基于NVO策略的CAI工质分层特性的模拟研究

应用通用流体计算软件STAR-CD建立了可控自燃(CAI)发动机模型,重点分析了负气门重叠(NVO)策略10°CA BTDC时工质的分层特性。研究了不同配气定时以及不同气门升程工质分层程度的变化规律以及影响因素,对自燃着火区域进行了统计分析。计算结果表明:随着进气门开启(IVO)时刻的逐渐推迟,工质分层程度增强,自燃着火区域体积变大;随着气门升程的逐渐变大,工质分层程度增强,自燃着火区域体积变大;工质分层程度主要受进气门关闭(IVC)时刻总湍流动能值的影响。总湍流动能值越大,混合越剧烈,压缩末期工质均匀性增强,分层程度减弱;压缩末期自燃着火区域体积的变化趋势与工质分层程度的变化趋势相同。

Simulation of CAI Charge Stratification Characteristics Based on NVO Strategy

The controlled auto-ignition(CAI)engine model was established with the STAR-CD software.Based on the negative valve overlap(NVO),the stratification characteristics of charge were analyzed emphatically at 10 °CA BTDC.For different valve timings and valve lifts,the rule and influencing factors of charge stratification were researched and the auto-ignition areas of chamber were statistically analyzed.The results indicate that the gradual delay of intake valve opening time makes the charge stratification more intense and the auto-ignition area of chamber larger.The gradual increase of valve lift also leads to the same results.It is found that for further the charge stratification is mainly influenced by the total turbulent energy of intake valve closing moment.The more the total turbulent energy is,the more intense the mixing process becomes.The charge is more homogeneous at the end of compression stroke.Accordingly,the stratification of charge becomes mild.The trend of auto-ignition area is similar to that of charge stratification.