低压冷却EGR增压汽油机准维爆震模型

摘要

针对发动机概念设计一维性能仿真优化阶段爆震约束问题,使用末端混合气自着火延迟期积分法,提出一个同时考虑温度、压力、EGR率和空燃比影响的爆震预测模型.通过一台带冷却废气再循环(EGR)系统的增压汽油机进行爆震试验,使用滤波法和图像处理方法提取爆震特征.采用绝热压缩求解每个爆震循环末端混合气温度,并探讨比热比的影响以及比热比求解方法对末端混合气绝热压缩温度的影响.结合多岛遗传算法对爆震模型系数进行标定,并对比改进后的新模型与Hoepke模型的预测性能.结果表明:升高进气温度或加浓混合气都会减小混合气比热比,而引入冷却EGR则会增加混合气比热比.采用定值比热比得出的末端混合气温度会大幅高于变比热比得出的末端混合气温度.Hoepke模型在非理论空燃比下预测误差偏大,重新优化后的误差仍然较大.改进后的考虑多参数影响的爆震模型预测性能较好,在不同发动机之间能保持较好的适应性.%In considering the knock constrain when dealing with the one-dimensional engine performance simulation during the concept design stage,a predictive knock model was developed based on the integration of ignition delay of end mixture.The new model introduces the effects of temperature,pressure,EGR and air-fuel ratio.Knock experiments were conducted using a turbocharged gasoline engine,equipped with cooled EGR (exhaust gas recirculation) system.Knock characteristics are captured with signal filtering and image processing method.End gas temperature of each knock cycle is calculated with the isotropic compressing equation,considering the impact of parameters on specific heat ratio,and the impact of specific heat ratio solving method on end gas temperature.The new model was calibrated with multi-island generic algorithm.The predicting accuracy of the new model was compared with the classical model.Both increases in intake temperature and enrichment of charge decrease the specific heat ratio of the mixture,while cooled EGR increases the specific heat ratio.Large error occurs when solving the end gas temperature using constant specific heat ratio,instead of using variable specific heat ratio.The predicting error does not meet the requirements for the Hoepke model even if the model is recalibrated,while the new model can obtain a good performance and adaptability under different engines.