DME燃料HCCI燃烧过程及排放的数值模拟

采用数值方法研究了二甲基醚HCCI模式下的燃烧过程及排放机理．实验在一台被改造的单缸直喷柴油机上进行．计算模型采用耦合了简化化学动力学的三维模型．模拟表明,三维模型在示功图的预测上比零维模型更接近实测值,因为三维模型考虑了流场内温度场和压力场的不均匀性及缸壁、活塞表面的传热．模拟还表明,CO主要出现于气缸壁附近及侧隙,这是由于气缸壁附近温度梯度较大,没有足够的活化自由基将CO氧化为CO2．主要的未燃碳氢为甲醛和二甲基醚,这两种产物主要来源于气缸壁附近和侧隙处,温度较低抑制二甲基醚的加氧反应, 同时不利于活化自由基的出现,导致未燃产物得不到充分氧化．

Numerical Simulation on DME Combustion Process and Emission Mechanism

Numerical approach was applied to investigate the HCCI combustion process and emission mechanism of DME. A series of experiment were carried out on a single cylinder engine. The numerical model combines CFD model with reduced chemical kinetic mechanism. Numerical study indicates that the 3D model is more accurate in predicting cylinder pressure than the zero-D model, because the inhomogeneous distribution of temperature and the heat loss through cylinder walls and piston surface are considered in the 3D model. CO mainly appears in the vicinity of cylinder walls and piston-ring crevice region. The large temperature gradient restrains the formation of radicals, which is important for the oxidization of CO. The unburned hydrocarbon emissions are mainly CH3OCH3 and CH2O, which are located in the piston-ring crevice region and the vicinity of cylinder walls. Low temperature restrains the first O2 addition process and the formation of radicals, which results in the incomplete oxidization of CH3OCH3 and CH2O.