【作者】 尹涛；

【导师】 孟祥慧； 李铁；

【作者基本信息】 上海交通大学 ， 机械工程， 2017， 硕士

【摘要】 发动机爆震的发生及其强度的大小具有高度随机的特征。然而,当前爆震模型研究大多聚焦于爆震起始时刻的预测,综合考虑爆震随机统计特征的爆震模型研究极少,因此当前爆震预测模型大多不能再现发动机临界爆震点时的实际工作状态。针对这一问题,本研究基于一款1.5升涡轮增压汽油发动机进行了宽范围爆震工况实验,对爆震起始时刻与爆震强度的统计学特征进行了分析,在此基础上构建了综合考虑爆震起始时刻预测与具有统计学分布特征的爆震强度预测的现象学爆震模型。爆震起始时刻的预测基于自着火延迟期积分法,同时考虑缸内压力、热点温度、EGR及过量空气系数λ的影响。最终标定得到的爆震起始角模型有着较好的预测性能,各工况预测值与实验提取值之间的均方根误差都小于1.2度曲轴转角。爆震强度建模方面,热点能量密度E和放热速率S是影响爆震强度的关键因素。S与爆震起始时刻的末端混合气温度、压力、EGR率、过量空气系数λ相关,E与缸内新鲜进气量、爆震起始时刻缸内容积相关,由整理后的放热速率因子α和能量密度因子β可得到Y_KI双因子爆震强度模型。Y_KI模型在研究范围内的所有爆震工况都有着较好的预测性能,其中,爆震临界点的判断标准Y_KICritical随转速升高而小幅增大。在改制后的GCR10上的爆震扫描实验结果表明,该模型可以较好地反映变几何压缩比后的爆震强度情况,适合用于预测性仿真。更多还原

【Abstract】 The occurrence and magnitude of engine knock are highly random.However,most of current knock models are focused on the prediction of knock onset and there are few researches on knock prediction which takes the stochastic characteristic into consideration.Therefore,these knock models cannot reproduce the actual engine working state when operating at the critical knock point.Aiming at this problem,we preformed engine bench tests at a wide range of knocking conditions in this study based on a 1.5-liter turbocharged gasoline engine.The knock onset moment and the statistical characteristic of knock intensity were analyzed.Then a phenomenological knock model was built,combining the knock onset prediction and the knock intensity prediction considering the statistical distribution of knock phenomenon.The prediction of knock onset is based on the auto-ignition delay integration method,taking the effects of cylinder pressure,hot spot temperature,EGR amount and excess air coefficientλinto account.The calibrated knock onset model has a good prediction precision.The root mean square error between the predicted value and the experimental value is less than 1.2 crank angle degree.In terms of knock intensity modeling,the hot spot energy density E and the heat release rate S are the key factors affecting the knock intensity.S is related to the temperature,pressure,EGR amount andλof the end gas on the knock onset while E is related to the trapped fresh air and the cylinder volume on the knock onset.Thus,the heat release rate Factorαand the energy density factorβcan be obtained to develop the Y_KI knock intensity model.Y_KII model has a good predictive performance at all knocking conditions in this study.The judgment criterion Y_KICritical for knock critical point slightly increases with the increase of engine speed.The knocking test result on the modified GCR10 engine shows that the developed model reflect the knock intensity well after changing the geometric compression ratio.Therefore,the new model is suitable for predictive simulation.更多还原