Effect of Compression Ratio on Combustion Performance and

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Biofuels and Biomass

Effect of compression ratio on combustion performance and emission characteristic of a DI diesel engine fueled with upgraded biogas-KME-DEE port injection Debabrata Barik, Asit Kumar, and S. Murugan Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01977 • Publication Date (Web): 19 Mar 2018 Downloaded from http://pubs.acs.org on March 20, 2018

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Energy & Fuels

Figures:

First stage purified biogas

Flow meter

Scrubbed biogas

Spray Activated carbon packing

Granite packing Raw biogas

Flow meter Pressure gauge

Scrubber II

Scrubber I

HP Pump

Solution of (water + NaOH)

Figure 1 Schematic representation of scrubber.

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Figure 2 Schematic depiction of the experimental setup. 1 engine, 2 intake manifold, 3 fuel injector, 4 pressure transducer, 5 biogas-air mixing kit, 6 DEE electronic injector, 7 DEE injection pump, 8 DEE storage tank, 9 air box, 10 air flow meter, 11 air intake, 12 biogas intake, 13 biogas filter, 14 biogas flow meter, 15 solenoid valve, 16 low fuel level optical sensor, 17 high fuel level optical sensor, 18 burette, 19 fuel tank, 20 exhaust gas sensor, 21 exhaust manifold, 22 smoke meter, 23 exhaust gas analyzer, 24 crank angle encoder, 25 coupling, 26 speed sensor, 27 dynamometer, 28 resistive load cell, 29 control panel, 30 data acquisition system, 31 computer.


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Cylinder pressure [bar]

90 80

(a)

70 60 50 40 30 20 10 70

Heat release rate [J/oCA]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

60 50

Diesel KME BUBDFM0.9/24.5/DEE6/16.5 BUBDFM0.9/24.5/DEE6/17.5 BUBDFM0.9/24.5/DEE6/18.5

(b)

40 30 20 10 0 -10 -40 -30 -20 -10

0

10

20

Crank angle

30

40

50

60

70

80

[oCA]

Figure 3 Variation of (a) cylinder pressure and (b) heat release rate with the CA at full load.


Energy & Fuels

Ignition delay [oCA]

30 25


(a)

20 15 10 5 0

Combustion duration [oCA]

50 40

(b)

30 20 10 0

Maximum cylinder pressure [bar]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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100 80

(c)

60 40 20 0 0

25

50 Engine load [%]

75

100

Figure 4 Variation of (a) ignition delay, (b) CD, and (c) MCP with the variation in load.


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40

40

(a)

30 25


(b)

35 30 BTE [%]

35

20 15

25 20 15

10

10

5

5 0

0 25

50 75 Engine load [%] 475 400 EGT [oC]

BSEC [MJ/kWh]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

25

100

50 75 Engine load [%]

(c)

325 250 175 100 25 0

25

50

75

100

Engine load [%]

Figure 5 Variation of (a) BSEC, (b) BTE, and (c) EGT with the variation in load.


100

Energy & Fuels

0.05

0.08

(a)

0.04 0.03


HC emission [g/kWh]

CO emission [g/kWh]

0.06

0.02 0.01 0 50 75 Engine load [%]

0.04 0.02

100

25

7


100

30

(c)

Smoke emission [%]

6

(b) 0.06

0 25

NO emission [g/kWh]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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5 4 3 2 1 0

25

(d)

20 15 10 5 0

25

50

75

100

0

Engine load [%]

25


Figure 6 Variation in emissions of (a) CO, (b) HC, (c) NO, and (d) smoke with load.


100

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Energy & Fuels

1

Effect of compression ratio on combustion performance and emission characteristic of a

2

DI diesel engine fueled with upgraded biogas-KME-DEE port injection

3

Debabrata Barik*1, 2, Asit Kumar2, S. Murugan2

4

*1

Department of Mechanical Engineering, Karpagam Academy of Higher Education,

5 6

Coimbatore-641021, India. 2

Department of Mechanical Engineering, National Institute of Technology, Rourkela-

7 8 9

769008, India. *1

E-mail: [email protected], *1Tel: +918895197745

Graphical Abstract

10


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Effect of compression ratio on combustion performance and emission characteristic of a

12

DI diesel engine fueled with upgraded biogas-KME-DEE port injection

13

Debabrata Barik*1, 2, Asit Kumar2, S. Murugan2 *1

14

Department of Mechanical Engineering, Karpagam Academy of Higher Education,

15 16

Coimbatore-641021, India. 2

Department of Mechanical Engineering, National Institute of Technology, Rourkela-769008,

17

India. *1

18

E-mail: [email protected], *1Tel: +918895197745

19

Abstract

20

This work is an attempt to divulge the influence of compression ratio (CR) on the behavior of

21

a 4.4 kW, single cylinder, air-cooled, diesel engine operated on up-graded biogas-Karanja

22

methyl ester (UBG-KME) dual fuel. Earlier, an experiment was conducted by the authors to

23

examine the use of UBG-KME-DEE (diethyl ether) in a dual fuel engine, and the results

24

indicate that, UBG-KME-DEE port injection functioned well and provided improved

25

performance and lower emissions in comparison to that of the raw biogas (RBG) RBG-KME-

26

DEE mode. Nevertheless, the engine produced a lower brake thermal efficiency (BTE)

27

compared to that of diesel operation. Hence, to increase the BTE, experiments were

28

conducted with varied CRs (16.5, 17.5, and 18.5) of the engine, and the KME was injected at

29

a fixed timing of 24.5 oCA bTDC, DEE supply to engine was limited at 6%, and the upgraded

30

biogas supply was made constant at 0.9 kg/h. The test results indicated that UBG-KME-DEE

31

operation with CR 18.5 gave optimum results than those of other CRs. An increase in heat

32

release rate of 60 J/o CA, and shorter ignition delay of 7.8 oCA was observed for UBG-KME-

33

DEE operation with CR 18.5, at full operating load. BTE was increased, and BSEC was

34

decreased by about 7% and 6.8%, respectively, for UBG-KME-DEE operation with CR 18.5

35

in comparison with KME. About 44, 42, and 42.8% decrease in the emissions of CO, HC,

36

and smoke were observed for UBG-KME-DEE at CR 18.5. However, the emission of NO for 2 ACS Paragon Plus Environment

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Energy & Fuels

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UBG-KME-DEE operation with CR 18.5 was 7.6% higher than diesel but, 1.2% lower than

38

KME, at full operating load. The novel findings of this study make possibilities of lowering

39

the NO-smoke emission tradeoff, which is a prime challenge in diesel engines. In addition,

40

the upgraded biogas-KME-DEE operated diesel engines (renewable nature) can substitute the

41

use of diesel and CNG.

42

Keywords: Biogas-biodiesel dual fuel, Compression ratio (CR); Combustion; Performance;

43

Emission.

44

Nomenclature aBDC ASTM

ID IT

Ignition delay, deg. CA Injection timing, oCA

KME LHV LPG MFB N2O NDIR NG

Karanja methyl ester Lower heating value, kJ/kg Liquefied petroleum gas Mass fraction burned Nitrous oxide Non-dispersive infrared Natural gas

NH3

Ammonia

NO

Nitric oxide, g/kWh

CD CH4 CI

After bottom dead centre American Society for Testing and Materials After top dead centre Biogas Brake specific fuel consumption, kg/kWh Before top dead centre Brake thermal efficiency, % Biodiesel upgraded biogas dual fuel mode Biodiesel upgraded biogas dual fuel-KME injection 24.5 oCA bTDC + upgraded biogas 0.9 kg/h and DEE injection of 6% at compression ratio 16.5. Biodiesel upgraded biogas dual fuel-KME injection 24.5 oCA bTDC + upgraded biogas 0.9 kg/h and DEE injection of 6% at compression ratio 17.5. Biodiesel upgraded biogas dual fuel-KME injection 24.5 oCA bTDC + upgraded biogas 0.9 kg/h and DEE injection of 6% at compression ratio 18.5. Cattle dung Methane Compression-ignition

NOx o CA PCCI

CNG CO CO2 CR DAS DEE DFM DI DME EGT

Compressed natural gas Carbon monoxide, g/kWh Carbon dioxide, g/kWh Compression ratio Data acquisition system Diethyl ether Dual fuel mode Direct injection Dimethyl ether Exhaust gas temperature, oC

PM RBG SCK SO2 SOC SOx UBG UHC θ Cp

GHGs

Greenhouse gases

Cv

Oxides of nitrogen Degree crank angle Premixed Charge Compression-Ignition Particulate matter Raw biogas Karanja de-oiled seed cake Sulphur dioxide Start of combustion Oxides of sulphur Upgraded biogas Unburned hydrocarbon Crank angle Heat specific @ constant pressure, kJ/kgK Heat specific @ constant

aTDC BG BSFC bTDC BTE BUBDFM BUBDFM0.9/24.5/ DEE6/16.5

BUBDFM0.9/24.5/ DEE6/CR17.5

BUBDFM0.9/24.5/ DEE6/CR18.5


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H 2S HC HCNG HRR

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γ

Hydrogen sulfide Hydrocarbon emission, g/kWh Hydrogen enriched CNG Heat release rate, J/oCA

volume, kJ/kgK Ratio of the specific heat

45

46

1. Introduction

47

In recent years, the global temperature rise and the diminution of the ozone layer increased

48

continuously owing to increase in greenhouse gases (GHG) emission. The main reasons for

49

the increase in global temperature and diminution of the ozone layer are due to the pollutants

50

exhausted from the power plants, combustion engines, and refrigeration plants [1-5]. The

51

increase in GW cannot be curtailed; rather it can be controlled by reducing pollutants, that

52

originate from combustion devices that uses fossil fuels, and by the use of renewable fuels

53

[6]. The use of biofuel originates from biomass would also reduce harmful pollutants. The

54

promising alternative biomass-based renewable fuels available are biodiesel, bio-ethanol, bio-

55

hydrogen, methanol, biogas and dimethyl ether [7-11]. Gaseous fuels are superior to liquid

56

fuels due to their easy mixability with the air, when used in an internal combustion (IC)

57

engine. Biogas is an emerging alternative fuel due to it's easy and simple production process,

58

environment friendliness and renewable nature [4,5].

59

Biogas is produced by the anaerobic bio-degradation of wastes originates from municipal,

60

industrial and agricultural sectors [4,7,12]. The major feedstocks used for biodiesel

61

production are non-edible seeds. The solid by-product remained in the expeller units after the

62

removal of oil from the oil seeds, is the seed residue. The disposal of these seed residue is a

63

big challenge, because of its toxic nature and the presence of oil (maximum about 2-5%).

64

These seed residue, can neither be directly used in agricultural sector nor can be used to feed

65

cattle [13]. Hence, these seed residue are generally disposed in open lands, and dump yards

66

for its bio-degradation to make bio-fertilizer. But, in a dump yard during degradation process


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Energy & Fuels

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the seed residue generates different anthropogenic gases, due to the action of abundant micro-

68

bacterias. Hence, the efficient utilization of these waste de-oiled seed cakes is evidently

69

necessary, and their use in the production of biogas has proven to be the best method for their

70

effective utilization [13]. Because, anaerobic digestion produces biogas, a clean energy and

71

the digested slurry as an excellent bio-fertilizer.

72

The gas constituents in biogas are CH4, CO2, N2, H2S and traces of O2. These compositions

73

differ based on the type of feedstock used, and the biogas production processes. Biogas

74

contains methane at a higher percentage of about 55-75%. The use of this methane rich

75

biogas in diesel engines reduces the CO2 and other greenhouse gases (GHGs) emission. In

76

addition, biogas has a high octane rating (about 120-135) and high auto-ignition temperature

77

(about 600-670 oC). This property makes it possible to operate the engine at a high

78

compression ratio. The higher octane rating also increases the capacity to resist knock at high

79

compression ratios [14,15]. Apart from this, the CO2 present in biogas acts as an agent to

80

reduce NOx emission, when used in dual fuel engines [16].

81

Bio-diesel offers added advantages as a fuel over diesel. It lowers the emissions of sulphur

82

dioxide (SOx), CO, PM, and HC due to its low sulphur content, presence of low aromatic

83

compounds, and oxygen-containing compounds [17,18]. However, the biogas-biodiesel dual

84

fuel operation has some major issue on the engine combustion and emission behavior. Dual

85

fuel operation of biogas contributed a longer delay period for ignition, and duration of

86

combustion [15-21]. Also, it experiences a higher CO and HC emissions [16-20,22-26], with

87

an upsurge in fuel consumption [17-19,23,27] and drop in brake thermal efficiency [15-

88

18,22-26]. These drawbacks can be eliminated by increasing the compression ratio or by

89

adopting a fuel having an increased cetane index with a greater content of dissolved oxygen

90

[17,27]. For this, an encouraging option is the use of diethyl ether (DEE). Because, it is


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91

renewable in nature, high miscibility with diesel and biodiesel and produced from ethanol at

92

an affordable cost [17,28,29].

93

Researchers investigated the use of biogas, CNG, and LPG as a gaseous fuels in diesel engine

94

with DEE, diesel and biodiesel or its blends as injected liquid fuels [17,27-30]. They

95

observed that, DEE injection near the inlet valve gave a shorter combustion duration and

96

delay period [17,31-33]. An increase in HRR and cylinder pressure were also observed with

97

DEE injection [17,32,34]. Geo et al. [31] and Li et al. [35] documented in their investigation

98

that, with the use of DEE the BTE of the engine was increased and the part load performance

99

of the engine was boosted. A drastic fall in HC, CO, and smoke emissions were observed by

100

Geo et al. [31], and Qi et al. [36] with the use of DEE in dual fuel mode. Barik and Murugan

101

[17], and Rakopoulos et al [37] investigated the application of DEE in diesel engine on dual

102

fuel mode revealed that the NO emission increased marginally. However, Geo et al. [31]

103

reported that a very high quantity of DEE injection (more than 40%) might lead to an

104

abnormal increase in the knock tendency of the engine.

105

In biogas operated dual fuel engine, varying the CR is a key parameter that widely influence

106

the engine operating parameters. Biogas-biodiesel dual operation with varying compression

107

ratio indicates that the ignition delay and combustion duration decreased, but the peak

108

pressure and HRR improved with subsequent raise in CRs [38]. The BTE increased with

109

increase in CR [16,38]. The HC and CO emission reduced drastically by operating the engine

110

at higher compression ratios [38,39]. The NO and CO2 emission increased, but, the smoke

111

emission decreased significantly with higher compression ratios [40]. Dual fuel operation

112

with variation in compression ratio and DEE injection provides good part load effectiveness

113

of the engine with a reduction in exhaust gas temperature (EGT) [7,41]. In addition, it saves a

114

maximum of about 80% pilot fuel consumption, which is compensated by the use of DEE and

115

biogas [17,42]. 6 ACS Paragon Plus Environment

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Energy & Fuels

116

In this investigation, an effort was furnished to operate the diesel engine only with renewable

117

fuels without compromising the engine efficiency and tailpipe emission levels. The raw

118

biogas was obtained from anaerobic decomposition of de-oiled seed cake and cattle dung

119

mixture. Furthermore, the raw biogas was scrubbed to remove the dissolved unwanted gas

120

constituents such as CO2 and H2S, to make it viable for the substitution to CNG and LNG

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operated vehicles. The suitable applicability of the upgraded biogas and its physiochemical

122

effect on the engine operating parameters were deeply analyzed. During the experimental

123

investigation, the CR of the engine was varied in the ranges of 16.5, 17.5, and 18.5. Also, a

124

provision was made to inject DEE through the engine suction manifold, with the intake

125

biogas-air mixture to increase the ignition quality of the biogas. A careful analysis of DEE

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port injection at different CRs has been performed to identify the optimum CR for the best

127

results in combustion, performance, and emission parameters.

128

2. Materials and method

129

2.1 Test fuels

130

In this investigation, diesel, methyl ester of Karanja (KME), and DEE were chosen to use as

131

injected liquid fuels and upgraded biogas was used as a gaseous fuel (inducted through the

132

manifold). The production of biogas and KME has been documented by the authors in the

133

earlier published articles [4,13,18]. The DEE was purchased from a chemical supplier in

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Rourkela, India. The properties of diesel, KME, and DEE are given in Table 1.

135

Table 1 Properties of diesel, KME and DEE.

136

It was observed that, the raw biogas contained about 17.3% CO2 and 0.23% of H2S. In nature,

137

CO2 is a combustion arrester, and H2S is corrosive to metal. Hence, for a long-term utilization

138

of biogas in a diesel engine, it is essential to remove the CO2 and H2S. Hence, the raw biogas

139

was purified using a vertical packed bed two-stage scrubber. The schematic representation of 7 ACS Paragon Plus Environment

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the scrubber is shown in Figure 1. The properties of upgraded biogas (UBG) were compared

141

with those of raw biogas (RBG), and natural gas (NG) given in Table 2. The gas constituents

142

present in the UBG, compared with NG and provided in Table 3.

143

Figure 1 Schematic representation of scrubber.

144 145

Table 2 Properties of UBG in comparison with RBG and NG.

146 147

Table 3 Gas constituents in RBG, UBG and NG.

148 149

2.2 Experimental setup

150

A schematic depiction of the experimental setup is depicted in Figure 2. A 4.4 kW, constant

151

speed, single cylinder, four stroke, air cooled, direct injection (DI) diesel engine, was

152

modified and operated on dual fuel. The test engine specifications are provided in Table 4.

153

The detail description on experimental methodologies, data acquisition techniques, emission

154

measurement device, DEE injection strategies and experimental error analysis were discussed

155

by the authors in the earlier published articles [17,43,44].

156

Figure 2 Schematic depiction of the experimental setup.

157 158

Table 4 Test engine specifications [18,43].

159

2.3 Design of experiment

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Initially, the engine was run with diesel and KME for the collection of baseline data for diesel

161

and KME. Then the configuration of the engine was modified to operate with biogas-KME

162

and DEE port injection, with variation in CR. The CR of the engine was varied from 16.5 to

163

18.5 in steps of 1. During the experiment, the biogas was supplied at a rate of 0.9 kg/h

164

(constant), KME injection timing was kept at 24.5 oCA bTDC, and DEE injection was held

165

constant of 6%, according to the earlier study reported by the authors [4,7,17,18,44-46]. A 8 ACS Paragon Plus Environment

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Energy & Fuels

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similar procedure was followed in all the subsequent test cases as described in formerly

167

published articles. The detailed test conditions for the present study are specified in Table 5.

168

The acronyms and experiment matrix for the investigation are given in Table 6.

169

Table 5 Test conditions.

170

Table 6 Acronyms and test matrix used for the present investigation.

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2.4 Variations of compression ratio

172

In the present study, the CR was varied by varying the clearance volume of the cylinder. This

173

was done by using the gaskets of dissimilar thickness, which were sandwiched between the

174

engine cylinder and cylinder head. The calculation of variation of CR is presented as below:

175

CR =

176

Total volume of cylinder = Swept volume (Vs ) + Clearance volume (Vc )

177

Vs =

178

Where, d = cylinder diameter = 8.75 cm, and L = length of stroke = 11 cm

179

For standard CR,

180

CR =

181

17.5 =

182

s Vc = 16.5 =

183

Gasket volume = 7.21 cm3 (d = 8.75 cm, t = 0.12 cm) [For CR 17.5]

184

Similarly for CR = 18.5

185

s Vc = 17.5 =

Total volume of cylinder (Vs+Vc)

(1)

Clearance volume (Vc)

πd2 4

×L

Vs +Vc Vc Vs Vc

V

(3)

= 17.5

(4)

+1

V

(2)

661.45 16.5

661.45 17.5

(5) = 40.08 cm3

(6)

= 37.79 cm3

(7) 9 ACS Paragon Plus Environment

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186

Clearance volume not including gasket volume + Gasket volume = 37.79 cm3

187

32.87 + Gasket volume = 37.79 cm3

188

Gasket volume necessary for CR 18.5 is 4.92 cm3 and gasket thickness necessary = 0.08 cm3

189

In a similar way gasket volume and thickness requisite for CR 16.5 was also calculated. The

190

volume of the gasket and the thickness corresponding to different CRs are provided in Table

191

7.

192

193

Table 7 Volume of the gasket and the thickness corresponding to different CRs. 3. Results and discussion

194 195

3.1 Analysis of combustion parameters

196 197

Figure 3 (a) depicts the variation of in-cylinder pressure at full load for diesel, KME, and dual

198

fuel operations with respect to change in crank angle. The peak in-cylinder pressure for diesel

199

and KME are found to be 75.7 bar and 71.3 bar, which occur at 7.4 oCA aTDC and 6.8 oCA

200

aTDC respectively, at full load. With an increase in the compression ratio, the peak cylinder

201

pressure increases gradually as expected. This may be attributed to the raise in the cylinder

202

charge temperature at the end of the compression stroke, due to the effect of a higher

203

compression ratio. Moreover, hence, the flames propagate more rapidly [16]. Dual fuel

204

operation with compression ratios of 16.5, 17.5, and 18.5 the peak cylinder pressure is found

205

to be higher by about 76.3 bar, 81 bar, and 84 bar respectively, in comparison to diesel at full

206

load. This higher cylinder pressure at CR 18.5 exhibits a higher temperature to the air-fuel

207

mixture. Hence, the commencement of ignition of fuel is early CA, that results in a shorter

208

delay period and a shorter combustion duration, which is evident from the cylinder pressure-

209

CA diagram. The shorter delay period enhances the combustion of biogas in the premix

210

phase of combustion and may increase the BTE of the engine. 10 ACS Paragon Plus Environment

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Energy & Fuels

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Based on the law of thermodynamics, the HRR at each crank angle for diesel and KME

212

operation were determined from the subsequent correlation [23].

213

dU dt

+ Ẇ = Q̇

(8)

214

where Ẇ is work done by the system (J). Q̇ is net heat release during combustion (J) and Q̇ LW

215

is the loss of heat throgh the cylinder cashing and wall (J). Taking into consideration unit

216

mass and ideal gas condition, Eq. (8) can be represented as:

217

C dV C dP Q̇ = [ v + 1] P + v V +Q̇LW

218

Replacing (t) with (θ), and C = γ

219

γ dV 1 dP Q̇ = γ−1 P dθ + γ−1 V dθ+Q̇LW

220

Where

221

the ratio of the specific heats, Cp /Cv , V is the cylinder volume in m3, and Q̇ LW is the unused

222

heat loss through the cylinder wall. A constant value for γ=1.35 is considered in this study,

223

for analyzing the heat release rate.

224

The HRR in the dual fuel operation can be articulated as follows;

225

f f HRR = m ∙LHV +σ(1−m )∙[(LHV

226

= LHVf

227

where mf is the fraction of fuel in the fuel mixture, and LHV is the lower heating value of the

228

fuel (kJ/kg).

229

The variation of HRR with CA for diesel, KME, and dual fuel operations with different CRs

230

are depicted in Figure 3 (b). Diesel and KME give HRR of 56.5 J/oCA, and 52.4 J/oCA. In the

231

dual fuel operation, with increase in CR the HRR increases. The dual fuel operation with CRs

232

of 16.5, 17.5, and 18.5 gives HRR of 55.4 J/oCA, 58.4 J/oCA, and 60 J/oCA. This increase in

233

HRR in the dual fuel operation, with the increase in CR is due to the boost in the combustion

R

dt

R

(9)

dt

Cp v

(10)

is considered as cylinder pressure,

is considered as crank angle, γ is considered as

m ∙LHV

f

f

f

(11)

CH4 ]

m ∙LHVf

(12)

f+UBG


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

234

efficiency of the biogas. This is because, as the CR increases, the clearance volume

235

decreases, which in turn increases the temperature and pressure of the charge at the end of the

236

compression stroke. The increased combustion temperature results in better combustion of

237

the fuel and increases the HRR [47,48].

238

Figure 3 Variation of (a) cylinder pressure and (b) heat release rate with the CA at full load.

239

Figure 4 (a) illustrates the variation of ignition delay with the variation in load. The ignition

240

delay for diesel is found to be longer than that of other fuels, irrespective of the load on the

241

engine. The shorter ignition delay for the dual fuel operation than that of diesel may be due to

242

the injection of DEE, which improves the ignition. In the dual fuel operation with the

243

increase in compression ratio, the ignition delay decreases throughout the load spectrum. This

244

is due to the increased pre-ignition reaction of the pilot fuel, and that is believed to affect the

245

ignition of the biogas [42]. The ignition delay for diesel and KME are about 11.5 oCA and

246

10.5 oCA, at full load. Dual fuel operation with the compression ratio of 16.5, 17.5, and 18.5

247

the ignition delay is shorter by about 10.4 oCA, 9 oCA, and 7.8 oCA respectively, at full load.

248

The variation of the combustion duration (CD) with load is depicted in Figure 4 (b). KME

249

operation gives a higher CD than that of diesel. This is due to the poor spray formation by

250

KME due to its higher viscosity. With the increase in load the CD increases regardless of the

251

fuels used. This is due to the intake of more quantity of fuel at comparatively higher loads.

252

Dual fuel operation with the increase in CRs the CD increases. This may be owing to the

253

shorter ignition delay and early start of the burning of the pilot fuel at high CRs, which

254

enhances the flaming speed of biogas in the premixed phase of incineration [49]. The dual

255

fuel operation with CRs of 16.5, 17.5, and 18.5 offers a dwindle in CD of about 36.7oCA,

256

34.6 oCA and 32.5 oCA respectively, than that of diesel at full load.


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Energy & Fuels

257

The variation of maximum cylinder pressure (MCP) with load is depicted in Figure 4 (c). The

258

cylinder pressure increases with the increase in the load, as expected. The MCP for diesel and

259

KME are about 75.7 bar and 71.3 bar at full load, respectively. It is noticed that with the

260

increase in CR the MCP increases. This is due to the increased pre-ignition reaction of the

261

pilot fuel, and that is believed to affect the ignition of the biogas rapidly, and increases the

262

cylinder pressure [50]. Dual fuel operation of BUBDFM0.9/24.5/DEE6/18.5 gives a MCP of

263

84 bar, than that of other dual fuel operations at full load.

264

Figure 4 Variation of (a) ignition delay, (b) CD, and (c) MCP with the variation in load.

265

3.2 Performance analysis

266

The variations of the brake specific energy consumption (BSEC) with load, for the test fuels,

267

are depicted in Figure 5 (a). The BSEC decreases with increase in load for all the test fuels in

268

both single and dual fuel operations. This is as a result of the increased cylinder temperature

269

at high operating loads compared to low loads. A higher BSEC is noticed for

270

BUBDFM0.9/24.5/DEE6/16.5 at part operation. This is due to the lower CR, which gives

271

lower cylinder temperature and prevents complete burning of biogas [4]. Another possible

272

reason can add to this is slow premix combustion during the initial stages of combustion at

273

low load gives higher BSEC. The difference in BSEC between diesel, KME and dual fuel

274

operations

275

BUBDFM0.9/24.5/DEE6/18.5 are not significantly different at high operating loads.

276

Because, at high load the dual fuel operation has similar fuel-energy conversion efficiency to

277

that of diesel and KME [51]. It is also observed that, dual fuel operation, with the increase in

278

compression ratio the BSEC decreases. This is due to the improved combustion and reduced

279

CD of the fuel at a high CR. The dual duel operations with CR of 16.5, 17.5, and 18.5 gives

280

higher BSEC of 13.4, 4.1, and 0.8% in comparison with diesel, at full load respectively.

of

BUBDFM0.9/24.5/DEE6/16.5,

BUBDFM0.9/24.5/DEE6/17.5,


and

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

281

The variation of brake thermal efficiency (BTE) with load is depicted in Figure 5 (b). Diesel

282

produces the highest BTE throughout the load spectrum irrespective of the test fuels used in

283

the present investigation. This is by reason of the higher heating value of diesel. Where as

284

KME produces BTE of about 28%, which is about 2.3% lower in comparison to diesel. With

285

the increase in load BTE for the test fuels increases. This is as a result of the increased

286

cylinder temperature at respective higher load operations. In dual fuel operation, the BTE

287

increases with the increase in compression ratio as expected. This is due to the increase in the

288

combustion efficiency of the biogas. Also the quick start of ignition of pilot fuel due to high

289

compression ratio, gives a better combustion phasing to biogas, and boosts the combustion

290

rate [16].

291

The variation of EGT with the load is depicted in Figure 5 (c). It can be observed from the

292

figure that, at full load KME exhibit the highest EGT than that of the other fuels tested in the

293

investigation. The presence of oxygen in the ester molecules enhances the combustion

294

process and results in a higher EGT. The dual fuel operation with compression ratio of 16.5

295

the EGT decreases. This may be due to the absorption of heat by the biogas to occur auto

296

ignition at lower compression ratio, and decreases the adiabatic flame temperature. But, with

297

the increase in compression ratio the EGT increases slightly. This is due to the high

298

temperature combustion of the air-biogas mixture at higher compression ratio of the engine

299

[52,53]. BUBDFM0.9/24.5/DEE6/18.5 gives exhaust gas temperature of 354.7 oC at full load,

300

which is about 2% lower than that of the KME.

301

Figure 5 Variation of (a) BSEC, (b) BTE, and (c) EGT with the variation in load.

302

3.3 Emission analysis

303

The CO emission with load is depicted in Figure 6 (a). KME gives a lower CO mission than

304

that of diesel, and dual fuel operations in all operating load conditions. This is owing to the 14 ACS Paragon Plus Environment

Page 20 of 27

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Energy & Fuels

305

presence of oxygen in KME, that contributes a comprehensive oxidation. Dual fuel operation

306

with the increase in compression ratio the CO emission decreases. This is as a result of the

307

high temperature combustion of the fuel because of the increase in compression ratio. High

308

compression ratio gives high temperature and at high temperature operation, the start of

309

ignition of biogas improves, and decreases the ignition delay period, and countenances more

310

time for oxidation of the charge, and the CO emission reduces [16]. A reduction in CO

311

emission of 44% and 22% is observed for BUBDFM0.9/24.5/DEE6/18.5 in comparison with

312

diesel and KME, at full load respectively.

313

The variation of HC emission with load is depicted in Figure 6 (b). KME gives a lower HC

314

emission than that of diesel and dual fuel operations, throughout the load spectrum. This is

315

attributed to the presence of oxygen in the KME that provides environment or complete

316

combustion. In the dual fuel operation, with the increase in compression ratio the HC

317

emission reduces. Because, high compression ratio results more growth of temperature during

318

the compression stroke, which results in better combustion. This leads to a low emission of

319

HC

320

BUBDFM0.9/24.5/DEE6/18.5, than that of diesel at full load.

321

Figure 6 (c) portrays the variation of NO emission with load. KME produces maximum NO

322

in comparison to other fuels. This is as a result of the higher percentage of oxygen in KME.

323

The emission of NO for the dual fuel operation is significantly lower than that of KME

324

throughout the load spectrum. This may be owing to the drop in volumetric efficiency by the

325

introduction of biogas through the intake manifold. The dual fuel operation with the increase

326

in compression ratio gives an increase in NO emission throughout the load spectrum. This is

327

by reason of the increase in the combustion temperature due to the higher compression ratio,

328

which gives a faster burning speed and a higher thermal NO [54]. The NO emission for

emission

[49].

A

drop

in

HC

emission


of

42%

is

observed

for

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 27

329

BUBDFM0.9/24.5/DEE6/18.5 is about 7.6% higher than that diesel. But it is 1.2% lower than

330

KME, at full load.

331

The concentration of smoke emission with load is depicted in Figure 6 (d). The smoke

332

emission increases with the increase in load irrespective of the fuels used. This is as a result

333

of the decrease in the excess air ratio and increase in diesel consumption at relatively high

334

loads, which gives a lower oxidation of soot particles. KME produces a lower density of

335

smoke than that of diesel. This is caused by the lower stoichiometric air requirement for

336

KME, because of existing oxygen in it. The dual fuel operation with rise in compression ratio

337

gives declined trend of smoke intensity irrespective of the load on the engine. This is

338

because, clearance volume decreases as the compression ratio increases, which increases the

339

temperature and pressure of the air fuel mixture at the end of the compression stroke. The

340

increase in combustion temperature results in healthier combustion of the fuel and the smoke

341

emission decreases [42]. BUBDFM0.9/24.5/DEE6/18.5 contributes a reduction in smoke

342

emission of 42.8% than that of diesel, at full load.

343

Figure 6 Variation in emissions of (a) CO, (b) HC, (c) NO, and (d) smoke with load.

344

4. Conclusions

345

The experimental results of the upgraded biogas dual fuel operation with the KME, and 6%

346

of DEE injection, with the variation in CR were analyzed. The summary of the results

347

indicated that BUBDFM0.9/24.5/DEE6/18.5 provided optimum results of the engine

348

operation. A shorter ignition delay of 7.8 oCA, and a higher heat release rate of 60 J/oCA was

349

observed

350

BUBDFM0.9/24.5/DEE6/18.5 was higher by about 7.1% than that of KME. But, it was 0.6%

351

lower than that of diesel, at full

352

BUBDFM0.9/24.5/DEE6/18.5 was observed to be higher by about 0.8% than that of diesel at

for

BUBDFM0.9/24.5/DEE6/18.5

at

full

load.

operating load condition.


The

BTE

for

The BSEC for

Page 23 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

353

full load, but it was 6.8% lower than KME at full load. BUBDFM0.9/24.5/DEE6/18.5

354

contributed a reduction in CO, HC and smoke emissions by about 44, 42, and 42.8%,

355

respectively

356

BUBDFM0.9/24.5/DEE6/18.5 was higher by about 7.6% that of diesel, but it was lower by

357

about 1.2% than that of KME, at full load.

358

Based on the results obtained in this investigation, it concludes that the engine performance

359

and emission parameters are improved and is a function of CR. The injection of DEE into

360

biogas operated dual fuel engine drastically reduced the ignition delay and the NO-smoke

361

tradeoff. The use of this technique will overcome the problems associated with LPG, LNG,

362

and CNG crises. In addition, the upgraded biogas can be directly used in CNG and LNG

363

operated automotive engines without any major engine modifications.

364

References

365 366

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than

that

of

diesel,

at

full

load.


The

emission

of

NO

for

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