喷油压力对柴油喷雾两阶段着火的影响

Effect of Injection Pressure on Two-Stage Ignition of Diesel Spray

基于流动式定容燃烧试验装置以及CONVERGE三维仿真模型,研究了冷起动工况对应缸内上止点环境下喷射压力对柴油自由射流的喷雾宏观特性及两阶段着火转化过程的影响.结果表明:在冷起动工况条件下,低喷射压力(20 MPa)条件下的液相贯穿距略大;随着喷射压力的增加,气相喷雾贯穿距增大,气/液相喷雾锥角增大,表明在喷雾体头部区域形成较大的混合气区域;不同喷射压力条件下,喷雾内的局部温度及局部当量比分布规律相似;但随着喷射压力的增大,高温低当量比区域面积增大,促进了低温反应的进行.另一方面,较高的喷射压力使得喷雾流速增大,抑制了喷雾低温核心区域CH_(2)O和热量的累积,进而恶化了低温反应阶段向高温反应阶段的过渡,使高温着火准备过程延长.最终导致高温着火滞燃期随喷射压力升高呈现先减小后增大的变化趋势.

Based on the flow-typed constant volume combustion test equipment and the CONVERGE simulation platform,the effect of injection pressure on macroscopic characteristics and two-stage ignition conversion process of a diesel free jet under cold start conditions were studied.The results show that the liquid penetration distance is slightly larger under lower injection pressure of 20 MPa.The gas phase spray penetration distance and the gas/liquid phase spray cone angle increase with the increase of injection pressure,leading to a larger mixture area in the spray head region.The local distributions of temperature and equivalence ratio in the spray are similar under different injection pressures.The areas of higher temperature and lower equivalence ratio increase with the increase of the injection pressure,which promotes the low-temperature reaction.On the other hand,the higher injection pressure increases the spray flow rate,which inhibits the accumulation of CH_(2)O and heat in the low-temperature region of the spray,further deteriorating the transition from the low-temperature stage to the high-temperature stage.The high-temperature ignition preparation process is also prolonged.And finally,the high-temperature ignition delay time shows a trend of first decreasing and then increasing with the increase of injection pressure.