汽油机部分负荷应用热废气再循环 实现临界爆震的性能优化
Performance Optimization of Partial Load of Gasoline Engine at Critical Knock Status Using Hot Exhaust Gas Recirculation

以某款1？？4 L缸内直喷汽油机为研究对象,结合其标定参数和实验结果,利用三维仿真软件Fire研究了热废气再循环对汽油机部分负荷的影响规律。结果表明:当进气压力为68 kPa和24 kPa时,在低于爆震限值的热废气再循环率(ηhot)范围内,随着ηhot的增大,混合气的爆震指数均呈现逐渐增大的趋势,且显著低于相同进气温度下的无废气再循环工况;热废气能够起到强化燃烧和降低进气泵气损失的双重效果,相比常温进气工况,在进气压力为68 kPa、ηhot=10％工况下的指示功增幅为4？？6％,在进气压力为24 kPa、ηhot=17.5％工况下的指示功增幅可达65？？8％;进气压力为24 kPa、ηhot=12？？5％工况与常温进气工况的火焰传播速度几乎相当,缸压峰值可提高约1/4,而且还能降低52％的CO排放量和78.3％的NO排放量;通过耦合进气加热或者废气中冷,可以进一步拓展热废气再循环的应用潜力,并且负荷越小耦合进气加热以后的改善效果越显著。
Effects of hot exhaust gas recirculation (EGR) on partial load performance of a gasoline engine are studied using the software CFD Fire based on a 1？？4 L gasoline direct injection (GDI) engine and its calibrated and experimental data. Results show that increasing hot EGR rate increases the knock index when the intake pressure are 68 kPa and 24 kPa within knock limit, but the knock index is significantly below that in same intake temperature conditions without EGR. Both enhancement of combustion and reduction of pumping loss can be acquired by introducing hot EGR. The indicated work increases by 4.6％ when the intake pressure is 68 kPa and ηhot=10％, and it increases by 65？？8％ when the intake pressure is 24 kPa and ηhot=17.5％, compared with that in normal intake temperature condition. The flame propagation velocity is almost the same as the one under the normal intake condition when ηhot is 12？？5％ and the intake pressure is 24 kPa, and the peak cylinder pressure increases by about 1/4. Moreover, emissions of CO and NO are reduced by 52％ and 78.3％, respectively. Great potential for further application of hot EGR exists by coupling heating intake air or cooling EGR, and more significant improvements can be obtained by coupling heating intake air with lower loads