A Simulation Study of Optimal Integration of a Rankine Cycle Based Waste Heat Recovery System into the Cooling System of a Long-Haul Heavy Duty Truck

摘要

As a promising solution to improve fuel efficiency of a long-haul heavy duty truck with diesel engine, organic Rankine cycle (ORC) based waste heat recovery system (WHR) by utilizing the exhaust gas from internal combustion engine has continuously drawn attention from automobile industry in recent years. The most attractive concept of ORC-based WHR system is the conversion of the thermal energy of exhaust gas recirculation (EGR) and exhaust gas from Tailpipe (EGT) to kinetic energy which is provided to the engine crankshaft. Due to a shift of the operating point of the engine by applying WHR system, the efficiency of the overall system increases and the fuel consumption reduces respectively. However, the integration of WHR system in truck is challenging by using engine cooling system as heat sink for Rankine cycle. The coolant mass flow rate influences strongly on the exhaust gas bypass which ensures a defined subcooling after condenser to avoid cavitation of pump. The coolant temperature decides the condensation pressure which impacts on the efficiency of WHR system. This paper aims to investigate the impacts of cooling conditions on WHR system by simulation. An optimal integration position of WHR condenser has been found. A complex 0D/1D-simulation model for a turbocharged production heavy duty engine with low-/high-temperature cooling circuits and a WHR system with ethanol as working fluid have been established in a conventional 1D-simulation software. A comparison between two WHR system layouts is made to determine WHR system concepts. An optimization for thermal management of the engine has been conducted to evaluate the maximal recovered energy in consideration of cooling fan engagement, thermostat operation and interactions between subsystems under transient conditions.