低温预混合燃烧模式的燃烧与排放特性试验研究

Combustion and Emission Characteristics of PCI Mode in a Light-Duty Diesel Engine

在一台电控高压共轨涡轮增压柴油机上研究了低温预混合燃烧模式对柴油机燃烧及排放的影响。采用早喷或晚喷预混方式,结合高废气再循环(EGR)率实现低温预混合燃烧,并研究了喷油正时、EGR、喷油压力和负荷率变化对预混燃烧模式的放热规律、排放特性和经济性的影响。研究结果表明:长的燃空预混合期是实现缸内预混燃烧的一个关键因素,中低负荷时,无论是早喷或晚喷预混模式,均具有长预混合期,短的扩散燃烧过程,兼具预混燃烧和低温燃烧的特征,高负荷下扩散燃烧比例增大;晚喷预混燃烧模式下,碳烟和氮氧化物(NO_x)排放同时获得降低,但低温燃烧和稀薄的混合气易导致燃烧不完全,喷油推迟较晚时引起HC和CO排放显著增加,并导致燃油消耗率增大;增加喷油压力可以同时改善碳烟、CO和HC排放,但是NOx排放增加,单纯提高喷射压力并不能获得性能的全面提高。

PPC（partially premixed combustion） combustion in a turbocharged four-cylinder light duty diesel engine was realized by using the injection timing of single injection and high EGR rate. The effects of injection timing, EGR, injection pressure and load rate on combustion, emission and heat release pattern were investigated. The experimental results indicate that a long fuel-air premixed duration is a key factor to realize PPC combustion. At low and medium loads, no matter what early or late injection mode, there are a long premixed duration and a relatively short diffusion combustion process. Together with premixed combustion and low temperature combustion characteristics simultaneously. At high loads, however, the portion of diffusion combustion will increase, coupled to the reduction of Soot and NOx emissions in late injection mode, but the low temperature combustion and diluted mixture may lead to incomplete combustion. Coupled to the strong increace of HC and CO emissions and hence fuel consumption. Increasing injection pressure can reduce the emissions of soot, CO and HC, but lead to inereased NOx emissions. In consequence, simply increasing injection pressure can not fully improve engine performance.