The natural gas vehicle industry struggles with safely and accurately achieving a full fill in a natural gas vehicle when using compressed natural gas dispensers. The technical challenges involved when filling an onboard storage tank with compressed natural gas can result in underfilling, or the inability to use 100 percent of the maximum tank capacity. Major fleets and industry experts cite underfilling of about 20 to 25 percent using current dispenser technology. Underfilling directly affects the operational cost and range of natural gas vehicles. Consistently achieving full fills also improves safety with compressed natural gas fueling by reducing the chances for overfilling and lowers costs by reducing the volume of storage needed onboard the vehicle. The causes preventing current natural gas vehicles from receiving a full fill include 1) inaccuracies in determining when a vehicle has reached a full fill condition, 2) uncertainty about the gas composition, and 3) heat generated when the gas is compressed.
This California Energy Commission project led by the Gas Technology Institute addresses these issues by developing an advanced full-fill algorithm and investigating various gas precooling technologies. The algorithm leverages communication between the vehicle and dispenser to measure the real-time temperature and pressure on the vehicle and then uses that information while considering variations in gas composition to deliver a full fill safely and accurately. The investigation of precooling technologies provides insight into viable methods for removing energy from the compressed natural gas before fueling to counteract heat of compression, and guarantee a full fill at higher ambient temperatures. Recommended precooling technologies include chillers and the development of a suitable expander design for enabling full fills.
