Abstract
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•Literature study indicates lack of comprehensive testing of automotive ORC.•ORC improves engine power and BSFC substantially.•Radial turbines are suitable candidates for unstable heat source conditions.•Turbine operating conditions have significant impact on system performance.
This study is experimentally exploring the feasibility of organic Rankine cycle (ORC) as a waste heat recovery (WHR) technology in internal combustion engines, aiming at improving engine’s power, fuel consumption and CO2 emissions. Exhaust gases of a heavy-duty diesel engine are used as heat source of the ORC system. However, as the engine’s operating conditions vary, powertrain performance changes substantially. Therefore and in order to provide a thorough overview, the system was tested at different engine points. The expansion machine is a custom-designed radial inflow turbine that is operating with NOVEC 649 as the working fluid. In order to assure a steady state testing, a thermal oil loop was installed between the exhaust gas and the ORC loop. For a robust study, the test results were compared with CFD ones. The coupled engine-ORC system presented an expansion power, turbine efficiency and thermal efficiency of 7.6 kW, 48% and 6.2%, respectively, when the turbine is running at maximum speed. The results also revealed that ORC systems have a promising influence in reducing the fuel consumption of diesel engine and providing extra power. Maximum percentages of improvements of BSFC and powertrain power were, respectively, 2.74 and 7.8% compared to engine without ORC.