Impact of organic Rankine cycle system installation on light duty vehicle considering both positive and negative aspects

This paper presents the analysis of organic Rankine cycle (ORC) based waste heat recovery system. Both the positive and negative effects of ORC system installation on a light duty vehicle were evaluated. Engine exhaust data for a light duty vehicle was used to design an ORC based system. Optimum cycle design suggests that ORC system installation is feasible.

Results presented that for the vehicle operation at 100km/h, engine power can be enhanced by 10.88% which is 5.92kW of additional power and at the lower speed of 23.5km/h, the engine power enhancement was 2.34%. ORC component weight data from manufacturers were used to estimate the weight of the designed system.

The performance decline due to added weight is calculated. Effects of added back pressure and performance decline due to the part-load operation of ORC unit were also calculated and an overall effect of waste heat recovery system was evaluated. The results then suggested that maximum power enhancement is 5.82% at the vehicle speed of 100km/h instead of previously mentioned 10.88% can be achieved if negative effects are also considered.

Furthermore, it was concluded that at speeds lower than 48km/h the waste heat recovery system was not beneficial at all and low-speed operation was in fact not preferable as it results in additional power demand from the engine by 6.39% at 23.5km/h. The vehicles for city driving cycles are not recommended for ORC installation.

Another finding revealed that if exhaust heat recovery heat exchanger is designed for maximum heat recovery, at part load operation, the heat exchanger is not suitable to maintain working fluid temperature below the critical temperature of working fluid and minimum exhaust gas temperature at heat exchanger exit.