废气再循环对燃用生物柴油发动机排放的影响

基于一台匹配冷却废气再循环系统(EGR)的轻型高压共轨柴油机,试验研究了EGR与主喷正时对燃用生物柴油发动机排放特性的影响.结果表明:外特性下,燃用生物柴油后,发动机的氮氧化合物(NO_x)排放明显增加,而总碳氢化合物(THC)排放和超细颗粒排放数量浓度都明显降低.在转速为2 200r·min~(-1)的25%负荷下,随着EGR率的增加,NO_x排放、超细颗粒总数量浓度都明显减少,THC排放以及燃油消耗率都降低,而随着主喷的滞后,NO_x排放和超细颗粒总数量浓度也明显减少,但燃油消耗率和THC排放却增加;在50%负荷,随着EGR率的增大和主喷的滞后,NO_x排放和超细颗粒总数量浓度也明显减少,但THC排放和燃油消耗率都增加;主喷正时对超细颗粒数量的影响相对较小.综合考虑排放和燃油经济性,在25%负荷时采用较大EGR率(26%)和较早主喷(提前7.7°曲轴转角)方案,而在50%负荷时采用中等EGR率(18%)和较早主喷(提前6.3°曲轴转角)方案.

Effects of EGR on Emission Characteristics of Low Duty Engine Fueled with Biodiesel

Based on a common rail diesel engine with cooling EGR and fueled with biodiesel, an experiment about the coupled effects of EGR and main injection time on engine emissions characteristics was conducted. The results show that at full load, the NOxemission increases, but THC emission and ultra particulate concentration decrease when the engine is fueled with biodiesel. At a load of 25% and a speed of 2 200 r?min-1, when the EGR rate increases, NOx emission, ultra particulate concentration, THC emission and BSFC (brake specific fuel consumption) decrease. However, with the main injection time retarded, NOx emission and ultra particulate concentration also decrease, but THC emission and BSFC increase. At a load of 25%, with the EGR rate increasing and main injection time retarded, NOx emission, ultra particulate concentration decrease, but THC emission and BSFC increase. The effect of main injection time on ultra particulate concentration is not so significant. Considering both emission and BSFC, at a load of 25%, a 26% of EGR and a main injection time of 7.7° CA BTDC are chosen. At a load of 50%, a 18% of EGR and a main injection time of 6.3° CA BTDC are chosen.