排气阀晚关对大型二冲程低速船机的影响

为了探究排气阀晚关对低速船机的详细影响机制,针对一大型二冲程低速船机建立了三维仿真模型并进行了实验验证,在此基础上仿真研究了排气阀晚关对缸内气流、燃烧过程及低速机性能的影响规律和机制。结果表明：随排气阀晚关角度的增加,燃油喷射后的缸内涡流比缓慢增加,着火滞燃期逐渐延长,最高燃烧压力先大幅降低后小幅上升,指示比油耗先大幅增加后小幅减小,NOx比排放先大幅下降后急剧上升。存在一排气阀晚关角度的临界值,当超出该临界值后,排气阀晚关能够明显增强燃料与空气的混合强度,促进缸内燃烧过程,但NOx比排放会急剧增加。

Influence of late exhaust valve closing on the large two-stroke low-speed ship engine

In order to explore the detailed influence mechanism of late exhaust valve closing (LEVC) on the low-speed ship engine, a three-dimensional simulation model was established for a large two-stroke low-speed ship engine. The simulation model was confirmed to be effective by the experimental results. Basis on the model, the effects and mechanisms of LEVC on the in-cylinder airflow, combustion process and engine performance were investigated. The results showed that with the increase of late closing angle of exhaust valve, the in-cylinder swirl ratio after fuel injection slowly increased, the ignition delay gradually extended, and the maximum combustion pressure decreased first and then increased slightly. The indicated specific fuel consumption increased first and then decreased slightly with the increasing late closing angle of exhaust valve. While NOx emission showed an opposite trend to the indicated specific fuel consumption. It dropped significantly first and then risen sharply. There was a threshold value of the LEVC angle. When the threshold value was exceeded, LEVC could significantly enhance the mixing intensity of the fuel and air, and promote the in-cylinder combustion process, but NOx emission might increase sharply.