多次喷射所组织的复合燃烧及其排放的影响因素  

Numerical of the Effects on the Emissions of Compound Combustion Using Multiple Flexible Injections

作　　者：于洋[1] 苏万华[1] 

机构地区：[1]天津大学内燃机燃烧学国家重点实验室,天津300072

出　　处：《内燃机学报》2010年第5期385-392,共8页Transactions of Csice

基　　金：国家重点基础研究发展规划资助项目(2007CB210000);国家自然科学基金重点资助项目(50636040)

摘　　要：针对多次喷射所组织的柴油复合燃烧过程进行了试验及模拟研究。复合燃烧过程包括预混压燃燃烧(PCCI)及主喷和后喷燃油产生的扩散燃烧。采用简化化学反应机理并结合特征时间燃烧模型对着火和燃烧过程及排放产物进行了模拟,计算结果与试验数据符合良好。当预喷射定时提前时,平均当量比较低导致局部温度超过1 800 K的区域减少,有利于形成低温燃烧,PCCI产生的NOx减少。由于低温燃烧形成的大量CO主要分布在挤流区域并且CO的含量较HC高得多,分布也较广。在主喷开始后,喷雾上沿进入PCCI燃烧产生的高温区域导致扩散燃烧加剧,因此主喷定时不宜过早以避免生成较高的NOx。主喷喷雾产生的流动在燃烧室的凸台壁面引导下进一步沿着凸台向上并促使CO向挤流区域扩散并燃烧放热使得较高温度的区域始终保持在唇口附近,有利于触发PCCI阶段产生的未燃CO的氧化,CO最终减少了约50%。The engine test and numerical study of the compound combustion organized by multiple injections were conducted.The compound combustion is organized by a sequential combustion processes including the stage of premixed charge compression ignition（PCCI）,the stage of diffusion combustion generated by main injection and the stage by post injection.A combustion model combining simplified chemical mechanism and characteristic-time combustion model was employed to explore the compound combustion process and emissions in a heavy duty diesel engine.The simulation results agreed with the experimental data well.It was found in this study when the start of pulse injection was advanced,the region with local temperature above 1 800 K decreased and NOx was produced less during PCCI stage.But a large amount of CO formed mainly in the squish volume due to the low temperature combustion.After the main injection started,the upper plume of spray entered the beforehand high temperature region of earlier PCCI,that led to intense combuston,so the timing of main injection should be late relatively to avoid higher NOx.The flow generated by the main injection spray was further guided upwards by the protrudent platform wall of the combustion chamber,so it promotes the CO diffusing upwards and releasing heat through its combustion which kept higher temperature region always around the lip area of the combustion chamber.That triggered burning of CO left in PCCI in the neighbor area of main plume so that the CO was reduced approximately by 50% finally.

关 键 词：多次喷射 复合燃烧 燃烧模型 排放 

分 类 号：TK421[动力工程及工程热物理—动力机械及工程]