某中速柴油机机内净化技术模拟

Simulation of cleaning technologies for a medium-speed marine diesel engine

为探索机内净化方法在中速船用柴油机上应用以满足IMO Tier III排放法规的潜力,依据某大功率中速柴油机台架性能实验数据,采用AVL Boost和Fire v2008软件分别建立整机流动及缸内燃烧的仿真模型,模拟多种Miller循环、高压缩比、喷油正时及EGR率方案。结果表明:NOx排放随进气门关闭正时提前而降低,预混合燃烧峰值不断增加,会逐渐抵消Miller循环降低NOx排放的作用;增加几何压缩比使预混合燃烧峰值降低,配合喷油正时滞后可进一步降低NOx;采用中度Miller循环匹配中度EGR技术可以使NOx排放降低80%以上,同时碳烟排放降低20%,将是一条可行的满足IMO Tier III法规NOx排放的技术路线。

In order to meet IMO Tier III emission regulations,this paper explores the potential of an internal purification method for medium speed marine diesel engines. Based on the test bench experimental data of a high-power medium speed diesel engine,the simulation models of the whole flow and in-cylinder combustion were established using AVL Boost and Fire v2008 software. Various cases of valve timing,Miller cycle,high compression ratio,injection timing,and EGR ratio were designed to investigate their influence on combustion and emissions. The results show that NOxemissions decrease as the inlet valve close timing is advanced,and the premixed combustion peak increases continuously at the same time. This will counteract the function of Miller cycle,which reduces NOxemission; the in-cylinder premixed combustion peak decreases when the geometrical compression ratio is increased,and together with injection timing delay can further reduce NOxemission; by using a moderate Miller cycle combined with moderate EGR technology,NOxemissions can decrease 80%,and soot emissions decrease 20%. This can be a feasible technical combination to meet IMO Tier III regulations about NOxemissions.