EGR对柴油-天然气双燃料发动机稀燃的影响

在一台由柴油机加装天然气供给系统改装而成的双燃料发动机上进行试验,分别研究了EGR率和过量空气系数(a)随喷油提前角变化对双燃料发动机的影响。结果表明:当EGR率为0时,a过大导致热效率降低。增大喷油提前角使着火提前,燃烧得以改善,最大压力升高率和最高燃烧压力提高,热值折合燃料消耗率降低。喷油提前角一定时,最大压力升高率、最高燃烧压力随EGR率的增大先升高后降低,热值折合燃料消耗率先降低后升高,EGR率为20%时热值折合燃料消耗率达到最低值。采用EGR技术能有效降低NOx排放,但HC,CO,CH4和炭烟排放随着EGR率的增大而增大;增大喷油提前角使缸内柴油预混燃烧比例增加,HC,CO,CH4和炭烟排放降低。因此,采用EGR时应适当增加喷油提前角。

Effects of EGR on Lean Burn of Diesel-natural Gas Dual Fuel Engine

The changes of EGR rate and excess air coefficient with injection advance angle were researched on a retrofitted dual fuel engine by mounting the natural gas system to diesel engine.The results show that the large excess air coefficient will lead to the low heat efficiency when the EGR rate is zero.The increasing of injection advance angle can advance the ignition, improve the combustion, raise the maximum pressure rise rate and the maximum combustion pressure and drop the fuel consumption equivalent to calorific value.For a constant injection advance angle, the maximum pressure rise rate and the maximum combustion pressure first increase and then decrease and the fuel consumption equivalent to calorie value changes conversely with the increase of EGR rate.The equivalent fuel consumption reaches the minimum value when the EGR rate is 20%.EGR can reduce NOx emission effectively, but will increase HC, CO, CH4 and soot emission.Increasing the injection advance angle can increase the proportion of in-cylinder premixed combustion and thereby reduce those four emissions.Accordingly, increasing the injection advance angle should be considered when using EGR.