Comparison of the Physical and Chemical Properties, Performance

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A comparison of the physical and chemical properties, performance and emissions of ethyl levulinatebiodiesel-diesel and n-butanol-biodiesel-diesel blends Zhiwei Wang, Tingzhou Lei, Lu Lin, Miao Yang, Zaifeng Li, Xiaofei Xin, Tian Qi, Xiaofeng He, Jie Shi, and Xiaoyu Yan Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b02851 • Publication Date (Web): 28 Mar 2017 Downloaded from http://pubs.acs.org on April 3, 2017

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Energy & Fuels

A comparison of the physical and chemical properties, performance and emissions of ethyl levulinate-biodiesel-diesel and n-butanol-biodiesel-diesel blends

Zhiwei Wang a,b,c*, Tingzhou Lei b*, Lu Lin d, Miao Yang a,b, Zaifeng Li

a,b

, Xiaofei Xin a,b, Tian Qi a,b,

Xiaofeng He a,b, Jie Shi a,b, Xiaoyu Yanc*

a

Energy Research Institute Co., Ltd, Henan Academy of Sciences, Huayuan Road 29, Zhengzhou, Henan

450008, PR China b

Henan Key Lab of Biomass Energy, Huayuan Road 29, Zhengzhou, Henan 450008,PR China

c

Environment and Sustainability Institute, University of Exeter Penryn Campus, Penryn, TR10 9FE, UK

d

School of Energy Research, Xiamen University, Xiamen, Fujian 361005, PR China

Abstract: In this study, fuel blends EL5-B10-D85 (5 vol.% ethyl levulinate, 10 vol.% biodiesel and 85 vol.% diesel), EL10-B15-D75, nBu5-B10-D85 (5 vol.% n-butanol, 10 vol.% biodiesel and 85 vol.% diesel), and nBu10-B15-D75 were compared on a horizontal, four-stroke and single-cylinde engine. Ethyl levulinate-biodiesel-diesel (EL-B-D) blends and n-butanol-biodiesel-diesel (nBu-B-D) blends showed good miscibility. Generally, EL-B-D blends were more effective than nBu-B-D blends for decreasing kinematic viscosity, increasing closed cup flash point and oxygen content, although nBu-B-D blends were more effective than EL-B-D blends for decreasing cold filter plugging point and distillation. Overall, when used in a diesel engine, the fuel blends showed slightly higher brake specific fuel consumption (BSFC) than neat diesel, with EL-B-D being slightly higher than nB-B-D. EL-B-D blends were more effective than nB-B-D blends for reducing carbon monoxide (CO) emissions and smoke opacity, while nitrogen oxides (NOx) and carbon dioxide (CO2) emissions increase was more obvious in EL-B-D blends. Compared with EL-B-D blends, hydrocarbon (HC) emissions of nBu-B-D blends were higher. The results provide a useful reference for further research of the effects of using these blends on emissions. Keywords: Ethyl levulinate-biodiesel-diesel blends; n-butanol-biodiesel-diesel blends; Physical, chemical properties; Diesel engine; Performance; Emissions 1

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1 Introduction The invention and improvement of combustion engines and related technologies have led to the widespread use of oil reserves and accelerated the depletion of oil resources 1. Growth of the world’s energy demand and the environmental impacts associated with petroleum-based fuels have motivated the search for renewable alternative fuels

2,3

. In recent years, numerous investigations have focused on the application of alternative

fuels such as biodiesel

4–6

, n-butanol

7–10

and ethyl levulinate (EL)

11,12

to reduce engine emissions and

petroleum consumption. Some success has been achieved with the partial substitution of diesel with one or several biofuels as an alternative to its full replacement 13–16. Biodiesel has been a lucrative commodity in global trade because of mounting concerns over environmental and oil depletion issues17. However, compared to neat diesel, biodiesel has properties of higher viscosity, cold filter plugging point (CFPP) and distillation temperature, which are not conducive to its use in diesel engines 18

. There are also disadvantages to use biodiesel in cold environments due to its higher pour point, higher

viscosity, and lower volatility compared with diesel

14,15

. Thus, it is very important to include other fuel

additives in the biodiesel blend to improve properties such as its viscosity, CFPP, and distillation temperature. Butanol has been suggested as a future fuel biocomponent that can be used with both gasoline and diesel 19–21

. Compared with gasoline and diesel fuels, butanol has excellent fuel properties and environmental

performance, such as wide production sources, higher oxygen content and higher heat of evaporation 22,23. In addition, compared with ethanol, butanol has more advantages with respect to volatility, heating value, corrosiveness, lower water absorption

24

, and less delay time25. Compared with neat diesel, butanol-diesel

blends lead to a positive effect on the reduction in the smoke opacity and particle concentration26. Butanol can be produced from the alcoholic fermentation of biomass feed stocks including edible materials such as corn, sugar cane and molasses, as well as agricultural wastes such as wheat straw, corn stover and other cellulose materials 19,27. The levulinates are produced through esterification of levulinic acid, which not only can be used in flavoring and fragrance industries, but also can be used as fossil gasoline and diesel fuel extenders 28,29. EL is a levulinate ester with an oxygen content of 33%. Fuel blends with 20 vol % EL, 79 vol % neat diesel and 1 vol % co-additive are reported to have a 6.9% oxygen content and produce lower smoke than diesel when burned30. Researchers have analysed the distillation properties of EL-diesel fuel blends30 and low temperature 2


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properties of EL-biodiesel fuel blends containing 2.5, 5, 10, and 20 vol % EL31. The performance and exhaust emissions in a horizontal single-cylinder four stroke diesel engine have been studied to evaluate EL as an additive to neat diesel. The diesel engine functions normally when running on EL-diesel blends containing up to 10% EL without any other latent solvent or co-additive 12. Biomass-based EL can be a blending component or oxygenated additive in biodiesel and diesel fuel blends for use in unmodified diesel engines

15,33

. Many

different kinds of starch and sugar crops as well as agriculture and forestry residues have been used to produce levulinic acid and ethanol

34,35

. Existing technology can already convert 50 wt %, 20 wt % and 30 wt % of

six-carbon sugars to levulinic acid, formic acid and tars, repectively 36. Wheat straw, for example, can be used as a potential raw material for producting EL directly with ethanol 37. Moreover, EL production processes can have low costs due to the higer conversion rate from cellulose to levulinic acid38. EL and n-butanol are typical representatives of levulinate esters and alcohols, respectively. Although EL or n-butanol blends with diesel and biodiesel have been investigated extensively as fuels for diesel engines 13,15,16,32,39,40

, comparisons of EL with n-butanol fuel blends used in the same diesel engines are limited. In this

study, we evaluated the effects of using EL and n-butanol as additives to biodiesel-diesel blends on physical and chemical properties, and the performance and emissions of a direct injection diesel engine. The objective of this research was to evaluate the potential of adding EL and n-butanol to different diesel-biodiesel blended fuels to improve the fuel’s overall physical and chemical properties. The performance and emissions of ethyl levulinate-biodiesel-diesel (EL-B-D) and n-butanol-biodiesel-diesel (nBu-B-D) blends in a diesel engine were also evaluated.

2 Experiment material and methods 2.1 Experiment material Diesel (0#) was purchased from the Henan Branch of China Petroleum and Chemical Corporation in Zhengzhou, China. EL was obtained from Xinxiang Xinfeng Industry Co. Ltd. (Xinxiang, China). Biodiesel (the main element of which is fatty acid methyl ester, the feedstock is waste cooking oil) was purchased from Zhengzhou Qiaolian Bio-Energy Co. Ltd. (Zhengzhou, China). N-butanol was purchased from Tianjin Fuyu Co. Ltd. (Tianjin, China). The fuel blends were labelled as ELx-Bx-Dx or nBux-Bx-Dx, where EL represents ethyl levulinate, B represents biodiesel, nBu represents n-butanol, D represents diesel, and x represents the 3


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component percent volume in fuel blends. For example, EL5-B10-D85 represents 5 vol % ethyl levulinate, 10 vol % biodiesel and 85 vol % diesel. Neat diesel, EL5-B10-D85, EL10-B15-D75, nBu5-B10-D85, and nBu10-B15-D75 blends were prepared for physical and chemical property analyses and engine testing (Fig. 1).

Fig. 1. A schematic representation of the experiment.

2.2 Experiment methods for physical and chemical properties Physical and chemical properties of the fuel blends were measured according to the China National Standards and Codes. Cold filter plugging point (CFPP) was determined according to the requirements of SH/T 0248 41, using a CFPP instrument (JSR1604; Jinshi, China) with a lowest measurement of -45oC (i.e. the lower limit of the instrument) and an accuracy of ± 0.5 oC. Distillation was determined according to the requirements of GB/T 6536

42

, using a distillation instrument (JSR1008B; Jinshi, China) with a maximum

distillation temperature measurement of 500oC and an accuracy of ± 0.5 oC. Kinematic viscosity (KV) was 4


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determined according to the requirements of GB 265 43, using a KV instrument (JSR1104; Jinshi, China) with a range of 0.5-10 mm2/s at 20oC, a test temperature range of 20-100 oC and an accuracy of ± 0.1 oC. Density was determined according to the requirements of GB/T 1884 44, using a density instrument (JSR1302; Jinshi, China) with a range of 20-95 oC and an accuracy of ± 0.1 oC. Closed cup flash points (CCFP) was determined according to the requirements of GB/T 261 45, using a CCFP instrument (JSR2901; Jinshi, China) with a range of 20-200 oC and an accuracy of ± 0.5 oC. Cetane number (CN) was evaluated according to the methods of insulating magnetic permeability 46, using a cetane index instrument (LAB-131, Beijing, China) with a range of 20-120 and an accuracy of ± 0.5. Latent heat of vaporization (LHV) was tested and calculated using an automatic vacuum distillation tester (300 CC; Pilodist, Germany) with a range of 20-420 oC and an accuracy of ±1oC; and an electronic balance (AL204; Mettler Toledo, Switzerland) with a range of 0.0001-210 g and an accuracy of ± 0.3mg. Heating value was determined according to the requirements of GB 384

47

, using an

automatic heating value tester (5E-KCIII; Changsha, China) with a range of 14-50 MJ/kg and an accuracy of ≤ 0.2%. The carbon (C), hydrogen (H), oxygen (O) content was determined according to the requirements of JJF 1321 48, using an elemental analyzer (EA3000; Eurovector, Italy) with an accuracy of ± 0.2%.

2.3 Experimental for performance and emissions A horizontal, four-stroke, single-cylinder diesel engine (L22; Changzhou, China) was employed to measure the performance and emissions of two kinds of fuel blends (see Table 1 for specifications). An intelligent measurement and control system (ET2000, Chengdu, China) was used to collect the signal of measurements. Engine torque, power and speed experiments were measured by an eddy current dynamometer (DW25; Chengdu, China) with a maximum torque of 120 N•m, the accuracy is ± 0.5 N•m; a maximum power of 25 kW, the accuracy is ± 0.1 kW; a maximum speed of 11000 rpm, the accuracy is ±1 rpm. Fuel consumption measurements were made by an intelligent digital fuel consumption meter (ET2500; Chengdu, China) with an accuracy of ± 8 g·h−1. The emission measurement system consists of three analysers: a gas analyser (Testo360, Lenzkirch, Germany) for carbon dioxide (CO2) and nitrogen oxides (NOx), a gas analyser (FGA-4100, Foshan, China) for hydrocarbon (HC) and carbon monoxide (CO), and a smoke opacity analyser (FTY-100, Foshan, China) for the light absorption coefficient (k). The measurement ranges and accuracies for different emissions were as 5


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follows: CO2: 0–20% vol, ± 1.5%; NOx: 0–1,000 10-6 vol, ± 3.8%; HC: 0–10,000 10-6 vol, ± 6%; CO: 0–9.99% vol, ± 1.0%; and k: 0–16 m−1, ± 2.0%. Table 1. Specifications of the diesel engine. Item

Description

Type

Horizontal, four-stroke, single-cylinder

Combustion system

Direct injection

Bore (mm)

110

Stroke (mm)

120

Displacement (L)

1.1403

Compression ratio

17:1

Rated power (kW)

15.5 (at 2,200 rpm)

Max torque (Nm)

≥75.4 (≤ 1,760 rpm)

Cooling

Water cooling system

Lubrication

Combined pressure and splashing

The performance and emissions measurement system was warmed up for more than 30 minutes before each test. The warm-up time was 3 hours when changing the fuel from one to another to ensure the fuel being changed can be replaced completely in the fuel lines and the engine with the new fuel. Screening tests with neat diesel were conducted over the full engine speed range of 800-2,200 rpm. The system stability results suggested a speed of 1,200 rpm was best in terms of test conditions and this value was chosen for all tests in this study 12. The average engine torque, engine power, fuel consumption, and emissions were recorded by the computer after the system became steady for 3 minutes. The torque was increased in increments of 10 Nm over a range of 11.4-82.5 Nm, the minimum and maximum torque 1,200 rpm.

3 Results and discussion 3.1 Properties of the fuel blends 3.1.1 Miscibility Miscibility is the basic requirement of fuels blended with each other for storage, transportation, and utilisation. Good miscibility means that each fuel is compatible with no phase separation and no cloudy performance, which is favourable for storage and combustion. In this study, the fuel blends were stored in 6


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sealed bottles and placed in a temperature test apparatus (EL-04KA; Espec Co., Shanghai, China). The tests were conducted on the basic of the China National Standards and Codes: GB 19147. CFPP Std. limits of Diesel (0#) is not more than 4°C in GB 19147, so miscibility test was from 4 ºC. Phase separation and cloudy appearance were not observed in all of the fuel blends for more than 72 hours at 4, 10, 15, 20, 25 and 30ºC using a programmable temperature controller, implying good miscibility for EL-B-D blends and nBu-B-D blends in suitable blended ratios.

3.1.2 Physical and chemical properties According to the test methods listed in Section 2.2, the blended fuels displayed the following physical and chemical properties: (1) CFPP is an important property of cold flow that can reflect the actual use of diesel fuel at low temperatures. As can been seen from Fig. 2, the CFPP of EL and n-butanol were lower than -45ºC, which was far lower than the CFPP of biodiesel and diesel. However, the CFPP of EL5-B10-D85, EL10-B15-D75 and nBu5-B10-D85 were similar to that of diesel; this is because biodiesel raised the CFPP of the blends, whereas EL and n-butanol lowered them. When n-butanol was blended at 10% vol, CFPP showed no major change as compared to diesel. However, when n-butanol was blended reached 15% vol, the CFPP (nBu10-B15-D75) became obviously lower than that of diesel. Previous studies also shown that EL and butanol has a positive effect on the low-temperature properties of fuel blends

32,49

. However, it should be noted that EL has been

shown to increase the cloud point of diesel blends and in the absence of biodiesel it can potentially negatively impact CFPP because of significant phase separation at low temperatures

50

. This effect was not able to be

reflected in our miscibility tests due to the Chinese national test standards adopted (i.e., with a lowest test temperature of 4 °C). (2) Distillation, kinematic viscosity (KV), density and closed cup flash point (CCFP) are the key properties of spray and evaporation characteristics, which have an obvious impact on the processes of injection, atomisation, ignition, combustion and emission of the engine. As can been seen from Fig. 2, compared with neat diesel, the addition of biodiesel raised the distillation temperature, and the addition of EL and n-butanol lowered the distillation temperature. Indeed, 10% distillation of nBu10-B15-D75 achieved a significantly lower temperature than that of neat diesel. However, 50% distillation of all blends was similar to neat diesel. And 90% and 95% distillation of the fuel blends were lower than neat diesel, in agreement with 7


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some earlier studies 31,51.The lower the 90% and 95% evaporation temperatures, the fewer heavy components were contained in the blends, and the higher the gasification and combustion processes of the blends. Compared with neat diesel, the KV of fuel blends were similar to that of neat diesel, although the KV of EL and n-butanol were lower than that of neat diesel. Similar results were reported in the literature about fuel blends of ethanol-biodiesel-diesel

52,53

. The KV of biodiesel was significantly higher than that of neat diesel.

The densities of the fuel blends and neat diesel were all similar and therefore suitable for use in diesel engines. The CCFP of fuel blends showed no significant change, except for nBu10-B15-D75. The CCFP of fuel blends EL-B-D blends were slightly higher than that of neat diesel, whereas the CCFP of nBu -B-D blends were slightly lower. (3) Cetane number (CN) represents the ignition reliability of the fuel combustion in engines, and fuels with higher CNs (not more than 65) are expected to have better combustion performance. As can been seen from Fig. 2, the CN of biodiesel was higher than that of diesel, and the CN of EL and n-butanol were not quantified because they were less than 20. The CN of the fuel blends were higher than that of neat diesel. Similar results were reported previously about fuel blends of ethanol-biodiesel-diesel 54,55. (4) Latent heat of vaporization (LHV) is an important property for a liquid fuel. The increased evaporative cooling effect due to high LHV can lower intake charge temperature and as a result increase the intake air density. As can been seen from Fig. 2, the latent heat of vaporization of n-butanol and EL were all higher than that of diesel. The heat of the fuel blends were slithtly higher than that of diesel. The LHV of n-butanol fuel blends were slightly higher than that of EL fuel blends. (5) Heating value is another very important property to determine suitability as an alternative to diesel fuel. Higher heating values (HHV) of fuel blends influence the power output of an engine directly. As can been seen from Fig. 2, the HHV of biodiesel, n-butanol and EL were all lower than that of diesel. The HHV of the fuel blends were lower than that of diesel; however, the HHV of all fuel blends were not lower than 42.76MJ/kg and not less than 93.74% of the HHV of diesel (45.61 MJ/kg). The amount of biofuel (biodiesel, ethyl levulinate or butanol) is increased in diesel blends, the heating value of the fuel blends decreases 11,56,57. (6) Oxygenated fuels can have more complete combustion and effectively reduce harmful emissions because of the additional oxygen available during the combustion process58. As can been seen from Fig. 2, the C content of neat diesel was higher than that of EL, n-butanol and biodiesel and slithtly higher than that of 8


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fuel blends. The H content of the neat diesel was slightly higher than that of EL, lower than that of n-butanol and similar to that of biodiesel, and fuel blends. The O content of EL was higer than that of n-butanol, biodiesel and fuel blends. No O content was tested in diesel. The C/H ratio of neat diesel, EL, n-butanol, biodiesel, EL5-B10-D85, EL10-B15-D75, nBu5-B10-D85, and nBu10-B15-D75 were 6.74, 7.00, 4.80, 6.27, 6.70, 6.69, 6.59 and 6.47%, respectively.

Fig. 2. Physical and chemical properties and variations of the fuel blends and neat fuels

9


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A summary comparison of the fuel blends and neat diesel with respect to the physical and chemical properties is presented in Fig. 2. Compared with neat diesel, the addition of EL and n-butanol gave the fuel blends a KV that was at least 17% lower than that of neat diesel, and the CN of the fuel blends was at least 21% higher than that of neat diesel. The CFPP, 50% distillation, density, CCFP, LHV, HHV and C/H ratio of fuel blends were similar to neat diesel. Generally, EL-B-D blends were more effective than nBu-B-D blends for improving CCFP, KV, CN and LHV, whereas nBu-B-D blends were more effective than EL-B-D blends for improving CFPP and 50% distillation temperature. Compared with neat diesel, the HHV and KV of EL-B-D blends showed greater decreases than nBu-B-D blends, and the CCFP and density of EL-B-D blends showed greater increases than nBu-B-D blends.

3.2 Performance and emission characteristics of the fuel blends 3.2.1 Effects of the fuel blends on performance Variations in the brake specific fuel consumption (BSFC) of the engine with fuel blends and neat diesel fuel are illustrated in Fig. 3. BSFC was significantly higher at low and high engine torque, and the minimum value occurred at about 50 N·m. The BSFCs of the fuel blends were about 5–10% higher than those of neat diesel, and increased with additive content. The probable reason for this behaviour was the higher heating value of the additive. Compared to diesel, the average increases in BSFC were 3.0, 9.6, 1.8 and 5.8% with the use of EL5-B10-D85, EL10-B15-D75, nBu5-B10-D85 and nBu10-B15-D75, respectively. The HHV of diesel, EL5-B10-D85, EL10-B15-D75, nBu5-B10-D85 and nBu10-B15-D75 were 45.61, 44.05, 42.76, 44.72 and 44.06 MJ/kg, respectively. The lower the heating value, the higher the BSFC, which is in agreement with previous studies on EL-B-D blends 15 and diesel-microalgae biodiesel-butanol blends 39. The higher density of fuel blends is the other reason leading to increase BSFC 59. The injection system used for diesel fuel, measures the fuel by volume thus the variation of the fuel density will affect the output power of the engine due to an altered mass of injected fuel 55. Lower kinematic viscosity of fuel blends in this study was not the reason for higher BSFC. The BSFC cannot describe the fuel economy completely because the energy contents of the fuel blends are less than that of neat diesel

15

. Brake specific energy consumption (BSEC) is a more useful

parameter than BSFC in terms of energy efficiency comparisons 60.

10


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Fig. 3. Variations in the BSFC and BSEC-torque characteristic of fuel blends and diesel (constant speed: 1,200 rpm, varying torque). Therefore, brake-specific energy consumption (BSEC, the fuel energy input required to deliver a unit of power 6) was calculated for all fuels based on their BSFC and LHV and is shown in Fig. 3. Compared to diesel, on average the BSEC decreased by 0.4% and 0.5% for EL5-B10-D85 and nBu5-B10-D85, respectively, and increased by 2.7% and 2.1% for EL10-B15-D75 and nBu10-B15-D75, respectively. These results indicated that the engine had better energy utilisation efficiency with fuel blends EL5-B10-D85 and

11


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nBu5-B10-D85 than with neat diesel, likely due to their higher combustion efficiency. Overall, the EL-B-D blends showed slightly higher BSFC and BSEC values compared to nBu-B-D blends.

3.2.2 Effects of fuel blends on emissions (1) NOx emissions

Fig. 4. Variations in the NOx emissions of different fuel blends and diesel (constant speed: 1,200 rpm, varying torque).

Variations in the NOx emissions of different fuel blends and neat diesel are illustrated in Fig. 4. In general, NOx emissions increased with increasing torque. As the engine torque increased, the effect of the lower oxygen content in the fuel injections became less notable, and the blends with higher oxygen contents had higher NOx emissions (see Fig.2). This may be attributed to the reduced soot radiative heat transfer and the subsequent increase in flame temperature61. With higher combustion efficiency and hence higher maximum temperature during combustion than diesel, the fuel blends could provide more favourable conditions for NOx formation. Compared to conventional diesel fuel at high load, biodiesel fuel blends produced increases in NOx emissions62. The increasing trend was similar to previous reports

12,63

. With increased EL-biodiesel and

n-butanol-biodiesel, NOx emissions of fuel blends increased for the same torque values, but the increases for EL-biodiesel blends were more obvious with the same additive volume, which may be attributed to the higher 12


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latent heat of vaporization of n-butanol-biodiesel blends resulting in some cooling effect in the engine (see Fig.2). Another reason is the shorter ignition delay due to the higher cetane number of EL-biodiesel blends (see Fig.2). The shorter the ignition delay is, the higher the NOx emissions become because of longer combustion duration of the fuel in the cylinder 5. Compared to diesel, the average increase in NOx emissions was 18.4% and 5.9% with fuel blends EL5-B10-D85 and nBu5-B10-D85, respectively, and 27.7% and 13.5% with EL10-B15-D75 and nBu10-B15-D75, respectively.

(2) CO emissions

Fig. 5. Variations in the CO emissions of different fuel blends and diesel (constant speed: 1200 rpm, varying torque).

Variations in the CO emissions of the engine with fuel blends and neat diesel fuel are depicted in Fig. 5. CO emissions increased slightly with increased engine torque (11.4–50 N·m), but increased noticeably at high torque (60 N·m). At the same torque, the CO emissions of all fuel blends were lower than those of neat diesel and the higher the proportion of additives, the greater the CO emissions reduction. However, for the same additive proportion, EL blends were more effective than n-butanol blends for reducing CO emissions. The main reasons for the reduction in CO emissions with fuel blends may be the significantly lower C/H, and 13


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higher oxygen content, ratio of fuel blends, which improves combustion in the cylinder. The reducing trend is similar to previous reports

64,65

. Compared to diesel, the average decrease in CO emissions was 37.3% and

15.0% with fuel blends EL5-B10-D85 and nBu5-B10-D85, respectively, and 50.9% and 27.1% with EL10-B15-D75 and nBu10-B15-D75, respectively. Oxygen content of EL5-B10-D85, nBu5-B10-D85, EL10-B15-D75 and nBu10-B15-D75 were 3.1%, 2.2%, 5.6%, and 3.8%, respectively. Therefore, EL-B-D blends were more effective than nBu-B-D blends for reducing CO emissions.

(3) CO2 emissions

Fig. 6. Variations in the CO2 emissions of fuel blends and diesel (constant speed: 1,200 rpm, varying torque).

Variations in the CO2 emissions of the engine with the fuel blends and neat diesel fuel are shown in Fig. 6. In general, CO2 emissions from the fuel blends were higher than those of neat diesel at the same engine torque. Compared with EL blends, n-butanol blends showed a greater increase in CO2 emissions, but the increase in the amplitude of CO2 emissions between n-butanol blends and EL blends was very similar. The higher CO2 emissions observed can be attributed to more oxygen contained in EL fuel blends (3.1% and 5.6%) and n-butanol fuel blends (2.2% and 3.8%). The increasing trend is similar to previous reports 12,66. Compared

14


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Energy & Fuels

to diesel, the average increase in CO2 emissions was 27.3% and 23.0% with fuel blends EL5-B10-D85 and nBu5-B10-D85, respectively, and 41.4% and 36.9% with EL10-B15-D75 and nBu10-B15-D75, respectively.

(4) Smoke opacity

Fig. 7. Variations in the smoke opacity of the fuel blends and diesel (constant speed: 1,200 rpm, varying torque).

Variations in the smoke opacity of the engine with fuel blends and neat diesel fuel are presented in Fig. 7. There were small increases in smoke opacity with increasing engine torque from 11.4 to 60 N·m, whereas smoke opacity increased significantly at engine torques greater than 60 N·m, similar to the trends observed for CO emissions. At the same torque, the smoke opacity of all fuel blends was less than that of neat diesel; the higher the blending proportion, the greater the reduction in smoke opacity. This could be because oxidants from the additives enable more complete combustion of the injected fuels and reduce the smoke emitted, and the oxygen atoms in fuel molecules can reduce smoke nuclei formation in the local fuel-rich region, and have the potential to promote smoke post-oxidation 7,12,15,39,40

67

. The reducing trend is consistent with previous work

. In engines, oxygenates provide substantial PM emission reductions, considerably greater than from

reduction of aromatic hydrocarbon content and more closely related to the fuel oxygen content 68. Compared 15


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Page 16 of 22

to diesel, the average decrease in smoke opacity was 45.6% and 19.5% with fuel blends EL5-B10-D85 and nBu5-B10-D85, respectively, and 64.8% and 30.0% with EL10-B15-D75 and nBu10-B15-D75, respectively. Therefore, EL-B-D blends were more effective than nBu-B-D blends for reducing smoke opacity.

(5) HC emissions

Fig. 8. Variations in the HC emissions of the fuel blends and diesel (constant speed: 1,200 rpm, varying torque).

The variations in HC emissions of the engine with fuel blends and neat diesel fuel are illustrated in Fig. 8. HC emissions of all fuel blends were higher than those of neat diesel, and increased with increasing EL-B and nBu-B blending proportions at the same engine torque. There were no major changes in HC emissions with increasing engine torque. Both increased and decreased HC emissions have been reported for diesel fuel containing alcohols. Lower blending levels of EL-biodiesel

15

and alcohols-biodiesel

67

can decrease the

formation of HC, but HC emissions increase when the blending levels are high 67,69. Compared to diesel, the average increase in HC emissions was 15.5% and 19.4% with fuel blends EL5-B10-D85 and nBu5-B10-D85, respectively, and 31.2% and 38.6% with EL10-B15-D75 and nBu10-B15-D75, respectively.

16


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Energy & Fuels

4 Conclusions EL and n-butanol were evaluated as additives to biodiesel and diesel in this study. The physical and chemical

properties,

performance

and

emissions

of

fuel

blends

EL5-B10-D85,

EL10-B15-D75, nBu5-B10-D85 and nBu10-B15-D75 were tested and the following conclusions can be drawn from the experimental results: (1) All of the fuel blends showed good miscibility. Compared to neat diesel, the addition of EL or n-butanol resulted in a lower distillation temperature and CFPP. The CN and O content of the fuel blends was higher than that of neat diesel and the HHV was slightly lower. In addition, the density, latent heat of vaporization, C/H ratio and CCFP of the fuel blends were still similar to those of neat diesel. In general, adding EL in biodiesel-diesel blends improved other properties such as CCFP and KV compared to adding n-butanol in biodiesel-diesel blends. However, n-butanol addition showed better improvements in properties of CFPP and distillation. (2) The fuel blends showed slightly higher BSFC than neat diesel because of their lower heating value. BSEC of EL10-B15-D75 and nBu10-B15-D75 were higher than that of neat diesel while that of EL5-B10-D85 and nBu5-B10-D85 were lower. EL-B-D blends demonstrated slightly higher BSFC and BSEC than nBu-B-D blends. CO emissions and smoke opacity of the fuel blends were lower than that of neat diesel, while NOx, CO2 and HC emissions were higher. EL-B-D blends were more effective than nBu-B-D blends for reducing CO emissions and smoke opacity, while NOx and CO2 emission increases were more obvious in EL-B-D blends. Compared with EL-B-D blends, HC emissions from nBu-B-D blends were higher. (3) This work shows that EL and n-butanol can be blended with diesel and biodiesel to achieve a range of improvements in both physical and chemical properties, performance and some emissions. The technical barriers to the use of biodiesel in diesel engines will be resolved in the future with further fuel blends studies. In addition, the research is benefitial in enhancing the utilisation efficiency of biomass resources and reducing some air pollutant emissions. The increased NOx emission might be a barrier to the use of these fuel blends given the more and more stringent regulations of NOx globally. Further research will be conducted to compare a more comprehensive set of physical and chemical properties and detailed combustion behaviours of the fuel blends, and to assess their life cycle environmental impacts prior to implementing their large-scale use as diesel additives. 17


Energy & Fuels

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Acknowledgments This study was supported by the National Natural Science Foundation of China (51506049). The authors thank Richard Little and Sam Barton of the University of Exeter for their assistance with the English language.

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Comparison of the Physical and Chemical Properties, Performance

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