高负荷下应用米勒循环提升高压比汽油机热效率机理研究

对高负荷工况下应用进气阀早关(EIVC)或者迟关(LIVC)技术实现的米勒循环进行仿真计算,基于热力学第一定律比较分析两者改善高压缩比增压直喷汽油机热效率的机理。结果表明:几何压缩比的增加提高了发动机的理论热效率,但由于高负荷时的爆震限制使油耗恶化了1.9%;米勒循环的应用可以有效降低爆震倾向,与原发动机相比,采用EIVC与LIVC策略燃油经济性的分别提升2.4%和3.0%;对比分析EIVC与LIVC对汽油机热效率的影响发现,LIVC策略能使燃烧相位更加优化、缸内燃烧更为充分,使得其燃油改善效果好于EIVC策略。

Analysis of Thermal Efficiency Improvement Implemented with Miller Cycle for High Compression Ratio Gasoline Engine at High Load

For a highly boosted ,high compression ratio and direct injection gasoline engine ,the Miller cycle realized by the early intake-valve closing (EIVC) or the late intake-valve closing (LIVC) strategy at high load was simulated and the improve-ment mechanisms of thermal efficiency for both strategies were compared based on the first law of thermodynamics .The results show that a higher geometric compression ratio can increase the theoretical thermal efficiency ,but lead to the fuel consumption increase by 1 .9% due to knock limit at high load .The application of Miller cycle can suppress knock tendency effectively and the fuel economy for EIVC and LIVC strategy improves by 2 .4% and 3 .0% respectively compared with the original engine . Compared with EIVC ,LIVC can bring about a better combustion phase and more thorough in-cylinder combustion .