天然气发动机不同转速下混合过程的定量评价与仿真分析

Quantitative Evaluation and Simulation Analysis ofNatural Gas Engine Mixing Process at Different Speeds

天然气缸内直喷相对于缸外供气方式,其掺混路径、掺混时间更短,导致缸内掺混效果难以保障;此外,掺混过程还易受发动机转速的影响。鉴于此,本文建立天然气发动机缸内直喷及掺混过程的计算流体力学模型,提出一种燃气发动机缸内掺混效果的定量评价机制,探究不同发动机转速对缸内掺混过程的影响规律。研究结果表明:缸内掺混过程在相空间中有三个阶段,在喷射阶段,燃料在气缸容积内迅速扩散,过渡阶段燃料混合气处于高度瞬变状态,而扩散阶段表现为混合气的均匀化。

Compared with the gas supply mode outside the cylinder,direct injection in the cylinder has a shorter mixing path and mixing time,which makes it difficult to guarantee the mixing effect in the cylinder.In addition,the mixing process is easily affected by the engine speed.In view of this,this paper establishes a computational fluid dynamics model for the in-cylinder direct injection and mixing process of natural gas engines,proposes a quantitative evaluation mechanism for the in-cylinder mixing effect of gas engines,and explores the influence of different engine speeds on the in-cylinder mixing process.The results show that the in-cylinder mixing process has three phases in the phase space.In the injection stage,the fuel rapidly diffuses in the cylinder volume,in the transition stage,the fuel mixture is in a highly transient state,and in the diffusion stage,the mixture is homogenized.