Organic Rankine cycle optimization for waste heat recovery of three-cylinder turbocharged gasoline engine

In conventional passenger cars, two-third of the energy is wasted from the exhaust gas and engine cooling system. The present study has investigated the performance of a waste heat recovery (WHR) system based on the Organic Rankine Cycle (ORC) for the turbocharged gasoline direct injection engine. The optimal working conditions along with the best working fluid of the organic Rankin cycle to obtain the maximum net output power (NOP) from the recovery cycle are investigated. The steady-state zero-dimensional thermodynamic model of basic ORC at a series of engine operating conditions is designed in Thermoflex software. The working point of the engine has obtained by simulation of vehicle performance based on the standard urban driving cycle. Considering numerous and varied working fluids, 23 working fluids including pure and mixture fluids are evaluated. The mass flow rate of working fluid, condenser pinch, turbine inlet pressure, and condenser working pressure are considered as the optimization design variables and the optimum operating conditions of the basic ORC extracted for each working fluid using the Downhill Simplex method. Finally, by having experimental data for 320 points of the engines map, the efficiency of the optimized basic cycle was analyzed in combination with engine’s entire operating region. The results showed that R-507a, R-410a and R-125 present highest NOP respectively which indicate better performance of zeotropic and Azeotropic mixtures in engine WHR by ORC and for the best case, NOP reached to 2.6 kw in small load region and 6.6 kw in the peak thermal efficiency region.