二冲程CNG直喷发动机混合气形成过程数值解析  

Numerical analysis of formation process of mixture gas in two-stroke CNG direct injection engine

作　　者：彭明国 许伯彦[1] 孙朝栋 姜龙龙 PENG Mingguo;XU Boyan;SUN Chaodong;SUN Chaodong(School of Mechanical and Electrical Engineering, Shandong Jianzhu University, Jinan 250101, China;Liaocheng Vocational and Technical College, Liaocheng 252000, China)

机构地区：[1]山东建筑大学机电工程学院,山东济南250101 [2]聊城职业技术学院,山东聊城252000 [3]大连理工大学能源与动力学院,辽宁大连116024

出　　处：《山东建筑大学学报》2019年第1期48-53,61,共7页Journal of Shandong Jianzhu University

基　　金：国家自然科学基金项目(51376113);山东省重点研发计划项目(2016GGX103036)

摘　　要：二冲程发动机具有结构简单、体积小、升功率高、便于维修等特点而应用广泛,良好的混合气质量可显著提升发动机的动力性、经济性及排放特性。文章采用壁面引导式二冲程压缩天然气CNG直喷发动机作为增程式电动车动力源,利用Solidworks建立二冲程CNG直喷发动机三维实体模型,通过光学纹影实验验证了数学模型的正确性,并采用CFD软件FIRE数值解析了不同工况下不同CNG喷射时刻发动机缸内混合气的形成过程,确定最佳燃料喷射时刻,改善缸内CNG-空气混合气质量。结果表明:增程模式下的部分负荷工况(4 800 r/min、60%负荷),CNG喷射时刻为60°～70°CA BTDC时,在火花塞点火时刻(25°CA BTDC)可形成良好的分层混合气,燃烧室内整体空燃比能达到40∶1;冷启动—暖机工况(1 800 r/min、20%负荷)和大负荷工况(4 800 r/min、100%负荷)运转时,在活塞上行排气道关闭前喷射CNG,优化喷射时刻能形成理想的均质理论混合气,且不造成燃料短路。Two-stroke engine is widely used because of its simple structure, small size, high power-up and easy maintenance. Good mixture quality can significantly improve the engine s power, economy and emissions characteristics. In this paper, the wall-guided two-stroke compressed natural gas (CNG) direct injection engine is proposed as the power source of the extended-range electric vehicle. The three-dimensional solid model of the two-stroke CNG direct injection engine is established by Solidworks, and the correctness of the mathematical model is verified by optical smear experiments. The CFD software FIRE numerical value is used to analyze the formation process of the engine cylinder mixture under different working conditions and different CNG injection timings, determine the optimal fuel injection timing, and improve the CNG-air mixture quality in the cylinder. The results show that the partial load conditions in the extended mode (4 800 r/min, 60% load) and the CNG injection time are 60 °~70 °CA BTDC, the stratified mixture is formed at the spark ignition timing (25 °CA BTDC).The overall air-fuel ratio in the combustion chamber can reach 40 ∶ 1. During cold start-warm condition (1 800 r/min, 20% load) and heavy load condition (4 800 r/min, 100% load), the CNG is injected before the upward exhaust passage of the piston closes. By optimazing injection timing, an ideal homogeneous theoretical mixture can be formed without causing a short circuit of the fuel.

关 键 词：二冲程直喷发动机 CNG混合气 壁面引导 数值解析 

分 类 号：TK43[动力工程及工程热物理—动力机械及工程]