Evaluation of automotive waste heat recovery for various driving modes

A computational study was performed to determine an optimum position of a superheater used in an automotive WHR (waste heat recovery) system integrated with a 3.3 L V6 gasoline direct injection engine, and the results were validated through an experimental study. Regardless of utilizing only half of the exhaust mass flow, the superheater mounted close to the exhaust manifold was found to be able to recover approximately 3.8 kW more waste heat from the exhaust of the particular engine. Based on the result, the optimum layout of a dual loop Rankine system for an automotive waste heat recovery was developed, and the automotive waste heat recovery rate was assessed for many driving test modes widely adopted in various regions of the world. The temperature and the mass flow rate of the engine exhaust increased as the load and speed of engine increased; thus, the technology is more suitable for vehicles that mostly run in either highway or city. In conclusion, the dual loop Rankine system is more advantageous for vehicles driven in the United State or Europe in terms of improving fuel economy of engine.