Abstract
To efficiently recover the waste heat from a diesel engine exhaust, a regenerative organic Rankine cycle (RORC) system was employed, and butane, R124, R416A, and R134a were used as the working fluids. The resulting diesel engine-RORC combined system was defined and the relevant evaluation indexes were proposed. First, the variation tendency of the exhaust energy rate under various diesel engine operating conditions was analyzed using experimental data. The thermodynamic model of the RORC system was established based on the first and second laws of thermodynamics, and the net power output and exergy destruction rate of the RORC system were selected as the objective functions. A particle swarm optimization (PSO) algorithm was used to optimize the operating parameters of the RORC system, including evaporating pressure, intermediate pressure, and degree of superheat. The operating performances of the RORC system and diesel engine-RORC combined system were studied for the four selected working fluids under various operating conditions of the diesel engine. The results show that the operating performances of the RORC system and the combined system using butane are optimal on the basis of optimizing the operating parameters; when the engine speed is 2200 r/min and engine torque is 1215 N·m, the net power output of the RORC system using butane is 36.57 kW, and the power output increasing ratio (POIR) of the combined system using butane is 11.56%.
Highlights
A significant amount of petroleum resources are consumed by automobiles
As seen in the figure, the amplitude of the optimized intermediate pressure variation is below 7 kPa for each working fluid under various operating conditions of the diesel engine
When the engine speed and engine torque are unchanged, namely under the same operating condition of the diesel engine, the order of the optimized intermediate pressure for the four selected working fluids decreasing in sequence is as follows: R134a > R416A > R124 > butane
Summary
A significant amount of petroleum resources are consumed by automobiles. the effective thermal efficiency is only about one third for vehicle engines, and the waste heat is released into the atmosphere through the engine exhaust and engine coolant [1,2]. The results indicated that the optimum exergy efficiency and the heat exchanger area per unit net power output of the RORC were obtained from the Pareto-optimal solution are 59.93% and 3.07 m2/kW, which are 8.10% higher and 15.89% lower than that of the basic ORC, respectively. The variation tendency of engine exhaust energy rate under various operating conditions was obtained by experiment; a RORC system was employed to recover the exhaust heat from the diesel engine by using four different working fluids. Electricity generation by recovering waste heat of vehicle engines may potentially save energy and reduce emissions This may be considered an efficient method for the internal combustion engine-electric motor hybrid vehicles in the near future
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