柴油机两级VNT混联系统整机效率优化

Whole engine efficiency optimization of two-stage VNT series-parallel system for diesel engines

为提高柴油机的余热回收利用率,提出一种基于可变喷嘴环式涡轮VNT(variable nozzle turbine)技术的两级涡轮混联系统。该系统根据柴油机运行工况,通过控制阀门的开闭来实现混联系统中串联工作模式和并联工作模式的转换。以涡轮的有效直径为参数来表征涡轮的流通能力,利用GT-Power仿真平台研究了两种工作模式下增压涡轮和动力涡轮的流通能力对发动机功率、动力涡轮功率及涡轮增压器性能的影响规律;提出了增压涡轮、动力涡轮与发动机的匹配策略;以系统整机效率最优为目标,针对柴油机不同运行工况进行混联方式的优化控制。结果表明:针对柴油机的不同运行工况,通过两级VNT复合系统混联优化运行方案,能够有效回收柴油机废气能量,额定工况下系统整机效率提高5.1%。

Abstract： A two-stage turbine series-parallel system based on VNT （variable nozzle turbine） was proposed to recover waste heat from the diesel engine. The system adopted valves to control the system and accomplish the transformation of the series or parallel work- ing modes. And the system was established under the concept of parallel and series working modes separately, and effective diameter was chosen as the parameter to define the flow ca- pability of the turbine. Besides, the influences of the effective diameters of the two-stage turbines on the engine power, the power turbine power and the turbocharger performance were analyzed via GT-Power, and the effective diameters of the two-stage turbines were matched according to the engine working condition. And the series or parallel working mode was controlled by the maximum value of the whole engine efficiency at the specific working condition of the diesel engine. Results showed that through the proper optimization and com- bination of the two-stage VNT and series-parallel working mode, the system could recover waste heat effectively and improve the whole engine efficiency by 5.1~ during the back tracking period.