Fuel Consumption Potential Gains of Rankine Thermal Power Recovery for Series Hybrid Electric Vehicles

Considerable efforts have been made in the automotive industry on powertrains in order to minimize the energy required by passenger cars. This can be done by improving factors such as the technologies used and the way the energy is used.Losses can be recovered from thermal irreversible power sources. The lost energy contained in the exhaust gases and the coolant can be recovered using two Rankine Machines. As Rankine Cycles work better on a stabilized operating point, a Series Hybrid Electric Vehicle (SHEV) would appear to have a great potential for this technology. The two Rankine machines can be chained: the high temperature machine recovers the lost exhaust gases energy, while the low temperature machine recovers both the lost energy coming from the coolant plus the energy coming from the low temperature side of the previous machine. In order to be sure to estimate the maximum potential gains from the use of chained Rankine machines on SHEVs, the degrees of freedom are optimised to maximize irreversible power source efficiency. Moreover, using optimal control theory is essential to minimize the overall vehicle energy consumption. Here, optimal control is used with dynamic programming that takes into account the battery state of charge dynamics. The architecture of chained Rankine machines has been tested for different atmospheric conditions. Simulation results show an average energy reduction of 20%.