米勒循环模式的柴油机性能及NO_x排放的数值研究

Numerical investigation on performance and NO_x emission of diesel engine with Miller cycle

为了使非道路柴油机达到第三阶段排放法规的要求,引入米勒循环技术。利用AVL Boost软件建立非道路D6114型柴油机的仿真模型,研究米勒循环对该柴油机的性能和NOx排放的影响。结果表明:进气门关闭正时提前,缸内的气体因膨胀降温过程,使压缩阶段的温度降低,NOx排放最大降低36%,但柴油机功率损失增加、油耗升高;压缩比的提高能改善柴油机的经济性,但同时会导致缸内爆发压力增高,柴油机机械负荷加重;推迟喷油正时可以使燃烧相位后移,缸内爆发压力降低,NOx的排放进一步降低。米勒循环、高压缩比、优化喷油正时等技术的结合,可以实现油耗仅升高2.2%的同时NOx排放降低30%,爆发压力降低2 MPa。该结论可以为非道路柴油机满足第三阶段法规而进行的改进设计提供参考。

Miller cycle technology is introduced to achieve the requirements of the third stage emisregulations of non-road diesel engine. A simulation model of non-road D6114 diesel engine is sion set up by using AVL software for analyzing the effect of Miller cycle on performance and NOx emissions of the diesel engine. The results show that by means of Miller cycle, lower charge temperatures inside the cylinder can be achieved by closuring intake valve early and the cooler combustion process, the NOx emission is reduced to 36%, but the loss of power and the fuel consumption is increased. Enhancing compression ratio can effectively improve the fuel economy and combustion characteristic of diesel engine, but maximum firing pressure significantly increases and diesel engine mechanical load grows worse. Delayed injection timing can make the combustion phase backwards, reduce in-cylinder explosion pressure and the NO, emissions further. Miller cycle with high compression ratio and optimization of injection timing can reduce 30% of NOx while fuel consumption is increased only 2. 2% and maximum firing pressure is reduced 2 MPa. This conclusion provides reference for revised design of non-road diesel engine to meet the third stage emission regulations.