CFD analyses of two-phase flow with vapor emission for automotive refueling system.

摘要

Automotive refueling is gaining greater importance because fuel vapors released during refueling are believed to increase ozone levels in urban areas. As a step towards On-Board Refueling Vapor Recovery (ORVR) designs, vapor generation and transport during refueling needs to be understood to develop recovery techniques. The objective of the present study is to understand the fluid flow inside the automotive gas tank filler pipe using commercially available Computational Fluid Dynamics (CFD) software. An estimation technique of air entrainment and vapor generation during refueling was established. The phenomena of well-back, the process of fuel flooding the filler pipe and flowing backwards at the filler pipe mouth, and the pressure transients inside the tank leading to premature nozzle shut-off were examined.; As part of experimental effort for flow visualization in automotive fuel filler pipe, dyes and smoke were introduced in water and air, respectively, for various flowrates. Video and still cameras were used for imaging. Features of the flow such as laminar-to-turbulent transition, progressive development of strong swirl along filler pipe axis, air entrainment and mixing with the liquid were observed in the experiments.; CFD simulations were conducted to quantitatively determine air entrainment and vapor emission during refueling by using Volume of Fluid (VOF) multiphase model. Extensive tests were conducted to evaluate the turbulence closure schemes for stratified free-surface multiphase flow. The simulation results were then compared with the available experimental results from open literature.; To determine evaporation rate during refueling, an algorithm was developed to simulate mass-transfer in two-phase systems in conjunction with VOF method. The algorithm was further enhanced for complex multi-component fluids like gasoline and diesel. This evaporative model was introduced in the CFD software and vapor emission during refueling was estimated.