In the last years an increasing interest has grown about the organic Rankine cycle (ORC) for waste heat recovery from the engine exhausts, as a feasible way to improve the efficiency of internal combustion engines (ICE). However, the highly variable working conditions in which an engine usually works make the operation of the ORC unit very challenging. In the management of ORC units, optimization and control are considered as an essential step in order to attain good performance during the whole operation of the ICE on a driving cycle. In this paper a GT-Power model of a 12.6?l turbocharged Diesel engine is used as a typical heavy duty Diesel engine to retrieve the temperature and the mass flow rate of the exhaust gases during a heavy heavy-duty driving cycle. An optimization process is performed to maximize the power output of the ORC as a function of the revolution speeds of the pump and of the turbine. For powertrain electrification purposes, two different ORC layouts are proposed in this paper, both seeking to store the recovered energy into a battery pack. The first layout is optimized based on mean values of exhausts temperature and mass flow rate, while the second layout is designed to control independently the revolutions of the pump and of the turbine of the ORC unit toward optimal values for maximum net power output. Both the layouts allow to recover an interesting amount of energy, in spite of a straightforward control strategy. Nonetheless, results show that optimizing the net power of the ORC cycle by decoupling the turbine and the pump may not ensure the maximization of the recovered energy. In fact, the storable energy from the ORC unit is strongly affected by the conversion efficiencies related to the specific layout.

» Author: M. Villani, L. Tribioli

» Reference: 10.1016/j.enconman.2019.02.078

» Publication Date: 01/05/2019

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