How to approach optimal practical Organic Rankine cycle (OP-ORC) by configuration modification for diesel engine waste heat recovery

Highlights: • A novel ORC configuration modification and evaluation method is proposed. • Optimal practical ORC is presented as target for configuration modification. • A basic ORC is modified to approach optimal practical ORC by proposed method. • After cycle modification, a modified ORC obtains a relative efficiency of 76.6%. -- Abstract: Conventional diesel engine has multiple waste heat sources, which make ORC configuration selection difficult. This paper proposed an ORC configuration modification and evaluation method. Pinch analysis technique was employed to integrate multiple waste heat sources into one composite curve. We presented an optimal practical ORC (OP-ORC) that matches the composite waste heat source and the cold source. ORC configuration modification was performed by improving the thermal matching between the ORC and the heat (cold) sources. Relative efficiency, which defined as the thermal efficiency ratio of the actual ORC to the OP-ORC, was used as criterion to evaluate various modified ORC configuration. An ORC modification case for multiple waste heat sources derived from a diesel engine was presented. With the thermal efficiency of 18.57% achieved by the OP-ORC, analysis results showed that the basic preheating ORC using Cyclopentane can only achieve a thermal efficiency of 9.28%. After cycle modification, a modified ORC could obtain a thermal efficiency of 14.23%, which is significantly close to the OP-ORC with a relative efficiency of 76.6%. This method would provide researchers with information to assess the benefit and the cost about each configuration modification and determine the direction of further improvement.