Experimental study of organic Rankine cycle system and expander performance for heavy-duty diesel engine

A small scale organic Rankine cycle system capable of generating electric power using exhaust gas of a 7.25 l heavy duty diesel engine was built and tested. A custom-designed radial inflow turbine was used as an expansion machine, and NOVEC649 was used as the working fluid. In order to maintain steady state operation, a thermal oil loop was installed in the system as an intermediate circuit between the exhaust gas and organic Rankine cycle loop. Compared to the previous study by the authors, the operating conditions were further extended. In addition, the effects of cooling water temperature and working fluid superheating temperature on turbine performance were explored in the current study. The coupled engine-organic Rankine cycle system presented an electrical power, turbine efficiency and thermal efficiency of 9 kW, 35% and 4%, respectively. The results showed that both cooling water temperature and working fluid superheating temperature had a negative impact on the radial turbine performance (generated power and efficiency). The average decrement of the generated power and turbine efficiency were 2.4% and 1.7%, respectively, when increasing the cooling water temperature by 2 degrees C, and 2.5% and 7.3% when increasing the working fluid superheating temperature by 2 degrees C. Moreover, the extended tests were beneficiary for validating the proposed performance prediction meanline model developed by the authors in a previous study. The maximum deviation between the measured and predicted turbine efficiency was 3.5%.