柴油机唇口射流燃烧室对燃烧及排放特性的影响

Effect of Lip Jet Combustion Chamber on the Combustion and Emission Characteristics of a Diesel Engine

为改善高压共轨直喷柴油机燃烧室内的油、气混合质量,提出了一种唇口射流结构燃烧室.通过计算流体动力学(CFD)仿真,探究了其油、气混合特性,分析了燃烧室结构和喷油参数对柴油机燃烧与排放的影响.结果表明:利用唇口射流原理可实现对燃烧室内部分燃油在射流唇口、射流唇背区域内分布的有效引导,形成燃烧室中心-射流唇口回流区-射流唇背回流区的内、中、外3层油、气混合,改善油、气混合质量;在转速为2000r/min、全负荷工况下,喷油夹角为80°时,凹曲面结构的回流区底面有利于喷雾扩散,在喷孔直径为0.12 mm的条件下,锥面结构的回流区底面能在回流区形成顺时针涡旋,有利于油束卷吸空气;与ω型燃烧室相比,在喷油夹角为80°、喷孔直径为0.12 mm时,采用圆柱状射流唇背和凹曲面状回流区底面结构的唇口射流燃烧室,可实现更均匀的油、气混合和更充分的燃烧,使NO_(x)与碳烟排放分别降低11.0%与32.4%.

To enhance the fuel-air mixture quality within the combustion chamber of a high-pressure common-rail direct injection diesel engine,a lip jet structured combustion chamber was proposed.The fuel-air mixing characteristics within the lip jet combustion chamber were examined utilizing computational fluid dynamics(CFD)simulation,and the impacts of the combustion chamber structure and fuel injection parameters on combustion and emission characteristics were analyzed.The results show that the lip jet can effectively guide the fuel to be better distribution at the lip-mouth and lip-back areas of the combustion chamber,thereby forming an internal,middle,and outer triple-layer fuel-air mixture in the combustion chamber center,lip-mouth re-circulation zone and lip-back re-circulation zone.As a result,the quality of fuel-air mixture is enhanced.At speed of 2000r/min and full load conditions,when the spray angleαis 80°,the concave surface structure of the bottom of the re-circulation zone is conducive to spray diffusion.Under the condition of the nozzle diameter of 0.12 mm,the cone surface structure of the bottom of the re-circulation zone can create a clockwise vortex in the re-circulation zone,promoting the fuel-air mixing.Compared with theωcombustion chamber,under the condition of theαof 80°and the nozzle diameter of 0.12 mm,the lip jet combustion chamber with a cylindrical jet lip-back and a concave surface re-circulation zone bottom structure can achieve more uniform fuel-air mixture and more thorough combustion,reducing NO_(x) and soot emissions by 11.0%and 32.4%,respectively.