通用小型汽油机油气混合两相流动分析与低排放研究

为降低通用小型汽油机尾气排放，满足美国EPA法规限值，研发低排放通用小型汽油机产品，该文以168F汽油机为例应用Fluent工程软件建立了汽油机进气系统油气混合的两相流动模型，模拟计算化油器结构参数变化对汽油机不同工况油气混合浓度的变化规律，依据欧美现行排放法规的试验方法，分析通用小型汽油机排放生成机理，得出了低排放汽油机油气混合浓度的变化特性，即随着汽油机负荷的减少，混合气浓度值需逐渐变稀，据此计算得出化油器参数匹配方案。用168F汽油机对优化的化油器匹配方案进行了试验，NOX的排放较原机下降了35.4%；HC的排放下降了20.3%，样机的排放达到了美国2012年计划执行的排放限值。

Investigation on the two-phase flow of air-fuel mixture and low emissions for small gasoline engines

168F spark ignition engine was discussed to reduce the exhaust emissions for meeting the EPA emission standard in this paper. The two-phase flow model of the air-fuel mixture inside the intake system was built by FLUENT. The laws between the structure parameters of carburetor and the excess air ratio were calculated under different working conditions of the engine. According to the testing cycles of the emission standard set by EU and EPA, the formation mechanism of the exhaust emissions was discussed, the characteristic of the excess air ratio for the low-emission S.I. engine was derived, and the air-fuel mixture concentration gradually leant with the engine load reducing. The carburetor parameters for the low emissions S.I. engine were obtained based on the simulation results. The sample engine matching the optimized carburetor was tested. The testing results showed that the NOX and HC emissions decreased by 35.4% and 20.3% respectively compared to the original engine. The optimized sample engine can meet the requirements of the emission standard of EPA which is planned to implement in 2012.