内外EGR和喷油压力对柴油机低温燃烧的影响

在1台装有电液可变气门的单缸柴油机上,通过改变内外EGR策略和喷油压力,对柴油机小负荷工况下低温燃烧的燃烧特性和排放特性进行了试验研究。内部EGR通过排气门两次开启实现,发动机转速和喷油量分别固定为1 500r/min和20mg/cycle。研究结果表明,通过高EGR率控制可以实现超低NOx排放,其中采用高喷油压力可以降低内部EGR的炭烟排放,而采用低喷油压力可以降低外部中冷EGR的HC和CO排放。在内外EGR耦合控制策略中,提高内部EGR比例可以降低HC和CO排放,但改善效果逐渐减弱,同时为了抑制炭烟排放,需要结合更高喷油压力,而提高外部中冷EGR比例可以获得较高热效率。

Effects of Internal and External EGR and Injection Pressure on Low Temperature Combustion of Diesel Engine

The combustion and emission characteristics of low temperature combustion at low load were investigated by chan -ging strategies of internal and external EGR and injection pressure on a single cylinder diesel engine equipped with a electro -hy-draulic variable valve actuator system .The internal EGR was achieved by opening exhaust valve twice during the intake process . The test was conducted at engine speed of 1500 r/min with 20 mg/cyc fuel injection .The results show that the ultra-low NOx emission can be obtained by controlling EGR rates .The soot emission of internal EGR reduces at a high injection pressure , while HC and CO emissions of external EGR reduce at a low injection pressure .For the coupling control strategy of internal and external EGR ,the increase of internal EGR ratio can reduce HC and CO emissions at a small range and a higher injection pres -sure is hence introduced to suppress soot emission .In addition ,the increase of the external EGR ratio can achieve higher ther-mal efficiency .