CNG Vehicle Fueling
CNG is moved from the fuel station storage tanks to the vehicle cylinders through a metered dispenser. During fueling, as pressure inside of the vehicle cylinders increases, so does the temperature. The dispenser shuts off when it determines the CNG cylinders are full.
CNG fuel cylinders cannot be filled to their full capacity of 3600 psi (24 800 kPa) in cooler weather. Since temperature change causes gas to expand and contract, less pressure in the cylinders on a cold day is equal to the same amount of gas at a higher pressure on a warm day. The fuel station dispenser has a temperature-pressure compensating device, which accounts for ambient temperature during fueling. See Table. for approximate full cylinder pressures at various temperatures.
Table 1, CNG Temperature/Pressure Compensation Values
|
CNG Temperature/Pressure Compensation Values |
||
|
Temperature: °F (°C) |
Fill Station Pressure Set Point |
|
|
3000 psi (20 684 kPa) Set Point |
3600 psi (24 821 kPa) Set Point |
|
|
100 (37.8) |
3415 (23 546) |
4086 (28 172) |
|
90 (32.2) |
3276 (22 587) |
3909 (26 952) |
|
80 (26.7) |
3138 (21 636) |
3754 (25 883) |
|
70 (21.1) |
3000 (20 684) |
3600 (24 821) |
|
60 (15.6) |
2861 (19 726) |
3445 (23 752) |
|
50 (10) |
2723 (18 774) |
3288 (22 670) |
|
40 (4.4) |
2584 (17 816) |
3131 (21 587) |
|
30 (-1.1) |
2446 (16 865) |
2973 (20 498) |
|
20 (-6.7) |
2307 (15 906) |
2814 (19 402) |
|
10 (-12.2) |
2169 (14 955) |
2655 (18 306) |
|
0 (-17.8) |
2031 (14 003) |
2495 (17 202) |
|
-10 (-23.3) |
1893 (13 052) |
2336 (16 106) |
|
-20 (-28.9) |
1755 (12 100) |
2180 (15 031) |
|
-30 (34.4) |
1616 (11 142) |
2024 (13 955) |
|
-40 (-40) |
1477 (10 184) |
1868 (12 879) |
Table 1, CNG Temperature/Pressure Compensation Values
Use the following steps to fuel a CNG vehicle.
- Shut down the engine and apply the parking brake.
- Ensure all fuel cylinder shutoff valves are open. See Fig..
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Fuel Cylinder Storage Box
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Fuel Cylinder Shutoff Valves (qty 5)
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High-Pressure Gauge
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Low-Pressure Gauge
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Fuel Fill Port
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Dust Cap
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Manual Shutoff Valve
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Fuel Panel Access Door
Fig. 1, CNG Fuel Cylinder Storage Box (5-cylinder system shown)
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- Ensure the vehicle fuel system main shutoff valve is open.
- Open the CNG fuel panel access door and remove the dust cap from the vehicle fuel fill port.
- Ensure the O-ring is present inside the fuel fill port. If the O-ring has been dislodged or is missing, the station dispensing nozzle will not connect securely to the fill port.
- Turn the selector knob on the service pump to the VENT position, if equipped.
- Connect the quick coupling on the dispensing nozzle securely to the vehicle fuel fill port.
- Turn the selector knob on the service pump to the FILL position, if equipped.
- Switch on the service pump. A slight hissing noise may be heard as the fuel cylinders fill.
- Watch the pressure gauge on the service pump. When the gauge reads approximately 3600 psi (24 800 kPa), or when the fill pressure stops climbing, the CNG cylinders are full. The service pump will shut itself down automatically. See Table. for pressure compensation values based on ambient temperatures.
- Move the selector knob on the service pump to the VENT position, if equipped. A short hiss will be heard as a small amount of natural gas is vented into the hose.
- Remove the station dispensing nozzle from the vehicle fill port.
- Install the dust cap on the vehicle fuel fill port and close the fuel panel access door.
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.
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.
Important: If at any time the service pump or vehicle begins to vent CNG uncontrollably, notify a station attendant or activate the service station emergency shut-off switch to cease the flow of CNG.
Warning: Do not attempt to remove the fill station nozzle from the tank fill fitting until venting of pressure is noted. If no venting occurs, ask for assistance from the station attendant. Removing an unvented coupling could result in an uncontrolled hose, which could lead to property damage or personal injury.