Development and Validation of a CFD Simulation to Model Transient Flow Behavior in Automotive Refueling Systems

Government regulations restrict the evaporative emissions during refueling to 0.20 grams per gallon of dispensed fuel. This requires virtually all of the vapors generated and displaced while refueling to be stored onboard the vehicle. The refueling phenomenon of spitback and early-clickoff are also important considerations in designing refueling systems. Spitback is fuel bursting past the nozzle and into the environment and early-clickoff is the pump shutoff mechanism being triggered before the tank is full. Development of a new refueling system design is required for each vehicle as packaging requirements change. Each new design (or redesign) must be prototyped and tested to ensure government regulations and customer satisfaction criteria are satisfied. Often designs need multiple iterations, costing money and time in prototype-based validation procedures. To conserve resources, it is desired to create a Computational Fluid Dynamics (CFD) tool to assist in design validation. A model that simulates the entire refueling system will be discussed here. This includes boundary conditions of the pump nozzle, the vapor return line, and an orifice that mimics the pressure drop across an activated carbon canister. Experiments are performed both to characterize boundary conditions for the CFD and to validate results from the model. Fuel tank pressure data gathered from both simulation and experiments shows good correlation. Steady state pressures of each method trend the same and have similar magnitude at multiple fuel flow rates. These results show the capability of the refueling system model as a development tool.