use of hot egr for nox control in a compression

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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)

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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).

http://www.elsevier.com/locate/renene

http://dx.doi.org/10.1016/j.renene.2006.04.017

mailto:[email protected],

mailto:[email protected],

http://dx.doi.org/10.1016/j.renene.2006.04.017

http://www.elsevier.com/locate/renene



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



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

V. Pradeep, R.P. Sharma / Renewable Energy 32 (2007) 1136–11541138



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)

V. Pradeep, R.P. Sharma / Renewable Energy 32 (2007) 1136–1154 1139



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.




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




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)


diesel bio-diesel

WITHOUT EGR

Fig. 3. Comparison of brake thermal efficiency (No EGR).




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)


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.




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).




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).




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%).




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 (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

)


Diese l(No load) JBD (No load)

Fig. 13. Variation of NO with EGR (20% and no load).




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).




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%.

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 )

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).




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.

ARTICLE IN PRESS

-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).




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

ARTICLE IN PRESS

-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).




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

ARTICLE IN PRESS

-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).




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.

ARTICLE IN PRESS

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




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

[15] Wei DP, Spikes HA. Fuel lubricity—Fundamentals and review. Fuels Int 2000;1(1):43–65.

ARTICLE IN PRESSV. Pradeep, R.P. Sharma / Renewable Energy 32 (2007) 1136–11541154

use of hot egr for nox control in a compression

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