多次喷射对重型柴油机影响的试验研究

EXPERIMENTAL STUDY OF MULTIPLE INJECTIONS ON A HD DIESEL ENGINE

本文在一台电控共轨柴油机上进行了多次喷射及多次喷射和EGR结合对重型柴油机影响的试验研究。EGR为基于VGT的高压冷却EGR系统。研究了不同喷射策略下喷射参数对柴油机性能和排放的影响。研究了EGR和多次喷射结合降低柴油机排放的效果;通过调整EGR率,将NO_x控制在2.0 g/(kW·h),研究喷射参数和EGR对柴油机的影响。研究结果表明,预喷射可以在小负荷时改善柴油机的NO_x、CO和比油耗,但在大负荷时没有明显的影响;两次预喷射可以促进油气混合;后喷射可以促进油气混合,提高碳烟的氧化速度,因而可以明显改善柴油机的烟度和CO;优化的喷射参数结合EGR可以显著降低NO_x和烟度。

The purpose of this paper is to investigate the effect of multiple injections and the combined effects of multi-injection and EGR on HD diesel engine emissions and performance. A common rail fuel injection system and high pressure EGR system based on variable geometry turbocharger （VGT） were used. Injection parameters were adjusted under different injection strategies to find out the influence of these parameters on combustion and emissions. Then while keeping NOx at 2.0 g/（kW.h） by adjusting EGR rate, the influence of injection parameters and EGR were tested to highlight their influence on smoke and BSFC. Results show that, pilot injection can reduce NOx, CO and BSFC at low load but has no obvious influence at high load; Double pilot injection can enhance air-fuel mixing; Post injection can accelerate the mixing and oxidation processes during late combustion period and can effectively reduce smoke and CO; Optimized injection parameters coupled with EGR can significantly reduce NOx and smoke while causing no serious penalty on BSFC. Key words diesel engine; multiple injections; EGR; emission