缸内直喷天然气射流混合过程的数值模拟  

Simulation on Mixing Process of Natural Gas Jet in Direct-Injection Engines

作　　者：范新雨 苏万华[1] Fan Xinyu;Su Wanhua(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,天津300072

出　　处：《内燃机学报》2018年第5期385-392,共8页Transactions of Csice

基　　金：国家自然科学基金资助项目(51236005)

摘　　要：采用数值模拟的方法,研究了天然气缸内直喷自由射流、撞壁射流以及涡旋结构在直口、缩口和敞口3种燃烧室形状中的形成过程,并在此基础上设计了适用天然气缸内直喷混合气形成的新型燃烧室.结果表明:采用较小的喷射夹角可以改善射流撞壁过程,提高混合气形成质量;喷射夹角为80°时,缩口燃烧室中,附壁射流脱壁后涡旋结构中燃料不易扩散,天然气混合速度较低,直口燃烧室和敞口燃烧室天然气混合速度接近.3种燃烧室形状中天然气射流混合过程会经历3个重要转折点:自由射流撞壁、附壁射流脱壁以及涡旋结构生长和扭曲阶段,其中在涡旋结构生长和扭曲阶段气体燃料与空气快速混合.最后,根据天然气射流在缸内混合过程设计出脱壁型燃烧室(SACC),大大增加形成可燃混合气的燃料比例,并能提高混合气的均匀度.Formation processes of free-jet,impinging-jet and vortex in direct-injection natural-gas engine with three different chambers were researched by numerical simulation.Then,a new chamber was designed suitable for the direct-injection natural-gas engine.This study suggests that,when spray angle is reduced from 100°to 80°,the quality of mixture is improved by the gas jet impinging process.For the spray angle of 80°,a slower mixing rate of natural gas presents in the contracted-carve chamber because it is hard for natural gas to diffuse in the vortex flow structure which is formed after the separation of wall-jet from wall in this chamber.The mixing rates of natural gas are close in both open-carve and vertical-carve chambers.Among those three chambers,the mixing process of natural-gas jet undergoes three indispensable processes including free-jet impinging,wall-jet separation from chamber wall,and vortex structure growing and distorting stage.The mixing rate of natural gas and air is rapid at the last stage.Finally,the separation advanced combustion chamber(SACC)was designed based on the mixing process of natural-gas jet in chambers.It is found that the SACC increases the mass friction of fuel in flammable mixture and the homogeneity of mixture obviously.

关 键 词：天然气 缸内直喷 燃烧室形状 气体射流混合 混合气形成 

分 类 号：TK432[动力工程及工程热物理—动力机械及工程]