复合稀释燃烧汽油机分层火焰特征  

Stratified Flame Characteristics in Hybrid Dilution Combustion Gasoline Engine

作　　者：姚远 陈韬[1] 谢辉[1] 赵华[1] Yao Yuan;Chen Tao;Xie Hui;Zhao Hua(State Key Laboratory of Engines,Tianjin University,Tianjin 300072,China)

机构地区：[1]天津大学内燃机燃烧学国家重点实验室

出　　处：《燃烧科学与技术》2019年第6期501-508,共8页Journal of Combustion Science and Technology

基　　金：国家重点研发计划资助项目(2017YFB0103402)

摘　　要：SI-CAI复合燃烧是一种双阶段放热的稀释燃烧方式,可以提升点燃式发动机的热效率.但是其前期的稀释火焰易产生明显的放热量波动,进而导致后期自燃过程失稳.分层火焰引燃策略(stratified flame ignition,SFI)尝试利用浓混合气火焰传播速度快的特点,抑制复合燃烧前期火焰传播的不稳定性.但是,复合燃烧通常会采用高压缩比提高温度并同时采用高稀释策略控制放热速度,其前期火焰特征与传统稀释火焰存在区别,为此,本研究通过光学实验分析复合燃烧高温和高稀释背景条件下的火焰特征.结果显示:在废气稀释条件下,浓混合气相对于稀混合气,火焰传播速度下降较少,分层火焰引燃策略具有可实现性,但废气分布的不均匀会导致火焰传播速度的各向异性.缸内温度的升高有助于加速稀释火焰,在高温、高稀释和浓混合气综合作用下,稀释火焰锋面前会出现少量自燃点,并逐渐与主火焰融合,从而提升火焰在局部方向上的传播速度,改善放热稳定性.Spark ignition-controlled auto-ignition(SI-CAI)hybrid combustion is a two-stage heat release dilution combustion mode,which can improve the thermal efficiency of SI engines.However,the diluted flame in the early stage is prone to produce obvious heat release fluctuations,leading to the instability of the later spontaneous combustion process.The stratified flame ignition(SFI)strategy attempts to suppress the instability of flame propagation in the early stage of hybrid combustion by utilizing the high flame propagation velocity of fuel enrichment.However,a high compression ratio is usually used in hybrid combustion to increase temperature,and the high dilution strategy is used to control the heat release rate at the same time.As a result,the flame characteristics in the early stage are different from those of the traditional dilution flame.In this paper,the flame characteristics of hybrid combustion under conditions of high-temperature and high-dilution were analyzed by optical experiments.Results show that under the condition of dilution by exhaust gas,the flame propagation velocity of fuel enrichment decreased less than that of the dilute mixture,and the SFI strategy was feasible.However,the inhomogeneous distribution of exhaust gas led to the anisotropy of flame propagation velocity.The increase in temperature in the cylinder helped to accelerate the dilution of flame.Under the combined effect of high temperature,high dilution and fuel enrichment,a small number of spontaneous combustion points would appear in front of the diluted flame front,and then gradually merged with the main flame,thus increasing the flame propagation velocity in one local direction and improving the heat release stability.

关 键 词：SI-CAI复合燃烧 分层火焰引燃策略 高稀释燃烧 火焰特征 

分 类 号：TK411.2[动力工程及工程热物理—动力机械及工程]