多限定参数条件下增压柴油机瞬变过程仿真

Simulation of Transient Load Step under Multiply Restrains of Turbocharged Diesel Engine

建立并校准了带二级串联式增压系统重卡柴油机的GT-Power数模。仿真与试验结果表明:建立的数模对整机及增压系统的特征参数吻合较好,仿真计算结果数据(如功率、油耗率、空气流量、平均有效压力)与实测数据的误差在3%以内。揭示了可调二级串联式增压系统中增压压力的控制特征。针对该柴油机瞬变工况条件下多项运行参数的控制要求,开发出描述各项运行参数之间关联关系的相应的子模型,如以废气再循环(EGR)率为目标的EGR阀开度控制子模型、燃烧放热参数随转速、扭矩及EGR率变化的实时跟踪模型等。展示了一套借助GT-Power对发动机中的复杂过程进行模拟仿真的方法。研究结果表明:开发出的子数模对瞬变过程中运行参数边界条件的控制与目标参数基本一致,可用于对瞬变工况下发动机状态的精准模拟。借助开发的数模对该柴油机的瞬变工况进行了预测,并对可变喷嘴涡轮增压器(VNT)位置的控制策略进行了对比优化。

A GT-Power model for process and performance simulation of a two-stage sequentially turbocharged heavy duty diesel engine was set up and calibrated. The simulated data agreed well with experimental results,errors between them （including power, specific fuel consumption, air flow rate, mean effective pressure） were all within 3 %. Control strategies for the boost pressure control feature of the system were revealed. For the control requirements of engine operation parameters under transient conditions, a series of sub-models representing correlation among operation parameters were developed, such as EGR valve opening control sub-model for EGR rate target, heat release rate sub-model tracking in real time variations of engine speed, torque and EGR rate, etc.. Modeling technique using GT-Power for the complex process during transient load step in the engine was demonstrated. Results show that the boundary conditions determined in the transient process by these sub-models meet basically the objective parameters,so these sub-models can be used to predict accurately the engine state under transient conditions. Transient load step performance of the heavy duty diesel engine is predicted and optimized for different VNT control strategies. These achievements provide a guidance for the calibration of the diesel engine transient process.