轻型柴油机预混合低温燃烧和排放性能的试验研究

An Experimental Study on the Low-temperature Premixed Combustion and the Emission Performance of Light-duty Diesel Engine

本文中对比分析了某四缸轻型车用柴油机喷射正时、废气再循环(EGR)率和喷射压力对燃烧过程和污染物排放的影响规律。结果表明:采用适时早喷或者晚喷策略均能延长滞燃期而改善可燃混合气的均匀性,以实现部分预混合燃烧,抑制碳烟排放。适时早喷策略相对晚喷策略更有利于降低碳烟排放,但将受到NO_x排放恶化的限制。引入EGR后,适时早喷不但可降低缸内燃烧温度抑制NO_x排放,还可有效解决因早喷带来的燃烧相位过早的问题,从而提高燃烧效率,改善燃油经济性,在高EGR率区域可兼顾有效燃油消耗率、NO_x和碳烟排放。而晚喷条件下,引入EGR后会进一步加重后燃现象,使有效燃油消耗率和碳烟排放有所恶化。随着喷射压力的提高,适时早喷时,燃烧放热过程变缓,瞬时放热率峰值和缸内平均温度降低,从而可同时降低NO_x和碳烟排放,而晚喷则相反,NO_x排放随着喷射压力的提高而有所上升。而不论适时早喷还是晚喷,有效燃油消耗率受喷射压力的影响很小。

The law of the effects of injection timing,exhaust gas recirculation（EGR） rate and injection pressure on the combustion process and the pollutant emissions of a four-cylinder diesel engine for light-duty vehicle are comparatively analyzed in this paper.The results indicate that either moderately advancing or retarding injection timing can prolong delayed burning period and hence improve the uniformity of combustible mixture,realizing partial premixed combustion and suppressing soot emissions.Compared with retarding injection timing,moderate advance of injection is more conducive to reducing soot emissions,but is limited by the deterioration of NO_X emissions.The introduction of EGR with early injection can not only lower in-cylinder combustion temperature and hence restrain the generation of No_X,but also effectively avoid the problem of too-early combustion phase caused by early injection and thus increase combustion efficiency and improve fuel economy.Effective specific fuel consumption and the emissions of NO_x and soot can be concurrently improved in high EGR rate region.But for retarding injection,the introduction of EGR may further exacerbate the phenomena of post-combustion and deteriorate effective specific fuel consumption and soot emission.With the increase of injection pressure,the process of combustion and heat release become slow and the transient peak of heat release rate and average in-cylinder temperature lower and hence the NO_x and soot emissions can be reduced simultaneously for moderately advancing injection,while it is just the opposite for retarding injection,the emission of NO_x goes up with the rise in injection pressure.However the injection pressure only has trivial effects on effective specific fuel consumption no matter with advancing or retarding injection timing.