汽油/柴油双燃料不同HPCC燃烧模式的数值模拟

摘要

Based on gasoline/diesel dual-fuel highly premixed compression combustion(HPCC)mode,thispaper carries out numerical simulation of the effect of early-injection and late-injection on combustion and emission charac-teristics,keeping injection mass and combustion phasing almost the same.The study shows that the ignition and com-bustion process of HPCC are mainly controlled by reactive radicals,i.e.,late-injection increases the local n-heptane concentration and reactivity,resulting in early heat release;early-injection restrains low temperature heat release, increasing the amount of reactive radicals,resulting in high heat release rate and maximal pressure rise rate.In L-HPCC mode,higher local concentration of n-heptane increases local temperature,and promotes NOx generation re-sulting in higher NOx emission then E-HPCC mode;however,higher local temperature promotes both soot generation and consumption,resulting in lower soot emission than E-HPCC mode.%针对汽油/柴油双燃料高比例预混燃烧(HPCC)模式，在总喷油量、主放热时刻(CA50)基本相当的条件下，对柴油早喷(E-HPCC)与柴油晚喷(L-HPCC)情况下的燃烧特性和排放特性进行了数值模拟研究。结果表明，HPCC着火和燃烧过程主要受缸内活性自由基控制，较晚喷射会导致缸内局部正庚烷浓度高、活性较大，造成高温放热提前；较早喷射正庚烷会抑制低温放热，从而增加着火时刻缸内活性自由基的数量，是放热率较高、最大压升率较大的主要原因。 L-HPCC模式下，高温放热时刻缸内局部正庚烷浓度较大造成了缸内局部温度较高，促进了NOx生成，相对E-HPCC模式NOx排放较高；虽然L-HPCC局部浓度较高会促进碳烟的生成，但同时较高的燃烧温度加强了碳烟的氧化，因此L-HPCC模式的碳烟排放低于E-HPCC模式。