摘要
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)、平均指示压力(IMEP)、废气再循环(EGR)率等基本相当的条件下,对单次喷射与两次喷射策略的燃烧机理进行了数值模拟研究.结果表明,汽油/柴油双燃料HPCC燃烧过程实质是缸内直喷柴油提高混合气活性与浓度分层共同作用的结果;单次喷油策略在高温放热前生成了较多的活性自由基,分布于燃烧室内较大的区域,这是导致其放热率增大的主要原因;而两次喷油中,靠近喷油器位置,较高的正庚烷浓度是触发其高温放热提前的主要原因.在两次喷油策略中,活性降低导致其燃烧放热速率较单次喷油策略低,第1次喷油过早使预混时间延长,减少了缸内混合气活性自由基的生成,抑制了低温反应,并导致明显的两阶段放热特性;相对较晚的第1次喷油策略中,第1次喷入缸内燃料的低温放热会促进第2次喷入燃料的氧化与分解,提高了缸内活性,使高温反应时刻提前,放热率增大.
This paper conducts a numerical study on the combustion mechanism of single-injection and doubleinjection of gasoline/diesel dual fuel HPCC（high premixed charge combustion）engine,under the same working condition including mass of injection,CA50,IMEP and EGR. The results indicate that the essence of gasoline/diesel dual fuel HPCC combustion is the result of interaction between increased fuel reactivity by direct injection of diesel and concentration stratification. Single-injection strategy can reduce PRR（pressure rise rate）by producing more reactive molecules before high temperature reaction. Under double-injection condition,high concentration of n-heptane near nozzle is the key reason for advancing high temperature reaction. In double-injection strategy,reduced incylinder reactivity is the key reason for reducing heat release rate（HRR）. Earlier first injection timing can prolong the mixing time of fuel,reducing the production of reactivity molecule,thus restraing low temperature reaction and causing two-stage heat release characteristics. In later first injection timing strategy,heat release of low temperature by first injected fuel can promote the oxidation and decomposition of second injected fuel,enhancing in-cylinder reactivity,advamcing high temperature reaction,and increasing pressure rise rate.
出处
《燃烧科学与技术》
EI
CAS
CSCD
北大核心
2015年第2期165-172,共8页
Journal of Combustion Science and Technology
基金
国家杰出青年科学基金资助项目(51125026)
关键词
高比例预混合低温燃烧
喷油策略
数值模拟
high premixed charge combustion（HPCC） injection strategy numerical simulation
