缸内活化热氛围对柴油机燃烧与排放特性的影响

Effects of In-Cylinder Active Thermo-Atmosphere Conditions on Diesel Engine Combustion and Emissions

采用气口喷射正庚烷形成稀薄均匀混合气，利用其低温和高温化学反应释放的热量和生成的活性基团在柴油喷入气缸前形成活化热氛围，研究了活化热氛围强度对直喷柴油燃烧和排放的影响。研究发现：随着正庚烷比例的增加，活化热氛围强度增大，柴油扩散燃烧着火时刻略有提前，最大放热率明显降低，高负荷下的NOx和烟度排放显著降低；活化热氛围强度超过某一临界点后，NOx抑制效果开始减弱并单调升高，而烟度排放开始升高到极大值后再次降低。综合各个负荷下的排放，热氛围强度不适宜过强，在试验条件下20％～30％最佳。

Port-fuel injection of n-heptane was used to prepare the lean fuel/air mixture, and active radicals and heat release were produced by means of the low temperature reaction （LTR） and high temperature reaction （HTR）. The premixed ratio of n-heptane was used to denote active thermo-atmosphere conditions （ATAC） intensity. The results show that with the increase of ATAC intensity, the peak value of diffusion combustion decreases, NOx emission and smoke opacity reduce substantially and attain to the lowest value at a certain point; once the ATAC intensity exceeds this critical value, NOx emission begins to increase monotonously, but the smoke opacity increases to a peak point and then begins to reduce. It is found that the optimal ATAC intensity is about 20 %-30 %.