转速对柴油机中负荷预混压燃燃烧和排放的影响

Effect of Speed on PCCI Combustion and Emissions in a Diesel Engine at Medium Load

试验和数值模拟研究了进气压力、转速、多脉冲喷油定时对重型柴油机中负荷预混压燃(PCCI)燃烧和排放的影响.结果表明:进气增压有助于提高指示热效率(ITE),减小燃烧损失.转速提高使得高温着火时刻推迟,过浓混合气质量分数降低;NO_(x)、碳烟、CO和未燃碳氢(UHC)排放均降低;ITE升高,燃烧损失降低,排气损失升高.多脉冲喷油定时推迟使得混合时间缩短,过浓混合气质量分数提高,初始碳烟生成量增加,但在混合空间和燃烧温度的共同作用下,碳烟、CO和UHC排放均降低,NO_(x)排放变化不大;ITE升高,燃烧损失降低,排气损失升高.

Effects of intake pressure,engine speed and multi-pulse injection timing on premixed charge compression ignition(PCCI) combustion and emissions were studied on a heavy-duty diesel engine at medium load. Results show that,intake boost helps to increase the indicated thermal efficiency(ITE) and decrease the combustion loss.With increasing the engine speed,the high temperature ignition timing is retarded,the ITE and the exhaust loss are increased,but the mass fraction of over-rich mixture,the combustion loss and all emissions including NO_(x),soot,CO and unburned hydrocarbon(UHC) are decreased. With the delay of multi-pulse injection timing,the mixing timing is shortened,the mass fraction of over-rich mixture and the initial soot generation are increased.However,due to the combined effects of mixture space and combustion temperature,the ITE and the exhaust loss are increased,the combustion loss and the soot,CO and UHC emissions are decreased,while the NO_(x)emissions are little changed.