alcohol blends having the same oxygen concentration

Accepted Manuscript Study of combustion, performance and emissions of diesel engine fueled with diesel/biodiesel/alcohol blends having the same oxygen concentration

Meisam Ahmadi Ghadikolaei, Chun Shun Cheung, Ka-Fu Yung PII:

S0360-5442(18)31009-0

DOI:

10.1016/j.energy.2018.05.164

Reference:

EGY 12999

To appear in:

Energy

Received Date:

27 February 2018

Accepted Date:

24 May 2018

Please cite this article as: Meisam Ahmadi Ghadikolaei, Chun Shun Cheung, Ka-Fu Yung, Study of combustion, performance and emissions of diesel engine fueled with diesel/biodiesel/alcohol blends having the same oxygen concentration, Energy (2018), doi: 10.1016/j.energy.2018.05.164

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ACCEPTED MANUSCRIPT

1 2

Study of combustion, performance and emissions of diesel engine fueled with diesel/biodiesel/alcohol blends having the same oxygen concentration

3

Meisam Ahmadi Ghadikolaeia, Chun Shun Cheunga, Ka-Fu Yungb

4 5 6

aDepartment bDepartment

of Mechanical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong

7

Abstract

8

This experimental study is conducted to investigate the combustion, performance and emissions of a

9

diesel engine fueled with different alternative fuels under five engine loads and at an engine speed of

10

1800 rpm. Seven fuels, including diesel (D), waste cooking oil biodiesel (B), methanol (M), ethanol

11

(E), 2-propanol (Pr), n-butanol (Bu) and n-pentanol (Pe)) were used to produce six blended fuels,

12

labelled as DB, DBM, DBE, DBPr, DBBu and DBPe. Each blended fuel has the same oxygen content

13

of 5.0% and very close carbon and hydrogen contents and LHV.

14

According to the average results of five loads, the blended fuels in general cause (a) increases in peak

15

HRR (except DB), ignition delay (except DB), COVIMEP (except DBM), COV Max(dP/dθ) (except DB and

16

DBM) and BSFC; (b) slight decreases in duration of combustion (except DB); and (c) similar peak in-

17

cylinder pressure and BTE (except DBM and DBBu) compared to diesel fuel. Moreover, all the

18

blended fuels lead to reductions in CO2 (except DB), CO, HC, NOX (except DB), PM, total number

19

concentration (except DBPr) and geometric mean diameter, compared to diesel fuel. Overall, DBM

20

shows the highest BTE, the lowest BSFC, and the lowest CO2, CO, HC, PM, NOX (after DBPr),

21

COVIMEP and COV

22

blended fuels.

Max(dP/dθ)

(after DB), while DB has the lowest influence, among all the tested

23 24

Keywords: Alternative fuels; Diesel engine; Emissions; Higher alcohols; Lower alcohols; Waste

25

cooking oil biodiesel

26 27 28 29

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1. Introduction

31

It was reported in Outlook for Energy [1], about 25% more affordable and reliable energy for homes,

32

transportation, business and industry will be needed from 2014 to 2040 due to increase in the world's

33

population from about 7.2 billion to 9 billion by 2040. It is expected that fossil oil will still be

34

predominant in 2040 for the transportation sector, while the demand for diesel engines in the

35

transportation sector will increase from 35% in 2014 to about 40% by 2040. This will cause a

36

challenge to the availability of diesel fuel and increase in emissions from diesel engines. In addition,

37

the cleaner production and sustainability of energy, which are concerned about the operations and

38

maximization of waste reduction, reusing and recycling in the environments [2], has drawn increasing

39

attention for environmental protection. It can be seen from the literature that several techniques have

40

been applied to solve these problems like the use of emission catalysts, different fueling systems,

41

modern combustion technologies or alternative fuels. In recent years and even in the future, the use of

42

alternative fuels (biofuels) in diesel engines seems to be attractive and promising because the biofuels

43

can be produced from renewable and sustainable sources. Among all the alternative fuels, biodiesel,

44

lower and higher alcohols or their blends with diesel fuel have been utilized in many studies to

45

investigate their effects on the combustion, performance and emissions characteristics of different

46

diesel engines.

47

In most of the former investigations, the effects of using different percentage of an alternative fuel,

48

and hence different percentage of oxygen, in the blended fuels were studied. However, very few

49

studies were conducted using blended fuels with the same oxygen content. For example, Wang et al.

50

[3] used blends of diesel with biodiesel, ethanol or diglyme with the same oxygen content for

51

comparison; but the carbon, hydrogen and lower heating values of their blended fuels were almost

52

different. Their experiments were conducted with five diesel–biodiesel blends and diesel–diglyme

53

blends with oxygen concentration of 2, 4, 6, 8 and 10%, and four diesel–ethanol blends with oxygen

54

concentration of 2, 4, 6 and 8%, under five engine loads and at the engine speed of 1800 rpm. It was

55

found that different blended fuels having the same oxygen content, have different effect on the

56

emissions, especially on PM emission.

2

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On the other hand, a few studies have been performed to compare the influence of different alternative

58

fuels, each having the same blending ratio, on the performance and emissions of diesel engines. For

59

instance, Kumar et al. [4] examined the impact of higher alcohol/diesel blends on the combustion and

60

exhaust emissions of a single-cylinder, naturally-aspirated, constant-speed (1500 rpm), four-stroke,

61

direct-injection (DI) diesel engine under four loads (1.3, 2.6, 5 and 5.3 BMEP). The tests were

62

performed with pure ultra-low sulfur diesel (ULSD) and four blended fuels (30% by volume of iso-

63

butanol, n-pentanol, n-hexanol or n-octanol blended with ULSD). The results revealed that the iso-

64

butanol blend had the longest ignition delay (ID), highest peaks of pressure and heat release rate

65

(HRR) and the shortest duration of combustion (DOC) in comparison with the other tested fuels. In

66

regard to the emissions, it was observed that iso-butanol blend had the lowest smoke opacity, NOX

67

and CO emissions and highest HC emission compared to the other tested fuels. The lowest HC value

68

was recorded for n-octanol blend.

69

In addition, Yilmaz et al. [5], examined the effect of quaternary blends of diesel (D), biodiesel (B),

70

higher alcohols (propanol (Pro) and pentanol (Pen)) and vegetable oil (VO) on fuel properties and

71

engine performance and emissions on a four-cylinder diesel engine generator at different engine loads

72

with constant engine speed of 1800 rpm. Four blended fuels of DB (D50-B50), DBVOPro (D40-B40-

73

VO10-Pro10), DBVOPen (D40-B40-VO10-Pen10) by volume percentages were used. It was found

74

that DBVOPro had higher BSFC and lower NOX compared to DB. It was also observed that the

75

addition of both higher alcohols into the DB caused increase in CO and HC emissions.

76

In another study, Atmanli [6] analyzed the basic fuel properties, engine performance and exhaust

77

emissions of a diesel engines fueled with diesel (D), biodiesel (B), propanol (Pr), n-butanol (Bu) and

78

1-pentanol (Pe). Experiments were carried out on a four-cylinder indirect injection (IDI) diesel engine

79

generator under a constant engine speed of 1800 rpm with four engine loads. Six fuels and blends

80

were used, including pure diesel, pure biodiesel, D50B50, D40B40Pr20, D40B40Bu20 and

81

D40B40Pe20 (by volume percentage). In respect of basic fuel properties, it was found that addition of

82

all the alcohols into the blends of diesel–biodiesel caused an improvement in cloud point and cold

83

filter plugging point and slight decreases in cetane number (CN), lower heating value (LHV), density,

84

kinematic viscosity and flash point. In regard to the engine performance, the results showed that the 3

ACCEPTED MANUSCRIPT 85

Pr blend had the highest brake specific fuel consumption (BSFC); while the Bu blend had the highest

86

brake thermal efficiency (BTE). For emissions, all the ternary blends caused an increase in CO (Pe

87

blend had the highest CO emission), while HC emissions were reduced significantly with the Bu

88

blend and the Pe blend but increased with the Pr blend in comparison with D50B50. It was also found

89

that all the ternary blends could lead to reduction of NOX, with the Pe blend having the lowest NOX

90

emissions.

91

Yilmaz et al. [7] also investigated the influence of some higher alcohols on the performance and

92

exhaust emissions of a four cylinder IDI diesel engine generator under different loads and at an engine

93

speed of 1800 rpm. 10% (by volume percentage) of propanol, n-butanol, and 1-pentanol was added

94

separately into the waste oil methyl ester (B100) to form the blended fuels, B90Pr10, B90Bu10, and

95

B90Pe10, respectively. It was observed that all the blended fuels led to increases in BSFC and exhaust

96

gas temperature in comparison with B100. However, the BTEs of B90Pr10 and B90Bu10 were

97

reduced, while B90Pe10 had a slight rise in BTE compared to B100. In regard to emissions, all the

98

blended fuels had lower CO and NOX emissions compared to B100; while B90Pe10 had the lowest

99

HC emissions among all the tested fuels.

100

Imdadul et al. [8] analyzed the influence of biodiesel (B), n-butanol (Bu) and pentanol (Pe) on the

101

performance and regulated emissions of a single cylinder, four-stroke, DI diesel engine under

102

different engine speeds. Seven fuels were tested, including diesel (D), D85B15, D70B15Bu15,

103

D70B15Pe15, D80B20, D60B20Bu20 and D60B20Pe20 (by volume percentage). It was found that

104

the blended fuels containing an alcohol improved the brake power and BSFC and reduced the CO and

105

HC emissions in comparison with those of diesel fuel, while, the effect of pentanol was better than

106

that of n-butanol on the engine performance and emissions.

107

According to the aforementioned literature review, most of the former studies are focused on (a)

108

effect of increasing alternative fuel concentrations; (b) effect of using the same percentage of different

109

alternative fuels and (c) effect of different alternative fuels blended to the same oxygen concentrations

110

(but different fuel C, H and LHV), using biodiesel or a few alcohols. All of those studies, according to

111

the authors’ knowledge, have been performed with blended fuels having different percentages of

112

carbon (C), hydrogen (H) and oxygen (O) contents and different lower heating values (LHV). The 4

ACCEPTED MANUSCRIPT 113

differences in C, H, O and LHV do not allow the establishment of similar conditions for comparing

114

various fuels in regard to the engine performance and emissions. Engine performance and emissions

115

are affected by many factors, which include the C/H ratio, oxygen content and lower heating value of

116

the fuel. It is of interest to know how the blended fuels would affect engine performance and

117

emissions if such parameters are fixed. In addition, there is lack of investigation on comparing the

118

effects of lower alcohols (methanol and ethanol) with higher alcohols (butanol, pentanol and

119

propanol) on the same engine under the same operating conditions. Therefore, the present research

120

aims at covering the above knowledge gaps by conducting experiments on a diesel engine with six

121

blended fuels which have almost the same percentages of C and H and the same percentage of O in

122

the resultant composition and hence they also have almost the same lower heating values as shown in

123

Table 3, involving the use of biodiesel produced from waste cooking oil and both lower and higher

124

alcohols. The use of constant or almost constant O, C, H and LHV for all the blended fuels proposed

125

in this study provides a unique and similar condition for comparing the effects of different blended

126

fuels, allowing the effects of these parameters be neglected and the influence of other fuel properties

127

be identified.

128

2. Experimental setup and procedure

129

The tested engine was a 4-cylinder direct injection (DI), water-cooled diesel engine. Similar engines

130

are still used in Hong Kong and China for the small trucks. An eddy-current dynamometer and Ono

131

Sokki heavy diesel engine test system were employed to control the engine speed and torque. The

132

specifications of the engine and schematic diagram of the experimental setup are shown in Table 1

133

and Fig. 1, respectively.

134

A heated flame ionization detector (300 HFID, CAI Inc.) was used to record HC, NOX was measured

135

by using a heated chemiluminescent analyzer (600 HCLD, CAI Inc.) and CO and CO2 were analyzed

136

through the non-dispersive infrared analyzers (300 NDIR, CAI Inc.). All the sampled gaseous

137

emissions were directly taken from the engine exhaust line. Before each test, the gas analyzers were

138

calibrated with zero and standard (span) gases.

139

In regard to the measurement of particulate emissions, the exhaust gas was sampled from the exhaust

140

manifold through an insulated and heated sampling line to prevent the condensation of volatile 5

ACCEPTED MANUSCRIPT 141

substances and deposition of solid particles on the interior pipe wall. A two-stage mini-diluter (Dekati

142

Ltd, Finland) was employed to dilute the exhaust gas. The first stage of diluter was heated by use of

143

an electrical heater while the second stage was not heated. The actual dilution ratio (DR) in the

144

present study was calculated according to the following equation.

145

𝐷𝑅 =

146

where [CO2] exhaust is the CO2 concentration of the exhaust gas before dilution, [CO2] background is

147

the CO2 concentration in the background and [CO2] diluted is the CO2 concentration after dilution. In

148

this research, depending on the engine operating conditions, the first-stage dilution ratio varied from

149

5.3 to 5.8 and the second-stage dilution ratio varied from 44.4 to 57.5. The first-stage output from the

150

dilutor was connected to a tapered element oscillating microbalance (TEOM 1105, Rupprecht &

151

Patashnick Co., Inc.) for measuring the particulate mass concentration while the second-stage diluted

152

exhaust gas with a sampling rate of 3 L/min was sent to a scanning mobility particle sizer (SMPS, TSI

153

Inc.) for recording the particle size distribution and number concentration with a size range of 15-750

154

nm. The SMPS consists of a TSI 3022 condensation particle counter (CPC) and a TSI 3071A

155

differential mobility analyzer (DMA). For particle number concentration and size distribution, four

156

measurements were recorded at each operating condition and the average of the four measurements is

157

presented. In addition, all gaseous emissions and particulate mass concentration were recorded over a

158

period of five minutes to obtain the average values over the five-minute period. The fuel consumption

159

was measured with an electronic balance with a precision of 0.1g. The exhaust gas temperature was

160

measured with a K-type thermocouple.

161

In the present study, the experiments were conducted at a constant engine speed of 1800 rpm with five

162

engine loads of 10, 30, 50, 70 and 90% of the full engine torque, corresponding to 28.5, 85.5, 142.5,

163

199.5 and 256.5 Nm. The engine was warmed up for several minutes before starting of measurements.

164

Then, at each operating condition, the engine was allowed to run for a few minutes until the exhaust

165

gas temperature, the cooling water temperature, the lubricating oil temperature as well as the CO2

166

concentration reached the steady-state conditions and data were recorded subsequently. Seven fuels

167

were used in present research, which include ULSD (ultra-low-sulfur diesel) (D), waste cooking oil

168

biodiesel (B), lower alcohols (methanol (M) and ethanol (E)) and higher alcohols (2-propanol (Pr), n-

[𝐶𝑂2]𝑒𝑥ℎ𝑎𝑢𝑠𝑡 ‒ [𝐶𝑂2]𝑏𝑎𝑐𝑘𝑔𝑟𝑜𝑢𝑛𝑑 [𝐶𝑂2]𝑑𝑖𝑙𝑢𝑡𝑒𝑑 ‒ [𝐶𝑂2]𝑏𝑎𝑐𝑘𝑔𝑟𝑜𝑢𝑛𝑑

(1)

6

ACCEPTED MANUSCRIPT 169

butanol (Bu) and n-pentanol (Pe)), were blended with various blending mass percentages to obtain six

170

blended fuels with constant fuel oxygen, almost constant carbon and hydrogen contents and almost

171

constant lower heating values. The six blended fuels are designated as DB (D53.7 B46.3), DBM

172

(D82.74 B9.26 M8), DBE (D79.25 B9.26 E11.49), DBPr (D75.71 B9.26 Pr15.03), DBBu (D72.22

173

B9.26 Bu18.52) and DBPe (D68.76 B9.26 Pe21.98). In each blended fuel, the fuel oxygen content

174

was maintained at 5.0%. When an alcohol was added, the biodiesel was kept at 9.26% to provide 1%

175

oxygen while the content of diesel fuel was reduced and the alcohol was added to contribute 4% of

176

the oxygen. Since methanol has the highest oxygen content, hence DBM contains only 8% methanol,

177

comparing with 21.98% of pentanol for DBPe. It can be seen from Table 3 that the carbon contents

178

vary from 82.2% to 81.7%, the hydrogen contents differ from 12.8% to 13.3% and the lower heating

179

values change from 40.2 MJ/kg to 40.3 MJ/kg for the blended fuels. Fuel samples were prepared and

180

observed for three weeks to understand the stability of the six blended fuels. For all the blended fuels,

181

no phase separation was observed during the experiments. Except DBM, the other blended fuels were

182

stable for three weeks. For the DBM sample, phase separation occurred after approximately 10 hours.

183

The use of surfactants (emulsifiers), co-solvents [9] or higher percentage of biodiesel can solve the

184

miscibility problem of methanol in DBM fuel. Since all the alcohol blended fuels (irrespective of

185

DBM) were stable with 9.26% of biodiesel (using low percentage of biodiesel to better sensing of

186

alcohols’ effects on the parameters) without using any chemical surfactants, the methanol suffered a

187

phase separation in DBM fuel; while the chemical surfactants (or higher percentage of biodiesel)

188

could not be utilized for DBM fuel due to fixing of a same condition compared to the other blended

189

fuels. Therefore, since no phase separation occurred during the experiments for the DBM case, the

190

results pertaining to DBM are included in this study for comparison.

191

All the alcohols used in this study had high purities of over 99.8%. In addition, the biodiesel was

192

produced by a local company (Dynamic Progress) using waste cooking oils collected from the

193

restaurants and the biodiesel qualities were in compliance with EN14214 standard. The compositions

194

of the waste cooking oil biodiesel are shown in Table 2 and the properties of the tested fuels are

195

presented in Table 3.

7

ACCEPTED MANUSCRIPT 196

The steady state experiments of this study were repeated two times for ensuring that the data were

197

repeatable within the experimental uncertainties of the measurements. The experimental uncertainties

198

at 95% confidence level in the measurements were calculated based on the methods proposed by

199

Moffat [10] and the results are presented as the error bars in the Figures. The experimental results

200

were compared using the two-tailed Student’s T-test to verify if they are significantly different from

201

each other at 95% significance level.

202

203

Table 1: Specifications of tested engine Model Isuzu 4HF1 Engine type In-line 4-cylinder DI Combustion chamber shape Omega Maximum power 88 kW/ 3200 rpm Maximum torque 285 Nm/ 1800 rpm Bore × stroke 112 mm × 110 mm Displacement 4334/cc Compression ratio 19.0: 1 Fuel injection timing 8° BTDC Injection pump type Bosch in-line type Injection nozzle Hole type (with 5 orifices) Table 2: Compositions of fatty acids in waste cooking oil biodiesel (from the same laboratory [11]) Fatty acid methyl esters Weight (%) C13 Methyl tridecanoate C14 Methyl myristate Cl6 Methyl palmitate Cl6:1 Methyl palmitoleate Cl8 Methyl stearate Cl8:1 Methyl oleate Cl8:2 Methyl linoleate Cl8:3 Methyl linolenate C24 Methyl lignocerate

204 205

Tridecanoic acid Myristic acid Palmitic acid Palmitoleic acid Stearic acid Oleic acid Linoleic Linolenic acid Lignoceric acid

1.12 1.11 11.46 0.6 4.22 35.22 39.73 6.24 0.3

Table 3: Properties of the tested fuels

Properties

Cetane number

Density (kg/m3) at 20 °C

Viscosity (mPa S) at 40 °C

Heat of evaporation (kj/kg)

Boiling point (°C)c

Flash point (°C)

52

Lower heating value (MJ/kg) 42.5

ULSD [12 a]

840

2.4

270

Biodiesel [12 a]

51

37.5

871

4.6

300

180360 -

Methanol [13 a]

5

19.58

791.3

0.58

1162.64

64.7

Ethanol [12 a]

8

26.83

789.4

1.13

918.42

30.63

803.7b

1.74

Propanol [14]

12

Hydrogen content (% mass)

78

Carbon content (% mass) 86.6

13.4

Oxygen content (% mass) 0

Sulfur content (% mass) <10

210 12

77.1

12.1

10.8

<10

37.48

12.58

50

0

78.3

17

52.14

13

34.8

0

727.88

97.1

11.7

59.96

13.42

26.62

-

2.22 2.89

581.4

117.5

35

64.82

13.6

21.6

-

308.05

137.9

49

68.13

13.72

18.15

-

Butanol [14]

17

33.09

809.7 b

Pentanol [14]

18.2

34.65

814.8 b

40.2

854.4

82.2

12.8

5.0

<10

40.2

839.0

81.8

13.2

5.0

<9.2

DB (D53.7 B46.3) DBM (D82.74 B9.26 M8)

8

ACCEPTED MANUSCRIPT DBE (D79.25 40.2 837.1 B9.26 E11.49) DBPr (D75.71 40.3 837.4 B9.26 Pr15.03) DBBu (D72.22 40.3 837.3 B9.26 Bu18.52) DBPe (D68.76 40.3 837.3 B9.26 Pe21.98) 206 a= from the same laboratory; b= at 15°C.

207 208

81.8

13.2

5.0

<8.851

81.7

13.3

5.0

<8.497

81.7

13.3

5.0

<8.148

81.7

13.3

5.0

<7.802

Fig. 1. Schematic diagram of the experimental setup.

209

3. Results and discussion

210

3.1. Engine combustion

211

The following parameters were selected to analyze the effect of alternative fuels on the engine

212

combustion characteristics and performance: in-cylinder pressure, heat release rate (HRR), ignition

213

delay (ID), duration of combustion (DOC), coefficient of variation (COV) of indicative mean

214

effective pressure (IMEP), COV of maximum cylinder pressure derivative (Max (dP/dθ)), brake

215

specific fuel consumption (BSFC) and brake thermal efficiency (BTE).

216

Combustion characteristics were obtained according to the in-cylinder pressure and HRR

217

measurements on the average of 500 cycles to minimize the influence of cycle-to-cycle variations.

218

First Law of Thermodynamics was employed to convert the pressure data to heat release rate data by

219

using the commercial software DEWESoftTM (DEWETRON GmbH). Start of combustion (SOC) is

220

defined as zero crossing of heat release (which means the beginning of rapid pressure rise or the

221

beginning of heat release) in the unit of crank-angle degree (°CA). Ignition delay is the interval 9

ACCEPTED MANUSCRIPT 222

between start of fuel injection (8 °CA BTDC) and SOC. End of combustion (EOC) is the point at 95%

223

of heat release. Duration of combustion is defined as the interval between SOC and EOC.

224

Typical curves of in-cylinder pressure and HRR are shown in Fig. 2 for low (28.5 Nm), medium

225

(142.5 Nm) and high (256.5 Nm) engine loads. Fig. 3 (a and b) reveals the peak in-cylinder pressure

226

and peak HRR, respectively. The similar in-cylinder pressure and heat release rate curves of the

227

blended fuels with diesel (Fig. 2) indicates that alternative fuels have undergone similar combustion

228

process, including a premixed combustion phase followed by a diffusion combustion phase.

229

Figs. 2 and 3 (a) illustrate that the in-cylinder pressure increases, with the peak value occurring further

230

away from the top dead center, with rise in the engine load for all the tested fuels which is due to

231

more fuel consumption at higher loads [15]. Similar behavior was observed in [9,12,16,17] with

232

diesel, DB, DBE and DBM. However, for HRR, Figs. 2 and 3 (b) show that the peak HRR increases

233

with rise in load only from 28.5 Nm to 142.5 Nm (except for D and DBPe at 199.5 Nm) and then it

234

decreases at the high load (256.5Nm) for all the tested fuels. Similar trend in the peak HRR (rise in

235

peak HRR at low and medium loads and reduce at high engine load) was also reported in the literature

236

[12,16,18] for diesel, biodiesel and DBE.

237

Figs. 2 and 3 (a) illustrate that all the blended fuels cause a slight reduction in the peak in-cylinder

238

pressure at the low engine load (except DB and DBM) and a slight rise at the medium and high loads

239

in comparison with diesel fuel. However, on the average of five loads, peak in-cylinder pressures of

240

all the blended fuels have only about 1% increase (almost similar) compared to that of diesel. Thus,

241

there is no significant difference between the blended fuels on the peak in-cylinder pressure. The

242

small drop in peak in-cylinder pressure at low load for the blended fuels is due to the lower

243

combustion temperature and the higher ignition delay (compared to other loads and use of diesel)

244

which cause initiation of combustion further away from the top dead center during the expansion

245

stroke [12,16].

246

For HRR, all the blended fuels (irrespective of DB) leads to an increase in the peak HRR at all loads

247

compared to pure diesel, as shown in Figs. 2 and 3 (b). This increase in the peak HRR can be

248

attributed to the better volatility and lower viscosity (better fuel atomization) of the alcohols and the

249

longer ignition delay associated with the lower cetane number of the alochols which cause 10

ACCEPTED MANUSCRIPT 250

accumulation of more fuel during the delay time to burn in the premixed burning phase and hence the

251

higher peak HRR [4,19,20]. In contrast, the higher viscosity and lower ignition delay of biodiesel

252

cause decrease in the peak HRR in comparison with diesel.

253

On the average of five loads, the higher alcohols have the same trend in the increase of peak HRR,

254

about 22.1% increase for DBPe, DBPr and DBBu, compared to that of pure diesel. However, the

255

lower alcohols cause less increase in the peak HRR, being 14.8% for DBE and 5.9% for DBM. In

256

contrast, biodiesel has a reduction of 3% in the peak HRR. Same behavior (increase in peak HRR for

257

alcohols and reduction in peak HRR for biodiesel) was also found in [4] for DBB and DBPe and [17]

258

for DB. It can be inferred that the magnitude sequence of the peak HRR is almost dependent on the

259

ignition delay of the fuels (as shown in Fig. 4 (a)).

260

Fig. 2. Variations of in-cylinder pressure and heat release rate with engine loads.

261

Fig. 3. Variations of (a) peak in-cylinder pressure (b) and peak HRR with engine loads.

262

Fig. 4 (a and b) indicates the variations of ignition delay and duration of combustion of the tested

263

fuels, respectively. It can be seen from Fig. 4 (a and b) that the increase in engine load causes

264

decrease in ID and increase in DOC for all the tested fuels. The ID is reduced due to increase in in-

265

cylinder temperature [21] as a consequence of rise in engine load. For DOC, the increase in load leads

266

to rise in duration of fuel injection, air/fuel mixture formation [22] and fuel combustion.

267

Fig. 4 (a and b) demonstrates that all the blended fuels (except DB) cause increase in ID and drop in

268

DOC in comparison with those of diesel fuel. The lower cetane number and higher latent heat of

269

evaporation of the blended fuels, as a consequence of the alcohols, cause decrease in in-cylinder

270

temperature and increase in ID compared to diesel fuel [23-25]. For DB, the higher bulk modulus and

271

higher viscosity of biodiesel cause earlier start of combustion and reduction in ID [26,27]. The drop in

272

DOC with use of alcohol in the blended fuels has various reasons. Firstly, the addition of alcohols into

273

the blended fuels leads to achieve higher HRR in the premixed combustion phase caused by the

274

longer ignition delay [28]. Secondly, faster flame propagation of alcohols can shorten the DOC [29].

275

Thirdly, oxygen content of alcohols can decrease the pyrolysis process and enhance the oxidation

276

during combustion resulting in shorter DOC [30].

11

ACCEPTED MANUSCRIPT 277

On the average of five engine loads, the increase in ID is in the order of DBPr (9.7%), DBPe, DBBu

278

and DBE (6.7%) and DBM (1.7%) compared to diesel, while DB has a reduction of 3.9% in ID. The

279

longest ID of DBPr is due to the slower H-abstraction and inhibition of isomerization in the branched

280

chain alcohols (2-propanol was tested) compared to the straight chain alcohols [31]. For DOC, the

281

average results show that the higher alcohols have similar effect in reduction of DOC (about 2.3% for

282

pentanol, propanol and butanol) while the lower alcohols have less influence in reduction of DOC

283

(1.1% for methanol and ethanol) compared to that of diesel. In addition, biodiesel has an identical

284

DOC (only 0.6% increase which was not significant with T-Test at 95% level) in comparison with

285

that of diesel. It can be found that the sequence of DOC is almost opposite the ID of the fuels.

286

Fig. 4. Variations of (a) ignition delay (b) and duration of combustion with engine loads.

287

Coefficient of variation in indicated mean effective pressure (COVIMEP) is an important parameter of

288

cyclic variability. COVIMEP is defined as the cyclic variability in indicated work per cycle. This

289

parameter is calculated based on the standard deviation in IMEP divided by the mean IMEP, and is

290

usually expressed in percent, while an excess of 10% in COVIMEP could result in vehicle drivability

291

problems [32]. Fig. 5 (a) shows that the COVIMEP (for 500 working cycles) of all the tested fuels varies

292

with engine load while the maximum and minimum COVIMEP are recorded at 28.5 Nm and 85.5 Nm,

293

respectively for all the tested fuel, except for DBM and DBE. The higher COVIMEP at the lowest load

294

(28.5 Nm) indicates a bigger variation of indicative work done among each cycle due to less stable

295

combustion associated with the lower combustion temperature and incomplete combustion.

296

The average data in Fig. 5 (a) reveals that despite of a slight reduction in COVIMEP by using DBM

297

(only 1.6%), the application of alternative fuels causes increase in COVIMEP in the order of DBBu and

298

DB (9%), DBE (7.8%), DBPe (5.8%) and DBPr (2.7%) compared to that of diesel fuel.

299

Coefficient of variation in maximum cylinder pressure (COV

300

combustion process which shows whether the combustion process of an engine is fast and robust or

301

that is slow and less repeatable [32]. COV Max(dP/dθ) also can implicitly reflect the level of combustion

302

noise. Fig. 5 (b) illustrates that the COV

Max(dP/dθ)

12

Max(dP/dθ))

is another indicator of

(for 500 working cycles) of all the tested fuels

ACCEPTED MANUSCRIPT 303

(irrespective of DBBu) increases from low load (28.5 Nm) to medium load (142.5 Nm) and then

304

decreases until the highest tested load (256.5 Nm).

305

It can be clearly seen from Fig. 5 (b) that the use of different fuels has various effects on COV Max(dP/dθ)

306

compared to diesel. Biodiesel causes a reduction of 3% and methanol has an identical value (only

307

0.5% reduction) in COV

308

lead to increase in COV Max(dP/dθ) in the sequence of DBPe (12.8%), DBPr and DBBu (7.5%) and DBE

309

(1.4%).

Max(dP/dθ)

a)

in comparison with diesel; while the other blended alcohols fuels

1.8

D DB DBM DBE DBPr DBBu DBPe

1.6

COV of IMEP (%)

1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0

28.5

85.5

142.5

199.5

256.5

199.5

256.5

Load (Nm)

310 b) COV of Max(dP/d ) (%)

2.0

1.5

D DB DBM DBE DBPr DBBu DBPe

1.0

0.5

0.0

311

28.5

85.5

142.5

Load (Nm)

312

Fig. 5. Variations of (a) COVIMEP and (b) COV Max(dP/dθ) with engine loads.

313

Fig. 6 indicates the variation of exhaust gas temperature (EGT) with engine load. It is clearly

314

observed that the increase in engine load causes increase in EGT for all the tested fuels. With increase

315

in engine load, more fuel is injected into the cylinder for burning which causes the rise in in-cylinder

316

temperature and thus increase in EGT [6]. The average data in Fig. 6 shows that all the alternative 13

ACCEPTED MANUSCRIPT 317

fuels lead to slight decreases (about 1.5% for all blends) in EGT compared to diesel. This small

318

reduction in EGT is due to the lower heating value and higher latent heat of evaporation (cooling

319

effect) of the alcohols and biodiesel which can reduce the combustion temperature [33] and thereby

320

reduce the EGT compared to diesel fuel. According to Fig. 6, the maximum reductions are recorded at

321

256.5 Nm for all the blended fuels which shows that the alternative fuels have a strong influence on

322

reductions of EGT only at higher engine loads.

Exhaust gas temperature (°C)

700 600 500 400 300 200 100 0

28.5

85.5

142.5

199.5

256.5

Load (Nm)

323 324

D DB DBM DBE DBPr DBBu DBPe

Fig. 6. Variation of exhaust gas temperature with engine loads.

325

3.2. Engine performance

326

Variations of BSFC and BTE are presented in Figs. 7 and 8, respectively. It can be seen that the best

327

engine performance occurs at 199.5 Nm which has the highest BTE and the lowest BFSC for all the

328

tested fuels. At low engine loads, the combustion temperature is low, therefore incomplete

329

combustion takes place; on the other hand, at very high loads, the combustion temperature is high and

330

the fuel/air ratio is richer, however there is not enough time for mixing of fuel and air, resulting in

331

incomplete combustion and decrease in BTE and increase in BSFC.

332

Fig. 7 also illustrates that all the blended fuels have higher BSFC (except for DBM at 256.5 Nm) at all

333

the tested loads compared to diesel fuel. Lower calorific value (due to using alcohols and biodiesel)

334

and lower density (due to use of alcohols) of the blended fuels are the reasons leading to the increase

335

in BSFC compared to ULSD [6,14,34,35]. And in order to maintain the same output power by the

14

ACCEPTED MANUSCRIPT 336

blended fuels, more fuel is required. The increases in BSFC on the average of five loads are found as

337

about 6.6% (DBE, DB, DBPr and DBPe), 4% (DBBu) and 2.3% (DBM) compared to that of diesel.

338

For BTE, the average results of five loads show that DBM (3.5%) and DBBu (1.5%) have higher BTE

339

and other blended fuels have similar BTE (about 1% reduction which is not significant with T-test) in

340

comparison with diesel fuel. The higher or similar BTEs (despite of increases in BSFC) of the blended

341

fuels is due to the lower fuel viscosity, improvement in fuel atomization and increase in oxygen

342

contents which improve the combustion process for converting the chemical energy of fuel into the

343

useful engine work and thereby increase the BTE compared to ULSD [16]. It can be inferred from the

344

above results that DBM shows the best performance, because it has the lowest BFSC among all the

345

tested blended fuels and the highest BTE among all the tested fuels. Methanol has the shortest chain

346

and the lowest molecular weight [14] among all the tested alcohols which leads to easier ignition and

347

better combustion and hence resulting in the lowest BSFC and the highest BTE. In addition, the

348

lowest boiling point of methanol among the tested alcohols causes reduction in heat losses and hence

349

resulting in higher BTE.

0.4

35 30

D DB DBM DBE DBPr DBBu DBPe

25

0.3

BTE (%)

BSFC (kg/kW.h)

40

D DB DBM DBE DBPr DBBu DBPe

0.5

0.2

20 15 10

0.1

5 0.0

350 351

28.5

85.5

142.5

199.5

0

256.5

Load (Nm)

Fig. 7. Variation of BSFC with engine loads.

352 353

28.5

85.5

142.5

199.5

256.5

Load (Nm)

Fig. 8. Variation of BTE with engine loads.

354

3.3. Exhaust gaseous emissions

355

Fig. 9 shows the variation of BSCO2 with engine loads. It can be seen from Fig. 9 that the behavior of

356

BSCO2 is almost similar to that of the BSFC (Fig. 7) at different engine loads. It is also found that the

15

ACCEPTED MANUSCRIPT 357

lowest BSCO2 is recorded at 199.5 Nm (which also has the lowest BSFC) and the highest BSCO2 is

358

observed at 28.5 Nm (which also has the highest BSFC) for all the tested fuels.

359

Fig. 9 also illustrates that all the blended fuels (except DB) can reduce BSCO2 compared to diesel

360

fuel. Similar trend in reduction of BSCO2 with ethanol and DBE was reported in [16,28,36] and a

361

slight increase and no significant effect in CO2 was found in [37] using pure biodiesel (5.63%

362

increase), DB50 (2.77% rise) and DB20 and DB10 (identical) compared to diesel. The lower carbon-

363

to-hydrogen ratio and the higher oxygen content of the blended fuels cause reduction of BSCO2 in

364

comparison with ULSD [36,38,39]. The reduction percentages in BSCO2 are 8.2% for DBM, 3.2% for

365

DBBu and about 1.8% for DBE, DBPe and DBPr, compared to ULSD, which are similar to the results

366

of BSFC. Moreover, DB has an identical BSCO2 (a slight increase of 1.4% was not significant with T-

367

test) compared to diesel. It can be inferred that only DBM is effective on the reducing BSCO2, with a

368

magnitude of 8.2%, which is due to its lowest BSFC (Fig. 7) among all the tested fuels. The other

369

blended fuels have almost similar effect on the BSCO2 compared to diesel.

1600

D DB DBM DBE DBPr DBBu DBPe

1400

BSCO2 (g/kW.h)

1200 1000 800 600 400 200 0

370

28.5

85.5

142.5

199.5

256.5

Load (Nm)

371

Fig. 9. Variation of BSCO2 with engine loads.

372

The effects of increase in in-cylinder temperature and complete combustion as a subsequence of rise

373

in engine load (except at 256.5 Nm) on reduction of BSCO emission can be seen in Fig. 10. Similar

374

behavior was observed in [28] for DBE. Fig. 10 also depicts that all the blended fuels (except DBM at

375

85.5 Nm) cause BSCO increase at lower loads (28.5 and 85.5 Nm) and decrease at higher loads (199.5

376

and 256.5 Nm) compared to diesel fuel. On the average of five loads, the reductions in BSCO using 16

ACCEPTED MANUSCRIPT 377

all alternative fuels are in the order of DBM (23.9%), DB (11.3%), DBPr and DBBu (6.4%), DBPe

378

(3.5%) and DBE (only 0.4%) in comparison with diesel. Other studies also found reductions in CO for

379

DB and DBBu [40] and for DBPe [41]. At low load the effect of lower combustion temperature

380

(cooling effect due to higher latent heat of evaporation) dominates the effect of oxygen content of the

381

blended fuels (complete combustion), which suppress the CO oxidation process, resulting in the

382

increase in BSCO emission compared to diesel [21,36]. However with rise in engine load, the effect

383

of combustion temperature becomes weaker and it can be seen at higher tested loads the BSCO

384

emissions of the blended fuels are lower than that of ULSD. It can be found from the above results

385

that DBM has the highest influence on reduction of BSCO (23.9%) which can be attributed to better

386

combustion and performance (lowest COVIMEP and BSFC and highest BTE) of DBM compared to the

387

other blended fuels. After DBM, DB shows high effect on reduction (11.3%) in BSCO which can be

388

attributed to the long duration of combustion, and hence longer time for oxidation of CO to CO2, as

389

shown in Fig. 4 (b).

20

D DB DBM DBE DBPr DBBu DBPe

18 16

BSCO (g/kW.h)

14 12 10 8 6 4 2 0

28.5

85.5

142.5

199.5

256.5

Load (Nm)

390 391

Fig. 10. Variation of BSCO with engine loads.

392

Fig. 11 depicts that the increase in load causes decrease in BSHC for all the tested fuels. At low

393

engine load the combustion temperatures are insufficient to initiate complete combustion resulting in

394

increments of BSHC emissions for all the tested fuels. However, at higher loads the combustion

395

temperatures are high enough to achieve a more complete combustion, leading to decrease in BSHC

396

for all the tested fuels. 17

ACCEPTED MANUSCRIPT 397

Fig. 11 shows that all the blended fuels (irrespective of ethanol at 85.5 Nm) can reduce the BSHC

398

from 85.5 Nm to the highest engine load (256.5 Nm). The increase in BSHC at the lowest load with

399

the blended fuels is similar to that in the case of BSCO (Fig. 10), which is due to incomplete

400

combustion as a consequence of higher latent heat of evaporations of alcohols and biodiesel compared

401

to ULSD. However, the effect of higher oxygen content of the blended fuels is a dominant factor at

402

higher engine loads (from 85.5 Nm to 256.5 Nm) which causes more complete combustion and

403

increases the oxidation of unburned hydrocarbons at higher in-cylinder temperatures [42] resulting in

404

lower BSHC emissions compared to ULSD. Some studies also found a rise in THC at lower and even

405

medium loads and a reduction at higher load with the use of alcohols blends (like DBE [28,43], DBBu

406

and DBPe [6] and BPn [7]) compared to diesel. In addition, other studies found that the use of DE and

407

DBE [25,44,45], DBPe [41] and diesel blended with ethanol or methanol [46] can increase the

408

combustion quality, due to more oxygen content in the fuel, and reduce the THC, in comparison with

409

diesel fuel. On the average of five engine loads, the reductions in BSHC are in the order of DBM

410

(24.3%), DBPe, DBPr and DB (12.3%) and DBE and DBBu (8.8%) compared to diesel fuel. It can be

411

concluded from the above results that, similar to BSFC and BSCO, the effect of using DBM on

412

reduction of BSHC (24.3%) is higher than the other blended fuels which is due to better combustion

413

and performances of DBM (lowest COVIMEP and BSFC and highest BTE). The other blended fuels

414

have almost similar impacts on the reductions of BSHC.

D DB DBM DBE DBPr DBBu DBPe

BSHC (g/kW.h)

10 8 6 4 2 0

415 416

28.5

85.5

142.5

199.5

256.5

Load (Nm)

Fig. 11. Variation of BSHC with engine loads. 18

ACCEPTED MANUSCRIPT 417

Fig. 12 shows that the BSNOX approximately decreases with rise in load which is in line with other

418

studies with use of diesel and DBE [16,28] and diesel, DBu and DPe [4]. Fig. 12 also reveals that all

419

the blended fuels (except DB at all loads and DBPe at 28.5 Nm) cause decreases in BSNOX at all the

420

tested loads compared to diesel fuel. On the average of five loads, reductions in BSNOX with use of

421

the blended fuels are in the order of 19.3% (DBPr), 14.2% (DBM), 11.7% (DBPe), 4.7% (DBE) and

422

(DBBu); while DB has an increase (5.8%) in BSNOX in comparison with that of diesel. Despite of the

423

huge effect of combustion temperature on formation of NOX, it can be found from the above results

424

that length of combustion duration (residence time) also has an effect on NOX formation. Because,

425

DBPr has the highest impact on the reduction of BSNOX (23.3%) among all the tested blended fuels

426

due to its shortest duration of combustion, as shown in Fig.4 (b), for formation of NOX. On the other

427

hand, DB leads to rise in BSNOX (5.8%) which can be attributed to the highest duration of

428

combustion. In addition, Koivisto et al. [31] reported that the increase in alcohol branch (from 1-

429

Octanol to 3-Octanol or adding two methyl group branches to 3-Octanol to form 3,7-Dimethyl-3-

430

octanol) caused reduction in NOX emission due to increase in ignition delay and decrease in adiabatic

431

flame temperature. The 2-propanol used in this study has higher branch than the other alcohols, which

432

DBPr has the longest ID (Fig. 4 (a)) and lowest NOX (Fig. 12). Reduction in BSNOX was also

433

reported in some studies using ethanol [16,28], butanol and pentanol [4] and butanol and propanol

434

[14]. In addition, the increase in NOX using biodiesel was also reported in many studies as mentioned

435

in the review paper [47].

436

It can be inferred from the above result that the effects of higher latent heat of evaporation and lower

437

heating value of alcohol fuels are dominant factors compared to other parameters (like lower cetane

438

number and higher oxygen content of blends which increase the combustion temperature) which cause

439

reduction in BSNOX for different loads.

19

ACCEPTED MANUSCRIPT

D DB DBM DBE

10

DBPr DBBu DBPe

BSNOx (g/kW.h)

8 6 4 2 0

28.5

85.5

142.5

199.5

256.5

Load (Nm)

440 441

Fig. 12. Variation of BSNOX with engine loads.

442

3.4. PM emissions

443

Fig. 13 illustrates that the increase in engine load (except at 28.5 Nm) leads to rise in BSPM for all

444

tested fuels. The small reduction in BSPM from low load (28.5 Nm) to medium load and then increase

445

until the highest load (256.5 Nm) was reported in other studies [12,16] for DBE and diesel. At higher

446

engine loads, the shorter time available for soot oxidation [19] causes increase in soot formation,

447

resulting in a rise of BSPM. Also, the fuel/air mixture is richer and there is lower oxygen

448

concentration for soot oxidation. Moreover, the ignition delay becomes shorter; therefore, more fuel is

449

burned during the diffuse combustion period, resulting in a rise in PM emissions [42].

450

Fig. 13 also shows that the utilization of blended fuels (except DB at 25.8 and 85.5 Nm) has a positive

451

effect on the reduction of BSPM at various loads compared to ULSD. According to the average of

452

five loads, the reductions in BSPM are in the sequence of DBE and DBM (70%), DBBu (61%), DBPr

453

(46.2%), DBPe (32.6%) and DB (only 5.2%) compared to diesel fuel. This finding is in line with

454

some other studies for DBE [12,48], pentanol [42], butanol and pentanol [49] and DBE and DBM

455

[15]. The reasons for the decrease in BSPM with oxygenate fuels can be attributed to the following

456

factors. Firstly, there are lower aromatic and sulfur contents (except DB) in the blended fuels [42].

457

Secondly, higher oxygen content of the blended fuels enhances the soot oxidation, because through

458

the hydroxyl radical (•OH) formation, the oxygen component consumes the soot precursors which

459

causes lower soot formation [33]. Thirdly, the carbon to hydrogen mass ratio of all the blended fuels 20

ACCEPTED MANUSCRIPT 460

is lower than that of diesel fuel [42]. It is found from the above results that all the alcohol fuels have

461

huge effects on the reductions of BSPM; while DB shows a small effect (only 5.2% reduction) on

462

BSPM compared to the other tested fuels. The small impact of DB on the reduction of BSPM is due to

463

its shortest ignition delay and hence longer diffusion combustion period, (resulting in higher particle

464

mass formation). In addition, the bonding of two oxygen atoms of biodiesel as R(C=O) OR with one

465

carbon [50,51] causes the decomposition of CH3O(CO)• radical to form CO2 (CH3+CO2) instead of

466

CO formation (CO+CH3O) [52-54] . While, for reduction in soot formation, each oxygen atom can

467

remove one carbon atom from the reactive pool (consuming the soot precursors by oxygen atoms);

468

however, for biodiesel, the two oxygen atoms can only remove one carbon atom which is less efficient

469

[50,54] compared to the fuels containing one oxygen atom in their structure like alcohols. Therefore,

470

biodiesel shows the weakest effect on the reduction (only 5.2%) of BSPM in comparison with the

471

other blended fuels with alcohol (especially DBE and DBM with 70% reduction). On the other hand,

472

the lowest BSPM of the DBE and DBM fuels can be attributed to the shorter chains of methanol and

473

ethanol which lead to easy extraction of oxygen atoms from the decomposition of their molecule

474

structures resulting in higher consumption of soot precursors by these free oxygen atoms compared to

475

the longer-chain alcohols like propanol, butanol and pentanol.

700

BSPM (mg/kW.h)

600 500

D DB DBM DBE DBPr DBBu DBPe

400 300 200 100 0

476 477

28.5

85.5

142.5

199.5

256.5

Load (Nm)

Fig. 13. Variation of BSPM with engine loads.

21

ACCEPTED MANUSCRIPT 478

Figs. 14 and 15 depict that the increases in engine load cause increases in both total number

479

concentration (TNC) and geometrical mean diameter (GMD) of the PM for all the tested fuels. In

480

other studies, the increases in TNC and GMD of diesel and DBE [16], diesel and pentanol [42] and

481

diesel, butanol and pentanol [49] with rise in engine load were also reported. Some factors have

482

influences on the increase of TNC with rise in engine loads. For example, lower availability of time

483

for soot oxidation at high loads [19] causes increase in particulate formation; richer mixture at high

484

loads, reduces oxygen concentration for soot oxidation; shorter ignition delay at high loads causes

485

burning of more fuel during the diffuse combustion period [42]; or incomplete combustion due to lack

486

of enough mixing time for fuel and air at high loads. Moreover, as the number of particles increase,

487

the particles coagulation rate increases and hence larger particles are formed, leading a rise of GMD

488

[55].

489

Figs. 14 and 15 also show that all the blended fuels have a positive influence on reduction of TNC

490

(irrespective of DBPr and DBPe at 142.5, 199.5 and 256.5 Nm) and GMD for different loads. On the

491

average of five loads, the reductions in TNC are in the order of DBE (37.3%), DBBu (31.1%), DBM

492

(22%), DB (9%) and DBPe (only 1.1%) compared to diesel; while DBPr has an identical TNC (only

493

0.2% increase which was not significant with T-test) with diesel. For GMD, the average results show

494

that the decreases are in the sequence of DBPr, DBE, DBBu and DBPe (10.3%) and DB and DBM

495

(5.25%) in comparison with diesel fuel. The decreases in TNC and GMD with use of alternative fuels

496

(ethanol, butanol and pentanol) were also found in the literature [12,16,42,49]. Lower aromatic and

497

sulfur contents (except DB) and lower carbon to hydrogen mass ratio of the blended fuels [42] and

498

higher oxygen content (enhances the soot oxidation) [33] of the blended fuels contribute to the

499

reductions in TNC and GMD compared to those of diesel fuel. In regard to the effect of ID on PM,

500

Koivisto et al. [31] found that the use of an alcohol caused increase in total particle number and

501

smaller particle size compared to those of hydrocarbon fuels due to longer ignition delay of the

502

alcohols. In the present study, the highest TNC and lowest GMD are also recorded for DBPr which

503

has the longest ignition delay.

22

16 14 12 10

D DB DBM DBE DBPr DBBu DBPe

120

Geometric Mean Diameter (nm)

Total Number Concentration x E+7 (#/cm³)

ACCEPTED MANUSCRIPT

8 6 4 2 0

28.5

85.5

142.5

199.5

80 60 40 20 0

256.5

Load (Nm)

504 505

100

D DB DBM DBE DBPr DBBu DBPe

28.5

85.5

142.5

199.5

256.5

Load (Nm)

508 509

506

Fig. 14. Variation of total number concentration

510

Fig. 15. Variation of geometric mean diameter

507

with engine loads.

511

with engine loads.

512

4. Conclusions

513

The present experimental research was conducted to investigate the impact of using biofuels on the

514

combustion, performance and emissions of a diesel engine at a constant engine speed of 1800 rpm

515

with five engine loads (10%-90% of the full load). Seven fuels were used, including diesel (D),

516

biodiesel (B), two lower alcohols (methanol (M) and ethanol (E)) and three higher alcohols (2-

517

propanol (Pr), n-butanol (Bu) and n-pentanol (Pe)) with various blending mass percentages to obtain

518

constant fuel oxygen content and almost constant carbon and hydrogen contents and lower heating

519

values. The blended fuels are designated as DB, DBM, DBE, DBPr, DBBu and DBPe. The major

520

conclusions drawn from the present study include the following points based on the average results of

521

the five engine loads and compared to the reference fuel (diesel).

522

 The peak in-cylinder pressures of all blends had only about 1% increases (almost similar).

523

 For the peak HRR, the higher alcohols caused higher increase of peak HRR (22.1%) and the lower

524

alcohols (DBE with 14.8% and DBM with 5.9%) caused lower rise in peak HRR; while, the DB had

525

a reduction of 3% in peak HRR.

526 527

 All the blended fuels (except DB with 3.9% reduction) led to the increase in ID in the order of DBPr (9.7%), DBPe, DBBu and DBE (6.7%) and DBM (1.7%). 23

ACCEPTED MANUSCRIPT 528 529 530 531

 For the DOC, the higher alcohols had a similar effect in reductions of DOC (2.3%), methanol and ethanol caused a slight drop of 1.1% in DOC; while biodiesel had similar DOC.  For engine performance, all blends had higher BSFC in the order of about 6.6% (DBE, DB, DBPr and DBPe), 4% (DBBu) and 2.3% (DBM).

532

 DBM (3.5%) and DBBu (1.5%) had higher BTE and other blends had similar BTE.

533

 In regard to the emissions, the reductions in BSCO2 were found as 8.2% (DBM), 3.2% (DBBu)

534 535 536 537 538 539 540 541 542 543 544 545 546

about 1.8% (DBE, DBPe and DBPr); while DB had similar BSCO2.  All the blended fuels caused reduction in BSCO in the order of DBM (23.9%), DB (11.3%), DBPr and DBBu (6.4%), DBPe (3.5%) and DBE (only 0.4%).  Also all blends had lower BSHC in the sequence of DBM (24.3%), DBPe, DBPr and DB (12.3%) and DBE and DBBu (8.8%).  Reductions in BSNOX were recorded in the order of 19.3% for DBPr, 14.2% for DBM, 11.7% for DBPe and 4.7% for DBE and DBBu; however DB caused an increase of 5.8% in BSNOX.  Reductions in BSPM were in the sequence of DBE and DBM (70%), DBBu (61%), DBPr (46.2%), DBPe (32.6%) and DB (only 5.2%).  All blends caused reductions in TNC in the order of DBE (37.3%), DBBu (31.1%), DBM (22%), DB (9%) and DBPe (only 1.1%); while DBPr had similar TNC with diesel.  For GMD, the decreases were in the sequence of DBPr, DBE, DBBu and DBPe (10.3%) and DB and DBM (5.25%).

547

Despite all the blended fuels have almost the same C/H/O compositions and lower heating values,

548

there are some differences in the influence of each fuel to the combustion, performance and emissions

549

of the diesel engine, even among those fuels with alcohols. According to the average of five engine

550

loads, it was observed that all the tested blended fuels using alcohols had almost similar trends on the

551

engine combustion, performance and emissions; while, the use of biodiesel blend (DB) had opposite

552

trends in some parameters. In detail, the alcohols blends had higher HRR, ID and COV

553

lower DOC, BSCO2 and BSNOX in comparison with diesel fuel; however, biodiesel blend (DB) had

554

lower HRR, ID and COV Max(dP/dθ), higher BSNOX and similar DOC and BSCO2 compared to those of 24

Max(dP/dθ)

and

ACCEPTED MANUSCRIPT 555

diesel fuel. It is noticeable that all the blended fuels with alcohol can reduce both NOx and particulate

556

emissions, which are major problems with diesel engines. Moreover, they have higher PM reduction

557

effects than the DB fuel.

558

In addition, it was found that DBM showed the best engine performance (highest BTE among all the

559

fuels and lowest BSFC among all the blends) and had the lowest emissions (BSCO2, BSCO, BSHC,

560

BSPM and BSNOX (after DBPr)), COVIMEP and COV

561

tested fuels. In contrast, DB had the weakest influences, compared to the other blended fuels.

562

Acknowledgements

563 564

The authors would like to thank The Hong Kong Polytechnic University for the financial support (RUAT).

565

Nomenclature

566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589

°CA B B100 BSCO BSCO2 BSFC BSHC BSNOX BSPM BTDC BTE Bu C CN COV Max(dP/dθ) COVIMEP CPC D DB DBBu DBE DBM

Crank angle degree 590 Biodiesel 591 Pure biodiesel 592 Brake specific carbon monoxide 593 Brake specific Carbon dioxide 594 Brake specific fuel consumption 595 Brake specific hydrocarbon 596 Brake specific Nitrogen oxides 597 Brake specific particulate matter 598 Before top dead center 599 Brake thermal efficiency 600 Butanol 601 Carbon 602 Cetane number 603 Coefficient of variation of maximum604 cylinder pressure derivative 605 Coefficient of variation of indicative606 mean effective pressure 607 Condensation particle counter 608 Diesel 609 Diesel- biodiesel 610 Diesel- biodiesel- Butanol 611 Diesel- biodiesel- Ethanol 612 Diesel- biodiesel- Methanol

Max(dP/dθ)

DBPe DBPr DI DMA DR E EGT EOC FC GMD H HRR ID IDI M O Pe Pr SMPS Temp TEOM TNC ULSD

(after DB) compared to all the other

Diesel- biodiesel- Pentanol Diesel- biodiesel- Propanol Direct injection Differential mobility analyzer Dilution ratio Ethanol Exhaust gas temperatures End of combustion Fuel consumption Geometric mean diameter Hydrogen Heat release rate Ignition delay indirect injection Methanol Oxygen Pentanol Propanol Scanning mobility particle sizer Temperature Tapered element oscillating microbalance Total particle number concentration Ultra-low-sulfur diesel

613

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614 615 616 617 618 619 620 621

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27

ACCEPTED MANUSCRIPT Highlights 

Combustion, performance and emissions of a diesel engine were investigated.



Fuels included diesel, biodiesel, methanol, ethanol, propanol, butanol and pentanol.



All blends had 5% oxygen and almost same carbon and hydrogen contents and LHV.



Methanol blend showed the best engine performance and almost the lowest emissions.



Biodiesel (waste cooking oil) blend had the weakest impact among the blended fuels.