The Research On Optimization Of ORVR System Based On China's Six-state Emission Limit

In October 2016,the Ministry of Environmental Protection issued the official draft of the country's six-state emission regulations.One of the biggest changes in the country's six-state emission regulations is to increase the VII-type tests that is pollutant emission test in refuelling process,stipulates that the fuel evaporation emissions no more than 0.05g/L.In order to adapt to the national laws and regulations,vehicles need to upgrade the Onboard Refueling Vapor Recovery(ORVR)system.To upgrade the ORVR system,consideration must be given to the design and calibration of key components of the fuel system and calibration of canister desorption.Domestic and foreign scholars mostly use the method of simulation and experiment for the study of refueling process.However,most of the simulations are based on the analysis of single or partial components of the ORVR system,and no complete ORVR system simulation model has been established.The content of this article is to test and analyze the influence of different refuelling gun on refueling emissions,to conduct in-depth research on the mechanism of ORVR system,and to establish a complete ORVR system simulation model with fuel filling pipe,fuel tank,circulation pipe and activated carbon tank,and replace the partial calibration test with simulation.In order to find the optimum restrictor orifice size for the FLVV valve and recirculate pipe to save cost and time and shorten the development cycle of the ORVR system.The specific research content and main conclusions are as follows:(1)Carry on the test to analysis the refueling process.A refueling emission test was performed on an ORVR system that had passed the fueling emission test,and the tank pressure,vent pipe flow rate,recirculate pipe flow rate,filling port intake volume,and fueling emission factor were measured to study the effect of different refueling guns(US OPW and German ZVA)on refuelling emissions.The test results show that:(1)At the same refueling flow rate(37L/min),the OPW refueling gun has a greater pressure inside the tank and the flow rate of the vent pipe and recirculate pipe is more;(2)ZVA refueling gun has relatively brought less air into the tank due to shearing and rolling suction,and the refueling port intake volume is also relatively small.So the ZVA refueling gun should be the primary consideration when adjusting the diameter of the restrictor of the rcirculate pipe.(2)Carry on simulation to analysis the refueling process.Select a vehicle ORVR system as a prototype,simplify it appropriately,and use CATIA software to establish its three-dimensional model;apply ANSA software for meshing;use STAR-CCM+ software for simulation calculation,where turbulence model selection can be achieved k-? model and the multiphase flow model select the VOF(Volume of Fluid)model.The simulation results of the flow rate of the vent pipe,the flow rate of the recirculate pipe,and the intake air amount of the filler port were compared with the test data,and the error was within 5%,which verifies the validity of the simulation model and could be used for subsequent optimization studies.(3)Optimize the model.(1)Optimize the diameter of the filling pipe.By analyzing the influence of the diameters of five different filler pipes on the oil and gas flow at the filler port to find the best filler pipe diameter,under which the filling pipe can form liquid seal,and meet the requirements for smoother fueling.(2)The restrictor orifice diameter of the recirculate tube is optimized.By analyzing the influence of the diameter of five different recirculate tube flow-restricting valve orifices on the oil and gas flow at the filler port,seeking the best orifice diameter of the recirculate tube,under which can reduce the load of the canister while satisfying the refueling emission limit.(3)Optimize the throttle orifice diameter of the FLVV valve.By analyzing the influence of five different orifice diameters of the FLVV valve on the oil and gas flow at the filler port,to find the best return pipe orifice diameter,under this diameter,it ensures the requirements for smoother fueling and increases the pressure of the fuel tank when refueling,which helps to reduce the evaporative emissions.