CFD Analysis On Evaporation During Refueling

A large amount of evaporation is discharged into the atmosphere during the refueling process,which brings serious environmental pollution,energy waste and potential safety hazard.Therefore,it is necessary to study the fuel evaporation law and its influencing factors,thereby guiding the improvement of fuel system and fuel tank system.Fuel evaporative emission were studied at home and abroad,mostly focused on the droplet evaporation mechanism of cylinder and oil tank or static fuel evaporation.But lack studies of evaporation law of dynamic fuel and accurate numerical simulation method of internal fuel tank in the process of gas-liquid flow field(such as temperature field,pressure field distribution research).CFD method is used to establish the mathematical model of mass transfer and heat transfer.The main contents and conclusions are as follows:(1)CFD simulation of refueling process.A fuel tank is selected as the prototype.Simplify the model and build three-dimensional fuel tank model through CATIA software;Meshing software is used to partition the grid and verify the independence of the grid;The Fluent software is used to simulate the system,in which the boundary setting and the k-? model and VOF model are used to deal with the oil flow problem.According to the simulation results,we can observe the fuel flow law during the refueling process which is consistent with the actual situation and verify the accuracy and rationality of the simulation model.It is found that the fuel filling process of the automobile is the process of the oil and gas displacement and the process of fuel evaporation,diffusion and mass transfer.(2)Based on the turbulent model and multiphase flow model,using the userdefined function(UDF)preparation of fuel heat and mass transfer model,added the corresponding evaporation source in Fluent software,completed the numerical simulation of gas-liquid phase change process of fuel and discussed influences of evaporative emission with different influence factors(such as temperature,velocity,and oil fuel tank structure the tank wall temperature).The results showed that the increased flow of fuel and temperature high significantly increase the rate of evaporation.But on the same amount of fuel gas conditions,improve the speed of gas and the diameter will reduce the fuel evaporation.This provides guidance for improving the fuel system and fuel tank structure.(3)The fuel tank is simulated by the prototype of the simulation model.The experimental results show that the concentration of the fuel vapor in the fuel tank outlet increases with the increase of the filling rate,and the growth rate of the concentration increases with the increase of the filling speed.Although there are some errors between two simulation results,they are in substantial agreement.The correctness of the simulation model is verified.