Working fluid selection for a small-scale organic Rankine cycle recovering engine waste heat

This paper reports the design and evaluation of a 1 kWe Organic Rankine cycle using different working fluids for engine coolant and exhaust recovery from a 6.5 kW small ICE. Six working fluids have been selected to evaluate and compare the performance of the ORC system. The net power output, thermal efficiency, rotational speed of the scroll expander and condenser load of the ORC system have been studied. Results indicated R134a and R125a have better overall performance than other candidates when the designed inlet temperature of the expander is higher than 150 °C. The highest net power and thermal efficiency are respectively 1.2 kW and 13% when R125a is used as the working fluid. R600 and R245fa are desirable to be used when the optimal rotational speed of the scroll expander is about 3000 RPM. The proposed ORC engine coolant and exhaust waste heat recovery system has the advantages of simple system layout, low dumped heat load of condenser, high power output.