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CSA NGV 4.3-2018 pdf free download
CSA NGV 4.3-2018 pdf free download.Temperature compensation guideline for compressed natural gas vehicle fueling.
Temperature compensation — theory (informative)
In the United States, station designs and installations are commonly covered by NFPA 52 and vehicle containers are verified under CSA NGV 2. In Canada, station designs and installations are commonly covered by CSA 8108 and vehicle containers are verified under CSA 851.
Accurate temperature compensation is essential to safety whenever a compressed natural gas vehicle is fueled, regardless of the type of fueling station. Temperature compensation is a feature of the dispenser or fuel delivery system to automatically limit its dispensed pressure based on sensing ambient or natural gas temperature with the goal being to prevent settled pressure in the vehicle container from exceeding 20 700 kPa (3,000 psi) at 21 ‘C (70 ‘F) for a P30 vehicle system, or 24 800 kPa (3,600 psi) at 21 .C (70 ‘F) for a P36 vehicle system, after the temperature of the gas in the container has equilibrated to 21 C (70 F). Since most CNG dispensers are typically not able to directly measure or be informed of the gas temperature inside the container(s) being tilled, an algorithm within the dispenser control system is typically used to compensate for the temperature rise that occurs (heat of compression) as the gas inside the container is compressed by the fuel flow into the container raising the pressure, and hence, density of the gas as well. Additionally, the temperature of the gas in the container may increase after fueling if the temperature of the environment increases before fuel from the container Is used and pressure is reduced, which may occur with warming outdoor temperatures or when moving a vehicle indoors.
Accurate temperature compensation allows dispensers to safely place a full fuel load on the vehicle during all weather conditions. Anytime the temperature of the gas in a container is higher than 21 ‘C (70 ‘F), the full container pressure (as in the case of a P36 vehicle system) can be greater than the commonly rated 24 800 kPa (3,600 psi) service pressure at 21 ‘C (70 F). This Is allowable as long as the pressure in the container does not exceed 125 percent of service pressure immediately after filling as allowed for by CSA/ANSI NGV 2, and the settled pressure at 21 ‘C (70 ‘F) does not exceed 24 800 kPa (3,600 psi).
While temperature compensation is a critical function for CNG vehicles that regularly operate in hot climates, it is also important, and required in moderate and cold weather, to prevent over- pressurization as the gas in the container becomes hotter than the surrounding environment during fueling. The safety rationale for accurate temperature compensation is especially strong in many areas of the U.S. and Canada where wide temperature swings throughout the day and throughout the year are common.
Temperatures effect on pressure (informative)
The CNG vehicle industry defines a full container (as in the case of a P36 vehicle system) as one in which the gas pressure is 24 800 kPa (3,600 psi) at 21 ‘C (70 ‘F). A dispenser with temperature compensation acts to shut down and stop the filling process when the container’s gas density reaches the fully-filled condition, thereby preventing overfilling.CSA NGV 4.3-2018 pdf free download.
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