Prediction of the Quantity of Vapor Displaced into the Canister during Automobile Refueling

Abstract

The design of efficient fuel systems requires the prediction of the air entrainment flow rate from the atmosphere into the fuel tank and clarification of the changes in the state of the mixed gas consisting of air and fuel evaporative gas (vapor) within the fuel tank. The air entrainment flow rate was predicted in a previous study. This study focused on the vapor newly generated by the entrained air and developed a formula to predict the corresponding quantity of vapor displaced into a canister during refueling in the initial design phase of a fuel tank system for automobiles. The displaced mixed gas comprises the gas pushed out by the supplied fuel and entrained air and that pushed out by the vapor generated by the entrained air. The state changes of the mixed gas within the fuel tank and its displacement process were modeled. Subsequently, the fundamental formula for the vapor displacement quantity was derived by applying the gas state equation and law of partial pressure. It was further developed to consider the effect of the recirculation line, which reduces the air entrainment flow rate, and changes in the physical properties of the vapor owing to temperature variations in the residual fuel. Finally, the vapor displacement quantity was calculated for actual vehicles by using the derived prediction formula and the results were compared with measurement results. The predictions showed good agreement with the measured values, confirming the applicability of the formula to the prediction of the quantity of vapor displacement.