Article pubs.acs.org/EF
Speciation of Hydrocarbon and Carbonyl Emissions of 2,5Dimethylfuran Combustion in a DISI Engine Ritchie Daniel,† Lixia Wei,†,‡ Hongming Xu,*,†,§ Chongming Wang,† Miroslaw L. Wyszynski,† and Shijin Shuai§ †
School of Mechanical Engineering, University of Birmingham, Birmingham, United Kingdom State Key Laboratory of Engines, Tianjin University, Tianjin, P. R. China § State Key Laboratory of Automotive Safety and Energy, Tsinghua University, Beijing, P. R. China ‡
ABSTRACT: It is known that species in the exhaust gas of automobile engines vary with fuel. As such, there is a need to understand the individual hydrocarbon (HC) and carbonyl (aldehydes and ketones) emissions from modern engines, especially as the use of alternative and renewable biofuels is set to rise. For gasoline, a promising candidate biofuel is 2,5-dimethylfuran (DMF). This work presents the key individual HCs that have been identified using gas chromatography mass spectrometry (GC/ MS) and quantifies the emissions of 13 different carbonyls as specified by the California Air Resources Board (CARB) Method 1004 using high performance liquid chromatography (HPLC). The tests were conducted on a single cylinder direct-injection spark-ignition (DISI) engine at 1500 rpm, λ = 1 and constant ignition timing. For the GC analysis, the midrange HCs were identified using the mass spectra. The results showed that unburned fuel (DMF) dominates the emissions. Other main emissions include cyclopentadiene, methyl vinyl ketone, 2-methylfuran, and aromatics. There was no evidence of the emissions of linear alkanes except methane. DMF produced the lowest overall carbonyl emissions compared with methanol, ethanol, n-butanol, and gasoline and, more importantly, the lowest emissions of formaldehyde.
1. INTRODUCTION In recent years, leading global economies have examined the use of biofuels in light-duty automobiles in order to tackle the growing energy security and environmental issues related to the use of fossil fuels.1,2 Government policy on energy use is also changing in emerging nations.3 Therefore, as the use of biofuels is set to rise, it is important to understand the impact of their emissions on human health and the environment. One emerging biofuel candidate is 2,5-dimethylfuran (DMF), since the discovery of high yields from fructose or glucose using catalytic-based conversion processes, as reported by Nature in 2007.4 This method reduces the production time scales and costs associated with biological methods (for ethanol).5 The laminar flame speed of DMF was studied by Wu et al.,6 and the combustion characteristics have been investigated by the authors’ group.7−9 The experiments in a modern directinjection spark-ignition (DISI) research engine have shown that DMF produces lower total hydrocarbon (HC) emissions than gasoline,9 as measured by a flame ionization detector (FID). The HC emissions from DMF is about 7−10% higher at the engine speed of 1500 rpm and engine load between 3.5−8.5 bar IMEP. However, the inherent reduced sensitivity of FIDs to oxygenated HCs10 suggests that a detailed analysis of the individual species will prove more accurate.11 The level of toxicity and ozone forming potential of each HC is important in scrutinizing its allowable emissions. The various levels of carcinogenicity of HCs are determined by the International Agency for Research on Cancer (IARC) and the National Toxicology Program (NTP). Known carcinogens include 1,3-butadiene, formaldehyde, and benzene, whereby acetaldehyde and furan are possible carcinogens.12,13 For the environment, the harmful impact of HCs is given by the © 2012 American Chemical Society
maximum incremental reactivity (MIR) scale. With the exception of benzene, the aforementioned carcinogenic HCs have high MIR values (>5 g ozone/g HC).14 Although believed to be noncarcinogenic, furan derivatives also have high MIR values (furan, 2-methylfuran, and DMF: 9.15, 8.3, and 7.88 g ozone/gHC, respectively14). As the combustion of oxygenated fuels has a profound influence on the total HC emissions measurement by an FID, it is important to perform HC speciation. For instance, the emissions of formaldehyde (CH 2 O) and acetaldehyde (CH3CHO) vary greatly when using ethanol, methanol, and n-butanol.15−17 Although these fuels have been examined individually, there is very little literature that makes a direct comparison, and as yet, nothing is compared to DMF. The aim of this work is therefore to understand which species are produced from the combustion of DMF. First, the main HCs are identified, and second, the carbonyl emissions are compared to those with gasoline and other gasolinealternative fuels (methanol, ethanol, and n-butanol). This investigation contributes to the work by the authors’ groups to detail the emissions of furan derivatives including DMF, in order to understand the toxicological and environmental impacts of their combustion.4
2. EXPERIMENTAL SETUP 2.1. Engine and Instrumentation. The experiments were performed on a single-cylinder, 4-stroke SI research engine, as shown in Table 1. The 4-valve cylinder head includes the Jaguar sprayReceived: July 24, 2012 Revised: September 26, 2012 Published: October 15, 2012 6661
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Table 1. Engine Specification engine type combustion system swept volume bore × stroke compression ratio engine speed injector fuel pressure and timing engine load ignition timing intake valve opening exhaust valve closing valve open duration
Table 3. Chromatography Equipment Setup and Procedure 4-stroke, 4-valve spray-guided DISI 565.6 cm3 90 × 88.9 mm 11.5:1 1500 rpm multihole nozzle 150 bar, 280° bTDC 5.5 bar IMEP 21° bTDCcomb 16° bTDCintake 36° aTDCintake 250 CAD
GC/MS separation detection column sample injection size split ratio flow rate test conditions test duration
guided direct-injection (SGDI) technology used in their V8 production engine (AJ133).18 The engine was coupled to a DC dynamometer to maintain a constant speed of 1500 rpm (±1 rpm), regardless of the torque output. The in-cylinder pressure was measured using a Kistler 6041A watercooled pressure transducer. Coolant and oil temperatures were precisely controlled to maintain at 358 and 368 K (±3 K), respectively, using a proportional integral differential (PID) controller. All temperatures were measured with K-type thermocouples. A 100 L intake buffer tank (approximately 200 times the engine’s swept volume) was used to stabilize the intake air flow. The engine was controlled using in-house control software written in LabVIEW. High-speed, crank-angle-resolved and low-speed, timeresolved data was also acquired using in-house LabVIEW program. The data was then analyzed using MATLAB to examine the combustion and emissions performance. The gaseous emissions were measured using a Horiba MEXA7100DEGR gas analyzer. Exhaust samples were taken 0.3 m downstream of the exhaust valve and pumped via a heated line (maintained at 464 K) to the analyzer. 2.2. Test Fuels. The DMF used in this study was supplied by Shijiazhuang Lida Chemical Co. Ltd. in China, at 99% purity. This was benchmarked against commercial 97 RON gasoline and ethanol, both supplied by Shell Global Solutions, U.K. The methanol and n-butanol used in the high performance liquid chromatography (HPLC) analysis were supplied by Fisher Scientific, U.K. (99.5 and 99% purity, respectively). A high octane gasoline was chosen, as this represents the most competitive characteristics offered by the market, and provides a strong benchmark to the two biofuels. The fuel characteristics are shown in Table 2. 2.3. Hydrocarbon and Carbonyl Speciation. The emissions equipment used in this work is shown in Table 3. The midrange HCs were identified using GC/MS (GC: Clarus600; MS: Clarus600T) using a thick film nonpolar phase Elite-1 capillary column (30 m length, 0.32 mm ID, and 3.0 μm film), both supplied by Perkin-Elmer.
HPLC
Perkin-Elmer Clarus600 Perkin-Elmer Clarus600T Elite-1: 30m × 0.32 mm × 3 μm Tedlar bag (10−15:1) 1 mL
Shimadzu LC20 Shimadzu SPD-M20A Luna: 250 × 4.6 mm × 5 μm DNPH (20 mL) 25 μL
20:1 2 mL/min 50 °C, 1 min; 12 °C/min; 200 °C, 1 min 14.5 min
1 mL/min 10:90 to 70:30 v/v MeCN/water, 120 min; UV λ = 360 nm 130 min
Tedlar bags were used to collect the exhaust gas, once diluted through a venturi dilution tunnel with dried, filtered, and HC-free workshop air at 10−15:1. The MS was calibrated before each test using heptacosa, as is commonly employed. In order to measure a clear signal, molecules with molecular weight (MW) between 35 and 200 were detected. This suppresses the influence from the background gases, such as the carrier gas helium, as well as water, nitrogen, and oxygen, so that the mass spectra of individual HCs could be clearly identified. A standard carbonyl mix was used for the HPLC tests (supplied by Sigma Aldrich) and was analyzed on a Shimadzu LC20. The DNPHderivative samples (1 μL injection) were then analyzed using a Luna tubular column supplied by Phenomenex with the following specification: 250 mm length and 4.6 mm diameter. The HPLC control program is shown in Table 3. 2.4. Experimental Procedure. 2.4.1. Engine Setup. The engine was considered warm once the coolant and lubricating temperatures had stabilized at 85 and 95 °C, respectively. The exhaust gas temperature was monitored throughout the test. Any test did not start until the exhaust temperature was stabilized. Each test was performed at the stoichiometric air−fuel ratio (AFRstoich) or λ = 1, ambient air intake conditions (approximately 25 °C ± 2 °C), and constant valve timing. The ignition timing for all the fuels was fixed at 21° bTDCcomb. The tests for both hydrocarbon speciation and quantification of carbonyl were carried out at fixed engine load (5.5 bar IMEP). The ignition timing of 21° bTDCcomb is the optimized spark timing (KL_MBT) for gasoline at 5.5 bar IMEP. The MBT timing is the spark timing, which provides the maximum IMEP for a fixed throttle position. Once knock or unstable combustion occurs (COV of IMEP > 5%), the MBT timing is retarded by 2 CAD. In such cases, the optimum ignition timing is referred to the knock-limited MBT (KLMBT) timing. For comparing emissions, the burning rate is an important parameter because slow burning rate will have relatively higher expansion stroke temperatures and more post fame oxidation. The burning rate is highly dependent on several factors, such as fuel properties, spark timing, load, etc. In this study, the aim was to
Table 2. Test Fuel Properties in Order of Increasing H/C Ratio chemical formula H/C ratio O/C ratio gravimetric oxygen content (%) density @ 20 °C (kg/m3) research octane number (RON) stoichiometric air−fuel ratio LHV (MJ/kg) calorific values of stoichiometric mixture (MJ/kg) initial boiling point (°C) a
DMF
gasoline
n-butanol
ethanol
methanol
C6H8O 1.333 0.167 16.67 889.7a 101.3b 10.72 32.89a 2.81a 92
C2−C14 1.795 0 0 744.6 96.8 14.46 42.9 2.77 32.8
C4H10O 2.5 0.25 21.6 811 98 11.2 32.71a 2.69a 118
C2H6O 3 0.5 34.78 790.9a 106c 8.95 26.9a 2.71a 78.4
CH4O 4 1 50 792 106c 6.47 19.83a 2.67a 65
Measured at the University of Birmingham. bAPI Research Project 45 (1956) and Phillips data. cHeywood, ref 39. 6662
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Figure 1. (a) Chromatogram of engine-out emissions using DMF. (b) Library and sample spectrum of DMF. compare the emissions from different fuels under certain engine conditions, and therefore, the spark timing and load was set constant for all fuels. The effect of spark timing on IMEP, exhaust temperature, and emissions (HC, CO) was already presented in a previous publication.9 When changing fuels, the high pressure fuel system was purged using nitrogen until the lines were considered clean. Once the line was repressurized to 150 bar using the new fuel, the engine was run for several minutes. This made sure that no previous fuel remained on the injector tip or any combustion chamber crevices before any data was acquired. The ETAS LA4 lambda meter settings were changed for each fuel using the AFRstoich, O/C, and H/C ratios. Each fuel was running under fuel specific stoichiometric A/F ratio. The total energy input into the engine at the fixed engine load for each fuel was almost the same because indicated efficiencies between different fuels were quite comparable. Due to the energy density difference between fuels, the injection pulse for each fuel was quite different in order to match the same engine load. Because the tests were carried out at stoichiometric A/F ratio, the throttle and injection pulse were adjusted simultaneously to achieve the engine operating condition of 5.5 bar IMEP engine load. 2.4.2. Hydrocarbon Speciation. For this work, the exhaust gases were collected in Tedlar bags. Although the 2 mL thick polyvinyl fluoride (PVF) Tedlar film is considered chemically inert to a wide-
range of compounds, some species, such as 1,3-butadiene, are considered unstable during long-term storage.19,20 Therefore, the samples were analyzed immediately, as recommended by others.21 The avoidance of HC condensation was obtained by diluting the emissions samples (via heated line) with compressed (and filtered) air, using a venturi dilution tunnel. The dilution ratio was maintained between 10 and 15:1, which reduces the partial pressure of each HC and thus the tendency to condense. Samples were extracted through the septum in the Tedlar bag using a 10 mL gas syringe with needle (supplied by Perkin-Elmer), and 1 mL of gas was subsequently injected in the GC/ MS. After each test, the Tedlar bags were purged 5 times with pure nitrogen using the polypropylene valve fitting in order to eliminate any trapped residual gas from previous tests. The use of mass spectrometry enabled the identification of the medium-range HCs (C6 to C12). This allows unknown compounds to be qualitatively found. The mass spectrum (mass-to-charge, or m/z ratio for each mass) of each peak was identified using a NIST (National Institute of Standards and Technology) library. The percentage match is reported in section 3. This temperature program used in this study is shown in Table 3. 2.4.3. Quantification of Carbonyls. In this study, the emissions of carbonyls (aldehydes and ketones) were investigated through the wet chemistry analysis of acidified 2,4-dinitrophenylhydrazine (DNPH) solution using HPLC. Although other methods are available for a 6663
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faster response,17,22 the aim of this investigation is to examine the carbonyls present in the emissions of a new fuel. Therefore, the commonly employed California Air Resources Board (CARB) Method 1004 has been used to quantify the carbonyls. The exhaust gas is bubbled at a constant flow rate (1 L/min) for a fixed time period (20 min) in acidified DNPH reagent (20 mL) as supplied by Sigma Aldrich. The interaction of the carbonyls in the exhaust gas with the DNPH reagent produces DNPH-carbonyl derivatives, which can then be analyzed through reverse phase HPLC. During the test, the acidified DNPH solution is maintained at 0 °C using an ice bath. Once collected, the samples were stored below 4 °C and analyzed within 24 h. The gas bubbler was fitted with a sinter in order to produce small bubbles and improve the reaction rate by increasing the surface area between the exhaust gas and DNPH solution. A long tube and exit trap were also used to help contain the DNPH solution during the test. A ultraviolet (UV) wavelength detector was used at a wavelength of 360 nm to detect the relative abundance of each compound. The mobile phase solvent included HPLC grade water (deionized) and acetonitrile at a fixed flow rate of 1 mL/min. The mixing ratio was then varied linearly from 10:90 v/v (acetonitrile (MeCN)/deionized water) to 70:30 v/v up to 120 min and then held constant until the end of the test (at 130 min). After each test, the mixing ratio was then linearly reduced back to 10:90 v/v for 10 min, ready for the next sample. This procedure was performed three times for each fuel in order to quantify the magnitude of repeatability. A standard solution containing 13 different carbonyls in acetonitrile (supplied by Sigma Aldrich) was used in the calibration. The peak area of each compound in the sample was then compared to the calibration in order to determine its concentration. In this study, 11 compounds are independently quantified. The separation of 2-butanone and butyraldehyde was inadequate, and so, the combined emission is reported. The separation of C3 carbonyls is also known to be very difficult but have been individually quantified in this study.23
The two reaction mechanisms to form MVK during the combustion of DMF are as follows: C2H3 + CH3CO(+ M) → C2H3COCH3(+ M)
(R1)
C2H3CO + CH3( +M) → C2H3COCH3(+ M)
(R2)
The third species detected is 2-methylfuran, MF (C4H3OCH3, tR = 3.36 min). This furan derivative might be produced from the reaction of DMF (CH3C4H2OCH3) with a hydrogen atom: CH3C4 H 2OCH3 + H → C4 H3OCH3 + CH3
(R3)
The analogous reaction of MF would then result in the formation of furan (C4H4O):27 C4 H3OCH3 + H → C4 H4O + CH3
(R4)
However, the signal for furan was not observed in Figure 1a using GC/MS. This might be attributed to the relatively low concentration of MF compared with DMF. Compared with the DMF concentration, which was mainly indicated by the area of signal peak in GC-MS, MF concentration is qualitatively low. This is because it only covered the speciation of hydrocarbon study, and no quantitative data is included for each hydrocarbon. It should be noted that the concentration of certain chemicals measured by GC-MS is dependent on several factors, such as the component itself and the signal area, not only on its relative abundance. The high concentration of DMF leads to a low signal of MF. Therefore, the low signal intensity of MF will undoubtedly lead to an even lower or possibly unobservable signal of furan. Further observations of Figure 1a at higher tR lead to the detection of 2-ethyl-5-methylfuran (EMF), ethylbenzene, and 1,4- and 1,2-dimethylbenzene (at 6.42, 7.53, 7.67, and 8.06 min, respectively). EMF (CH3C4H2OCH2CH3) can be produced from the combination of methyl (CH3) with 5-methylfuranylmethyl (CH3C4H2OCH2), which is easily produced by the H-abstraction reaction of DMF, as shown in reactions R5 and R6:
3. RESULTS AND DISCUSSION 3.1. Hydrocarbon Speciation. Figure 1a presents the chromatogram of the engine-out emissions from the testing engine fueled by DMF as obtained through the GC/MS. The chromatogram window starts from 2 min in order to avoid the large peak created by CO2. It shows that the midrange HCs are dominated by the emissions of unburned DMF, which is common for pure component fuels.24,25 It has been reported that FID may not be sensitive toward oxygenated hydrocarbon (such as in this case, DMF). For this reason, total hydrocarbon measured by FID may be underestimated. This is an uncertainty faced by all the emission measurement of oxygenated fuels using FID and further studies should be carried out using FTIR. This suggests the total unburned HCs is different from the FID analysis shown in previous work,9 due to the sensitivity of FIDs.10 According to the previous work, the HC emissions from DMF is about 7−10% higher at the engine speed of 1500 rpm and engine load between 3.5−8.5 bar IMEP. Each compound has a characteristic mass spectrum (MS), which is clearly shown in Figure 1b for that of DMF (MW = 96). The MS was analyzed by comparing the experimental signal with the library. The two MS signals are well matched, which thus verifies the emissions of unburned DMF. The emissions of aromatics (benzene and toluene at 4.26 and 5.98 min, respectively) are measured by GC/MS. Here, three additional species have been identified by GC/MS. In the order of tR, the first HC identified is cyclopentadiene (tR = 2.63 min). The second species is methyl vinyl ketone, MVK (C2H3COCH3, tR = 2.96 min). It should be noted that MVK is also common in the emissions from gasoline combustion.26
CH3C4H 2OCH3 + R → CH3C4 H 2OCH 2 + HR
(R5)
CH3C4 H 2OCH 2 + CH3 → CH3C4 H3OCH 2CH3
(R6)
where R may be OH, H, O, or CH3, etc. in reaction R5 and the following reactions, with HR being H2O, H2, OH, or CH4, etc., correspondingly. The formation of ethylbenzene (C6H5CH2CH3), 1,4-dimethylbenzene (1,4-CH3C6H4CH3), and 1,2-dimethylbenzene (1,2-CH3C6H4CH3) is a result of the presence of toluene (C6H5CH3). These aromatics are formed in a similar manner to that of EMF (reactions R5 and R6) and MF (reaction R3) from DMF, respectively:28 C6H5CH3 + R → C6H5CH 2 + HR
(R7)
C6H5CH 2 + CH3 → C6H5CH 2CH3
(R8)
C6H5CH3 + CH3 → 1, 4‐CH3C6H4CH3 + H
(R9)
C6H5CH3 + CH3 → 1, 2‐CH3C6H4CH3 + H
(R10)
Although 1,3-dimethylbenzene would be eluted at a similar time to 1,4-dimethylbenzene, it is unobservable from Figure 1a. This is due to the selectivity of the benzene ring addition reaction. Xylenes have three dimethylbenzene isomers (i.e., 1,2-, 1,3-, and 1,4-dimethylbenzene). Methyl radicals are more likely to be added in priority to the ortho- or para- positions of 6664
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the first methyl group on the benzene ring in toluene, rather than the meta-position, according to the rules of orientation on the benzene ring. Overall, the area under the chromatogram of each HC detected is very low (≤5%) relative to the area of the largest emissions (unburned DMF). 3.2. Quantification of Carbonyls. The carbonyl emissions analysis relies on the match of tR. Quantification is then performed by comparing the areas between the standard and the sample on a C1 (formaldehyde) basis. The emissions of the three highest carbonyls when using gasoline (formaldehyde, acetaldehyde, and benzaldehyde) are compared to ethanol and DMF in Figure 2.
DMF and gasoline. However, the emissions of formaldehyde when using ethanol are similar to gasoline, in agreement with the previous work.30 3.2.2. DMF. When using DMF, the emissions of formaldehyde and acetaldehyde are at least 50% lower than with gasoline and ethanol. It is known that formaldehyde and acetaldehyde are formed during low temperature oxidation of HC fuels.33,34 However, DMF appears to have a high combustion temperature or at least its combustion takes place in higher temperatures for optimized spark timing,9 which may help to inhibit the production of formaldehyde and acetaldehyde. According to the previous work, the maximum in-cylinder temperature for DMF is about 50−110 K higher than that for gasoline at the engine speed of 1500 rpm and engine load between 3.5−8.5 bar IMEP. The low production of formaldehyde and acetaldehyde is also due to the chemical structure of DMF. First, DMF might be consumed by the oxidation of each methyl group,35 and this leads to the formation of ketenyl (HCCO) and propyne (C3H4), analogous to that of furan:27
Figure 2. Formaldehyde, acetaldehyde, and benzaldehyde engine-out emissions concentrations (C1-equivalent) using ethanol, DMF, and gasoline.
The reaction of ketenyl will lead to the products of complete combustion: CO2 and H2O. Propyne may lead to the formation of propargyl; the first aromatic ring (benzene) is formed:36
2C3H3 → C6H6
3.2.1. Gasoline and Ethanol. The high paraffin content in gasoline (approximately 35%) is responsible for producing the highest carbonyl emission of formaldehyde.29 The formation of acetaldehyde when using ethanol is much higher than formaldehyde (by a factor of 4) and much higher compared to DMF and gasoline. This high emission of acetaldehyde in oxygenated fuels has been reported in other work and is closely related to the structure of the fuel.30 Ethanol (CH3CH2OH) is mainly consumed in three ways; reactions R12 and R13 are more dominant than R11:31 CH3CH 2OH + OH → C·H 2CH 2OH + H 2O
(R11)
CH3CH 2OH + OH → CH3C·HOH + H 2O
(R12)
CH3CH 2OH + OH → CH3CH 2O· + H 2O
(R13)
The reaction of benzene (C6H6) with a methyl radical (CH3) during the combustion of DMF will lead to the formation of toluene (C7H8). Further oxidation of toluene will then lead to the formation of benzaldehyde:37
This reaction sequence R17 → R18 → R19 competes with other reactions of DMF. As a result, the formations of formaldehyde and acetaldehyde are reduced. Since the radical combination reactions, R18, are less favorable, the concentration of benzaldehyde cannot be very high, as shown in Figure 2. The remaining carbonyl emissions are shown in Figure 3. In addition to the three common aldehydes of formaldehyde (CH 2 O), acetaldehyde (CH 3 CHO), and benzaldehyde (C6H5CHO), higher aldehydes were detected in the emission of DMF combustion. The total emissions concentration of these higher carbonyls is in the following order: gasoline > DMF > ethanol (115.5, 89.6, and 15.4 ppm, respectively). Clearly, the incomplete combustion of ethanol first forms acetaldehyde and then forms formaldehyde, at which point, little remains to form other higher carbonyls. The relative concentration using each fuel is shown in Figure 4. For gasoline, the proportion of nonaromatic carbonyls emitted decreases as the number of carbon atoms in each carbonyl increases.30 This is common in HC flames, since
The CH3C·HOH and CH3CH2O· radicals formed in R12 and R13 will then mainly turn into acetaldehyde (CH3CHO), leading to a high concentration in the exhaust:31 CH3C· HOH + M → CH3CHO + H + M
(R14)
CH3CH 2O· + M → CH3CHO + H + M
(R15)
This significant increase in acetaldehyde emissions with ethanol is also reported by others.16,32 The reaction of acetaldehyde then leads to the formation of methyl. Oxidation of methyl then results in the formation of formaldehyde: CH3 + O2 → CH 2O + OH
(R18)
(R16)
This reaction mechanism of reaction R14 is dominant in the emissions with ethanol, and so, there is a greater tendency for oxygenated HCs such as acetaldehyde to be produced. As a result, the concentration of acetaldehyde relative to formaldehyde in ethanol combustion is much higher compared with 6665
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Figure 5. Formaldehyde and acetaldehyde engine-out emissions concentrations (C1-equivalent) using methanol, ethanol, n-butanol, DMF, and gasoline.
Figure 3. Higher carbonyl engine-out emissions concentrations (C1equivalent) using ethanol, DMF, and gasoline.
butanol (also compared with the previous data for gasoline and ethanol) in order to relatively position the emissions of DMF. It is shown that the total carbonyl emissions when using ethanol are higher than with methanol, whereby the main carbonyl emissions were acetaldehyde and formaldehyde, respectively. This behavior is in agreement with the previous work22,29,30,38 because during combustion, methanol oxidizes to form formaldehyde in the following reaction path: 2CH3OH + O2 → 2CH 2O + 2H 2O
(R20)
The dominance of these carbonyl emissions is unsurprising, as they are produced directly from the fuel, which is further reflected in the emissions of butanone/butyraldehyde during the combustion of n-butanol.15 Figure 5 shows that, among the four oxygenated fuels and gasoline, DMF produces the lowest emissions of formaldehyde and acetaldehyde (ethanol > n-butanol > gasoline > DMF, with methanol excluded). The result can be explained by that fact that the total carbonyl emissions increase as the H/C ratio increases, as was recognized by Zervas et al. who drew a particular link to the emissions of formaldehyde, acetaldehyde, propionaldehyde, and benzaldehyde.38 This is because benzaldehyde is produced from low H/C ratio fuel components (largely fuel aromatics) whereas formaldehyde, acetaldehyde, and, to a lesser extent, propionaldehyde, are all formed from high H/C ratio fuel components. Figure 6 presents the correlations between H/C (fuel) ratio, the total of formaldehyde, acetaldehyde, propionaldehyde, and benzaldehyde emissions, and exhaust gas temperature. Here, H/C refers to the fuel. For each fuel at the same test load (5.5 bar IMEP) and spark timing (21° bTDCcomb), the exhaust gas temperature (x-axis) is different for the engine testing condition. Zervas et al. noticed the inverse relationship of these carbonyl emissions with exhaust temperature (except for benzaldehyde, which increases with exhaust temperature). The combustion of DMF results in high exhaust temperatures despite similar spark timing due to lower combustion duration and thus high combustion temperature.9 Although this increases the tendency for benzaldehyde and propionaldehyde production, the emissions of formaldehyde and acetaldehyde are dramatically reduced. The emissions result from the combustion of DMF shows a clear integration into this correlation.
Figure 4. Variation of carbonyl engine-out emissions concentrations (C1-equivalent) using ethanol (a), DMF (b), and gasoline (c).
aldehydes with more carbon atoms bear more hydrogen atoms and are thus more easily reacted during combustion. This behavior is also partially evident when using DMF. For ethanol, it is very clear that the abundance of acetaldehyde dominates the carbonyl formation, which is then followed by formaldehyde, as found in other work.30 In Figure 5, the emissions of formaldehyde and acetaldehyde in DMF combustion are given along with methanol and n6666
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■
Figure 6. Relationship between fuel H/C ratio and the sum of formaldehyde, acetaldehyde, propionaldehyde, and benzaldehyde with exhaust temperature.
REFERENCES
(1) DIRECTIVE 2009/28/EC. On the Promotion of the use of Energy from Renewable Sources. Official Journal of the European Union, 2009. (2) CurtisB.U.S. Ethanol Industry: the Next Inflection Point. NREL: Washington, DC, 2008 (3) Wang, Q.; Tian, Z. Biofuels and the Policy Implications for China. Asian-Pacific Economic Literature 2011, 25 (1), 161−168. (4) Roman-Leshkov, R.; Barrett, C. J.; Liu, Z. Y.; Dumesic, J. A. Production of Dimethylfuran for Liquid Fuels from Biomass-Derived Carbohydrates. Nature 2007, 447, 982−986. (5) Kazi, F. K.; Patel, A. D.; Serrano-Ruiz, L. C.; Dumesic, J. A.; Anex, R. P. Techno-economic Analysis of Dimethylfuran (DMF) and Hydroxymethylfurfural (HMF) Production from Pure Fructose in Catalytic Processes. Chem. Eng. J. 2011, 169 (1−3), 329−338. (6) Wu, X.; Huang, Z.; Wang, X.; Jin, C.; Tang, C.; Wei, L.; Law, C. K. Laminar Burning Velocities and Flame Instabilities of 2,5Dimethylfuran−Air Mixtures at Elevated Pressures. Combust. Flame 2011, 158, 539−546. (7) Tian, G.; Li, H.; Xu, H.; Li, Y.; Satish, M. R. Spray Characteristics Study of DMF Using Phase Doppler Particle Analyzer. SAE Int. J. Passeng. CarsMech. Syst. 2010, 3, 948−958. (8) Tian, G.; Daniel, R.; Li, H.; Xu, H.; Shuai, S.; Richards, P. Laminar Burning Velocities of 2,5-Dimethylfuran compared with Ethanol and Gasoline. Energy Fuels 2010, 27 (7), 3898−3905. (9) Daniel, R.; Tian, G.; Xu, H.; Wyszynski, M. L.; Wu, Z.; Huang, Z. Effect of Spark Timing and Load on a DISI Engine Fuelled with 2,5Dimethylfuran. Fuel 2011, 90, 449−458. (10) Cheng, W. K.; Summer, T.; Collings, N. The Fast-Response Flame Ionization Detector. Prog. Energy Combust. Sci. 1998, 24, 89− 124. (11) Grob, R. L. Modern Practice of Gas Chromatography, 2nd ed.; John Wiley and Sons, Inc.: Hoboken, NJ, 1985. (12) IARC. Agents Classified by the IARC Monographs. International Agency for Research on Cancer: Lyon, France, 2011. (13) NTP. Report on Carcinogens. U.S. Department of Health and Human Services, National Toxicology Program: Research Triangle Park, NC, 2011. (14) CARB. Tables of Maximum Incremental Reactivity (MIR) Values. California Code of Regulations; California Air Resources Board: Sacramento, CA, 2010. (15) Wallner, T.; Frazee, R. Study of Regulated and Non-Regulated Emissions from Combustion of Gasoline, Alcohol Fuels, and their Blends in a DI-SI Engine. SAE Technical Paper 2010-01-1571, 2010. (16) Storey, J. M. E.; Barone, T. L.; Norman, K. M.; Lewis, S. A. Ethanol Blend Effects On Direct Injection Spark-Ignition Gasoline Vehicle Particulate Matter Emissions. SAE Int. J. Fuels Lubr. 2010, 3, 650−659. (17) Zhang, F.; Zhang, X.; Shuai, S.; Xiao, J.; Wang, J. Unregulated Emissions and Combustion Characteristics of Low-Content Methanol−Gasoline Blended Fuels. Energy Fuels 2010, 24, 1283−1292.
4. CONCLUSIONS
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DISI = direct-injection spark-ignition DMF = 2,5-dimethylfuran DNPH = 2,4-dinitrophenylhydrazine ETH = ethanol GC/FID = gas chromatography flame ionization detector GC/MS = gas chromatography mass spectrometry HC = hydrocarbon HPLC = high performance liquid chromatography PVF = polyvinyl fluoride IMEP = indicated mean effective pressure MIR = maximum incremental reactivity MTH = methanol MW = molecular weight ULG = unleaded gasoline UV = ultraviolet
1. The HC emissions of DMF are dominated by unburned fuel. However, other species identified by GC/MS (≤5% of the unburned DMF) include cyclopentadiene, methyl vinyl ketone, 2-methylfuran, benzene, toluene, 2-ethyl-5methylfuran, ethylbenzene, 1,4-dimethylbenzene, and 1,2-dimethylbenzene. 2. In total, 12 carbonyls were identified in the exhaust of DMF. The emissions of formaldehyde, acetaldehyde, and benzaldehyde were lower than with gasoline (decreases of 62%, 52%, and 6%, respectively). The formation of benzene and toluene during DMF combustion results in similar benzaldehyde emissions to gasoline. 3. DMF produces the lowest total carbonyl emissions and more significantly, the lowest emissions of the more harmful formaldehyde and acetaldehyde among the four oxygenated fuels and gasoline.
AUTHOR INFORMATION
Corresponding Author
*Tel.: +44 (0)121 414 4153. Fax: +44 (0)121 414 3958. Email:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This study was funded by the EPSRC under Grant No. EP/ F061692/1, Advantage West Midlands (AWM), and Royal Society Sino-British Fellowship (Dr. Lixia Wei). The authors would like to acknowledge the support from Jaguar Cars Ltd., Shell Global Solutions, U.K., and technicians from the School of Chemistry (Graham Burns, Chi Tsang, and Peter Ashton), University of Birmingham.
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ABBREVIATIONS AFR = air−fuel ratio aTDC = after top dead centre bTDC = before top dead centre BUT = butanol CAD = crank angle degrees CARB = california air resources board 6667
dx.doi.org/10.1021/ef301236f | Energy Fuels 2012, 26, 6661−6668
Energy & Fuels
Article
(39) Heywood, J. B. Internal Combustion Engine Fundamentals; McGraw-Hill: New York, 1988.
(18) Sandford, M.; Page, G.; Crawford, P. The All New AJV8. SAE Technical Paper 2009-01-1060, 2009. (19) Kaiser, E. W.; Siegl, W. O.; Cotton, D. F.; Anderson, R. W. Effect of Fuel Structure on Emission from a Spark-Ignited Engine. 2. Naphthene and Aromatic Fuels. Environ. Sci. Technol. 1992, 26 (8), 1581−1586. (20) Kaiser, E. W.; Siegl, W. O. High Resolution GC Determination of the Atmospheric Reactivity of Engine-Out HC Emissions from SI Engine. J. High Resolut. Chromatogr. 1994, 17, 264−270. (21) McCarrick, A. Long Term Storage of Air SamplesA Study of Two Bag Materials. SAE Technical Paper 2000-01-2502, 2000. (22) Wei, Y.; Liu, S.; Liu, F.; Liu, J.; Zhu, Z.; Li, G. Formaldehyde and Methanol Emissions from a Methanol/Gasoline-Fueled SparkIgnition (SI) Engine. Energy Fuels 2009, 23, 3313−3318. (23) Coutrim, M. X.; Nakamura, L. A.; Collins, C. H. Quantification of 2,4-Dinitrophenyl-Hydrazones of Low Molecular Mass Aldehydes and Ketones using HPLC. Chromatographia 1993, 37 (3/4), 185−190. (24) Kar, K.; Cheng, W. Speciated Engine-Out Organic Emissions from PFI-SI Engine Operating on Ethanol/Gasoline Mixtures. SAE Int. J. Fuels Lubr. 2009, 2, 91−101. (25) Zhu, Z.; Li, D. K.; Liu, J.; Wei, Y. J.; Liu, S. H. Investigation on the Regulated and Unregulated Emissions of a DME Engine under Different Injection Timing. Appl. Therm. Eng. 2011, 35, 9−14. (26) Westerholm, R.; Almén, J.; Li, H. Exhaust Emissions from Gasoline-Fuelled Light Duty Vehicles Operated in Different Driving Conditions: A Chemical and Biological Characterization. Atmos. Environ. 1992, 26 (1), 79−90. (27) Tian, Z.; Yuan, T.; Fournet, R.; Glaude, P. A.; Sirjean, B.; BattinLeclerc, F.; Zhang, K.; Qi, F. An Experimental and Kinetic Investigation of Premixed Furan/Oxygen/Argon Flames. Combust. Flame 2011, 158, 756−773. (28) Dagaut, P.; Pengloan, G.; Ristori, A. Oxidation, Ignition, and Combustion of Toluene: Experimental and Detailed Chemical Kinetic Modeling. Phys. Chem. Chem. Phys. 2002, 4 (10), 1846−1854. (29) Held, T. J.; Dryer, F. L. A Comprehensive Mechanism for Methanol Oxidation. Int. J. Chem. Kinetics 1998, 30 (11), 805−830. (30) Magnusson, R.; Nilsson, C. The Influence of Oxygenated Fuels on Emissions of Aldehydes and Ketones from a Two-Stroke Spark Ignition Engine. Fuel 2011, 90, 1145−1154. (31) Marinov, N. M. A Detailed Chemical Kinetic Model for High Temperature Ethanol Oxidation. Int. J. Chem. Kinetics 1999, 31 (3), 183−220. (32) Niven, R. K. Ethanol in Gasoline: Environmental Impacts and Sustainability Review Article. Renewable Sustainable Energy Rev. 2005, 9, 535−555. (33) Brackmann, C.; Nygren, J.; Bai, X.; Li, Z.; Bladh, H.; Axelsson, B.; Denbratt, I.; Koopmans, L.; Bengtsson, P.; Aldén, M. LaserInduced Fluorescence of Formaldehyde in Combustion using Third Harmonic Nd:YAG Laser Excitation. Spectrochim. Acta Part A 2003, 59, 3347−3356. (34) Ogawa, H.; Li., T. Volatile Organic Compounds in Exhaust Gas from Diesel Engines under Various Operating Conditions. Int. J. Engine Res. 2011, 12 (1), 30−40. (35) Wu, X.; Huang, Z.; Yuan, T.; Zhang, K.; Wei, L. Identification of Combustion Intermediates in a Low-Pressure Premixed Laminar 2,5Dimethylfuran/Oxygen/Argon Flame with Tunable Synchrotron Photoionization. Combust. Flame 2009, 156, 1365−1376. (36) Miller, J. A.; Melius, C. F. Kinetic and Thermodynamic Issues in the Formation of Aromatic Compounds in Flames of Aliphatic Fuels. Combust. Flame 1992, 91 (1), 21−39. (37) Murakami, Y.; Oguchi, T.; Hashimoto, K.; Nosaka, Y. Theoretical Study of the Benzyl + O2 Reaction: Kinetics, Mechanism, and Product Branching Ratios. J. Phys. Chem. 2007, 111 (50), 13200− 8. (38) Zervas, E.; Montagne, X.; Lahaye, J. Emission of Alcohols and Carbonyl Compounds from a Spark Ignition Engine. Influence of Fuel and Air/Fuel Equivalence Ratio. Environ. Sci. Technol. 2002, 36, 2414− 2421. 6668
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