Unregulated Emissions and Combustion Characteristics of Low


Telephone: +861062772515. .... The test catalyst was a conventional TWC bought from the Delphi Company. Table 3 shows the specifications of the TWC...
0 downloads 0 Views 5MB Size

Energy Fuels 2010, 24, 1283–1292 Published on Web 12/03/2009

: DOI:10.1021/ef900974p

Unregulated Emissions and Combustion Characteristics of Low-Content Methanol-Gasoline Blended Fuels Zhang Fan, Zhang Xia, Shuai Shijin,* Xiao Jianhua, and Wang Jianxin State Key Laboratory of Automotive Safety and Energy, Tsinghua University, Beijing 100084, China Received September 2, 2009. Revised Manuscript Received November 11, 2009

Unregulated emissions, such as methanol and formaldehyde, from the methanol-gasoline engine are one of the most serious concerns regarding the use of low-content methanol applications in conventional gasoline engines. Gasoline, M10, M15, M20, and M30 were used as fuels in a port fuel injection (PFI) gasoline engine EQ491i without any modification. The load performances of the engine were tested on an engine test bench. A Fourier transform infrared (FTIR) spectrometer was used to measure the unregulated emissions before and after a conventional three-way catalyst. The test results showed that the low-content methanol-gasoline blended fuels had little influence on the engine power output and energy consumption. The cylinder pressure and heat release rate showed no significant variation with the increase of the methanol content in the blended fuel. However, engine-out methanol and formaldehyde, as unregulated emissions, increased almost linearly with the methanol content in the fuel, while the ethanol and acetaldehyde emissions were little influenced by methanol addition. The conventional three-way catalyst had a high conversion efficiency for the unregulated emissions and ultimately reduced the regulated and unregulated emissions from the methanol-gasoline engine to the same levels as those generated by a conventional gasoline engine.

gasoline engines have been widely researched. The U.S. Environmental Protection Agency (EPA) examined the performance of high-level methanol fuel blends with gasoline in a turbocharged, port-fuel-injected, high-compression-ratio, medium-duty engine. The results clearly pointed a way to cost-effective, highly efficient means of using bioderived spark-ignition fuels.5 Exhaust emissions were measured in a fleet of 1993 production flexible/variable-fueled vehicles (FFV/VFV) on methanol fuels blended with a reformulated gasoline by U.S.A. vehicle companies. Within the FFV/VFV fleet, CO and NOx with the methanol fuels were not significantly different than their base gasoline.6 Considered from the standpoint of environmental aspects, the potential toxicity of unregulated emissions from methanol engines cannot be ignored. Unburned methanol and formaldehyde emissions from methanol engines are harmful to the environment as well as to human health.7 If low-content methanol-gasoline blended fuels are used in current port fuel injection (PFI) gasoline engines, the conversion efficiencies of unburned methanol and formaldehyde emissions on the conventional three-way catalyst (TWC) need to be intensively evaluated. Previous experimental studies have mainly concentrated on the measurement of engine-out unregulated emissions from methanol-gasoline engines rather than tailpipe-out emissions. The former measurement methods for unregulated emissions include gas chromatograph (GC) methods and

1. Introduction As a liquid fuel, methanol has significantly different storage and delivery requirements than gasoline and diesel, with differences in water tolerance and materials compatibility, including metal corrosion and elastomers. However, methanol can be produced from a great number of different raw and renewable material resources. Therefore, methanol has attracted significant interest in the 20th century. Certain governments and car companies in Europe and the United States have been actively promoting research into methanol vehicles since the beginning of the 1970s.12 Nonetheless, at the end of the 20th century, Europe and the United States abandoned the use of methanol in vehicles. The reason was primarily the high cost of production of methanol, which was generated primarily from natural gas. Since then, the development of methanol use in vehicles has entered into a phase of stagnation.3 However, the use of coalgenerated methanol as a practical alternative fuel is one of the most realistic options for China, because of the “oil-lean, gaslacking, and coal-rich” structure of Chinese energy resources.4 The influences of methanol content on the combustion characteristics, fuel economy, and regulated emissions of *To whom correspondence should be addressed. Telephone: þ861062772515. Fax: þ861062772515. E-mail: [email protected] edu.cn. (1) Kenneth, J.; Brent, K.; Timothy, C.; Wendy, C.; Leslie, E.; Peter, L. FTP emissions test results from flexible-fuel methanol Dodge Spirits and Ford Econoline Vans. SAE Tech. Pap. 961090, 1996. (2) Yutaka, T.; Shigeru, U.; Mayumi, K.; Ichiro, K.; Hisashi, K. The history of M100 methanol vehicles penetration in Japan. SAE Tech. Pap. 2000-01-1216, 2000. (3) Robert, E.; Vincent, M.; Jean-Claude, G. Well-to-wheels analysis of future automotive fuels and powertrains in the European context. SAE Tech. Pap. 2004-01-1924, 2004. (4) Walter, M.; Han, W.; Dennis, S. Economic, environmental and energy life-cycle assessment of coal conversion to automotive fuels in China. SAE Tech. Pap. 982207, 1998. r 2009 American Chemical Society

(5) Matthew, J. High efficiency with future alcohol fuels in a stoichiometric medium duty spark ignition engine. SAE Tech. Pap. 2007-013993, 2007. (6) Vaughn, R.; William, J.; Jack, D.; Robert, A.; James, A. Emissions with reformulated gasoline and methanol blends in 1992 and 1993 model year vehicles. SAE Tech. Pap. 941969, 1994. (7) Yan, X.; Huang, H.; Huang, X. Evaluation of toxicity and environmental impact of vehicle-used methanol fuel. J. Occup. Health Damage 2004, 19 (2), 117–118.

1283

pubs.acs.org/EF

Energy Fuels 2010, 24, 1283–1292

: DOI:10.1021/ef900974p

Fan et al.

Figure 1. Engine test-bench layout. Table 2. Specifications of Gasoline and Methanol Fuels

Table 1. Engine Specifications item

EQ491i

fuel type

bore  stroke (mm) cylinder number displacement (L) compression ratio

in line four stroke water cooling naturally aspirated 90.82  76.95 4 1.933 9

RON density at 20 °C (g/m3) low heat value (MJ/kg) vaporization latent heat (MJ/kg) minimum ignition energy (mJ) (stoichiometric mixture) flame propagation speed (cm/s) (stoichiometric mixture)

type

high-performance liquid chromatograph (HPLC) methods. The sampling methods include gaseous direct collection and solid absorption.8-12 These measurement methods have some disadvantages, including noncontinuous measurement and long measurement duration. Because of the somewhat large differences between results generated by these measurement methods, it is difficult to systematically and comprehensively evaluate the levels of unregulated emissions from methanol-gasoline engines. Therefore, there is a need for a reliable measurement method with high accuracy and good repeatability, to evaluate the use of low-content methanol-gasoline blended fuels directly in current PFI gasoline engines. The derived method should have the ability to comprehensively assess the characteristics of engine-out and tailpipe-out unregulated emissions.

gasoline

methanol

93 738 43.5 0.33 0.2

110 792 19.9 1.088 0.14

37.7

52.3

Table 3. Catalyst Specifications catalyst type carrier volume (L) carrier dimensions diameter  length (mm) noble metal content (g/ft3) cell density (cell/in.2) Pt/Pd/Rh proportion

conventional three way 0.8 Φ 100  104.8 28 400 4:0:1

The test engine is a conventional multi-point PFI gasoline engine. The engine exhaust pipe is connected to two emissionsampling pipes, which are used to separately measure the regulated and unregulated emissions before and after the TWC. An AVL CEB-II emission analyzer and an AVL multicomponent emission analyzer are used to measure the concentrations of emissions. The engine fuels are supplied by small fuel tanks and pumps, so that these could easily be switched among different content methanol-gasoline blended fuels. Table 1 shows the main technical parameters of the test engine. 2.2. Test Fuels and Catalyst. One of the test fuels is 93 research octane number (RON) gasoline, which complies with current China fourth-stage fuel standards. The fuel was directly purchased from a Beijing market. The gasoline density at 20 °C was 0.738 g/mL, and the low heat value was 43.5 MJ/kg. The other fuel used in the experiments was a type of high-purity industrial methanol bought from the market. The methanol density at 20 °C was 0.792 g/mL, and the low heat value was 19.9 MJ/kg. The methanol purity, measured by GC, was 99.85%. Table 2 shows the specifications of gasoline and methanol fuels. The test catalyst was a conventional TWC bought from the Delphi Company. Table 3 shows the specifications of the TWC. 2.3. Unregulated Emissions Test System. The unregulated emissions test system used in the experiments is a Fourier transform infrared (FTIR) spectrometer manufactured by the AVL Company. In comparison to conventional infrared (NDIR) analyzers, which use a single wavelength of infrared light to measure a single gas component, the AVL FTIR SESAM spectrometer uses a wide range of wavelengths to

2. Experimental Section 2.1. Engine Test Bench. Figure 1 shows the layout of the engine test bench. The engine test bench consists of an exhaust gas measurement system, a fuel supply system, an intake and exhaust system, a data acquisition and processing system, etc. (8) Zhang, Z.; Fan, G.; Song, C.; Hang, Q.; Wang, Y; Hou, Y. Unregulated emissions characteristics from SI electronic control methanol engine. J. Combust. Sci. Technol. 2006, 12 (1), 86–89. (9) Abu-Zaid, M.; Badran, O.; Yamin, J. Effect of methanol addition on the performance of spark ignition engines. Energy Fuels 2004, 18, 312–315. (10) L€ u, S.; Li, H.; Eddy; Qi, D.; Liu, S. Measurement of nonregulated pollutants from SI engine fuelled with methanol/gasoline blends. Trans. CSICE 2006, 24 (1), 57–61. (11) Wang, Y.; Wang, J.; Shi, C.; Wang, X.; Fan, G. Study on the emission characteristic of a methanol fuel gasoline engine. Trans. CSICE 2007, 25 (1), 73–76. (12) Yao, C.; Peng, H.; Liu, Y.; Li, S. Formaldehyde emission characteristic from diesel/methanol compound combustion engine. Trans. CSICE 2008, 26 (3), 233–237.

1284

Energy Fuels 2010, 24, 1283–1292

: DOI:10.1021/ef900974p

Fan et al.

Table 4. Comparative Analysis of Different Unregulated Emission Measurement Methods item

GC

accuracy test duration/ frequency test components

high 10-20 min

continuous measurement synchronization measurement instrument price

CH3OH C2H5OH HCHO CH3CHO no

HPLC high 1-2 h

FTIR

SP

high 1 Hz

relative high 10-20 min

25

no

yes

CH3OH C2H5OH HCHO CH3CHO no

yes

yes

yes

no

relative low

relative high

high

relative low

aldehydes ketones

Figure 3. Engine load characteristics of equivalent fuel consumption at 2400 and 3600 rpm.

spectrophotometry (SP). Table 4 shows the measuring principles and instrument characteristics of all of these different measurement methods. The table shows that FTIR has a number of outstanding advantages, such as continuous online sampling, synchronous multi-component analysis, accurate high-efficient measurement, etc. Thus, FTIR was used in the present study to measure unregulated emissions of the engine fueled with low-content methanol-gasoline blended fuels. Through the calibration, FTIR could simultaneously measure up to 25 kinds of exhaust emissions. The sampling turnover frequency is 1 Hz. The volume of the sample cell is 200 mL. The optical path length is 2 m. Figure 2. Load characteristics of the fuel consumption at 2400 and 3600 rpm.

3. Influences on Engine Operation and Combustion Characteristics

simultaneously measure all spectral information of the gas sample. Using the Fourier transform method, the absorption spectrum (intensity/wavelength) is calculated from the measured interferogram (intensity/time). The individual exhaust gas components are determined from the spectrum using reference spectra (from the FTIR evaluation method packages) and specially developed mathematical functions to minimize crossinterference. FTIR has been used to measure engine exhaust emissions. The Lund University used FTIR to measure the formaldehyde emission from three different types of homogeneous charge compression ignition (HCCI) engines for a range of fuels, including methanol fuel.13 A series of chassis dynamometer test trials were conducted to assess the performance of a FTIR system developed for on-road vehicle exhaust emission measurements by the University of Leeds.14 Besides FTIR, there are other methods available to measure unregulated emissions, including GC, HPLC, and

3.1. Engine Economy. The characteristic engine load tests were carried out under the conditions of engine speeds n = 2400 and 3600 rpm, using pure gasoline (defined as M0), M10 (methanol volume content is 10%), M15, M20, and M30 as fuels. The calibration data of engine ECU remained the same as the engine fuels were varied. The selected load points were engine torques T = 40, 70, 100, 115, 130, 140, and 145 N m (engine switching from closed-loop control to open-loop control mode) and the wide open throttle (WOT) point. All tests were run on a fully warmed engine. Figure 2 gives the load characteristics of the brake-specific fuel consumption (BSFC) at engine speeds n = 2400 and 3600 rpm using different proportional methanol-gasoline blended fuels. During the engine closed-loop control mode, the BSFC increased monotonously with the increment of methanol content in blended fuels. The fuel consumption of M30 was about 15% higher than for gasoline. Because the low heat value of methanol is lower than gasoline, the low calorific value of methanol-gasoline blended fuel decreases with the increment of methanol content. Thus, the fuel consumption needs to be increased to supply the same engine output.

(13) Mikael, L.; Anders, H.; Andreas, V.; Henrik, N.; Hakan, P.; Bengt, J. Quantification of the formaldehyde emissions from different HCCI engines running on a range of fuels. SAE Tech. Pap. 2005-013724, 2005. (14) Hu, Li.; Karl, R. Evaluation of a FTIR emission measurement system for legislated emissions using a SI car. SAE Tech. Pap. 2006-013368, 2006.

1285

Energy Fuels 2010, 24, 1283–1292

: DOI:10.1021/ef900974p

Fan et al.

Figure 5. MBF versus engine load under different methanol contents.

Figure 6. COV versus engine load under different methanol contents.

blended fuels at engine speeds n = 2400 and 3600 rpm. The equivalent fuel consumption does not apparently vary with increments in methanol content, when the engine burns low-content methanol-gasoline blended fuels. The maximum variation is not more than 3%, which is within the measurement error range. Therefore, when the engine works around the range of gasoline stoichiometric ratio (14.5), the increment of methanol content (not more than 30%) in blended fuels has little influence on the engine thermal efficiency and energy economy. 3.2. Combustion Characteristics. To investigate the effects of the methanol content on engine performance, the cylinder pressure was recorded for 50 engine cycles. The average statistic method was used to obtain the mean cylinder pressure. The rate of heat release (ROHR) was calculated from the mean cylinder pressure. The tested fuels were gasoline (M0), M10, M20, and M30. The engine speed was 2400 revolutions/min. The brake mean effective pressure (BMEP) was 0.25, 0.50, and 0.76 MPa, which respectively represented low, medium, and high loads. Figure 4 shows that the cylinder pressure and ROHR of different blended fuels are nearly the same, especially at low and medium loads. It indicates that the increment of lowcontent methanol in blended fuel has no serious effects on the combustion characteristics. However, at high load, the ROHRs of methanol-gasoline blended fuels, especially M30, are slightly faster than with pure gasoline. The difference in the ROHR curves between serial blended fuels is reduced with the decrement of the engine load. Figure 5 shows the position of a 50% mean burn fraction (MBF50%) varying with engine load and methanol content. The position of MBF50% advanced with the increment of methanol in blended fuel. The difference between blended

Figure 4. Cylinder pressure and ROHR curves under different methanol contents.

In accordance with the principles of the equivalent heat value, the measured actual BSFC value can be converted into the equivalent fuel consumption values according to the density and low heat value of gasoline and methanol, as follows: ! Hm Fm BSFCequivalent ¼ BSFCactual Vg þ Vm Hg Fg where BSFCequivalent is the equivalent brake-specific fuel consumption, BSFCactual is the actual brake-specific fuel consumption; Vg(Vm) is the gasoline (methanol) volume fraction, Hg(Hm) is the gasoline (methanol) low heat value, and Fg(Fm) is the gasoline (methanol) density at 20 °C. Figure 3 shows the load characteristics of the equivalent fuel consumption with different methanol contents in 1286

Energy Fuels 2010, 24, 1283–1292

: DOI:10.1021/ef900974p

Fan et al.

Figure 7. Load characteristics of air/fuel ratios at 2400 and 3600 rpm.

Figure 8. Load characteristics of CO emission at 2400 and 3600 rpm.

fuels was reduced when the engine load decreased. In comparison to gasoline, the MBF50% position of M30 advanced 1.6 °CA at high load as well 0.7 °CA at medium load. At low load, the MBF50% positions of four fuels were almost the same. The average statistical method was used to calculate the coefficient of cyclic variation (COV) varying with different methanol contents and engine loads. Figure 6 shows that the difference in COV increased with methanol content and decreased slowly with engine load. The increment in methanol

therefore enhanced the combustion stability of the engine, especially at low load. The above three figures can be analyzed according to the differences in physical and chemical properties of gasoline and methanol. In comparison to gasoline, the vaporization latent heat of methanol is about 3 times that of gasoline. The evaporation of methanol in the cylinder will absorb more heat than that of gasoline, causing further retardation of fuel atomization and the delay of combustion ignition. On the other hand, the flame propagation speed of methanol is 1287

Energy Fuels 2010, 24, 1283–1292

: DOI:10.1021/ef900974p

Fan et al.

Figure 9. Load characteristics of THC emission at 2400 and 3600 rpm.

Figure 10. Load characteristics of NOx emission at 2400 and 3600 rpm.

about twice as fast as that of gasoline, resulting in an increment of the fuel combustion rate and a decrease in combustion duration. This is a pair of mutual restraining factors, so the combustion characteristics of methanol-gasoline blended fuels show different trends depending upon methanol content and engine load. Methanol could easily atomize and evaporate at high load because of the high cylinder temperature; therefore, the factor of flame propagation speed plays a

leading role. Conversely, the latent heat of vaporization plays a leading role at low load because of the low cylinder temperature. Furthermore, the minimum ignition energy of methanol is lower than gasoline, which means that the addition of methanol into gasoline will improve the ignition and reduce the misfire possibility at low load. Consequently, the COV of methanol-gasoline blended fuels is lower than that of pure gasoline. 1288

Energy Fuels 2010, 24, 1283–1292

: DOI:10.1021/ef900974p

Fan et al.

3.3. Air/Fuel Ratio Characteristics. The actual air/fuel ratio was calculated from CO2, O2, CO, total hydrocarbon (THC), and NOx emissions in the exhaust, measured by an AVL CEB-II emissions analyzer, according to chemical equilibrium and mass conservation. To compare the mixture concentrations of different proportional methanol-gasoline blended fuels, only the carbon-hydrogen ratio of pure gasoline was used to calculate the air/fuel ratio. That is, the actual air/fuel ratio of methanol-gasoline fuels is converted into the equivalent air/fuel ratio of pure gasoline. Figure 7 shows the engine load characteristics of air/fuel ratios before and after the catalyst at engine speeds n = 2400 and 3600 rpm. The air/fuel ratios before and after the catalyst are almost invariable as the methanol content changes. Because the engine works in the closed-loop control mode, ECU could adjust the pulse width of fuel injection with the increment of methanol content according to the variations in oxygen-sensor voltage. Therefore, the engine would always work around the stoichiometric ratio. As the

load increases, the engine begins to operate in the open-loop control mode; therefore, the mixture is richened and the air/ fuel ratio decreases. In fact, one of the most significant limitations affecting the use of fuels containing higher levels of methanol in vehicles is the higher volumetric fuel rates required as the methanol content increases. The results show that, at engine speeds n = 2400 and 3600 revolutions/min, the maximum volumetric fuel rate of the engine injector has reached the requirement of M30. According to the above test results, it could be concluded that low-content methanol-gasoline blended fuels (not more than 30%) have little influence on the engine economy, combustion characteristics, and air/fuel ratio, without any modification on the engine. 4. Influences on Engine Emissions 4.1. Regulated Emissions. Figures 8-10, respectively, show the load characteristics of CO, NOx, and THC regulated emissions at n = 2400 and 3600 revolutions/min. As shown in the figures, CO, NOx, and THC regulated emissions before the catalyst did not vary remarkably with the increment of methanol content in the blended fuels. The maximum variation was no larger than 5%, which was caused by the fluctuations in the engine air/fuel ratio. The engine works around the stoichiometric ratio in the closedloop control mode at medium and low loads; therefore, the catalyst works in a high-efficiency zone. Thus, regulated emissions of low-proportional methanol-gasoline blended fuels after the catalyst are very low, essentially the same as those of gasoline. 4.2. Unregulated Emissions. The load characteristics of methanol (MEOH), ethanol (ETOH), formaldehyde (HCHO), and acetaldehyde (MECHO) unregulated emissions, measured by the AVL FTIR analyzer, are shown in Figures 11-16, respectively.

Figure 11. Characteristics of methanol emission before the catalyst with varying methanol contents.

Figure 12. Load characteristics of methanol emission at 2400 and 3600 rpm.

1289

Energy Fuels 2010, 24, 1283–1292

: DOI:10.1021/ef900974p

Fan et al.

Figure 13. Load characteristics of ethanol emission at 2400 and 3600 rpm.

conversion efficiency is somewhat reduced. After the TWC lights off, the tailpipe-out methanol emission reduces to a very low level in the close-loop control mode, because of the high conversion efficiency of the TWC. In the open-loop control mode, adding methanol could change the air/fuel ratio, because the engine control strategy was calibrated based on gasoline. Thus, a rich air/fuel ratio leads to a lower TWC efficiency. Nonetheless, the methanol emission of methanol-gasoline blended fuels is about 10 ppm after the catalyst, which is the same level as that from pure gasoline. As shown in Figure 13, low-content methanol-gasoline blended fuels have a slight influence on ethanol emission. Ethanol emission before the catalyst was about 10 ppm, which was slightly affected by engine load. In the closed-loop control mode, the conversion effect of the catalyst for ethanol emission is not obvious. In the open-loop control mode, the mixture is richened and ethanol emission after the catalyst shows a substantial increment, indicating that ethanol emission has been generated in the catalyst surface reaction. Figure 14 shows that formaldehyde emission before the catalyst has a similar trend to that seen for methanol emission. Formaldehyde emission before the catalyst increases nearly linearly with the increment in methanol content, but the increment of formaldehyde is lower than that of methanol. Figure 15 shows that formaldehyde emission increases at low and medium loads as the load increases but decreases at high load. Because formaldehyde is a product of incomplete combustion of methanol, there are two key factors influencing formaldehyde generation: methanol concentration and combustion temperature. The increment of fuel injection causes the methanol concentration to increase at low and medium loads, which promotes the generation of formaldehyde emission. However, the high combustion temperature at high load, even at full load in the open-loop control mode, plays a dominant role in restraining formaldehyde

Figure 14. Characteristics of formaldehyde emission prior to the catalyst.

As shown in Figure 11, there is a substantial amount of unburned methanol emission prior to the catalyst, which increases almost linearly with the increment of the methanol content in the blended fuels. Figure 12 shows that methanol emission before the catalyst increases at low and medium loads as the load increases but decreases at high load in the closed-loop control mode. The fuel injection amount therefore apparently increased with the increment of engine load at low and medium load, so that more unburned methanol emission remained in the exhaust. In contrast, the engine is heated at high load; therefore, the wall-quenching and crevice effects diminish, which causes a decrease in the formation of unburned methanol. When the engine assumes the open-loop control mode, the rich mixture aggravates the incomplete combustion, causing the generation of more unburned methanol emission. Unburned methanol emission in the engine exhaust is almost completely converted by the catalyst in the closedloop control mode. In the open-loop control mode, the 1290

Energy Fuels 2010, 24, 1283–1292

: DOI:10.1021/ef900974p

Fan et al.

Figure 15. Load characteristics of formaldehyde emission at 2400 and 3600 rpm from fuel with varying contents of methanol.

Figure 16. Load characteristics of acetaldehyde emission at 2400 and 3600 rpm.

formation. Moreover, the catalyst has a high conversion efficiency for formaldehyde emission regardless of the engine control mode; therefore, formaldehyde emission is nearly zero after the catalyst. As shown in Figure 16, low-content methanol-gasoline blended fuels have little influence on acetaldehyde emission. Acetaldehyde emission before the catalyst of all test fuels was about 10 ppm and was slightly influenced by engine load. In the closed-loop control mode, acetaldehyde emission was almost completely converted by the catalyst. In the openloop control mode, the air/fuel ratio was enriched; therefore,

the conversion efficiency for acetaldehyde emission was reduced. Acetaldehyde emission of methanol-gasoline blended fuels and pure gasoline was at the same level after the catalyst and was lower than 5 ppm. Figure 17 shows the exhaust temperatures in the inlet and outlet of the TWC, varying with engine load and methanol content. The exhaust temperatures before the catalyst are higher than 550 °C, which makes the catalyst fully light-off to convert the engine emissions completely. In conclusion, the methanol content (less than 30%) in low-content methanol-gasoline blended fuels had a large 1291

Energy Fuels 2010, 24, 1283–1292

: DOI:10.1021/ef900974p

Fan et al.

Figure 17. Load characteristics of exhaust temperatures at 3600 rpm.

influence on methanol and formaldehyde emissions. As the methanol content increased from 0 to 30%, methanol emission increased from about 10 to 100 ppm, while formaldehyde emission increased from around 20 to 60 ppm. Ethanol and acetaldehyde emissions (about 10 ppm) were unaffected by the methanol content. The conventional TWC has a high conversion efficiency for methanol, formaldehyde, and acetaldehyde unregulated emissions. Methanol, ethanol, formaldehyde, and acetaldehyde emissions from blended fuels after the catalyst were at the same levels as those of unregulated emissions from pure gasoline.

methanol-gasoline blended fuels, CO, NOx, and THC emissions before the catalyst do not vary remarkably with increments in the methanol content of blended fuels. Levels of regulated emissions from blended fuels after the catalyst are the same as those for pure gasoline. (4) The methanol content in low-content methanol-gasoline blended fuels has a large influence on methanol and formaldehyde emissions but only a slight influence on ethanol and acetaldehyde emissions. Methanol, ethanol, formaldehyde, and acetaldehyde emissions after the catalyst were the same as those for pure gasoline. Because tailpipe-out methanol and acetaldehyde emissions were similar to those for pure gasoline under warmed-up, steadystate conditions, the use of low-level methanol blends would not be expected to increase these emissions in widespread use. Conventional TWCs used in present gasoline engines could solve the problem of unregulated emissions from methanol blends. To investigate the transient exhaust emissions, cold-start and driving cycle tests should be carried out in further work.

5. Conclusions (1) When an engine works around the gasoline stoichiometric ratio (14.5), the increment of methanol in blended fuels has only a slight influence on engine thermal efficiency and energy economy. (2) The cylinder pressure and heat release rate do not obviously vary with the increment in the methanol content in the fuels. The COV difference gradually decreases as the methanol content increases, especially at low load. The MBF50% position advances as the methanol content increases, especially at high load. (3) For low-content

Acknowledgment. This work was financially supported by the National High Technology Research and Development Program of China (“863” Program) “Adaptability Research on Methanol Vehicle”, under Grant 2006AA11A1A4.

1292