Simulation of the effects of mixed-refrigerants and pure refrigerants on diesel engine waste heat recovery system

The characteristics of a vehicle diesel engine exhaust gas under various operating conditions were studied experimentally and a set of organic Rankine cycle (ORC) was designed. The effects of four kinds of pure fluids, four kinds of azeotropic mixtures and four kinds of zeotropic mixtures on the performance of ORC-engine combined system under various operating conditions were compared and analyzed by simulation. Results show that, with the increase of engine speed and accelerator opening, the net power outputs of the ORC system for these twelve organic working fluids and the exergy destruction rates of system and its components as well gradually increase, but the growth rates are different. The averaged net power output of the ORC system for R504 under various operating conditions of diesel engine gives its maximum value of 7.29 kW, which is 18% higher than R227ea. The ORC system thermal efficiency of mixed-refrigerants is generally higher than that of pure working fluids. The exergy efficiency of ORC system for zeotropic mixture increases by 14% than that of pure mixtures and R415B gives the maximum value.