CHANGES IN REID VAPOR PRESSURE OF GASOLINE IN VEHICLE TANKS AS THE GASOLINE IS USED

There is concern that fuel vapors in the vapor space in passenger car fuel tanks might approach the flammability limit as the fuel weathers. This concern is increased with recently enacted U. S. Environmental Protection Agency RVP regulations and the common use of electric fuel pumps within the fuel tank. The objective of this program was to develop data to assist in evaluating the potential occurrence of a flammable mixture in the vapor space in the fuel tank.

Three gasolines with RVP values of 11, 9, and 7 psig were tested in five different vehicles over a consumer-type driving cycle during the warm months in South Texas. Periodic samples of the fuel in the tank were obtained and the RVP was related to the vehicle type, initial dispensed fuel RVP, and fuel consumption.

Results of this study showed that significant reductions of RVP occurs as the fuel is consumed, and this reduction is greatest with the higher RVP fuels and as the fuel level in the tank approaches empty.