后喷时刻和EGR率对柴油低温燃烧和排放的影响

Effect of post-injection timing and EGR ratio on diesel low temperature combustion and emission

为了研究不同EGR(废气再缩环)率下后喷时刻对柴油机性能的影响,在一台改造的单缸柴油机上,总循环喷油量固定为每循环50mg,后喷油量为每循环8mg,通过改变EGR率大小和后喷时刻的方法开展了试验研究。研究结果表明:加了后喷之后,缸内峰值压力降低,燃烧相位后移,EGR率较低时放热率峰值略有增高,而EGR率较高时放热率峰值逐渐降低;与无后喷相比,后喷时刻(上止点后)为15℃A和25℃A时,指示热效率降低;EGR率较低,后喷时刻(上止点后)为5℃A时NOx排放有所升高,高EGR率时,后喷时刻对NOx排放几乎没有影响;不同EGR率下,后喷时刻对Soot(碳烟)排放影响不同,主要取决于后喷时的缸内温度;虽然后喷时刻对CO和THC排放影响较小,但在高EGR率下,随后喷时刻推迟,CH4所占比例降低。

In order to study the effect of post-injection timing on diesel engine performance at dif- ferent EGR rates, experimental study was carried out on a modified single diesel engine by chan- ging EGR rate and post-injection timing. Total injection fuel mass was 50 mg/cyc and post-injec- tion fuel mass was 8 mg/cyc. The results show that with post-injection, in-cylinder peak pressure decreases and combustion phase retards. At low EGR rate, peak heat release rate has a slight in- crease. While at high EGR rate, peak heat release rate decreases gradually. Compared with non post-injection, indicated thermal efficiency decreases at post-injection timing of 15 °CA and 25 °CA. Under low exhaust recirculation （EGR） rate, NOx emission increases at post-injection timing of 5 °CA. And post-injection timing has almost no effect on NOx emission under high EGR rate. Under different EGR rates, the effects of post-injection timing on soot emission are different, mainly depending on in-cylinder temperature at the timing of post-injection. Although post-injec- tion timing has little effect on CO and THC emission, CH4 proportion decreases under high EGR rate at delayed post-injection timing. 1 tab, 6 figs, 13 refs.