天然气发动机燃烧室对性能的影响及优化

摘要

采用AVL Fire软件开展了天然气发动机燃烧室的优化设计,通过对燃烧室型线的敏感性分析,获得了两个燃烧室优化设计方案.对放热率、湍动能及速度场分析后发现:缩小碗口直径有利于增强燃烧室内气体的滚流与涡流运动,从而提升湍动能与气体运动速度,加快燃烧放热过程;然而燃烧室优化方案Ⅰ中小凸台的存在增加了进气能量的耗散,点火时刻湍动能较低,使其火焰发展期并没有缩短,不过快速燃烧期在挤流运动的作用下得以加快.开展的发动机台架试验结果表明:燃烧室优化方案Ⅱ实现了有效燃气消耗率下降2.9％以及分管排温平均降低18.3℃的改善效果.通过优化标定,燃烧室优化方案Ⅱ在达到相同氮氧排放的情况下,有效燃气消耗率较原燃烧室方案改善了1.5％.%AVL Fire numerical simulation software was used to make the optimal design of combustion chamber on a natural gas engine.Based on the analysis of combustion chamber configuration,two optimized combustion chambers were obtained.Based on the analysis of heat release rate,turbulent kinetic energy and velocity fields,it is found that reducing the combustion bowl diameter is conducive to enhance the tumble and swirl flow motion,thus accelerates the combustion process due to the increase of the turbulent kinetic energy and gas velocity.However,the small convex platform in the optimized scheme Ⅰ increases the energy dissipation of intake gas,leading to a lower turbulent kinetic energy at ignition timing,and there was no improvement in the flame development duration,while the rapid combustion duration has been speeded up under the effect of squish flow.Bench test work shows that the optimized chamber Ⅱdecreases by 2.9％ in brake specific gas consumption and an average of 18.3 ℃ reduction of exhaust temperature.Furthermore,the optimizing calibration results show that brake specific gas consumption of the optimized scheme Ⅱ has improved by 1.5％ than the original combustion chamber in the case of same nitrogen oxides emissions.