The prospect of using methanol as an alternative fuel for vehicles in China is enticing because of its good combustion properties, low production cost, and renewable capacity, but the in-cylinder combustion of methanol also brings extra emissions concerns, such as alcohols and aldehydes. For the impact of methanol–gasoline blends on the pollutant emissions of spark ignition (SI) engines to be investigated, a GEELY MR479Q port fuel injection SI engine was selected for tests of burning different methanol–gasoline blends at wide-open throttle operating conditions, and an AVL Fourier-transform infrared multicomponent gas analyzer was used to measure all of the emissions. Test results show that the methanol-containing fuel blends had positive effects on the engine-out regulated emissions. Nitrogen oxide, carbon monoxide, and nonmethane hydrocarbon emissions were all dramatically reduced when the test engine was fueled with methanol–gasoline blends. Other hydrocarbon emissions such as ethylene, propylene, and soot precursors like acetylene and aromatic hydrocarbons were also reduced with the methanol–gasoline blends. However, the methanol in the fuel blends caused significant elevation of engine-out unburned methanol (CH3OH) and formaldehyde (CH2O) emissions at the same time, especially for high methanol-containing fuel blends, such as M50 and M70. When fueled with M70, engine-out unburned CH3OH emission could reach as high as 500 ppm, and CH2O emission was almost 4 times as much as that of M0. Other emissions like ethanol, acetaldehyde, and 1,3-butadiene were observed to be only slightly influenced by methanol during the engine tests.

A reduced combustion kinetic model for the methanol-gasoline blended fuels for SI engines was developed. Sensitivity analysis and rate constant variation methods were used to optimize the kinetic model. Flame propagation, shock-tube and jet-stirred reactor systems were modeled in CHEMKIN. The laminar flame speed, ignition delay time and change in concentrations of species were simulated using the reduced kinetic model. The simulation results of reduced chemical mechanism agreed well with the relevant experimental data published in the literature. The experimental investigations on engine bench were also carried out. The in-cylinder pressure and exhaust emissions were obtained by using a combustion analyzer and an FTIR (Fourier transform infrared spectroscopy) spectrometer. Meanwhile, an engine in-cylinder CFD model was established in AVL FIRE and was coupled with the proposed reduced chemical mechanism to simulate the combustion process of methanol-gasoline blends. The simulated combustion process showed good agreement with the engine experimental results and the predicted emissions were found to be in accordance with the FTIR results.Methanol-gasoline, chemical mechanism, SI engine, CFD simulation Citation:Ling X C, Wu F, Yao D W. A reduced combustion kinetic model for the methanol-gasoline blended fuels on SI engines. Sci China Tech Sci, 2016, 59: 8192,

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The ethanol-gasoline blends have brought new challenges to the in-cylinder mixture air-fuel ratio control for the variable fuel characteristics especially in the traditional PFI (Port Fuel Injection) SI (Spark Ignition) engines. This paper studied all the dynamic links in the intake fuel transfer process from the fuel injectors to cylinders, including the wall-wetting effect and injector fuel flow characteristics. A wall-wetting fuel film evaporation model and an injector fuel flow model were then built, and a new intake port fuel dynamic model was constructed. All of these models have considered the impact of ethanol component in the blend fuels. On this basis, a model based air-fuel ratio control strategy for PFI SI engines fueled with ethanol-gasoline blends was proposed. The strategy combined the traditional fuel feedforward and feedback corrections, and introduced a linear oxygen sensor based blend fuels' mixing ratio self-learning algorithm, to achieve the fuel adaptive compensation for the intake wallwetting effect and injector fuel flow characteristics. The test results show that, the model based air-fuel ratio control strategy can always adjust the in-cylinder mixture air-fuel ratio near the stoichiometric one. The maximum relative control deviation of airfuel ratio under steady conditions has not exceeded ±2%, while for transient conditions, the control deviation is still less than ±4%, much better than traditional map based control strategy. Moreover, the control strategy has a good adaptability to different ethanol-gasoline blends.