柴油预喷参数对进气预喷甲醇柴油机燃烧和排放的影响

Effect of diesel pilot injection parameters on combustion and emission of diesel engine with methanol pre-injected in intake air

在一台满足国Ⅵ排放的柴油机基础上,采用进气预喷甲醇的方式替代原机的尿素辅助的选择性还原技术(SCR),探究不同柴油预喷油量和预喷时刻对发动机燃烧、性能和排放的影响.结果表明:在最大扭矩转速1690 r·min^(-1)和280 N·m(1.25 MPa BMEP)工况下,当甲醇在整个燃料的能量占比(占总燃料能量的63%~65%)和柴油预喷时刻不变时,柴油预喷油量从1.5 mg·cyc^(-1)(占循环喷油量8%)增加到7.5 mg·cyc^(-1)(占循环喷油量48%)可以有效改善甲醇混合气的活性,此时达到50%燃料燃烧放热量(CA50)会提前,燃烧速率增大,气缸内燃烧爆压(P_(max))和最高压力升高率(R_(max))提高,同时有效热效率(Brake Thermal Efficiency, BTE)增加6%,PM、CO和THC比排放分别降低50%、61%和29%.但预喷油量超过6 mg·cyc^(-1)时,NO_x排放显著增加.相比之下,柴油预喷时刻的变化对发动机燃烧的影响较小.适当提前预喷可以在降低P_(max)和R_(max)的同时减少NO_(x)、CO和PM比排放.因此,采用优化的柴油预喷参数可以获得更高的有效热效率和极低的排放.

The effect of different diesel pilot injection quantity and pilot injection timing on combustion,performance and emission of the engine is investigated by adopting methanol pre-injected in intake air of a diesel engine meeting China VI emission without selective catalytic reduction(SCR).The result shows that the activity of methanol mixture can be effectively improved by increasing the amount of diesel pilot injection quantity from 1.5 mg·cyc^(-1)(8%of fuel injection per cycle)to 7.5 mg·cyc^(-1)(48%of fuel injection per cycle)at 280 N·m(1.25 MPa BMEP)of 1690 r·min^(-1) when the energy proportion of methanol in the whole fuel(63%~65%of the total fuel energy)and the pilot injection timing of diesel remain unchanged.At this time,the increase of combustion rate and the advance of CA50 lead to the increase of the combustion explosion pressure(P_(max))and maximum pressure rise rate(R_(max))in the cylinder.At the same time,the brake thermal efficiency(BTE)increases by 6%,and the specific emissions of PM,CO and THC decrease by 50%,61%and 29%respectively.However,when the amount of diesel pilot injection exceeds 6 mg·cyc^(-1),the NOx emissions increase significantly.In contrast,the change of diesel pilot injection timing has little effect on engine combustion.When the pilot injection timing is in the range of 35~59℃A BTDC,advancing pilot injection properly can reduce the specific emissions of NO_(x),CO and PM while P_(max) and R_(max) are decreasing.Therefore,higher BTE and very low emissions can be obtained by using optimized diesel pilot injection parameters.