后喷对高压共轨柴油机排放及燃油经济性的影响

摘要

在一台高压共轨直喷国Ⅳ柴油机上，研究了后喷策略对常规排放物和燃油消耗率的影响规律．结果表明，随着后喷油量的增加或者后喷时刻的推迟，颗粒物(PM)排放呈现出先降低后升高的趋势，而氮氧化物(NOx)排放则是逐渐降低；随着后喷油量的增大，碳氢化合物(HC)和一氧化碳(CO)排放量呈现出先减少后增大的趋势，HC 和CO 随着后喷油时刻的推迟，排放量逐渐增大．在1800,r/min，负荷率75%工况下，后喷油量6,mg，后喷时刻1,100,μs 时为最优排放后喷工况；与单次喷射相比较，PM 排放降低16.42%，NOx排放降低4.78%，CO 排放降低28.99%，HC排放降低6.16%，同时燃油消耗率变化不大．因此，优化后喷策略可以在不引起燃油消耗率增加的情况下，保持CO和HC排放标准，同时降低颗粒物和NOx排放．%The effects of post-injection strategy on the regulated exhaust emissions and brake specific fuel consump-tion(BSFC) were investigated in a diesel engine in this study. The experiment was conducted on a four-cylinder di-rect-injection engine,and the post-injection parameters(post injection quantity and timing) were adjusted to investi-gate their influences on particulate matter(PM),nitrogen oxides(NOx),hydrocarbon(HC),carbon monox-ide(CO)emissions and BSFC. Results shows that with the increase of post injection quantity and the delay of post injection,particulate matter(PM) emission first decreases and then increases,while nitrogen oxides(NOx) emission shows a downward trend. The emissions of hydrocarbon(HC) and carbon monoxide(CO) decrease at the beginning and then increase as the post injection quantity increases,while with the delay of post injection timing,HC and CO emissions increase gradually. When post injection quantity is set at 6,mg and post injection timing at 1,100,μs under the operating condition of 1,800,r/min and 75% engine load,the decreases of PM,NOx,CO and HC emissions are 16.42%,4.78%,28.99% and 6.16%,respectively,as compared with the single injection,and the BSFC is almost unchanged. Overall,a decrease in PM and NOxemissions can be obtained by optimizing the post injection strategy without affecting CO,HC emissions and BSFC.