Study On The Characteristics Of Combustion And Exhaust Particulate Matter From Gasoline Direction Injection Engine Fueled With Methanol-gasoline Blended Fuel

Energy depletion and environmental pollution is the most important issue of human society development. With a high octane value and a good anti-knock property, methanol is widely used in gasoline as an alternative fuels. By the application of methanol, the compression ratio can be improved, increasing the thermal efficiency of gasoline engines. Direct injection has good cold starting performance, low fuel consumption, and fast response, which enables lean-burn combustion, stratified combustion and other combustion mode. It has become the trend of gasoline engines development. However, because of its diffusion combustion mode, direct injection gasoline engine has a particulate emission to some extent. Furthermore, because of the wall chilling effect, part of the unburned oil droplets discharged in the form of tiny liquid particles. This part of the particles can easily form semi-volatile organic particles in atmospheres, which is harmful to human body. In order to study the characteristics of particulate matter emissions in the direct-injection gasoline engine with methanol, fuel and their mixture, this article conducted the relevant particulate matter emissions experiments on a turbocharged gasoline engine.The following results were obtained: Particulate matter exhausted by direct-injection gasoline engine included nuclear mode particles and accumulation mode particles. In common working conditions, the number concentration of nuclear mode presented a bimodal distribution and was much higher than that of accumulation mode, while the mass concentration of nuclear mode particles was somewhat lower than that of accumulation mode. This study further investigated the influence of different combustion control parameters on particulate matter exhausted, such as ignition timing, fuel injection timing and excess air ratio. Experiments were conducted under the common working conditions of 2000 rpm and 2bar. The results showed that under the same working conditions and combustion control parameter,with the increase of methanol content,the maximum explosion pressure and the average temperature gradually rose, the peak value of heat release rate curve moved ahead, and the number concentration and mass concentration of both nuclear states particle and accumulation mode particle decreased significantly. The addition of methanol had a bigger influence on accumulation mode particle than nuclear states particle. With the increase of methanol content, the variation of combustion control parameters had a less influence on particulate matter emission. In order to investigate the influence of spray characteristic on particulate matter, which was generated by using the mixture of methanol and gasoline as fuel in the common working conditions, experiments under the working conditions of 2000 rpm and 2bar were conducted. By contrast, spray characteristic under different methanol content differed a little. Therefore, the differences of spray characteristic were not the main reasons for the differences of particulate matter emission under common working conditions. The influence of engine oil on the particulate matter from the mixture of methanol and gasoline was investigated. Results showed that engine oil had a very significant role in promoting gasoline engine particulate matter emission, especially for accumulation mode particle. However, with the increase of methanol content, the impact of engine oil on the particulate matter emissions reduced. The experimental data were further analyzed and the following conclusion can be drawn. With the increase of methanol content, the concentration number of both nuclear states particulate matter and accumulation mode particle decreased. This phenomenon is due to the existence of oxygen in methanol itself.