Experimental investigation of a spark ignition engine fueled with acetone-butanol-ethanol and gasoline blends

Accepted Manuscript Experimental investigation of a spark ignition engine fueled with acetone-butanolethanol and gasoline blends

Yuqiang Li, Lei Meng, Karthik Nithyanandan, Timothy H. Lee, Yilu Lin, Chia-Fon Lee, Shengming Liao PII:

S0360-5442(16)31916-8

DOI:

10.1016/j.energy.2016.12.111

Reference:

EGY 10113

To appear in:

Energy

Received Date:

22 March 2016

Revised Date:

02 December 2016

Accepted Date:

26 December 2016

Please cite this article as: Yuqiang Li, Lei Meng, Karthik Nithyanandan, Timothy H. Lee, Yilu Lin, Chia-Fon Lee, Shengming Liao, Experimental investigation of a spark ignition engine fueled with acetone-butanol-ethanol and gasoline blends, Energy (2016), doi: 10.1016/j.energy.2016.12.111

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT 

ABE (acetone-butanol-ethanol) was used as a green alternative fuel.



ABE-gasoline blends with various ratios of ABE, ABE component and water were test.



Combustion, performance and emissions characteristics were investigated.



Adding ABE into gasoline can enhance BTE and reduce CO, UHC and NOx emissions.

ACCEPTED MANUSCRIPT Experimental investigation of a spark ignition engine fueled with acetonebutanol-ethanol and gasoline blends Yuqiang Li a, Lei Meng b, Karthik Nithyanandan c, Timothy H Lee c, Yilu Lin c, Chia-Fon Lee c, d*, Shengming Liao a a

School of Energy Science and Engineering, Central South University, Changsha, Hunan 410083,

China b

School of Information Engineering, Wuhan University of Technology, Wuhan, Hubei 430070,

China c

Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign,

IL 61801, USA d

School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China

*Corresponding author: E–mail: [email protected] Tel: 1-217-3335879 Fax: 1-217-2446534

1

ACCEPTED MANUSCRIPT 1

Abstract

2

Bio-butanol is typically produced by acetone-butanol-ethanol (ABE) fermentation, however,

3

the recovery of bio-butanol from the ABE mixture involves high costs and energy consumption.

4

Hence it is of interest to study the intermediate fermentation product, i.e. ABE, as a potentially

5

alternative fuel. In this study, an experimental investigation of the performance, combustion and

6

emission characteristics of a port fuel-injection SI engine fueled with ABE-gasoline blends was

7

carried out. By testing different ABE-gasoline blends with varying ABE content (0 vol.%, 10

8

vol.%, 30 vol.% and 60 vol.% referred to as G100, ABE10, ABE30 and ABE60), ABE formulation

9

(A:B:E of 1:8:1, 3:6:1 and 5:4:1 referred to as ABE(181), ABE(361) and ABE(541)), and water

10

content (0.5 vol.% and 1 vol.% water referred to as W0.5 and W1), it was found that ABE(361)30

11

performed well in terms of engine performance and emissions, including brake thermal efficiency

12

(BTE), brake specific fuel consumption (BSFC), carbon monoxide (CO), unburned hydrocarbons

13

(UHC) and nitrogen oxides (NOx) emissions. Then, ABE(361)30 was compared with conventional

14

fuels, including E30, B30 (30 vol.% ethanol or butanol blended with gasoline) and pure gasoline

15

(G100) under various equivalence ratios and engine loads. Overall, a higher BTE (0.2-1.4%) and

16

lower CO (1.4-4.4%), UHC (0.3-9.9%) and NOx (4.2-14.6%) emissions were observed for

17

ABE(361)30 compared to those of G100 in some cases. Therefore, ABE could be a good alternative

18

fuel to gasoline due to the environmentally benign manufacturing process (from non-edible biomass

19

feedstock and without a recovery process), and the potential to improve energy efficiency and

20

reduce pollutant emissions.

21

Keywords: ABE; Performance; Combustion; Emissions; Alternative fuel; SI engine

2

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1. Introduction

23

Due to the challenges of limited fossil-fuel resources and stringent emission norms, interest in

24

developing clean and sustainable energy sources has grown considerably. Biofuels, derived from

25

biomass and thus being renewable, biodegradable and oxygenated, are receiving increasing public

26

and scientific attention [1-3]. In the United States, EISA (Energy Independence and Security Act) of

27

2007 mandated that 36 billion gallons of renewable fuels were to be blended into US transportation

28

fuels by 2022 [4]. Biofuels were promoted at the EU (European Union) level through the

29

introduction of directive 2003/30/EC, which set an indicative target that the percentage share of

30

biofuels should achieve 10% of the total volume of fuel consumed in EU transportation by 2020 [5].

31

In China, the NDRC (National and Development Reform Commission) announced that renewable

32

energy as a share of total primary energy consumption should rise to 15% by 2020. Biofuels are

33

expected to play an important role in the achievements of this target [6].

34

The first-generation biofuels are produced from edible crops and vegetables and that may lead

35

to food shortages. In contrast, the second-generation biofuels can be produced from alternative

36

lignocellulosic materials, such as wood, vegetable waste and non-edible plants, offering an even

37

more favorable well-to-wheel CO2 balance without negative impact on food supply. Many

38

researchers have investigated the application of second-generation biofuels in internal combustion

39

engine. Contino et al. tested the combustion and emissions characteristics of engine fueled with

40

diesel blended with 20 vol.% butyl and pentyl valerate [7]. Although butyl and pentyl valerate

41

showed a slightly longer ignition delay compared to diesel, engine performance and emissions were

42

not significantly modified. Shihadeh and Hochgreb investigated the combustion behavior of NREL

43

pyrolysis oil and ENSYN pyrolysis oil in a direct injection diesel engine [8]. It was found that these

44

two pyrolysis oils exhibited excessive ignition delay and required a moderate degree of combustion 3

ACCEPTED MANUSCRIPT 45

air preheating to ignite reliably. Zheng et al. intended to achieve simultaneous reduction of NOx and

46

soot emissions in biodiesel engine using low temperature combustion [9]. An experiment was

47

carried out to study the combustion and emissions of 2,5-Dimethylfuran on a single-cylinder direct-

48

injection gasoline engine [10]. 2,5-Dimethylfuran showed a shorter combustion duration and similar

49

CO, HC, and NOx emissions when compared to gasoline. Among various second-generation

50

biofuels, alcohols have been extensively investigated as alternative fuels because of their great

51

potential for improving engine performance and reducing pollutant emissions [11-16]. In

52

comparison with ethanol, butanol has received increased attention due to its several advantages over

53

them, such as a higher heating value, higher viscosity, lower water absorption and better blending

54

ability [17]. Due to its physical properties being similar to those of gasoline, butanol is as easily

55

transported as gasoline, which could make it more cost-effective with the existing gasoline

56

infrastructure [18]. However, the high costs for recovering and dehydrating butanol from the ABE

57

mixture and the low production efficiency have prohibited industrial scale production of butanol

58

[19].

59

If the intermediate ABE mixture could be directly used for clean combustion, the cost of

60

recovery and dehydration processes would be eliminated. Qureshi and Blaschek detailed an

61

economic assessment of ABE fermentation from corn using the newly developed Clostridium

62

beijerinckii BA101. The results showed that the price of ABE was projected to be US$0.27 kg-1,

63

which is close to the price of gasoline, i.e. US$0.22 kg-1. With the development of strains,

64

substrates, and fermentation technologies for improving productivity, ABE as a potential biofuel

65

could become economically feasible [20]. In this regard, some studies on ABE combustion have

66

been carried out recently. The effects of water-containing ABE and diesel blends on performance

67

and emissions of diesel engine were investigated by Chang et al. [21]. It was found that 20 vol.% 4

ACCEPTED MANUSCRIPT 68

ABE and 0.5 vol.% water enhanced the brake thermal efficiency (BTE) by 3.26-8.56% and reduced

69

the emissions of particulate matter (PM), nitrogen oxides (NOx), polycyclic aromatic hydrocarbon

70

(PAHs) and toxicity equivalency of PAHs (BaPeq) by 5.82-61.6%, 3.69-16.4%, 0.699-31.1% and

71

2.58-40.2% when compared to diesel, respectively. They also added water-containing ABE to

72

biodiesel and diesel blends to solve the problem of increasing NOx with biodiesel use. The results

73

showed that the use of water-containing ABE-biodiesel-diesel blends could simultaneously reduce

74

PM and NOx by 4.30-30.7% and 10.9-63.1%, respectively [22]. In addition, the spray and

75

combustion characteristics of ABE-diesel blends were studied in a constant volume chamber [23-

76

31]. A wide range of ratios of ABE (0 vol.%-80 vol.% referred to as D100-ABE80) blended with

77

diesel were combusted under various ambient temperatures (800K-1200K) and ambient oxygen

78

concentrations (11%-21%) [23-27]. It was found that ABE-diesel blends showed shorter

79

combustion duration and lower natural flame luminosity compared to those of pure diesel. The

80

shorter combustion duration made the combustion process more close to constant volume

81

combustion, which was beneficial for increasing thermal efficiency. In addition, the natural

82

luminosity was generally contributed to by two sources, chemiluminescence and soot

83

incandescence, but the latter was much stronger than the former one, thus it was reasonable to argue

84

that the soot luminosity can be well represented by the natural luminosity. Therefore, ABE could

85

potentially increase thermal efficiency and decrease soot emissions. Meanwhile, ABE50 displayed

86

combustion characteristics similar to those of neat diesel. The differences in spray and natural flame

87

luminosity images between ABE, n-butanol and diesel showed that a longer “gap” between liquid

88

spray and flame in ABE combustion, which provided more space and time for the droplets to

89

evaporate and mix with the ambient air [28-30]. The impacts of acetone on the spray and

90

combustion of ABE and diesel blends were investigated through the comparison between ABE 5

ACCEPTED MANUSCRIPT 91

fuels with different component volumetric ratios (A:B:E of 6:3:1; 3:6:1; 0:10:0) [31]. ABE(6:3:1)20

92

presented much lower soot formation compared to other fuels. Zhao et al. [32, 33] proposed a

93

phenomenological soot model of ABE with the modification of the fuel pyrolysis process.

94

To realize the practical application of ABE, three aspects should be considered, including fuel

95

properties, production cost, and application in internal combustion engines. Based on the above

96

literature review, it was found that the application of ABE in gasoline engine was rarely reported

97

[34-37]. Therefore, in this study, the combustion, performance and emissions characteristics of a

98

port fuel-injection spark ignition (SI) engine fueled with ABE-gasoline blends were further

99

investigated in this study by: (1) changing ABE content (0 vol.%, 10 vol.%, 30 vol.% and 60 vol.%

100

ABE referred to as G100, ABE10, ABE30 and ABE60) in ABE-gasoline blends; (2) changing ABE

101

formulation (A:B:E of 1:8:1, 3:6:1 and 5:4:1 referred to as ABE(181), ABE(361) and ABE(541));

102

(3) adding less than 1 vol.% water (0.5 vol.% and 1 vol.% water referred to as W0.5 and W1); (4)

103

comparing with conventional fuels, including ethanol, butanol and gasoline under various

104

equivalence ratios and engine loads.

105

2. Experimental methods

106

2.1. Fuel preparation

107

In this study, pure commercial summer gasoline with a research octane number (RON) of 92

108

was selected as the baseline fuel. Analytical grade acetone (99.5%), butanol (99.5%) and ethanol

109

(99.8%) were mixed with gasoline using a temperature-controlled magnetic stirrer to make the

110

ABE-gasoline blends. The properties of individual fuels and fuel blends are listed in Table 1 [38-

111

43]. The stability of fuel blends was tested using a gravitational test. The prepared fuels were

112

deposited in test tubes at 25 ˚C and 1 atm for 14 days. The fuels displayed a clear single phase

113

throughout the stability test. 6

ACCEPTED MANUSCRIPT 114

2.2. Test engine

115

The engine used in this study was a single cylinder port fuel injection (PFI) SI engine with

116

cylinder geometry identical to that of a 2000 Ford Mustang Cobra V8. The peak power output of the

117

original V8 engine was 239 kW and 407 Nm of torque resulting in a peak output for the single

118

cylinder engine of slightly less than 30 kW and 52 Nm. The general specifications are shown in

119

Table 2. The engine was connected to a GE type TCL-15 class 4-35-1700 dynamometer controlled

120

by a DYN-LOC IV controller. A DyneSystems DTC-1 controller was used to control throttle

121

position. A Megasquirt V3.0 electronic control unit system was used to control air-fuel ratio (AFR)

122

and spark timing. In-cylinder pressure was measured by a Kistler type 6125B pressure transducer,

123

and the pressure data from 25 engine cycles was recorded several times and then averaged by a

124

National Instruments (NI) data acquisition system with LabVIEW code. The engine was controlled

125

by a calibrated Megasquirt II V3.0 Engine Control Unit (ECU), which allowed on-line adjustment

126

to change the fuel injecting time and spark advanced angle. A Bosch injector # 0280150558 rated at

127

440 cm3/min at a fuel pressure of 300 kPa was selected to guarantee enough fuel mass for lower

128

stoichiometric air-fuel ratio fuels. The crank angle position was acquired with a BEI XH25D shaft

129

encoder. The measurements of air/fuel ratio (AFR) and NOx emissions were conducted using a

130

Horiba MEXA-720 analyzer. A Horiba MEXA-554JU analyzer was used to measure UHC and CO

131

emissions. Water vapor in the exhaust gas was condensed out before emissions measurements. The

132

measuring range, accuracy, and resolution of the experimental apparatus are listed in Table 3. A

133

picture and a schematic diagram of the engine setup are shown in Fig. 1.

134

2.3. Test conditions and parameters

135

In this study, the engine speed was fixed at 1200 rpm. The throttle plate was fully opened and

136

the intake manifold air pressure (MAP) was fixed at 60 kPa and 90 kPa by regulating the 7

ACCEPTED MANUSCRIPT 137

compressed air supply, which corresponded to engine loads of 310.33 kPa BMEP (Brake Mean

138

Effective Pressure) and 524.07 kPa BMEP, respectively, for gasoline. Using this method to change

139

engine load can avoid the fluctuation of intake manifold air pressure because throttle plate position

140

could be slightly changed by high negative pressure using throttle plate adjustment. In addition, this

141

eliminates throttling losses and this effect can be quantified directly based on volumetric efficiency.

142

For the potential usage of alternative fuels, one area of interest is direct replacement of the gasoline

143

in the in-use vehicles; in other words, a “drop-in” fuel test. Therefore, the engine was operated at

144

the spark timing corresponding to gasoline's MBT (Maximum Brake Torque) (18° Before Top Dead

145

Center (BTDC) at 310.33 kPa BMEP and 15° BTDC at 524.07 kPa BMEP). In practical SI engine

146

operating condition, equivalence ratio is not uniform and also varies in each individual cylinder on a

147

cycle-by-cycle basis. For example, it is advantageous to use lean condition for best efficiency at

148

part-load operation and rich condition for maximum power at full-load operation. Therefore, the

149

equivalence ratio in this study was varied over a range of lean, stoichiometric and rich conditions,

150

i.e. Φ ranging from 0.83 to 1.25. Measurements of engine torque, equivalence ratio, and NOx

151

emission were averaged in a 60-second period, while UHC and CO emissions were recorded

152

directly from the emissions analyzer. The tests of each fuel were performed three times in a single

153

day, and the datasets for each fuel were then averaged. The experiments were performed on several

154

consecutive days in a temperature and humidity-controlled laboratory. The test conditions

155

mentioned above have been summarized in Table 4.

156 157 158

In each test, the investigated parameters for combustion and performance characteristics of the engine are calculated based on Eqs. (1-5). - The normalized mass fraction burnt (MFB),

8

ACCEPTED MANUSCRIPT 159

MFB 

MF MT

(1)

160

where MF is the integrated heat release at (up to) each crank angle degree (CAD), and MT is the total

161

heat released in the cycle. The ratio MF upon MT is considered as the normalized MFB with limits

162

from 0 to 1. The heat release rate is calculated from the pressure trace using the first law of

163

thermodynamics as expressed in Eq.(2).

164

dQn  dV 1 dp dQht  p  V  d   1 d   1 d d

(2)

165

where γ is the polytropic index; p is the in-cylinder pressure; V is the cylinder volume; and θ is the

166

engine crank angle; Qht is the heat transfer to the wall.

167 168

Based on the MFB profiles, initial combustion duration (ICD) and main combustion duration (MCD) are given by 0-10% MFB and 10-90% MFB, respectively.

169

-The brake mean effective pressure, BMEP (in bar)

170

BMEP   4 T / VH  102

171

(3)

where T is brake torque (in Nm), and VH denotes the displaced volume of the engine (in L).

172

- The brake specific fuel consumption, BSFC (in g/kWh)

173

BSFC 

m f P



m a / AFR T  2 N / 60   103

(4)

174

where P is brake power (in kW); N is engine speed (in r/min); ṁf and ṁa are the mass flow rate of

175

fuel and intake air (in g/h), respectively.

176

- The brake thermal efficiency, BTE (in %)

177

3600   BTE    100  BSFC LHV 

178

(5)

where LHV is lower heating value of fuel (in MJ/kg).

179

9

ACCEPTED MANUSCRIPT 180

3. Results and discussion

181

3.1. Effects of ABE ratio on performance, combustion and emissions characteristics

182

Fig. 2 and Table 5 show the effect of changing ABE content on combustion, performance and

183

emissions characteristics at stoichiometric condition and 302.69-310.33 kPa BMEP corresponding

184

to 60 kPa MAP. The ABE mixture was first prepared at a volume ratio of 3: 6: 1 (A: B: E), which is

185

the typical product (ratio) from the fermentation process. It can be seen from Fig. 2 that

186

ABE(361)60 showed the most advanced combustion phasing, resulting in the highest peak cylinder

187

pressure. To further evaluate the combustion phasing of different fuels, the ICD, MCD and 50%

188

MFB location were studied as shown in Table 5. During the ICD, i.e. early combustion period, the

189

combustion rate is mainly impacted by the laminar flame speed (LFS) [39]. However, the ICD also

190

depends on two important thermodynamic properties, i.e. the latent heat of vaporization and the

191

vapor pressure. The latent heat of vaporization exerts a charge cooling effect which reduces the pre-

192

ignition temperature, and thus decreases the chemical reaction rate and prolongs the ICD time.

193

Although the engine used in this study is port-fuel injected, previous studies [44, 45] have shown

194

that a charge cooling effect still exists because liquid droplets can be observed in the combustion

195

chamber after the intake process. As for the vapor pressure, it has been found that the vapor

196

pressure of butanol is much lower than that of acetone, ethanol and gasoline, which means that

197

butanol would need a higher temperature or a longer time to get completely vaporized [36]. Wallner

198

et al. and Deng et al. [46, 47] found that combustion phasing was retarded after adding butanol to

199

gasoline. Compared to G100, ABE(361)30 and ABE(361)60 had 3.9% and 8.4% shorter ICD, but

200

ABE(361)10 did not, which could be explained by the fact that a small addition of a component

201

with higher LFS does not show any major effects on the LFS of the blend [48, 49], and it has been

202

shown that the first stage of combustion strongly depends on the LFS [37]. During the MCD, which 10

ACCEPTED MANUSCRIPT 203

consists of fully developed bulk burn, the combustion is dominated by the turbulent flame. The

204

MCD of the test fuels followed a sequence similar to that of the ICD. This is because the ICD could

205

influence the following MCD, the higher pressure built up during the early combustion phase

206

promotes the mixing of fuel and air due to the increase in turbulence, and it improves the

207

combustion rate in the following flame propagation [39]. ABE(361)60 showed 1°CA, 1.25°CA and

208

0.5°CA advanced 50% MFB location compared to G100, ABE(361)10 and ABE(361)30,

209

respectively.

210

Table 5 compares the engine performance of G100, ABE(361)10, ABE(361)30 and

211

ABE(361)60, including brake thermal efficiency (BTE) and brake specific fuel consumption

212

(BSFC). The BTE indicates how well an engine can convert chemical energy in the fuel into

213

mechanical energy. The results showed that G100 had the highest BTE; this is because the engine

214

was operating at the spark timing of gasoline’s MBT, and the improper combustion phasing of

215

ABE-gasoline blends resulted in an overall decrease of net useful work. The lower BTE of

216

ABE(361)10 could also be caused by poor combustion quality reflected by the increased UHC

217

emission. However, a BTE similar to that of G100 was observed with ABE(361)30 likely due to

218

improved combustion quality owing to the fuel-borne oxygen of ABE offsetting the loss in net work

219

owing to improper combustion phasing to a certain extent. For ABE(361)60, combustion phasing

220

was more advanced and more net work loss was caused. Although oxygen concentration increases,

221

its effect on combustion quality improvement was limited, and then a reduced BTE was obtained

222

[50]. In addition, it can be seen that the engine had a relatively high fuel consumption, which is due

223

to the high friction owing to it being a single-cylinder engine; it could also be caused by

224

carbon deposition in the engine, or aging of the sparkplug. The BSCF of ABE(361)10, ABE(361)30

225

and ABE(361)60 is 4.6%, 10.4% and 24.3% higher than that of G100, respectively, due to the lower 11

ACCEPTED MANUSCRIPT 226

LHV of ABE.

227

Table 5 also compares the emissions of G100, ABE(361)10, ABE(361)30 and ABE(361)60,

228

including CO, UHC and NOx. Generally, a higher CO emissions level could be caused by a locally

229

rich mixture, insufficient oxidizer or low combustion temperature. After adding ABE, the lack of

230

oxygen should not lead to increased CO emissions. Previous studies have explained that alcohol-

231

containing fuels can cause charge cooling effect and produce more products in terms of heat

232

capacity of the combustion products, which reduce temperature at sparking timing and combustion

233

process, respectively [14, 36, 51, 52]. This reduced temperature further slow down the post-flame

234

oxidation of CO emissions. The following lists stoichiometric chemical reactions of gasoline,

235

ethanol, butanol and acetone. UHC emissions are mainly influenced by the combustion quality. The

236

oxygen content in ABE is beneficial to improve combustion quality. However, the lower AFR of

237

ABE also led to more fuel being injected, which resulted in a higher amount of fuel getting into the

238

crevice volumes or absorbed in oil layers and deposits [53]. Compared to the UHC emission of

239

gasoline, ABE(361)10 showed a larger one, while ABE(361)30 and ABE(361)60 showed a lower

240

one. It could be due to the positive effect of increasing oxygen concentration on UHC emission

241

reduction becoming larger than the negative effect of more fuel being injected with ABE blend ratio

242

increase. In addition, the poor combustion quality of ABE(361)10 reflected from low BTE can also

243

result in UHC emission increase. Zeldovich thermal activation is the predominant mechanism for

244

NOx emissions formation from internal combustion engines. The higher combustion temperature

245

and local oxygen concentration in the peak temperature zone favor NOx emissions formation [54].

246

By using ABE(361)10, the NOx emissions were13.1% higher than that from G100. However, with

247

continuously increasing ABE ratio, a 6.3% and 27.3% decrease in NOx emissions were produced by

248

ABE(361)30 and ABE(361)60, respectively. Najafi et al. [55] and Zhuang et al. [56] had reported 12

ACCEPTED MANUSCRIPT 249

that oxygenated fuels could increase NOx emissions due to the fuel-borne oxygen. In contrast, the

250

higher oxygen content in the fuel blend could also decrease the NOx emissions by lowering

251

combustion temperature, as described in the discussion of CO emissions [57, 58]. Therefore, the

252

various NOx emissions levels in this part could be explained by the balance between fuel-borne

253

oxygen and reduced combustion temperature. Gasoline : C7 H13.3  10.33(O 2 + 3.785 N 2 )  7 CO 2 + 6.66 H 2 O+ 39.10 N 2

254

Acetone :  C3 H 7 OH+10.33(O 2 + 3.785 N 2 ) = 7.74 CO 2 + 7.74 H 2 O+ 39.10 N 2 Butanol :1.72 C4 H 9 OH+10.33(O 2 + 3.785 N 2 ) = 6.88CO 2 + 8.60 H 2 O+ 39.10 N 2 Ethanol :3.44 C2 H 5OH+10.33(O 2 + 3.785 N 2 ) = 6.88CO 2 +10.32 H 2 O+ 39.10 N 2

255

3.2. Effects of ABE mixture formulation on performance, combustion and emissions characteristics

256

In a typical ABE fermentation process, acetone, butanol and ethanol are produced at a ratio

257

of 3:6:1, respectively. The products proportion of ABE fermentation is mainly affected by substrate,

258

strain, and production process. With the development of ABE fermentation technology, such as

259

producing new strains of bacteria by mutagenesis, evolutionary or metabolic engineering, using

260

upstream processing of pretreatment, hydrolysis or detoxification, replacing batch and fed-batch

261

fermentation processes by continuous fermentation processes, etc., the ratio of acetone, ethanol,

262

butanol and by-products can be adjusted in a certain extent. [59, 60]. Therefore, the effects of

263

changing the ratio of acetone and butanol in ABE mixture on performance, combustion and

264

emissions characteristics at stoichiometric condition and 304.87-309.24 kPa BMEP corresponding

265

to 60 kPa MAP were investigated in Fig. 3 and Table 6 based on the comparisons between

266

ABE(181)30, ABE(361)30 and ABE(541)30 with the A:B:E ratio of 1:8:1, 3:6:1 and 5:4:1,

267

respectively. Fig. 3 shows the pressure and MFB traces of the three fuels. It was found that a similar

268

peak pressure was obtained, while combustion phasing was slightly advanced with increasing

269

butanol concentration. As shown in Table 6, compared to ABE(541)30, ABE(181)30 and ABE(361) 13

ACCEPTED MANUSCRIPT 270

had a 2.1% and 2.0% shorter ICD, 2.6% and 1.2% shorter MCD, and 0.75°CA and 0.5°CA

271

advanced 50% MFB location, respectively.

272

Among the ABE-gasoline blends with various ABE component ratios, ABE(361)30 obtained

273

better results for the BTE and BSFC as shown in Table 6. ABE(361)30 showed a 1.4% and 1.5%

274

higher BTE, and 0.8% and 2.5% lower BSFC than those of ABE(181)30 and ABE(541)30,

275

respectively. In comparison with ABE(361)30, the advanced combustion phasing and the lower

276

oxygen content of ABE(181)30 caused a higher loss in net work and a lower combustion quality,

277

and therefore a reduced BTE. The lower BTE of ABE(541)30 might be due to its longer

278

combustion duration and lower combustion temperature which can be linked to the results of CO

279

and NOx emissions in next section. ABE(541)30 showed the largest BSFC due to its relatively

280

lower LHV.

281

Table 6 also shows the effect of changing acetone and butanol ratios on the emissions. The CO

282

emissions of ABE(541)30 were significantly increased by 31.2% and 36.1% relative to

283

ABE(181)30 and ABE(361)30, respectively. With increasing acetone ratio, the increased

284

combustion duration and oxygen concentration were beneficial for CO oxidation. Therefore, the

285

relatively higher CO emissions for ABE(541)30 might be attributed to the lower combustion

286

temperature. In addition, UHC emissions decreased with increasing acetone ratio in ABE, and

287

ABE(541)30 showed 38.5% and 21.2% lower UHC emissions than that of ABE(181)30 and

288

ABE(361)30, respectively. Increasing acetone concentration caused an increased oxygen

289

concentration, which led to a better combustion quality and resulted in the lowest UHC emissions

290

from ABE(541)30. However, the higher oxygen content of ABE(541)30 produced 6.6% and 2.5%

291

higher NOx emissions than that of

292

3.3. Effect of containing water on performance, combustion and emissions characteristics 14

ABE(181)30 and ABE(361)30, respectively.

ACCEPTED MANUSCRIPT 293

If the dehydration process is eliminated, less than 1% water will be contained in the ABE

294

mixture [61]. The effects of containing water on performance, combustion and emissions

295

characteristics were studied by comparing ABE(361)30, ABE(361)29.5W0.5, and ABE(361)29W1

296

at stoichiometric condition and 309.24-314.71 kPa BMEP corresponding to 60 kPa MAP. Fig. 4

297

and Table 7 investigated the combustion characteristics of the fuels. It was found that the ICD and

298

MCD of ABE29.5W0.5 were increased by 5.9% and 1.4%, while those of ABE29W1 were

299

decreased by 0% and 2.9%, respectively, when compared to ABE30. Das et al. investigated the

300

effect of water addition on the combustion of H2/CO-air mixtures, and found that water addition

301

improved chain reactions and increased combustion rate [62]. Dryer and Rajan explained the

302

improved combustion rate as a result of the catalytic activity of water vapor due to increased OH

303

radicals [63, 64]. However, the water addition can also reduce combustion temperature and lower

304

combustion rate. Then, ABE29W1 showed a shorter MCD compared to G100, but ABE29.5W0.5

305

did not. The physical and chemical kinetic roles of water in hydrocarbon fuels combustion are still

306

not completely understood and elucidated [65].

307

The performance results in Table 7 showed that ABE(361)29.5W0.5 and ABE29W1 had 0.6%

308

and 0.9% higher BTE compared to that of ABE(361)30, respectively. It could be caused by the

309

shorter combustion duration and catalytic activity of water vapor for ABE29W1, and the

310

combustion phasing being more close to that of gasoline for ABE(361)29.5W0.5. In addition,

311

ABE(361)29.5W0.5 and ABE(361)29W1 showed a 1.5% and 2.8% reduction in BSFC than that of

312

ABE(361)30, respectively, due to the higher thermal efficiency.

313

The emissions results in Table 7 showed that CO emission was reduced for

314

ABE(361)29.5W0.5 and ABE(361)29W1 compared to ABE(361)30 because of the water-gas shift

315

mechanism describing the reaction of carbon monoxide and water vapor to form carbon dioxide and 15

ACCEPTED MANUSCRIPT 316

hydrogen over the temperature range of 600-2000 K. For UHC emission, a trend opposite to that of

317

CO emission was found based on the fact that UHC oxidation reactions were retarded by the

318

reduced combustion temperature owing to water addition [66], which also led to the decrease of

319

NOx emission [65].

320

3.4. Comparison with conventional fuels under various equivalence ratios and engine loads

321

According to the results mentioned above, ABE(361)30 performed well in terms of both

322

engine performance and emissions. ABE(361)30 was further compared with E30, B30, G100 under

323

the equivalence ratios ranging from 0.83 to 1.25 and the engine loads of 274.28-310.33 and 485.17-

324

524.07 kPa BMEP corresponding to 60 and 90 kPa MAP, respectively. The combustion

325

characteristics of different fuels are shown in Fig. 5. It was apparent that the ICD and MCD

326

decreased with increasing equivalence ratio and engine load. A higher cylinder temperature was

327

attained under high engine load, which caused a faster combustion rate. Gauthier et al. [67] had also

328

found that ICD decreased with increasing equivalence ratio. In addition, with the increases of

329

equivalence ratio and engine load, the differences in ICD and MCD between different fuels were

330

reduced, which were consistent with results from [67, 68]. Overall, compared to G100, E30, B30

331

and ABE(361)30 had a more advanced combustion phasing due to the higher LFS, and presented

332

2.8-9.6%, 2.4-11%, and 0.4-3.9% shorter ICD, and 3.2-10.9%, 1.6-13.8% and 1.6%-8.3% shorter

333

MCD, respectively.

334

Fig. 6 shows the BTE and BSFC of E30, B30, ABE(361)30 and G100 with respect to

335

equivalence ratio and engine load. The BTE increased with decreasing equivalence ratio and

336

increasing engine load. The higher combustion temperature at 90 kPa MAP resulted in an improved

337

combustion quality and thus a higher BTE. When equivalence ratio was decreased, increased

338

dilution improved isentropic efficiency by lowering temperatures and increasing the adiabatic index 16

ACCEPTED MANUSCRIPT 339

value [69]. At stoichiometric and rich conditions, G100 had a higher BTE due to the fact that the

340

engine was running at gasoline’s MBT timing and the advanced combustion phasing of E30, B30,

341

and ABE30 resulted in a higher net work loss in the compression stroke as mentioned above.

342

However, it should be noted that E30, B30 and ABE30 obtained 0.4-2.1%, 0.5% and 0.4-1.4%

343

higher BTE at lean conditions compared to G100, respectively. It can be explained by the fact that

344

the combustion phasing of fuels typically is retarded at lean conditions due to an increased ICD and

345

MCD, and spark timing needs to be advanced to improve combustion phasing. Therefore, the

346

advanced combustion phasing of E30, B30 and ABE30 was more appropriate compared to G100.

347

Meanwhile the fuel-borne oxygen of E30, B30, and ABE30 was beneficial in improving BTE. The

348

BSFC increased with increasing equivalence ratio and decreasing engine load because of the

349

decreased BTE. Due to the lower LHV, E30, B30 and ABE(361)30 showed a 11.5-15.4%, 7.7%-

350

11.3% and 8.1-10.4% higher BSFC than that of G100, respectively.

351

Fig. 7 shows the variations of CO, UHC and NOx emissions with equivalence ratio and engine

352

load for E30, B30, ABE(361)30 and G100. It was observed that the equivalence ratio controlled CO

353

emissions until lean condition were reached after which CO emissions did not vary significantly.

354

These low CO emissions under lean conditions could be explained by the fact that there was more

355

than enough oxygen available to complete the oxidation process [70]. ABE(361)30 produced 1.2-

356

36.7%, 0.6-76.7% and 1.4-4.4% lower CO emissions compared to E30, B30 and G100,

357

respectively, which might be caused by a better balance between the increased oxygen content and

358

the decreased combustion temperature. On the other hand, UHC emissions increased under rich

359

conditions because of incomplete combustion as the combustion quality deteriorated [70]. Due to

360

the improved combustion quality as a result of fuel-borne oxygen, E30, B30 and ABE30 showed

361

12.1-25.1%, 12.4-27.5% and 0.3-9.9% lower UHC emissions relative to G100, respectively. It was 17

ACCEPTED MANUSCRIPT 362

observed from Fig. 6(c) that the highest NOx emissions were seen at Φ=0.9-1.0 with a decrease as

363

the equivalence ratio got relatively richer or leaner because relatively complete combustion was

364

attained under Φ=0.9-1.0 which led to a higher peak combustion temperature [71]. Similarly, higher

365

NOx emissions were produced at 90 kPa MAP due to the higher cylinder temperature. In

366

comparison with G100, although a higher oxygen concentration was provided, a decreased

367

combustion temperature was also caused such that 0.4-10.4%, 2.3-11.1% and 4.2-14.6% lower NOx

368

emissions were produced at lean and stoichiometric conditions for E30, B30 and ABE(361)30,

369

respectively. It was also observed that E30, B30 and ABE30 presented a higher NOx emissions

370

compared to G100 at some rich conditions. It is likely due to the fuel-rich prompt mechanism of

371

NOx emissions formation [13], which means more hydrocarbon radicals generated from E30, B30

372

and ABE30 due to their lower molecular weight, and a higher amount of fuel injected increased the

373

formation of HCN and led to higher NOx emissions.

374

4. Conclusions

375

This experimental study revealed the potential of ABE-gasoline blends as a green fuel for SI

376

engines. The effects of ABE-gasoline blends on performance, combustion and emissions

377

characteristics were investigated. Some conclusions were obtained as follows.

378

1. By comparing ABE-gasoline blends with varying ABE content under stoichiometric condition,

379

it was found that ABE(361)30 and ABE(361)60 showed an advanced combustion phasing with

380

a shorter ICD and MCD when compared to G100. ABE addition caused a reduction in BTE

381

because the engine was running at the spark timing corresponding to gasoline’s MBT and the

382

decreased BTE caused by improper combustion phasing of ABE-gasoline blends could not be

383

offset by improved combustion quality due to fuel-borne oxygen. In comparison with different

384

ABE-gasoline blends, ABE(361)30 provided better results based on its slight decrease in BTE 18

ACCEPTED MANUSCRIPT 385

(0.6%), and lower CO (8.7%), UHC(5.8%) and NOx (5.2%) emissions than those of G100.

386

2. The study on ABE-gasoline blends with various ABE component ratios under stoichiometric

387

condition showed that the combustion phasing was retarded with increasing acetone and

388

decreasing butanol, which also caused decreased UHC, increased NOx emission, and initially

389

decreased then increased CO emissions. As for engine performance, ABE(361)30 displayed a

390

higher BTE and a lower BSFC than that of ABE(181)30 and ABE(541)30.

391

3. The investigation of water-containing ABE-gasoline blends under stoichiometric condition

392

showed that ABE(361)29.5W0.5 and ABE(361)29W1 had a retarded and advanced combustion

393

phasing , respectively, when compared to ABE(361)30. Meanwhile, the addition of 0.5 vol.%

394

and 1 vol.% water improved BTE and reduced BSFC, CO and NOx emissions, but increased

395

UHC emission.

396

4. Among the different ABE-gasoline blends mentioned above, ABE(361)30 performed well in

397

terms of both engine performance and emissions, and thus it was further compared with E30,

398

B30 and G100 under various equivalence ratios and engine loads. E30, B30 and ABE(361)30

399

had a generally advanced combustion phasing. A higher BTE than that of G100 was attained by

400

E30, B30 and ABE(361)30 at lean conditions due to improved combustion phasing; meanwhile,

401

the combustion quality was improved by fuel-borne oxygen. In addition, decreased emissions

402

were also produced by E30, B30 and ABE(361)30. In general, the higher BTE (0.2-1.4%) and

403

the lower CO (1.4-4.4%), UHC (0.3-9.9%) and NOx (4.2-14.6%) emissions were observed for

404

ABE(361)30 when compared to G100.

405 406

Acknowledgments This material is based upon work supported by the National Science Foundation (Grant No. 19

ACCEPTED MANUSCRIPT 407

CBET-1236786). This work was also supported in part by China Scholarship Council and by the

408

Fundamental Research Funds for the Central Universities (Grant No. 2012zzts016).

409

References

410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448

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ACCEPTED MANUSCRIPT 558

Figures:

559 560

Fig. 1. Engine setup

561 4000 3500

Pressure (kPa)

3000

1500 Pressure (kPa)

(a)

2500

1400 1300 1200 1100 1000 -6.0

2000

-5.5

-5.0

-4.5

-4.0

Crank Angle (°CA ATDC)

1500 G100 ABE(361)10 ABE(361)30 ABE(361)60

1000 500 0 -30

-20

-10

0

10

20

30

Crank Angle (°CA ATDC)

(b)

1.0

G100 ABE(361)10 ABE(361)30 ABE(361)60

Mass Fraction Burnt

0.8 0.6 0.4 0.2 0.0 -20

-15

562

-5 0 5 10 15 Crank Angle (°CA ATDC)

20

25

17.50

24 17.75

17.50

16 12

16.75 12

13.31

13.31

12.81

12.56

ion (°CA ATDC)

20 16 and ABE30(541) (c)of pressure Fig. 2. Comparisons and0-10% MFB MFB between G100, ABE30(181), ABE30(361) 10-90% MFB 50% MFB 0-90% MFB (°CA)

563

-10

ACCEPTED MANUSCRIPT (a)

4000 3500

Pressure (kPa)

3000

ABE(181)30 ABE(361)30 ABE(541)30

2500 2000 1500 1000 500 0 -30

(b)

1.0

Mass Fraction Burnt

0.8

-20

-10 0 10 Crank Angle (°CA ATDC)

20

30

ABE(181)30 ABE(361)30 ABE(541)30

0.6 0.4 0.2 0.0 -20

-15

-10

0

5

10

15

20

25

Crank Angle (°CA ATDC)

564

Fig. 3. Comparisons of pressure and MFB between ABE(181)30, ABE(361)30 and ABE(541)30 20

0-10% MFB

10-90% MFB

50% MFB

16

17.29

17.5

17.74

12

12.56

12.81

12.82

8

16 12 8

4 3.31 0

20

ABE(181)30

3.81

4.06

ABE(361)30 Fuels

ABE(541)30

25

4 0

50% MFB Location (°CA ATDC)

(c)

0-10% MFB and 10-90% MFB (°CA)

565

-5

ACCEPTED MANUSCRIPT (a)

4000 3500

ABE(361)30 ABE(361)29.5W0.5 ABE(361)29W1

Pressure (kPa)

3000 2500 2000 1500 1000 500 0 -30

-20

-10

0

10

20

30

Crank Angle (°CA ATDC)

(b)

1.0

Mass Fraction Burnt

0.8 0.6 0.4 0.2 0.0 -20

566 567

ABE(361)30 ABE(361)29.5W0.5 ABE(361)29W1

-15

-10

-5

0

5

10

15

20

25

Crank Angle (°CA ATDC)

Fig. 4. Comparisons of pressure and MFB between ABE(361)30, ABE(361)29.5W0.5 and ABE29W1

26

ACCEPTED MANUSCRIPT (a)

-30

4000

=0.83 E30 =0.83 B30 =0.83 ABE(361)30 =0.83 G100 =1.0 E30 =1.0 B30 =1.0 ABE(361)30 =1.0 G100 =1.25 E30 =1.25 B30 =1.25 ABE(361)30 =1.25 G100

3500

Pressure (kPa)

2500 2000 1500 1000

Crank Angle (°CA ATDC) -10 0 10

20

30 1.0

60 kPa MAP 0.8 0.6 0.4

Mass Fraction Burnt

3000

-20

0.2

500 0 -30

-20

-10

0

10

20

0.0

30

Crank Angle (°CA ATDC)

(b)

20

60 kPa MAP

90 kPa MAP

E30 B30 ABE(361)30 G100

0-10% MFB (°CA)

15

10

5

0

0.83

0.91

1.0

1.1

1.25

0.83

25

1.0

1.1

60 kPa MAP

90 kPa MAP

20 10-90% MFB (°CA)

1.25

Equivalence Ratio

Equivalence Ratio

(c)

0.91

E30 B30 ABE(361)30 G100

15 10 5 0

568 569 570

0.83

1.1 0.91 1.0 Equivalence Ratio

1.25

0.83

1.1 0.91 1.0 Equivalence Ratio

1.25

Fig. 5. Comparisons of combustion characteristics between E30, B30, ABE(361)30 and G100 under various equivalence ratios and engine loads: (a) Pressure and MFB; (b) 0-10% MFB; (c) 10-90% MFB.

27

ACCEPTED MANUSCRIPT (a)

30

90 kPa MAP

60 kPa MAP

E30 B30 ABE(361)30 G100

BTE (%)

25

20

15

0.83

0.91

1.0

1.1

1.25

0.83

Equivalence Ratio

(b)

600

BSFC (g/kWh)

500

1.1 0.91 1.0 Equivalence Ratio

60 kPa MAP

E30 B30 ABE(361)30 G100

1.25

90 kPa MAP

400 300 200 100 0

571 572 573

0.83

0.91

1.0

1.1

1.25

0.83

0.91

1.0

1.1

1.25

Equivalence Ratio

Equivalence Ratio

Fig. 6. Comparisons of engine performance between E30, B30, ABE(361)30 and G100 under various equivalence ratios and engine loads: (a) BTE; (b) BSFC

28

ACCEPTED MANUSCRIPT (a)

7

90 kPa MAP

60 kPa MAP

E30 B30 ABE(361)30 G100

6

CO (% Vol.)

5 4 3 2 1 0

0.83

0.91

1.0

1.1

1.25

0.83

Equivalence Ratio

(b)

500

UHC (ppm Vol.)

1.0

1.1

1.25

Equivalence Ratio

60 kPa MAP

E30 B30 ABE(361)30 G100

400

0.91

90 kPa MAP

300 200 100 0

0.83

0.91

1.0

1.1

1.25

0.83

Equivalence Ratio

(c)

2000

0.91

1.0

1.1

Equivalence Ratio

60 kPa MAP

90 kPa MAP

E30 B30 ABE(361)30 G100

1500 NOx (ppm)

1.25

1000

500

0

574 575 576

0.83

0.91

1.0

1.1

1.25

Equivalence Ratio

0.83

0.91

1.0

1.1

1.25

Equivalence Ratio

Fig. 7. Comparisons of emissions between E30, B30, ABE(361)30 and G100 under various equivalence ratios and engine loads: (a) CO; (b) UHC; (c) NOx

29

ACCEPTED MANUSCRIPT 577

Tables:

578 Parameters

Table 1 Properties of the test fuels Individual fuels Gasoline

Acetone

Butanol

Fuel blends Ethanol

ABE (181)

Chemical formula C4-C12 C3H6O C4H9OH C2H5OH Research octane number 92 117 96 121 Oxygen content (wt.%) 27.6 21.6 34.8 23.5 Density (kg/m3) 715-765 791 813 795 809 Lower heating value (MJ/kg) 43.4 29.6 33.1 26.8 32.1 38-204 56 118 78 Boiling Temperature (℃) Latent heat at 298 K (kJ/kg) 380-500 518 582 904 607.8 Stoichimometric AFR 14.7 9.5 11.2 9.0 10.8 343 420 Auto-ignition temperature (℃) 228-470 465 A B C Laminar flame speed (cm/s) 33-44 34 48 48C Note: Ap=1 atm, T =298-358K, Φ=1; Bp=1 atm, T = 298 K, Φ=1; Cp=1 atm, T =343 K, Φ=1 579 580

ABE (361)

ABE (541)

24.7 804.6 31.4

25.9 800.2 30.7

595 10.5

582.2 10.1

37B

Table 2 Engine specifications Engine type Fuel Injection Displaced volume (cm3) Stroke (mm) Bore (mm) Connecting rod length (mm) Compression ratio Number of valves Number of cylinders

SI engine Port Fuel Injection (PFI) 575 90.1 90.3 150.7 9.6:1 4 1

581 582

Table 3 Measuring range, accuracy and resolution of the experimental apparatus Apparatus Engine speed Torque Exhaust gas temperature CO emission HC emission CO2 emission NOx emission Lambda Mass flow meter Pressure transducer Shaft encoder

Measuring range 1-5000 rpm 0-300 Nm 0-900 ℃ 0-10% Vol 0-10000 ppm Vol 0-20% Vol 0-3000 ppm 0.65-13.7 0-800 L/min 0-25000 kPa 0-30000 rpm

583 584 585 586 587 588

30

Accuracy (±) 0.2% 0.5% 1℃ 0.06% 12 ppm Vol 0.5% 3% 0.3 % 1% 0.4% 0.5 bit

Resolution 1 rpm 0.1 Nm 0.1 ℃ 0.01% Vol 1 ppm Vol 0.01% Vol 1 ppm 0.01 0.1 L/min 1 kPa 12 bit

ACCEPTED MANUSCRIPT 589

Table 4 Test conditions Throttle position (%) Engine speed (rpm) Load (kPa BMEP) Equivalence ratio Fuel pressure (bar) Spark timing (° BTDC)

590 591 592

100 1200 310.33 and 524.07 0.83-1.25 3 18 and 15

Table 5 Comparisons of combustion, performance, and emissions characteristics between G100, ABE(361)10, ABE(361)30 and ABE(361)60 Combustion

Performance

Emissions

Fuel

ICD (°CA)

MCD (°CA)

50%MFB (°ATDC)

BTE (%)

BSFC (g/kWh)

CO (g/kWh)

UHC (g/kWh)

NOx (g/kWh)

G100 ABE(361)10 ABE(361)30 ABE(361)60

13.31 13.31 12.81 12.56

17.50 17.75 17.50 16.75

4.31 4.56 3.81 3.31

21.56 21.23 21.42 20.94

384.7 402.6 424.7 478.0

13.5 13.4 12.5 19.8

6.7 8.0 6.3 4.5

8.4 9.5 7.9 6.6

593 594 595

Table 6 Comparisons of combustion, performance, and emissions characteristics between ABE(181)30, ABE(361)30 and ABE(541)30 Combustion

Performance

Emissions

Fuel

ICD (°CA)

MCD (°CA)

50%MFB (°ATDC)

BTE (%)

BSFC (g/kWh)

CO (g/kWh)

UHC (g/kWh)

NOx (g/kWh)

ABE(181)30 ABE(361)30 ABE(541)30

12.56 12.81 12.82

17.29 17.50 17.74

3.31 3.81 4.06

21.12 21.42 21.10

428.4 424.7 434.5

13.8 12.5 18.1

7.2 6.3 5.2

7.6 7.9 8.1

596 597 598

Table 7 Comparisons of combustion, performance, and emissions characteristics between ABE(361)30, ABE(361)29.5W0.5 and ABE29W1 Combustion

Performance

Emissions

Fuel

ICD (°CA)

MCD (°CA)

50%MFB (°ATDC)

BTE (%)

BSFC (g/kWh)

CO (g/kWh)

UHC (g/kWh)

NOx (g/kWh)

ABE(361)30 ABE(361)29.5W0.5 ABE(361)29W1

12.81 13.56 12.81

17.50 17.75 17.00

3.81 4.56 3.56

21.42 21.54 21.61

424.7 418.3 412.9

12.5 9.6 7.5

6.3 9.7 8.2

7.9 6.1 5.7

599

31