喷油控制参数对中置喷油器GDI发动机喷雾及燃烧的影响

Effects of Injection Control Parameters on Spray and Combustion of GDI Engine with Centrally-Mounted Injector

针对匹配中置高压喷油器的直喷汽油光学发动机,试验研究了不同喷油时刻及喷油压力下的缸内燃烧及喷雾发展特性,分析了燃油喷射控制参数对直喷汽油机缸内喷雾及燃烧的影响规律。研究结果表明:随第三段喷油时刻(θ_(SOI3))提前,燃烧持续期与滞燃期均先减小后增大,燃烧特征参数均在θ_(SOI3)=120°BTDC时存在明显拐点,此时平均指示压力(p_(mi))的循环变动系数C_(OVpmi)相对较小;第三段喷油时刻过晚,活塞上行距上止点较近,易导致油束冲击活塞表面;提高喷油压力可缩短燃烧持续期,有助于改善燃烧定容度,但喷油压力过大,油束贯穿距进一步延长,油束冲击缸壁的倾向增加,滞燃期及燃烧持续期反而延长。

The effects of injection control parameters such as injection timing and injection pressure on combustion and spray characteristics of GDI optical engine with a centrally-mounted injector were investigated.The results indicate that the combustion duration and ignition delay first decrease and then increase with the advance of third stage injection timingθSOI3.The combustion parameters both show an obvious inflection and the cycle variation coefficient of indicated mean effective pressure becomes small at 120°BTDC.The short distance between piston and top dead center in compression process led by the too late injection of third stage fuel will easily cause fuel beam to impact the piston surface.Increasing the injection pressure may shorten the combustion duration and improve the degree of constant volume combustion.However,the too large injection pressure will prolong the fuel penetration,the tendency of fuel beam to impact cylinder wall becomes more obvious,and hence the ignition delay and combustion duration extend.