三缸车用小型汽油机富氧燃烧特性的研究

Study on oxygen-enriched combustion characteristics of a 3-cylinder small gasoline vehicle engine

为研究富氧燃烧对发动机燃烧特性和排放特性的影响,基于一台三缸PFI小型车用汽油机,以三维CFD与一维流动计算、基元反应计算相耦合的计算方法对不同进气氧含量下的缸内燃烧进行仿真。研究结果表明,进气富氧能够强化缸内燃烧,当进气氧含量由23.3%增加到31.3%时,发动机的缸压峰值由5.24MPa升高到8.45MPa,缸压峰值相位由13.3℃A ATDC提前到5.8℃A ATDC,放热率重心也由12.6℃A ATDC提前到6.1℃A ATDC;且此时发动机的指示功率由6.0kW提高到7.2kW,升高约20%,富氧燃烧能够有效提高发动机的功率输出;另外富氧燃烧使缸内的平均燃烧温度升高,导致发动机传热损失和燃烧废气带走的能量增加,使发动机指示热效率降低,油耗增加。研究结果还表明随着进气氧含量的增加发动机最佳点火提前角推后,进气氧含量每增加1%,最佳点火提前角推迟1.5℃A。

On a 3-cylinder small gasoline engine with port fuel inject（PFI）,the effect of oxygen-enriched percentage on the engine combustion and emissions has been investigated,by coupling 3-D CFD simulation,1-D flow simulation,and elementary reactions simulation.The results show that oxygen-enriched intake air can enhance the combustion,when increasing the oxygen concentration from 23.3% to 31.3%（by mass）,the peak cylinder pressure increases from 5.24 MPa to 8.45 MPa,and its phase position advances from 13.3℃A ATDC to 5.8℃A ATDC,and the centroid of heat release rate curve advances from 12.6℃A ATDC to 6.1℃A ATDC.Meanwhile the indicated power increases from 6.0kW to 7.2kW,that is to say the engine power improved by about 20%.Oxygen-enriched combustion can effectively improve the engine power output.In addition oxygen-enriched combustion makes the level of mean combustion temperature rise,so that the heat transfer loss and the power taking away by the exhaust gas increase,resulting in slight fall of thermal efficiency,and slight increase of the indicated fuel consumption.It is also found that with the oxygen concentration increases,the engine optimal spark timing varies.In detail,the MBT ignition time delays 1.5℃A when the oxygen concentration increases by 1%.