Research On The Combustion And Emission Characteristics Of Methanol-Gasoline Blend Engine

As China's energy structure is "poor-oil, less-gas, rich-coal", the development and promotion of the coal-based methanol fuel as a gasoline alternative fuel is one of the feasible options. The application of methanol in the gasoline engine is a hot issue in China. However, at this stage there are unregulated emissions, catalyst conversion efficiency, cold-start performance, and other key issues, which need further in-depth studies of the methanol fuel in China. It would provide a theoretical reference on the feasibility of the large-scale application in China.The steady-state tests were carried out on the engine test bench using different-content methanol-gasoline blended fuels, which investigated the effects of the methanol content in fuels and the engine load on the economy performance, air-fuel ratio, combustion characteristics, regulated emissions, unregulated emissions, power performance and exhaust temperature of the engine; the catalyst performance evaluation and rapid aging tests were carried out, which investigated the catalyst air-fuel ratio characteristics, light-off temperature characteristics and durability; the cold-start tests were carried out on the engine test bench and vehicle chassis dynamometer, which investigated the emission and combustion characteristics during the cold-start process. The results showed that the power performance, economy performance, combustion characteristics and regulated emissions characteristics of the low-content methanol-gasoline engines were basically the same. The methanol and formaldehyde emissions increased with the methanol content increasing in fuels. The methanol emission had the high conversion efficiency in the lean air-fuel ratio zone. The formaldehyde methanol had the high conversion efficiency during the whole air-fuel ratio zone. The formaldehyde light-off temperature T50 was lower than other emissions. Compared to the gasoline aging, M15 made the catalyst light-off temperature rise and the high-conversion window width became smaller. However, the variations were small. In the cold-start process, the transient methanol and formaldehyde emissions before the catalyst were determined by the methanol content in fuels. The emissions in the low-temperature condition were significantly higher than those in the ambient temperature. The conventional three-way catalyst could solve the problem of unregulated emissions after the light-off of the catalyst. With the increase of the methanol content in fuels, the combustion duration shortened in the cold-start the process. The cylinder indicated mean effective pressure increased slightly. The cylinder combustion performance improved slightly.In order to model and predict the combustion and emission characteristics of the methanol-gasoline engine, a detailed chemical kinetic model of the methanol oxidation was built based on the research of the literature. The experimental data of the shock tube and flow reactors were utilized to verify the model. Based on the model, the oxidation chemical kinetics model of the surrogate gasoline fuel was added to build a methanol-gasoline oxidation chemical kinetics model. The experimental data of the jet-stirred reactor were utilized to verify the methanol-gasoline model. The Fractal or Vibe combustion model was coupled with the methanol-gasoline oxidation chemical kinetics model to build a numerical model of the spark-ignition engine working process. In this model the formaldehyde emissions of different-content methanol-gasoline fuels were simulated. The engine load was varied to calculate the formaldehyde emission curve of M30 with the engine load. The simulation results were basically consistent with the experimental data. The methanol content in fuels was varied to predict the formaldehyde emissions of the high-content methanol-gasoline fuels.