柴油机多品位余热回收低损跨临界联合循环模拟

Simulation of a Transcritical Combined Organic Rankine Cycle with Low Exergy Destruction Used for Multiple Grades Waste Heat Recovery of Diesel Engine

为了提高柴油机多品位、大温差余热的回收利用率,提出了一种低损跨临界有机朗肯联合循环,其中高温级循环用于回收温度较高的柴油机排气余热和废气再循环(EGR)余热,低温级循环回收柴油机冷却水余热、增压空气余热、与高温级循环换热后的排气余热和EGR余热.高温级对比分析了3种硅氧烷工质MM、MDM和D4,低温级选用了R143a,模拟研究了高低温级参数对循环性能的影响.结果表明:高低温级均存在最优的蒸发压力,高温级冷凝压力在允许范围内越低越好;高温级采用MM较MDM和D4循环性能更好,循环净功最高可以达到36.36,kW,损只有4.5,kW;各部分余热的利用率均在86%以上;增加高低温级的回热效能均可以提高循环性能.

Diesel engine has multiple grades waste heat with large temperature difference. In order to improve the efficiency of waste heat recovery,a transcritical combined organic Rankine cycle with low exergy destruction is pre-sented. High-temperature stage cycle recovers high grades waste heat including exhaust and exhaust gas recircula-tion（EGR）,while low-temperature stage cycle recovers low grades waste heat including cooling water,supercharged air,exhaust and EGR after rejecting heat at high-temperature stage cycle. Considering MM,MDM and D4 as the working fluid for high-temperature stage cycle,and R143a for low-temperature stage cycle,the effect of cycle pa-rameters is simulated and analyzed. The results show that both high-and low-temperature stage cycles have an optimal evaporating pressure,and high-temperature stage condensing pressure should be smaller within its allowable range. MM system has better performance than that using MDM and D4 with maximum net power being 36.36,kW and the exergy destruction being 4.5,kW. Each grade of waste heat recovery ratio is above 86%. Increasing the regenerator efficiency of both the high-and low-temperature stage can improve cycle performance.