天然气/柴油双燃料发动机燃料喷射及着火特性

基于计算流体动力学(CFD)软件CONVERGE模拟了缸内高压直喷式柴油微引燃液化天然气(LNG)发动机的燃料喷射混合以及着火过程,校核和验证了湍流模型对模拟结果的影响,分析了天然气喷射正时、天然气喷射持续期及柴油与天然气射流中心轴线的夹角对缸内柴油和天然气射流发展、混合和着火的影响.结果表明:Smagorinsky大涡模拟湍流模型更适用于缸内高压直喷式LNG发动机的模拟;柴油与天然气射流中心轴线夹角越大,火核倾向于在天然气喷束的两侧形成从而点燃天然气;天然气喷射正时提前,天然气喷入缸内时与柴油的距离更近,利于天然气被引燃;天然气循环喷射量不变,天然气喷射持续期越短,天然气喷孔处压力更大,对柴油油束的冲击更强,促进了柴油的燃烧从而有利于天然气射流的着火.

Spray and Ignition Characteristics of a High-Pressure Direct-Injection Natural Gas Engine

Based on the computational fluid dynamics(CFD)software of CONVERGE,a simulation was carried out on a high-pressure direct-injection natural gas engine,which is ignited by a micro pilot injection of diesel fuel,in order to study injection characteristics and ignition processes.The influence of different turbulence models on the simulation result were analyzed and verified.The effects of injection timing and duration of natural gas and the angle between the natural gas jet and the diesel jet on the spray development and ignition characteristics were analyzed.Results show that the Smagorinsky large eddy simulation(LES)model is more suitable for the simulation of the high-pressure direct-injection natural gas engine.With the increase of the angle between the natural gas jet and the diesel jet,more ignition kernels tend to form at the surrounding areas of the gas jet and then ignite the natural gas.The natural gas is conducive to be ignited when the natural gas injection timing is advanced and the distance between the natural gas jet and the diesel jet is decreased.As the duration of natural gas injection decreases,the nozzle pressure of natural gas increases and the impact of the natural gas jet on the diesel spray increases,which is beneficial to the combustion of the diesel fuel and the ignition of the natural gas jet.