【摘要】 通过建立三维计算流体动力学(CFD)柴油/天然气双燃料喷射模型,研究不同EGR率对高压直喷(HPDI)发动机燃烧和排放特性的影响.结果表明:高温区主要是由柴油引燃的天然气射流燃烧形成.另外,由于喷射的天然气与燃烧室边缘碰撞,高温区域被分成两个部分:一部分进入燃烧室凹坑区并形成顺时针旋转的滚流;另一部分进入挤流区与新鲜空气进一步混合燃烧.NO的形成区域与天然气射流中心线形成的高温区基本重合.在挤流区,由于燃料的氧化速率和停留时间有限,因而产生了较多的CO.此外,HPDI发动机的颗粒物(PM)形成区域与CO形成区域大致相同,这是由燃料的低氧化率造成的.随着EGR率增加,NO排放降低,而CO和PM排放随之增加.更多还原

【Abstract】 The analysis of combustion and emission characteristics of a high pressure direct injection(HPDI) engine with different exhaust gas recirculation(EGR)rate were performed with an introduction of the diesel/natural gas dual fuel injection model into a multi-dimensional simulation code.The results reveal that the high temperature regions are mainly formed by the combustion of the gas jet combined with an ignition generated by the pilot diesel fuel.Moreover,the high temperature region is split into two parts due to the impingement of the gas jet to the piston bowl edge.One part enters into the piston bowl and forms a clockwise-rotating vortex.The other part enters the squish area to further mix with the fresh air over there.The NO formation regions are similar to that of the high temperature region,especially along the centerline of the gas jet.CO emissions are mainly generated in the squish area due to the lower oxidation rate and insufficient time available.In addition,the particulate matter(PM)emission regions from the HPDI engine are similar to that of the CO emission region due to the low oxidation rate of the soot.With the increase of the EGR rate,NO emission decreases,but CO and PM emissions increase.更多还原