Modeling the fast fill process in natural gas vehicle storage cylinders

摘要

The on-board storage capacity of natural gas vehicles (NGVs) is a critical issue to the wide spread marketing of these alternate fueled vehicles. Underfilling of NGV cylinders, during fast fill (< 5 min.) charging operations, can occur at fueling stations, at ambient temperatures greater than 50{degrees}F or 60{degrees}F. The resulting reduced driving range of the vehicle is a serious obstacle which the gas industry is striving to overcome, without resorting to unnecessarily high fueling station pressures, or by applying extensive overpressurization of the cylinder during the fueling operation. Undercharged storage cylinders are a result of the elevated temperature which occurs in the NGV storage cylinder, due to compression and other processes which have not, to the author`s knowledge, been analyzed and documented to date. This paper presents a model and solution methodology which quantifies the cylinder undercharging phenomena which occurs during rapid (< 5 min.) fueling. The effects of heat transfer from the cylinder gas to its constraining walls and ambient are considered in the model analysis. The ramifications of the results on fueling station and cylinder designs are discussed. Suggestions are made for controlled experimental programs to verify the theoretical results, and for fueling station design studies which could minimize or eliminate cylinder underfilling.