LNG Vehicle Fueling

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The LNG fuel tank is designed to be filled from any LNG fuel source that has a 100 micron or finer fuel filter and a fuel delivery pressure between 120 and 225 psi (827 and 1551 kPa).

The LNG fuel tank is designed to be top-filled through a single hose with no vent return. As cold LNG is sprayed into the vapor space of the tank, the cold liquid condenses the vapor and creates space for itself inside the tank, eliminating any need to vent during the filling process.

The LNG tank is equipped with a small internal ullage tank for vapor space, which allows for fuel expansion and increases vehicle standby time. When an LNG tank is full, fuel can continue to flow into the ullage tank. However, if the ullage tank is completely filled during fueling, standby time will be reduced to zero and the primary relief valve will open almost immediately after fueling, allowing excess LNG vapor to escape. If fueling is stopped when the ullage tank is empty (i.e., the fuel tank has sufficient vapor space to accommodate fuel expansion due to temperature increase), the vehicle will have approximately one week of standby time before venting will occur.

Use the following steps to fuel an LNG vehicle.

  1. Shut down the engine and apply the parking brake.

    2. Warning: Liquefied natural gas is a cryogenic liquid stored at approximately -259°F (-162°C). Cryogenic burns can be caused by coming into contact with the pressurized liquid stream, or by coming into contact with fuel system components that have been cooled to cryogenic temperatures. Always wear gloves and a face shield, and cover exposed skin when fueling.

    Important: Close all windows and doors during the fueling process. Keeping windows and doors closed allows for easier leak detection inside the cab after fueling.

  2. Remove the fuel fill fitting dust cap. See Fig..

    1. Fuel Fill Fitting

    2. Fuel Outlet Line

    3. Primary Relief Vent Line

    4. Fill Vent Fitting

    5. Shroud Cover

    6. Shroud Cover Latches

    Fig. 1, LNG Fuel Tank

  3. Using compressed air, remove any dirt, debris, or water that may have collected in the fuel fill fitting and the station dispensing nozzle. Contaminants in the fuel system can cause drivability problems.

    4. Warning: Natural gas fuel tanks, lines, and valves are always pressurized. Always observe safety precautions. Failure to do so could lead to loss of control over a filling hose or to ignition of the natural gas, which could cause serious bodily injury, death, or severe property damage.

  4. Connect the station fueling nozzle to the tank fuel fill fitting.
  5. Connect an electrical ground clamp and cable to the fuel tank.

    Important: An LNG tank which is first installed, or is on a vehicle that has not been operated in approximately ten days, is considered to be a hot tank. When fueling a hot tank, LNG entering the tank will immediately vaporize, causing tank pressure to spike above 250 psi (1724 kPa) and automatically shutting down the station fuel pump. To prevent the pump from shutting down, connect a vent line to the fill vent fitting on the LNG tank to capture escaping vapor, then open the shroud cover and open the vapor shutoff valve ( see Fig. , Item 2).

      1. Important: When fueling a hot tank, initially put 5 to 10 gallons (19 to 37 liters) of LNG in the tank and manually stop the fueling process. Drive the vehicle for 15 to 20 minutes to cool the tank and reduce tank pressure, then continue fueling the tank to full.

    1. Open the station's fill valve, if equipped, and start fueling. Monitor the flow or line pressure as filling progresses. When filling begins, line pressure will spike quickly until the vehicle tank cools down. The flow and pressure will then remain stable during the remainder of the filling procedure.

      1. Pressure Control Regulator

      2. Vapor Shutoff Valve

      3. Fuel Fill Hose

      4. Secondary Relief Valve (red cap)

      5. Fuel Fill Fitting

      6. Fuel Level Sender Box

      7. Primary Relief Valve

      8. Tank Pressure Gauge

      9. Fill Vent Fitting

      10. Excess Flow Valve

      11. Fuel Shutoff Valve (liquid)

      12. Fill Check Valve

      Fig. 2, LNG Fuel Tank Plumbing Components

    2. When the tank is full, the line pressure will rapidly spike and the flow rate will fall. When a pressure rise or flow rate drop is observed, close the station's fill valve, if equipped.

      3. Note: Do not over-fill an LNG tank. If the ullage tank is completely filled during fueling, tank standby time will be reduced to zero and the primary relief valve will open almost immediately after fueling.

    3. Disconnect the station hose from the tank fuel fill fitting.
    4. Disconnect the electrical ground clamp and cable from the fuel tank.
    5. Install the dust cap on the tank fuel fill fitting.
    Note:
    Parent topic: Natural Gas Fuel Tank Filling Procedures
    Document Number: 0000117824
    Manual Publication Date: 2025-02-11
    Topic Publication Date: 2024-05-09