Usable fuel storage capacity
Usable fuel storage capacity means the amount of fuel that is available to a vehicle starting from a complete refueling event until the vehicle stops (or until driveability deteriorates to the point that further driving is unlikely or impractical). For liquid fuels, the usable fuel storage capacity represents the difference between the total fuel volume after a complete refueling event and the fuel volume that remains in the fuel tank after the vehicle runs out of fuel. For other fuels, use good engineering judgment to determine the full and empty conditions consistent with typical consumer behavior. For example, for natural gas vehicles, the full condition would be the point at which a typical operator would stop refueling based on the increasing system pressures, which are determined by temperature effects related to the refueling process; this does not necessarily represent the maximum amount of fuel the tank can hold under equilibrium conditions. The empty condition would be the point at which fuel pressure drops enough that the engine is unable to maintain stable air-fuel ratios for acceptable continued operation.
40 CFR § 600.002
The following definitions apply throughout this part: