Optimization Of Exhaust Heat Recovery System Of Diesel Engine Based On Ranking Cycle

Nowadays,the widespread use of traditional fuel vehicles has brought a series of environmental pollution problems.As one of the important ways of energy saving and emission reduction,the waste heat recovery of internal combustion engine can make full use of engine exhaust energy.At present,the key of waste heat recovery technology based on Rankine cycle lies in how to design a more efficient and compact waste heat recovery system matching with engine,which can not only make full use of exhaust gas,but also recover more energy while ensuring sufficient efficiency.In this paper,the waste heat recovery system of 6BG332 diesel engine is studied.In this paper,the heat transfer model of elliptical spiral tube evaporator is established.The results show that with the increase of evaporation pressure and exhaust gas outlet temperature,the outlet temperature of working medium and exhaust gas utilization rate decrease.With the increase of mass flow rate,the availability of exhaust gas increases,and the working medium and exhaust gas outlet temperature of evaporator decreases.The paper establishes the Matlab/Simulink model of expander.The results show that the influence of piston stroke on the performance of expander is less than that of cylinder diameter.The relative clearance volume coefficient shall be reduced as much as possible to ensure sufficient efficiency of the expander.It is advisable to select the intake advance angle of 10°and the exhaust advance angle of 20°～30°.The influence of the inlet temperature of the expander on the output power of the expander is far less than the evaporation pressure.Considering the influence of output power and adiabatic efficiency,the final structural parameters of the expander are selected as cylinder diameter,piston stroke 100 mm,relative clearance volume coefficient 0.045,intake advance angle 10°,intake angle 50°,exhaust advance angle 20°,exhaust angle 100°.With the use of the genetic algorithm,taking the system efficiency and the output power of the expander as the optimization objective,the speed of expander and working pressure as the optimization variables,the operation parameters are calculated.The results show that with the increase of the engine speed and load,the recoverable power increases gradually.When the engine is in the state of high speed and high load,the adiabatic efficiency and exhaust gas availability are relatively low.The heat efficiency of Rankine cycle is more than 13.5%,the power improvement rate of the system is 7.26%～7.82%,and the total efficiency of the system is 27.38%.