Performance Evaluation of a Heavy-Duty Diesel Truck Retrofitted with Waste Heat Recovery and Hybrid Electric Systems

The interest of long-hauling companies about the conversion of their fleets into low-emission and fuel-efficient vehicles is growing, and retrofitting options may represent a suitable solution. Powertrain hybridization and waste heat recovery are considered among the most promising methods to further improve the fuel economy of road vehicles powered by internal combustion engines. In this article, not only the effect of retrofitting a heavy-duty truck with an electrification-oriented ORC unit or with a series hybrid system is investigated, but also the possibility of implementing both at the same time. The conventional vehicle is powered by a heavy-duty 12.6 liters diesel engine. It is shown that, despite such a large engine has high potential for waste heat recovery, on the other hand it represents a very challenging constraint when designing a hybrid retrofitting. Four powertrain options are considered: conventional vehicle (engine-only powered), waste heat recovery retrofit, hybrid retrofit, waste heat recovery+hybrid retrofit. For the hybrid powertrains, the optimal control strategy is analyzed and used as a starting point to develop an online implementable rule-based control strategy. The performance of the different powertrains have been numerically simulated over a set of driving cycles. The results show that, compared to the conventional powertrain, the hybrid retrofit allows the greatest reduction in fuel consumption (up to 17%), and the best employment of the waste heat recovery system.