A technical review on waste heat recovery from compression ignition engines using organic Rankine cycle

- Engine exhaust gas has highest potential of heat recovery than EGR and cooling water.
- Thermal efficiency of standalone engine-ORC system is about 10-25%.
- Overall combined efficiency of engine and engine-ORC system is about 60-90%.
- R245fa is the best suitable working fluid for engine-ORC application.
- Shell&tube heat exchangers and Scroll expanders are suitable for engine-ORC.

The study deals with the utilization of organic Rankine cycle (ORC) to recover waste heat from compression ignition (CI) engines and produce additional power output. A review on the potential of waste heat recovery from exhaust gas, water jackets and intake charge air of CI engines was carried out. Research challenges associated with engine-ORC technology such as selection of organic working fluid, type of evaporator/condenser, back pressure due to additional ORC components in the exhaust line are discussed. The evaporator for the engine-ORC needs to be designed by keeping a view of variable exhaust gas heat source (variable temperature and mass flow rate profiles). It is explored from the literature study that engine-ORC system could operate with the maximum thermal efficiency range about 10-25%. The main reason for low thermal efficiency could be due to lower operating temperatures in the ORC. However, the overall efficiency of combined system (engine and engine-ORC with exhaust gas/water jackets/intake air/use of hot water from condenser for heating/refrigeration application) is significantly higher (60-90%) than the conventional standalone ORC system (10-25%). It is also found that R245fa is the better organic working fluid for engine-ORC application based on better performance, availability, economic and environmental aspects.