柴油机有机朗肯循环余热回收系统的动态效应

Dynamic Behavior of a Diesel-Engine ORC Exhaust Heat Recovery System

车辆在道路运行过程中,其发动机基本处于动态变工况运行状态,排气流量和温度呈现出强烈的瞬变特征,揭示有机朗肯循环余热回收系统在瞬变热源条件下的动态效应是其实现车用化的关键.基于柴油机有机朗肯循环余热回收系统的试验平台和仿真平台,首先讨论了有机朗肯循环系统在小时间尺度上的瞬态响应特征.研究发现,蒸发器的传热惯性是有机朗肯循环系统阶跃响应的主导特征,可用1阶惯性方程建模,同时受到相变边界移动、蒸发压力与温度耦合作用的影响.其次,研究了有机朗肯循环系统在大时间尺度上的道路运行特征,从宏观层面揭示了有机朗肯循环系统的综合能效与循环工况的关联关系.结果表明,循环工况的平均车速越高,怠速次数越少,则朗肯循环系统的有效做功时间越多,且蒸发压力和蒸气温度的控制效果越好,进而系统的综合能效就越高.

The working state of a vehicular engine is highly dynamic during driving cycles. As a result,exhaust mass flow and temperature are of strong fluctuation,which reveals the significant dynamic behavior of the organic Rankine cycle（ORC） exhaust heat recovery system. An experimental bench and a simulation model were built first. Then,the step response characteristics of the ORC system were discussed in a small time scale. Results indicate that the heat transfer inertia of the evaporator is a dominant factor. The average feature can be described using a one-order inertia model. The step response is also affected by the moving phase-change boundary and the coupling interactions between evaporating pressure and temperature. Finally,the on-road dynamic characteristics of the ORC system were investi-gated in a large time scale. And the association relationship between driving cycle features and ORC fuel-saving ca-pacity was uncovered. The study found that,with higher average vehicle speed and fewer stops,the ORC effective working time will increase,and the control performance of evaporating pressure and temperature will get im-proved. As a result,the fuel-saving capacity is greater.