ARTICLE

J. Cent. South Univ. (2019) 26: 2244-2258

DOI: https://doi.org/10.1007/s11771-019-4170-z

Experimental investigation on combustion and unregulated emission characteristics of butanol-isomer/gasoline blends

LI Yuan-xu(李元绪)^{1, 2, 3}, NING Zhi(宁智)^{1, 2}, YAN Jun-hao(闫峻豪)³, Timothy H LEE³, Chia-fon F LEE³

1. School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University,Beijing 100044, China;

2. Beijing Key Laboratory of New Energy Vehicle Powertrain, Beijing Jiaotong University, Beijing 100044, China;

3. Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign,IL 61801, USA

Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2019

Abstract: Effects of butanol isomers on characteristics of combustion and emission were studied on PFI SI engine. Experiments were operated under the condition of 3 and 5 bar brake mean effective pressure (BMEP) engine loads and different equivalence ratios (φ=0.83-1.25) with engine speed of 1200 r/min using blends made of 70 vol.% gasoline and 30 vol.% butanol isomers (N30, S30, I30 and T30). The results indicated that compared with gasoline, all butanol isomer blends have higher cylinder pressure. N30 has the highest and most advanced peak pressure, and T30 shows a higher brake specific fuel consumption (BSFC) and lower brake thermal efficiency (BTE). N30 presents a lower UHC emissions and I30 has slightly higher CO emissions than other blends. For unregulated emissions, compared with gasoline, butanol isomer blends have higher acetaldehyde, and N30 produces a higher emission of 1,3-butadiene than other blends. A reduction in benzene, toluene, ethylbenzene and xylene (BTEX) has been found with butanol isomer blends.

Key words: Butanol isomers; unregulated emission; combustion characteristics; gas chromatograph; SI engine

Cite this article as: LI Yuan-xu, NING Zhi, YAN Jun-hao, Timothy H LEE, Chia-fon F LEE. Experimental investigation on combustion and unregulated emission characteristics of butanol-isomer/gasoline blends [J]. Journal of Central South University, 2019, 26(8): 2244-2258. DOI: https://doi.org/10.1007/s11771-019-4170-z.

1 Introduction

Due to the concern about the decrease in petroleum reserves and the increasingly restrictions on exhaust emissions from internal combustion engines, the interests of investigations on sustainable energy sources have been enhanced recently. Biofuels, which are some of the most promising renewable energy sources [1-5], have been receiving more and more attention from the researchers, not only because they have higher oxygen content, but also because they could be obtained from renewable energy sources instead of fossil fuel [6, 7]. Among these biofuels, ethanol has been commonly used in internal combustion engines. Ethanol has presented several advantages in aspect of engine performance and efficiency as a partial substitute for gasoline [8, 9].However, there are still several drawbacks when using ethanol as an alternative fuel. The heating value of ethanol is lower than gasoline, which results in a higher fuel consumption [10]. In addition, ethanol has a higher latent heat than gasoline, resulting in a poor evaporation during cold start [11].

Compared with ethanol, butanol has received more and more attention as a more promising biofuel candidate recently because of its important advantages. Butanol has a lower vapor pressure, which could avoid the vapor lock [12]. Besides, butanol has a higher heating value (33.1 MJ/kg) and larger energy density (26.82 MJ/L) than ethanol (26.8 MJ/kg heating value and 21.17 MJ/L energy density) [13, 14]. Additionally, it has a better blending ability in gasoline at high fraction without modifying the engine [15-17].

Based on different hydroxyl (—OH) group locations and carbon chain constructions, butanol has four different structures, which are normal butanol (N), secondary butanol (S), isobutanol (I) and tertiary butanol (T). There is a straight chain structure and a terminal carbon-OH group for N-butanol. S-butanol also has a structure with straight chain but the internal carbon-OH group. Both I-butanol and T-butanol indicate the same branched structure. However, the only difference is the location of —OH group. The —OH group of I-butanol is on the terminal carbon whereas that of T-butanol is on the internal carbon [15, 18]. The main structures and applications of these butanol isomers are shown in Table 1. Although different structures of the butanol isomers cause some impacts on their properties, they have similar main applications such as industrial cleaners, gasoline additives and solvents. Besides, all butanol isomers could be derived from biological fermentation processes [21].

Among all butanol isomers, N-butanol has been considered a prospective alternative fuel. WALLNER et al [10] studied the combustion and emission behaviors on a DI SI engine using 10% ethanol and 10% butanol addition in gasoline. The results showed that 10 vol.% butanol blend had lower nitrogen oxide (NO_x) emissions and volumetric fuel consumption than those of ethanol blend. Their further study [22] also investigated the impact on both regulated and unregulated emissions of butanol gasoline blends or ethanol gasoline blends, and they found that higher butanol blend ratios could reduce regulated emissions and increase unregulated emissions. YANG et al [23] conducted engine dyno tests with a gasoline engine by using blends of gasoline and butanol, ranging from 10% to 35%. Their conclusions showed that when the concentration of butanol is under 20%, no modification is needed for maintaining the engine power level. Besides, the gasoline-butanol blends could reduce raw HC and carbon monoxide (CO) emissions but increase NO_x emissions. As for S-butanol, I-butanol and T-butanol, there is a relatively small amount of research on them. IRIMESCU [24] studied the effect of 50% I-butanol blended with gasoline (IB50) in a PFI engine. The results indicated that fuel conversion efficiency showed a 6% increase when using the IB50. ALASFOUR [25-27] studied the emission characteristic of a SI engine using 30 vol.% I-butanol mixed with gasoline. The results showed that I-butanol blends reduced 9% NO_x emissions and 12% hydrocarbon emissions compared with those of gasoline. VELOO et al [28] carried out experimental and computation investigations on the flames propagation of saturated butanol isomers. They found that flames of T-butanol propagate much slower than those of other butanol isomers, and N-butanol has the faster flame propagation than S-butanol and I-butanol.

Table 1 Molecular structures and main applications of butanol isomers [19, 20]

As mentioned above, the comparative investigations on combustion and emission behaviors of internal combustion engines using butanol isomers are rarely reported. Furthermore, there is hardly any study about the unregulated emissions analyzation of butanol isomer combustion. Since unregulated emissions are harmful to the human neurological and immune systems [29, 30], it is equally important to measure the unregulated emissions. In this investigation, the characteristics of combustion and emission on a PFI SI engine using gasoline (G100), blends with 70% gasoline and 30% N-butanol (N30), 30% S-butanol (S30), 30% I-butanol (I30) and 30% T-butanol (T30) respectively, were investigated under different equivalence ratios and engine loads. Besides regulated emissions, some representative unregulated emissions classified by Environmental Protection Agency of United States (USEPA) as toxics, including aldehydes, olefins, aromatic hydrocarbons [31], were also measured and discussed in detail.

2 Experimental setup

2.1 Test fuels

The butanol isomers supplied by Sigma- Aldrich Co.and gasoline with an octane number of 92 were used in this study. 30 vol.% butanol isomers were respectively mixed with 70 vol.% gasoline by a magnetic stirrer to give N30, S30, I30 and T30, while using pure gasoline as a reference fuel (G100). Table 2 shows the properties of test fuels.

2.2 Engine setup and test conditions

In this study, a single cylinder from a 2000 Ford Mustang Cobra V8 engine (the rest seven cylinders have sealed the intake and exhaust valves, and removed the pistons and crankshaft connecting rod), which has a 239 kW peak power and a 407 N·m torque, was used, and the engine specifications are shown in Table 3. The engine control unit (ECU) is Megasquirt II V3.0. The dynamometer of type TLC-15 GE is controlled by a DyneSystems DYN-LOC IV controller and uses a BEI XH25D shaft encoder to obtain the crank angle position. A type 6125B Kistler pressure transducer and a LabVIEW code were used for recording and measuring cylinder pressure. A schematic of the experimental setup is presented in Figure 1 and Table 4 presents the measurements’ error analysis for experimental apparatus.

For operation conditions of this study, the engine speed was maintained at 1200 r/min under 3 and 5 bar brake mean effective pressure (BMEP). 0.83 to 1.25 were used as the equivalence ratio. Each fuel’s spark timing was set to the time at which is each of the maximum brake torque (MBT), which could generate the maximum power and efficiency. Since the results under 5 bar BMEP showed similar trends to those under 3 bar BMEP with different equivalence ratio, only the results under 3 bar BMEP are shown for brevity’s sake. Table 5 shows the test conditions, and the spark timings for the maximum brake torque of each fuels are listed in Table 6.

2.3 Emissions analysis

For regulated emissions, a Horiba MEXA-720 was used for air-fuel ratio (AFR) with the measurement range of 0.65-13.70, and NO_x emissions with the measurement range of (0-5000)×10^-6. And a Horiba MEXA-554JU measured CO emission with measurement range of (0-1000) vol.% and UHC emissions with measurement range of (0-10000)×10^-6.

Table 2 Properties of test fuels [19, 32]

Table 3 Specifications of test engine

For unregulated emissions, a gas chromatography-mass spectrometer (GC-MS) was used to identify gas samples, and a gas chromatography-flame ionization detector (GC- FID) was used to quantify gas samples. The gas sample from the engine was collected by a sampling collection device and was then pushed into GC sampler by helium, which was used as the carrier gas at a flow rate of 1.2 mL/min. Both GC-MS and GC-FID used the Agilent DB-1 123-1063E capillary column and same operational condition. Table 7 lists all detailed analysis parameters. Three tests were performed for each condition, and the datasets were averaged.

3 Results and discussion

3.1 Cylinder pressure

The engine cylinder pressure traces for test fuels at stoichiometric condition and low engine load are presented in Figure 2. Among them, cylinder pressure traces are the average results of a hundred consecutive cycles traces at each operate condition. All butanol isomer blends have a relatively higher peak cylinder pressure than gasoline due to their higher laminar burning velocity. N30 has the highest and most advanced peak pressure among all test fuels, followed by those of S30, I30 and T30. These can be explained that the molecular structure of butanol isomers has main effects on their laminar burning velocities [12]. The laminar burning velocity is reduced by branching (—CH₃). A higher laminar burning velocity showed from the —OH group on terminal carbon atoms compared with that from the —OH on the inner carbon atoms. Since N-butnaol has no branching in its molecular structure and the —OH is on the terminal carbon atom, it has the highest laminar burning velocity. Conversely, T-butanol shows the lowest laminar burning velocity among all butanol isomers due to the most branching and —OH located at inner carbon atom.

Figure 1 Schematic of engine test bench

Table 4 Measurements’ error analysis for experimental apparatus

Table 5 Operation conditions

Table 6 Spark timing for the maximum brake torque of each fuel

Table 7 GC-MS and GC-FID analysis parameters

Figure 2 Cylinder pressure at 3 bar BMEP under stoichiometric condition (ATDC: after top dead center)

3.2 Mass fraction burnt profiles

At low engine load and φ=1, the mass fraction burnt (MFB) profiles of all test fuels are shown in Figure 3. All test blends’ MFB variations have a similar trend to their cylinder pressure traces. Besides, Figure 4 shows the flame development duration (FDD), calculated by the duration of crank angles of 0-10% MFB, the rapid combustion duration (RCD), calculated by the duration of crank angles of 10%-90% MFB, and the CA50 calculated by the crank angle of 50%.

Figure 3 Mass fraction burnt at 3 bar BMEP under stoichiometric condition

Figure 4(a) presents flame development duration of blends under different engine loads at stoichiometric condition. N30 shows the shortest FDD, and I30 and S30 have similar but slightly longer FDD, followed by T30. G100 has the longest FDD among all test fuels, which are consistent with the results in Ref. [14]. Figure 4(b) presents the CA50 of all test fuels at the same conditions. At low engine load, all butanol-isomer blends show relatively more advanced CA50 than that of gasoline. Among four different butanol isomers, N30 shows the most advanced CA50 than others. However, the trend of CA50 at high engine load is different to that at low engine load. Among all tested blends, S30 shows the most advanced CA50 and T30 indicates the similar CA50 to that of G100. Figure 4(c) presents the RCD of different blends. The RCD of all blends does not show much difference at high engine load, whereas I30 has a relatively longer RCD at low engine load.

Figure 4 FDD (a), CA50 (b) and RCD (c) at 3 and 5 bar BMEP under stoichiometric condition

Figure 5 indicates the flame development duration and rapid combustion duration at various equivalence ratio under low engine load. As the equivalence ratio increases, FDD and RCD of all blends decrease gradually, which is consistent with the conclusions in Ref. [33]. This can be due to the slower development of the flame under lean conditions, which could lead to a much longer duration, resulting in a larger FDD and RCD [34]. Among various equivalence ratios, N30 exhibited the shortest FDD and RCD. For other butanol isomers, I30 has a shorter FDD than S30 and T30, whereas has the slightly higher RCD than all the other test fuels.

Figure 5 FDD (a) and RCD (b) at 3 bar BMEP under various equivalence ratios

3.3 Brake specific fuel consumption and brake thermal efficiency

Figure 6 shows brake specific fuel consumption (BSFC) of all blends at low engine load and different equivalence ratios. Since the butanol isomer blend has a lower energy content than gasoline, they all exhibit a higher BSFC than gasoline. Among all butanol isomer blends, T30 has the highest BSFC due to its lowest energy content. Figure 7 presents brake thermal efficiency (BTE) of all blends at low engine load and various equivalence ratios. All butanol isomer blends have higher BTE than gasoline due to their fuel-borne oxygen, which leads to the improved combustion quality. Among all blends, N30 has higher BTE and T30 has lower than other blends. This can be explained by the fact that terminal carbon atom C—H bond has a higher dissociation bond energy than inner carbon atom C—H bond [12]. N-butanol has the most inner C—H bonds, thus reducing the required energy for H-extraction reaction, which leads to the highest BTE among all test fuels. Similarly, since all C—H bonds are terminal carbon in T-butanol, it requires the highest dissociation bond energy in T-butanol compared with other butanol isomers, leading to the relatively lower BTE among those of butanol isomer blends.

Figure 6 BSFC at 3 bar BMEP under various equivalence ratios

Figure 7 BTE at 3 bar BMEP under various equivalence ratios

3.4 Regulated emissions

Figures 8-10 show the impact of various equivalence ratios and engine loads on regulated emissions (UHC, CO and NO_x emissions) of all blends. The standard deviations among runs are presented as error bars in these figures.

Figure 8(a) shows UHC emissions of all blends under stoichiometric condition and different engine loads. Compared with gasoline, the UHC emissions of anol isomer blends are lower at different load conditions, which is consistent with Ref. [11]. The N30 has the lowest UHC emissions, followed by I30, S30 and T30. These are also the reflection of their BTE variation, mainly due to the dissociation bond energies of C—H in different structures of butanol isomers. However, compared with low load conditions, all butanol isomer blends have slightly lower UHC emissions at higher loads. At 3 bar BMEP, the variation of UHC emissions of all blends under the impact of equivalence ratio is presented in Figure 8(b). As the equivalence ratio increases, all blends’ UHC emissions increase.

Figure 8 UHC emissions at stoichiometric condition (a) and 3 bar BMEP (b) under various equivalence ratios

Figure 9 CO emissions at stoichiometric condition (a) and 3 bar BMEP (b) under various equivalence ratios

Figure 10 NO_x emissions at stoichiometric condition (a) and 3 bar BMEP under various equivalence ratios (b)

Under stoichiometric condition, CO emission of all blends under various engine loads is presented in Figure 9(a). I30 has higher CO emission than other test fuels and S30 has the lowest under different engine loads. As engine load increases, the CO emission from G100 increases, while most of butanol isomer blends except S30 show lower CO emission. CO emissions of all blends at different equivalence ratios at low engine load are shown in Figure 9(b). For all test fuels, their CO emissions are relatively low under leaner conditions, and lead to high CO formation under rich conditions. Under various equivalence ratios, compared with all blends, I30 shows the highest CO emission and S30 shows the lowest.

Figure 10(a) indicates NO_x emissions of all blends at engine loads of both low and high under φ=1. At two different engine loads, I30 has higher NO_x emissions, while other blends’ NO_x emissions are lower and almost the same. As engine load increases, the NO_x emissions from all test fuels increase. Figure 10(b) shows NO_x emissions of all blends under different equivalence ratios at low engine load. As equivalence ratio increases, NO_x emissions of all blends increase first and then decrease, and I30 has the higher NO_x emissions. Under lean conditions, T30 shows the lowest NO_x emissions while N30 shows the lowest under rich conditions.

3.5 Unregulated emissions

Based on other previous studies [31, 35-39], the target unregulated emissions in this investigation measured the concentrations of acetaldehyde, 1,3-butadiene, benzene, toluene, ethylbenzene and xylene isomers.

Figure 11 shows these target-unregulated emissions’ chromatogram, the retention time is determined by the corresponding peak of each compound in the chromatogram as presented in Table 8. However, the m- and p-xylene emissions are presented as total because of the limitation by the chromatography’s resolution. Furthermore, because the mass spectra of xylene isomers are similar (Figure 12), more identification and measurement works should be done including both retention time and mass spectrums. Based on the Figure 11 and Table 8, all the unregulated emissions could be recognized, and their corresponding concentration could also be measured.

Figure 11 Chromatogram of unregulated emissions

Table 8 Target unregulated emissions’ retention time

Figures 13-19 present unregulated emissions of all blends at different engine loads and equivalence ratios. In each experiment, the concentration of each unregulated emission is an average of three repeated tests, and the standard deviations among runs are shown as error bars.

3.5.1 Acetaldehyde

Figure 13(a) shows the acetaldehyde emission variation under various engine loads at stoichiometric condition. Compared with gasoline, all butanol isomers have higher acetaldehyde at the same engine load. Among all blends, S30 shows the most acetaldehyde emission. Previous literatures showed that the butanol addition in gasoline could increase acetaldehyde emission [22, 39-41]. When the engine load gets increased, G100, N30 and I30 have a slightly higher acetaldehyde emission whereas acetaldehyde emissions of S30 and T30 decrease, which could probably due to the different structures of these butanol isomers. The variation of acetaldehyde emission with the impact of equivalence ratio is presented in Figure 13(b). The acetaldehyde emission increases when the equivalence ratio gets higher.

Figure 12 Mass spectrometry of m- and p-xylene (a) and o-xylene (b)

Figure 13 Acetaldehyde at stoichiometric condition (a) and 3 bar BMEP under various equivalence ratios (b)

Figure 14 1,3-butaduene at stoichiometric condition (a) and 3 bar BMEP under various equivalence ratios (b)

Figure 15 Benzene at stoichiometric condition (a) and 3 bar BMEP under various equivalence ratios (b)

Figure 16 Toluene at stoichiometric condition (a) and 3 bar BMEP under various equivalence ratios (b)

3.5.2 1,3-butadiene

Figures 14(a) and (b) indicate variance of all test fuels’ 1,3-butadiene under various equivalence ratios and engine loads. Under both low and high engine load at stoichiometric conditions, compared with other blends, N30 produces the highest 1,3-butadiene emission whereas S30 has the lowest. With an increasing engine load, 1,3-butadiene emission indicated a decreased trend. A relatively high engine load results in a higher combustion temperature, and thus accelerating the oxidation of pyrolytic products [31]. The effect of equivalence ratio also presented a similar trend as well. 1,3-butadiene formation mainly occurred under leaner condition, and this is consistent with the results in Refs. [42, 43].

3.5.3 Benzene, toluene, ethylbenzene and xylene (BTEX) emissions

BTEX emissions are being considered the most reactive volatile organic compounds (VOC). The production of BTEX is mainly from the unburned fuel and pyrosynthesis [44].

Figure 17 Ethylbenzene at stoichiometric condition (a) and 3 bar BMEP under various equivalence ratios (b)

Figure 18 m/p-xylene at stoichiometric condition (a) and 3 bar BMEP under various equivalence ratios (b)

Figure 19 o-xylene at stoichiometric condition (a) and 3 bar BMEP under various equivalence ratios (b)

Typically, the benzene comes from unburned fuel or from aromatic and non-aromatic compounds combustion [45]. Figures 15(a) and (b) present benzene emission of all blends at different equivalence ratios and engine loads. Compared with gasoline, all butanol isomers have lower benzene emission, which attributes to the higher concentration of oxygen in butanol isomers blends, thus promoting the oxidation and reducing the benzene emission. Among these butanol isomers at the same condition, N30 has the highest benzene emission. This could be explained that the C4/C2 route to benzene depends on production of the 1,3-butadiene radicals, which combine to produce benzene via rearrangement of fulvene, and this intermediate is easily derived from the oxidation of 1,3-butadiene [46]. Since the N30 has the highest 1,3-butadiene emission among all butanol isomer blends, its benzene emission gets relatively higher as well.

Toluene is normally presented the largest amount in volatile organic compounds.Figures 16(a) and (b) show toluene variation of all blends under the impact of engine load and equivalence ratio. All butanol isomers have lower toluene emission than G100, and I30 has the lowest one. This is more likely due to the decreased aromatics concentration in fuel blends rather than chemistry reaction during combustion process [47]. When engine load increases, the injection of more fuel in the engine results in an increase in toluene, and a same trend could also be found when equivalence ratio gets increased as well.

Figures 17(a) and (b) indicate the ethylbenzene at various equivalence ratios and engine loads. At stoichiometric condition under both low and high engine loads, all butanol isomers show higher ethylbenzene compared with G100, and I30 has the most. Previous investigations have found that compared with gasoline, butanol-gasoline blends lead to an increase in ethylbenzene emission [37, 44]. Figures 18 and 19 show the variation of xylene emissions with the impact of equivalence ratios and engine loads. When equivalence ratio and engine load get increased, xylene emissions from all blends increase, with S30 having the highest xylene emissions and I30 having the lowest xylene emissions.

In summary, compared with gasoline, the butanol isomer blends have a lower total BTEX emissions probably due to the blends containing a lower concentration of aromatics and its higher oxygen content. In addition, the shorter ignition delay and combustion duration of the butanol- containing blends also results in improved combustion and better performance compared with gasoline, which reduces BTEX emissions.

4 Conclusions

In this paper, the feasibility of using different butanol isomers and gasoline blends in SI engines was investigated. The characteristics of combustion and emission using butanol-isomers/gasoline blends under different engine loads and equivalence ratios were studied. The main conclusions obtained can be summarized below.

Compared with gasoline, butanol isomer blends have higher cylinder pressure, more advanced combustion phasing, shorter FDD and RCD. Among four different butanol isomers, the laminar burning velocities of butanol isomers are affected by different molecular structures. N30 has the highest and most advanced peak pressure, followed by those of S30, I30 and T30.

Since butanol isomer blends have lower energy content, they indicated a higher BSFC than gasoline. T30 showed the highest BSFC among all test fuels. As for the BTE, the BTE of all blends was higher than that of gasoline. N30 has higher BTE and T30 has lower than other blends, which can be explained that energies of dissociation bond on terminal C—H are larger than that of inner C—H.

N30 showed the lowest UHC emissions among all test fuels, followed by I30, S30 and T30. I30 showed the highest CO emission and S30 had the lowest. No obvious difference was found in NO_x of all blends except I30, which showed a higher NO_x.

For all blends’ unregulated emissions, butanol isomer blends show higher acetaldehyde than that of gasoline. S30 has a higher acetaldehyde emission and lower 1,3-butadiene emission, whereas N30 produced a higher 1,3-butadiene among all blends. There is a generally reduction in BTEX using butanol isomer-gasoline might because of their higher oxygen content and lower number of aromatic components.

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(Edited by ZHENG Yu-tong)

中文导读

丁醇同分异构体/汽油混合燃料的燃烧和非常规污染物特性的试验研究

摘要：本文研究了丁醇同分异构体与汽油混合燃料在进气道喷射的火花点火发动机中的燃烧和排放特性。试验在发动机转速为1200 r/min、发动机负荷为3 bar BMEP和5 bar BMEP以及不同混合气空燃比条件下(φ=0.83~1.25)进行，使用了70%体积比的纯汽油和30%体积比的丁醇同分异构体混合燃料(N30，S30，I30和T30)。结果表明，相比于纯汽油，所有的丁醇同分异构体/汽油混合燃料表现出更高的缸内压力，其中N30有最高的缸内压力峰值和最早的缸内压力峰值相位；T30表现出较高的brake 燃油消耗率(BSFC)和较低的制动热效率(BTE)；相比于其他燃料，N30的UHC排放较低而I30的CO排放较高。在非常规排放物特性方面，相比于纯汽油，丁醇同分异构体/汽油混合燃料有较高的乙醛排放；相比于其他混合燃料，N30的1,3-丁二烯排放较高。使用丁醇同分异构体/汽油混合燃料可以有效地抑制单环芳烃类质(BTEX)的排放。

关键词：丁醇同分异构体；非常规污染物；燃烧特性；气相色谱；火花点火发动机

Foundation item: Projects(51776016, 51606006) supported by the National Natural Science Foundation of China; Projects(3172025, 3182030) supported by Beijing Natural Science Foundation, China; Project(2017YFB0103401) supported by National Key Research and Development Program; Project(NELMS2017A10) funded by the National Engineering Laboratory for Mobile Source Emission Control Technology, China; Project(2018RC017) supported by the Talents Foundation of Beijing Jiaotong University, China; Project(DE-EE0006864) supported by the Department of Energy; Project(201507090044) supported by China Scholarship Council

Received date: 2019-04-17; Accepted date: 2019-07-19

Corresponding author: NING Zhi, PhD, Professor; Tel: +86-10-51684663; E-mail: zhining@bjtu.edu.cn; ORCID: 0000-0002-9003- 1358; Chia-fon F LEE, PhD, Professor; Tel: +1-217-333-5879; E-mail: cflee@illinois.edu; ORCID: 0000-0003- 4932-982X