进气增压对负阀重叠HCCI发动机燃烧特性的影响研究

The Influence of Intake Boosting on the Characteristics of Combustion in HCCI Engine Using Negative Valve Overlap

基于一台缸内直喷汽油机进行了进气增压对负阀重叠HCCI发动机燃烧与排放特性的试验与仿真研究。试验结果表明:相同供油量下,随着进气压力从0.10MPa增大到0.15MPa,着火时刻提前了6°CA,缸内最高燃烧压力增大了0.9MPa,放热率峰值下降了18%,燃烧持续期变长,指示热效率先增大后减小,平均指示压力循环变动率仍保持在4%。由于进气增压使内部残余废气率提高了7%,造成比热容上升而降低了缸内温度。仿真计算揭示了随着进气压力增加,导致负阀重叠期燃油发生改质变化,OH基和O基反应速率减缓,以及C2H2等活性分子浓度上升了80%和CH4等稳定分子浓度下降了37%,使得HCCI热着火温度略微下降,提高了HCCI着火稳定性。

The tests and simulations were carried out on a modified gasoline direct injection （GDI） engine to investigate the influence of intake boosting on the characteristics of combustion and emissions from homogeneous charge compression ignition （HCCI） engine with negative valve overlap. The test results show that, with the same fuel supplied, as the intake pressure increased from 0.10 MPa to 0.15 MPa, the start of combustion was advanced by 6 ℃A and the cylinder pressure increased by 0.90 MPa. Meanwhile, the peak heat release rate was decreased by 18% and the duration of combustion increased, but the indicated efficiency was increased firstly and then decreased, the variation coefficient of indicated mean effective pressure was always 4% with the increase of intake pressure. The in-cylinder residual exhaust gas rate was increased by 7% due to intake boosting, resulting in the rising of specific heat, so as to reduce combustion temperature. The simulation results show that because intake boosting led to the change in fuel reforming during negative valve overlap （NVO）, the reaction rates of OH and O radicals were slowed down, the concentration of C2H2 increased by 80% and CH4 decreased by 37%, so the ignition temperature of HCCI was decreased slightly, and then the combustion stability of HCCI would be improved.