Computational Simulation of Fuel Shut-off During Refueling

A state-of-the-art, characteristic-based upwind, interface capturing multiphase gas-liquid numerical formulation has been utilized to shed insight into the complex physics that characterize premature fuel nozzle shut-off during a typical refueling event. Interactions amongst several sub-processes are entailed which occur over widely different length and time scales. Detailed numerical simulations indicated that the physics is governed by:

1. a)
   transient flow in vent and fill pipe during fuel nozzle shut-off;
2. b)
   multiphase interactions at fuel/air/vapor interfaces and entrained air bubbles in fuel;
3. c)
   formation of boundary layers in vent pipe and boundary layer displacement effects on wave propagation;
4. d)
   formation of “vena contracta” at entrance to vent pipe; and,
5. e)
   strong dependence of acoustic speed upon level of dissolved gases.

The simulations indicate air/vapor is trapped in the vapor dome and is compressed by rising fuel as the fuel rises in the tank and seals the entrance to the vent pipe. Pressure increase as the air/vapor is compressed, forces fuel into the vent pipe and initiates a standing wave in the fill pipe. Entrained fuel is accelerated up the vent pipe, leading to compression waves ahead of it. These waves coalesce to produce a pressure rise at the vent pipe exit. Shut-off occurs when either the fuel entrained in the vent pipe of fuel displaced in the fill tube by the standing wave impinges on the fuel dispenser sensing port.