柴油机燃烧室匹配参数对撞壁喷雾特性的影响

利用高速纹影摄像技术，研究了喷油器喷孔角度、喷孔与活塞顶面间的撞壁距离、燃烧室缩口半径和凸台夹角对柴油撞击燃烧室壁面后喷雾特性的影响。研究结果表明，试验条件下适宜的喷孔角度为75°，增大喷孔角度可以促进喷雾撞壁后的油气混合，但是喷孔角度过大会增加油束撞击气缸盖和气缸套的风险;适宜的撞壁距离为4.2mm，即压缩上止点前15°CA（CA指曲轴转角）,较小的撞壁距离会促进喷雾液滴在凹坑区域的碰撞与黏结，而较大的撞壁距离不利于燃烧室中心区域的空气利用;此外，适当增大缩口半径可以促进燃油与空气的混合，减小燃烧室壁面的燃油湿壁面积;改变凸台夹角可以控制撞壁后喷雾在燃烧室中心区域的扩散速度。

Effects of Diesel Engine Combustion Chamber Matching Parameters on Wall Impinging Spray Characteristics

The effects of different injector nozzle angles, impinging distances between nozzle and piston top surface, the combustion chamber reentrant radius and convexity angles on spray characteristics after diesel impinging on the combustion chamber walls were investigated through schlieren photography with high speed digital camera. The results show that, for the injectors and pistons in experiments, the proper nozzle angle is as 75°. The mixing of fuel and gas after wall impingements may be promoted by increasing nozzle angle, but too large nozzle angle will increase the risk of fuel impinging on cylinder heads and cylinder liners. The proper impinging distance is as 4.2mm (15°CA before top dead center of compression stroke). Smaller impinging distances may prompt spray droplet collision and bounding in the pit area, and larger impinging distances may hinder the reaction of air in the central region of combustion chambers. In addition, moderate increasing the reentrant radius may promote the mixing of fuel and air, and hence reduce wall wetting in the combustion chambers. Suitable changes of the convexity angles may control the spray diffusion velocities in the center zones of combustion chambers after diesel impingements.