Research On Engine Exhaust Waste Heat Recovery And Warm-up Utilization

At present,the thermal efficiency of conv entional engines is generally 20%?40%,and most of the heat generated by fuel combustion is lost to the atmosphere in the form of waste heat through exhaust gas,coolant and body radiation.Among them,the exhaust heat in the exhaust gas reaches one third of the total combustion heat,and recovering the waste heat in the engine exhaust gas means a lot to improve the energy utilization rate of the engine.During the cold start warm-up phase,the engine body temperature is low,the fuel atomization is poor,and the fuel mixing is bad,which results in insufficient combustion in-cylinder and severe deterioration of emissions.Improving the warm-up process and reducing the warm-up time are of great significance for engine emission reduction.In this paper,Suzuki GSX-R600 engine is taken as the research object.The effect of heating the coolant by a heat exchanger which recovers heat from the exhaust gas during the cold start warm-up process to reduce the engine warm-up time is studied.The study was finished through the combination of GT-POWER simulation and bench test.In this paper,the flow coefficients C_D of intake and exhaust valves and the injection pulse width MAP of the injector are measured by means of airway test and bench calibration test,and the sim ulation model of the target engine is established based on the test results and theoretical analysis.The accuracy of the model is verified by experimental data.The results show that the relative error of the model is less than 5%,and the simulation mode l can meet the accuracy requirements.The simulation models of heat exchange module,cooling system and lubrication system of target engine are established by measur ed structural data,and the simulation model of warm-up system is established by coupling with the engine model.The accuracy of the model is verified by experimental data,and the results show that the model of the warm-up system has high accuracy.By analyzing the variation of exhaust physical parameters with time,the exhaust heat energy flow rate of the target engine during the warm-up process is calculated.The exhaust heat energy flow rate can reach 1850J/s,accounting for 17% of the heat of fuel combustion per second during warm-up process,which shows great recovery potential.A warm-up system scheme of using exhaust heat to accelerate the warm-up process is designed,which accelerates the warm-up process by using a heat exchanger to recover exhaust energy to heat the coolant in the small cycle of the engine.A concentric tube heat exchanger was designed.The performance of the heat exchanger was simulated by FLUENT software,and the variation of pressure drop,temperature rise and heat exchange rate with time was obtained.According to the designed scheme,a test-bed was set up,and an experimental study was carried out.The test results show that with the designed warm-up scheme,the time to reach the warm-up steady state in the idle condition is shortened by 300 s,and the warm-up time reduction rate is 36.5%.Further simulation studies under different warm-up conditions show that the improvement of warm-up effect decreases with increasing engine load.Finally,a flat finned tube heat exchanger was designed,which was 96.7% smaller than the concentric tube heat exchanger.The simulation c alculation analysis of the warm-up system which utilizes the flat finned tube heat exchanger shows that compared with the one utilizing the concentric tube heat exchanger,the warm-up steady state time is further shortened by 135 s,and the warm-up time reduction rate has further increased by 25.9%,which means the total warm-up time is reduced by 435 s,and the total warm-up time reduction rate is 53%.The research in this paper shows that using the exhaust waste heat recovery and warm-up utilization scheme designed in this paper,effectively recover the exhaust heat of the warm-up process and significantly shorten the warm-up time can be achieved through reasonable heat exchanger design.