Investigations On A Vehicular Diesel Engine With An ORC Exhaust Heat Recovery System

Aiming an ORC system applied on a heavy-duty truck for recovering exhaust heat from a diesel engine,a study has been conducted to investigate its operation performance and its impacts on the engine performance via experiments and simulations.The cooling method of the on-board exhaust heat recovery system has been determined.The power and economic performance of a heavy-duty truck with the ORC system application have also been evaluated.The main research contents and conclusions are summarized as follow:A small scale ORC system test bench was developed for recovering exhaust heat from a diesel engine.The performance variations of the engine and ORC system at different working conditions were investigated based on experiments.The experiment results indicated that,the backpressure of the engine integration with the ORC system has little increment at low engine torque conditions,and the power output of the ORC system expander increases with the increasing of the engine speed.The working fluid mass flow rate and the operation pressure of the configured ORC system have important effects on the engine backpressure.The model of a diesel engine which integrates an ORC exhaust heat recovery system was developed with GT-suite and Simulink.The integration performance of the engine with the ORC system was further evaluated through simulations.The effects of the operating conditions of the engine and the ORC system on the integration system performance were also discussed.The simulation results indicated that integration with the ORC system can significantly improve the engine power performance when the engine operates at the working condition range in which the ORC system can operate normally.Both the optimization speeds of the ORC system pump and the expander and lower cooling water temperature at the condenser inlet have positive effects on improving the engine power performance.An on-board ORC exhaust heat recovery system using air or water cooling method was designed,and the comparison analysis of the performance of the on-board ORC system at different engine operating conditions was presented.The results showed that,compared with the air cooled system,integration with the ORC system using water cooling method can more effectively improve the engine power performance.The water cooled ORC system has higher thermal efficiency and can effectively decrease the engine exhaust gas outlet temperature.Effects of the water cooling system operating condition,the engine working condition and the ambient temperature on the performance of the on-board ORC exhaust heat recovery system were analyzed based on simulations.The results indicated that optimization of the cooling system fan speed and the water pump speed can effectively improve the on-board system net power output at all engine working conditions.The potential of the exhaust heat recovery system for improving the engine performance increases with the decrease of the ambient temperature.The maximum power output improvement of the engine can reach up to 6.15 k W at the ambient temperature of 263 K.Both the on-board ORC system thermal efficiency and the engine fuel economy are further improved for optimizing the recovered exhaust gas mass flow rate when the engine operates with high speeds and torques under high ambient temperature conditions.The optimization analysis of working fluids and condensers of the on-board ORC exhaust heat recovery system was presented.The results showed that the engine has high power performance improvement when the ORC system selects R123 as the working fluid,and the power output improvement increases with the increasing of the engine speed and torque.The performance of the on-board ORC system with plate condensers which have the same volume and different structure parameters was evaluated.The results indicated that the plate heat exchanger which has large plate width and short plate length is more suitable as the on-board ORC system condenser.The power performance of a heavy-duty truck with the ORC system application at different driving conditions was further evaluated through simulations.Both the vehicle total weight and the propelling power requirement of the heavy duty truck equips with the on-board ORC system have little increment.The power improvement of the truck with no-load is not obvious.However,the power improvement of the truck increases with the increasing of the truck velocity and the cargo mass,and the fuel saving effect of the truck is more obvious with the increasing of the driving distance.