in compensating for oxygen deficient operation under EGR.
JBD was found to be environmental friendly as far as CO and HC were considered.
Smoke emission from JBD was found to be lower than diesel at peak loads with and
without EGR.
Smoke emissions were found to be higher for JBD in the lower load region because of
slightly higher viscosity, low volatility and probably due to the presence of water
content. Analysis of combustion parameters have also indicated comparable heat release rates
cylinder pressures, cumulative heat release, combustion duration and noise free
operation with and without EGR.
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Table 4
Comparison of full load values for diesel and Jatropha based bio-diesel
Parameter Diesel 0% EGR JBD 0% EGR JBD 15% EGR
BTE (%) 31.5 31 30.1
BSEC (MJ/kW h) 11.4 11.6 11.9
NO (ppm) 1255 1350 780
Smoke opacity (%) 58.8 36.8 58
CO (% Vol) 0.03 0.01 0.03
HC (ppm) 20 10 20
Cylinder pressure (bars) 52.5 53.9 53
Rate of heat release (J/deg. CA) 48.4 51.7 47.7
Rate of pressure rise (bar/deg.) 5.8 6.2 5.7
Combustion duration (deg.) 80 78 79
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Acknowledgements
The authors thank Prof. A Ramesh and Prof. Pramod S Mehta of IC Engines
Laboratory, IIT Madras, India for their enthusiastic support and help during this work.
Authors thank Mr. K. Chandrasekhar, Jatropha consultant, Jatropha Oil SeedDevelopment & Research, Hyderabad, India for the support and help during this work.
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Further reading
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ARTICLE IN PRESSV. Pradeep, R.P. Sharma / Renewable Energy 32 (2007) 1136–11541154