Liquefied Natural Gas (LNG) is a cryogenic hydrocarbon liquid used as a transportation fuel and by its very nature as a cryogen changes in composition as it is transferred from the LNG production facility to fueling station and then to the vehicles fuel storage system. At present there are no guidelines that can help the industry manage the change in composition of LNG so that the end user receives a fuel that meets the specifications required for proper operation of the vehicle. The time sensitive nature of LNG is unique in the transportation industry and SAE J1616 is needed to provide a methodology to determine LNG useable lifetime.
The only agency in North America that provides a minimum composition level of natural gas vehicles is CARB. This regulation is a Compressed Natural Gas standard and the reference to water, CO2, sulfur, and lubricates which do not apply to LNG, the hydrocarbon components of natural gas do apply. The minimum level of methane and max levels of ethane, propane, butane, and nitrogen, provide important references for engine manufactures. These minimum and maximum levels of constituents in the fuel composition are crucial in the engine design.
When using LNG as a vehicle fuel, it is stored at some combination of cryogenic temperature and relatively low pressure. It is not uncommon for the fuel to go through several transfers as it is moved from production site storage, to a transport tank, transport tank to a local refueling station tank and then into the vehicle tank. During each transfer, and during periods of storage, heat transfers into the fuel, which if left to evaporate its composition will change.
In order to provide fuel to the engine that meets the minimum hydrocarbons requirement of CARB, the LNG vaporization must be controlled and LNG inventories must be managed. Therefore, this document includes the information required to calculate a “dispense by” date for LNG. With a fixed set of assumptions on evaporation rates, a known initial fuel composition, the future fuel composition can be calculated. While this document is based on CARB requirements, the same methodology can be used for different fuel composition targets were required.
The purpose of this document is to provide the fixed assumption and calculation so that LNG producers can provide the require product information data which fuel composition and it’s “dispense by” dates can be calculated. The “dispense by” date provides users the date when the fuel no longer meets the minimum hydrocarbon requirement of CARB, which may compromise the engine emission performance, warranty or reliability. The “dispense by” date provides users the time/date when the fuel meets the minimum hydrocarbon requirement of CARB. Beyond this date/time the fuel composition may compromise engine emission performance, warranty or reliability.
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