对置活塞二冲程汽油机燃烧过程组织研究

Organization of Combustion Process on Opposed-piston Two-stroke Gasoline Engine

燃烧室形状不仅反映混合气的分布,而且与火花塞位置的匹配决定了火焰前锋面位置和火焰传播距离。分别针对平顶活塞配合单、双火花塞点火和凹坑活塞配合单火花塞点火3种方案,通过三维CFD软件AVL-Fire模拟了对置活塞二冲程汽油机燃烧室形状和点火方式对燃烧过程的影响。结果显示,缸内燃烧速度主要由湍流燃烧速度决定,湍流燃烧速度相对层流燃烧速度提高10倍以上。采用平顶活塞配合单火花塞点火时,火焰发展期的湍流燃烧速度明显较低;同时火焰传播距离较长,不利于快速组织燃烧。采用凹坑活塞方案在减小燃烧室面容比的同时,可增强缸内湍动能促进火焰传播。凹坑活塞的燃烧过程较快,相比平顶活塞缸内压力峰值增加16.1%且提前6°CA,爆震反应率降低44.3%。

Combustion chamber shape not only reflects the mixture distribution but also determines the flame propagation distance by matching with the spark plug position. This paper aims to analyze the flat piston matching single spark plug and dual spark plug scheme and pit piston matching single spark plug scheme. Using the 3D CFD simulation tool AVL-Fire, the effects of combustion chamber shape and ignition mode on combustion process for opposed-piston two-stroke gasoline direct injection engine were simulated.Results showed that in-cylinder combustion rate was mainly decided by the turbulent combustion rate,which increased by more than 10 times than laminar combustion rate. Turbulent combustion rate significantly lower in flame developing period for the flat piston matching single spark plug scheme, which was not conducive to rapid combustion organization because of the longer flame propagation distance. Pit piston matching single spark plug scheme not only reduced the surface-volume ratio of combustion chamber, but also increased the in-cylinder turbulent kinetic energy to promote the flame propagation. For pit piston matching single spark plug scheme, in-cylinder pressure peak value increased by 16.1% and in advance 6°CA, knock reaction rate was reduced by 44.3%.