Structure Optimization Of ORVR Carbon Canister

With the increasing number of motor vehicles in our country,the pollution of oil and gas emissions is becoming more and more serious in the process of vehicle refueling.The hydrocarbons volatilized from oil and gas to the environment make the situation of air quality problems such as PM2.5,ozone content and haze more and more serious.The United States has adopted a mandatory requirement for all vehicles to install onboard oil and gas recovery(ORVR)system,which has been used for more than 20 years.The data shows that the recovery rate of volatile oil and gas is as high as 98%.From the comparison between the emission limits and measurement methods of light vehicle pollutants(the sixth stage in China)(the sixth stage in China)and the fifth stage in 2016,it is found that the emission limits of automobile oil and gas are more and more strict,and the research on ORVR technology in China starts late,so it is necessary to study this technology.This paper focuses on the structure optimization design of ORVR carbon canister,which is the core part of ORVR system.Firstly,a U-tube fixed bed and a straight tube fixed bed were set up,and the mixture of n-butane and nitrogen was used to replace the volatile oil gas.According to the measured temperature and the concentration of n-butane at the outlet,the adsorption kinetic analysis and the calculation of adsorption calorific value were carried out,and the saturated adsorption capacity,adsorption breakthrough curve and time,adsorption rate constant,adsorption heat and other adsorption performance parameters of the activated carbon were obtained.Secondly,according to the device size,experimental data and activated carbon adsorption performance parameters of the straight tube fixed bed,ANSYS ICEM and fluent were used to establish the straight tube fixed bed model and simulate the adsorption process of the fixed bed.The mass source term SM and energy source term st in the model are established by using the fixed value expression and the UDF(user defined function)compiled mathematical expression.The temperature field and n-butane concentration field in the fixed bed are studied and analyzed according to the simulation data.The deviation rate between the simulation results of the two models and the experimental data was calculated,and the accuracy of the straight tube fixed bed model was verified.On the basis of model a,sensitivity analysis was carried out on the concentration of imported n-butane and intake velocity.The results showed that the maximum temperature rise of fixed bed was positively correlated with the above two parameters.The simulation results of the straight tube fixed bed are in good agreement with the experimental data,which shows the feasibility of using fluent simulation to study the adsorption process of the fixed bed.Secondly,referring to the main body size and appearance structure of ORVR carbon canister(two chambers)designed by General Motors Co.,Ltd.,combined with the above active carbon adsorption performance parameters and UDF source term expression,the ORVR carbon canister model is established on fluent.Based on the simulation results,the optimal volume ratio of carbon canister is 5:3.On this basis,adjust the diameter of the inlet and outlet of the model,and study the influence of the diameter of the inlet and outlet on the performance of the carbon canister.The simulation results show that the optimal diameter is 10 mm.The ORVR carbon tank designed in this paper adopts a porous medium area of 5:3 volume ratio and a 10 mm inlet and outlet diameter as the optimal structure.Finally,according to the optimal structure of ORVR carbon tank,a physical device is made.The mixture of high concentration n-butane and nitrogen is used to replace the volatile oil gas to simulate the adsorption process of ORVR carbon tank.The temperature in the carbon tank and the concentration of n-butane at the outlet are measured during the adsorption process.The deviation rate between the experimental data and the simulation data is within 5%.It shows that the optimal structure of ORVR determined by fluent simulation is The results of the carbon canister and the experimental device are in good agreement,and the accuracy of the simulation results is good to verify the reliability and correctness of the ORVR carbon canister designed by fluent.In this study,the structure of ORVR carbon tank is optimized by the method of mutual verification of experiment and numerical simulation,which verifies the feasibility of fluent in the design of ORVR carbon tank,and provides theoretical basis and accurate and feasible method for the optimization design of ORVR carbon tank structure in vehicle refueling system.