| As the energy crisis intensifies and the consumption of petroleum fuels increases,how to maximize the use of fuel has become the more urgent problem we need to solve.In the energy distribution of the engine,the energy lost by exhaust is high and has much exergy,If it can be recycled,the energy loss can be reduced,thereby improving fuel utilization and achieving energy saving.In this thesis,the exhaust heat of a gasoline engine was taken as the research object,its recovery potential was analyzed.A recovery system was designed for the exhaust heat,the working fluid and key components were selected for the system,and working parameters was set up for components.Then,this system model was build in the GT-Power software,the system performance was analyzed by model simulation,and the mass flow rate of working fluid was matched for working conditions.The main work and conclusions of the paper are as follows:1)In the GT-Power software,the engine model was built according to the structural parameters of a gasoline engine,and the engine external characteristic test was carried out.The accuracy of the model was calibrated by using the external characteristic test data.The exhaust energy and exergy were calculated.The calculation results show that when the engine speed is higher than 2800r/min,the exhaust energy is above 30 kW,and 46.2% of the energy in the exhaust can be converted into useful work.When the engine speed is between 2800 r/min and 4000 r/min,the exhaust energy recovery potential is the largest.2)Based on the organic rankine cycle,the double-loop structure waste heat recovery system was designed.According to the constructed thermodynamic model,the theoretical calculation was carried out,and the net output power,thermal efficiency and exergy loss of the four structure recovery systems were compared and analyzed.The analysis shows that the double-loop structure waste heat recovery system has certain advantages over the other three structures.3)The principle of working fluid selection was used to initially screen the working fluid for the recovery system.The effects caused by evaporation pressure and superheat on the system performance were investigated by theoretical calculation.The calculation results show that the evaporate pressure can be increased to improve the thermal efficiency of the system.The increase of superheat degree has less improvement on the thermal efficiency of the system.The performance of the system is better when water is used as the working fluid in high temperature circulation and R123 is used as the working fluid in low temperature circulation.4)A recovery system model was built in GT-Power software,and the theoretical calculation results were used to calibrate the models of each component.After the model was coupled,the system performance was simulated in the engine speed range of the maximum recovery potential.The simulation results show that the recovery power can reach up to 6.12 kW,the power increase rate is up to 8.25%,and the highest thermal efficiency is 13.67%.Compared with before,the engine exhaust temperature drops about 400?.5)Six working conditions were selected to match the mass flow rate of the working fluid.The simulation results show that under the same working condition,the net output power increases first and then decreases steadily with the increase of pump speed.The optimal mass flow rate of working fluid under the six working conditions is determined.the simulation was done after the mass flow rate matching,the recovery power and thermal efficiency have increased a lot,and the exhaust temperature has dropped about 550?. |
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