Long-Term Behavior of Fuel Vapor Retaining Systems for Pure (E0) and Blended Fuels (E10) Part 2: Regeneration with Nitrogen of 70% Relative Humidity

Abstract

In gasoline-driven vehicles, fuel vapor retaining systems are used to prevent the emission of hydrocarbons from the fuel tank into the atmosphere. In this paper, which is Part 2 of our publication, measurements of regeneration processes of the activated carbon by flushing it with humid nitrogen gas of 70% relative humidity are represented. Using purge air with high relative humidities, representing realistic conditions, it can be observed that water is accumulated in the activated carbon. For ethanol-containing fuel blends, additional accumulation of ethanol in the carbon occurs, decreasing the adsorption capacity of the carbon for standard fuel’s components considerably. State-of-the-art testing procedures use purge air with about 50% relative humidity for the regeneration of the activated carbon filters. As this often does not represent real operation conditions, the working limits of the fuel vapor retaining systems could not be identified up to now. Furthermore, the determination of the butane working capacity as a quality parameter of the fuel vapor retaining systems is also based on the assumption of relatively low air humidity. Consequently, a new quality criterion has to be established.