Natural Gas Vehicles

Natural Gas Vehicles, General Information

The vehicle can be equipped with a compressed natural gas (CNG) fuel system, or a liquefied natural gas (LNG) fuel system. CNG is made by compressing natural gas to less than 1% of its volume at standard atmospheric pressure. LNG is created by condensing natural gas into a liquid by cooling it to approximately -259°F (-162°C).

When vaporized at ambient temperatures, natural gas is less dense than air, and it rises and disperses. However, LNG is initially heavier than air due to its cryogenic temperature. When released in large amounts, it may drop or pool on the ground before its temperature rises enough to vaporize. Cold atmospheric conditions may prevent natural gas from dispersing quickly when released in large amounts.

Natural gas is nontoxic, but it can cause asphyxiation if present in very large concentrations.

CNG often contains an odor-producing chemical, while LNG does not have any odor. Users of natural-gas-fueled vehicles should never expect to detect natural gas leaks by scent.

For natural gas to burn, it must first vaporize, then mix with air in the proper proportions (flammable range is 5 to 15% by volume in air), and then be ignited.

A typical natural gas fuel system consists of:

Fuel supply cylinders that store compressed gas at high pressure (CNG), or a tank that stores liquefied gas at an extremely low temperature (LNG).

A vaporizer or heat exchanging device that changes LNG to gaseous form (LNG fuel systems only).

Pressure relief and manual fuel shutoff valves.

A filling connection with a check valve that prevents the gas from flowing back out of the fuel filling line.

High-pressure and low-pressure fuel filters.

A pressure control regulator that reduces the high fuel tank or cylinder pressure to the lower pressure needed for the engine.

A fuel contents gauge that indicates the fuel supply in the tank or cylinders.

Figure 25.1 shows the locations of various components of a CNG installation.

1. Sleeper Leak Sensor (zone 3)
2. Engine Compartment Leak Sensor (zone 2)
3. Leak Detection Control Panel (zone 1) (overhead console)
4. Cylinder Shutoff Valve (back-of-cab box)
5. Shutoff Valve, Right Side Cylinder
6. Shutoff Valve and System Components, Left Side Cylinder
7. Fill Panel

Fig. 25.1, CNG Component Locations

Natural Gas Vehicles, Safety Precautions

Natural gas is highly flammable. Failure to observe the following safety precautions could lead to the ignition of the natural gas, which could cause serious bodily injury or death.

CNG systems should be maintained and inspected exclusively by trained personnel with certifications in accordance with the applicable codes. As with all pressure vessels, CNG storage and fuel delivery systems are inherently dangerous and should be treated as such. Individuals involved in any aspect of CNG fuel system maintenance, emergency response, servicing, or testing must be properly trained and certified. Individuals who are not trained and certified in all aspects concerning CNG fuel delivery systems are not permitted to service, maintain, test, or inspect a system in any way.

Follow these safety precautions when operating or repairing a natural gas vehicle.

Only certified LNG personal can fuel LNG trucks.

Do not start the engine if a natural gas leak is detected.

Transferring fuel is only allowed as long as a non-static hose is used. if a non-approved hose is used, static can build up and ignite the fuel. A correct hose can be obtained through Agility fuel systems.

Do not attempt to cut any fuel supply piping components.

Avoid open flames or sparks near a natural gas vehicle.

Cover eyes and exposed skin when working on a natural gas fuel system or fueling a natural gas vehicle.

Permit no smoking or other ignition sources in, or within thirty feet of, a natural gas vehicle.

Have CO₂fire extinguishers (ABC minimum) located in a highly visible and easily accessible location.

Use Purple-K powder (PKP) or a similar dry powder to extinguish an LNG fire. Do not attempt use water around an LNG fire.

Always purge the fuel lines before performing maintenance or repairs on a natural gas fuel system. Refer to the system manufacturer's service manual or the vehicle's workshop manuals for the proper purging procedure.

Always use a natural gas detector to test the system for leaks, whether an odor is present or not. Routinely inspect the fuel filtering and regulating mechanisms, and the fuel lines. An approved natural gas bubble solution can be used to pinpoint the exact location of leaks. Do not use soap and water. Soap and water can cause premature failure of the O-rings in the system.

Make sure black caps are always on the PRD vent lines to reduce water build up in lines.

Do not store a natural gas vehicle indoors for any extended period of time. Do not bring a natural gas vehicle indoors unless the workshop is equipped with a methane detection and ventilation system.

In Case of Emergency

If a vehicle has sustained damage or a leak has been discovered:

Turn the ignition switch off, and set the parking brake.

Exit the vehicle leaving as many doors and windows open as possible. Get at least 30 feet from the vehicle, and allow it to vent until it is safe to do the steps below.

Remove all ignition sources from the area surrounding the vehicle.

If it is safe to do so, close all fuel shutoff valves.

Use a natural gas detector, or approved NG bubble solution, to identify leaks in the fuel system.

Natural Gas Fuel Tank Filling Procedures

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 25.1 for approximate full cylinder pressures at various temperatures.

CNG Temperature/Pressure Compensation Values
Temperature: °F (°C)	Fill Station Pressure Set Point
Temperature: °F (°C)	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 25.1, CNG Temperature/Pressure Compensation Values

Use the following steps to fuel a CNG vehicle.

Shut down the engine and apply the parking brake.

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.

NOTE: If the fuel system has only back of cab tanks, the fuel fill is located behind the fuel access panel on the lower part of the cabinet, or below the tank cabinet in a separate box. If truck has saddle mount tanks, the fuel panel is located on the back end of the left side tank. Vehicles with back-of-cab cabinets and saddle tanks are have the fuel fill panel on the back end of the left side tank. See Fig. 25.2 for side tanks, or Fig. 25.3 for back-of-cab cabinet mounted fuel panel.

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.

Ensure all fuel cylinder shutoff valves are open. See Fig. 25.2 .

1. High-Pressure Gauge
2. Fuel Cylinder Information Sticker
3. Manual Shutoff Valve
4. Fuel Fill Port

Fig. 25.2, CNG Fuel Cylinder Fill Panel (side tank shown)

1. High Pressure Gauge
2. Low Pressure Gauge
3. Manual Fuel Shutoff Valve
4. Fuel Fill Port and Dust Cap

Fig. 25.3, CNG Under Cabinet Fuel Panel (under cabinet shown)

Ensure the vehicle fuel system main shutoff valve is open.

If equipped, 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.

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.

Switch on the service pump. A slight hissing noise may be heard as the fuel cylinders fill.

10.

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 25.1 for pressure compensation values based on ambient temperatures.

11.

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.

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.

12.

Remove the station dispensing nozzle from the vehicle fill port.

NOTE: Some fill ports and dust caps contain a magnetic start interrupt sensor to prevent a truck from being started and driven away with the fill hose connected. These caps must be installed correctly or vehicle will not start.

13.

Install the dust cap on the vehicle fuel fill port and close the fuel panel access door, if equipped.

LNG Vehicle Fueling

Only certified LNG fueling personnel are authorized to fuel an LNG vehicle.

Natural Gas Detection System

A gas detection system is standard in all Daimler Trucks natural-gas-fueled vehicles. This system has a sensor in the engine compartment, one in the cab, and one in the sleeper (if equipped), all situated in high areas to detect natural gas buildup as a result of leaks.

The AMGaDS III Plus is a natural gas detection system. This device is meant to serve as a supplemental warning only. It is not intended to replace standard safety practices that should be conducted around flammable gases.

IMPORTANT: To function properly, the gas detection system must be powered at all times. The gas detection system is directly powered by the batteries, and can only be powered off by disconnecting the batteries. When servicing a natural-gas-fueled vehicle, disconnect the batteries only when necessary, and do not leave the batteries disconnected for extended periods of time.

The lower flammability limit (LFL) is the smallest amount of the gas that supports a flame when mixed with oxygen and ignited. Zero percent (0%) LFL indicates a gas-free atmosphere. One hundred percent (100%) LFL indicates that gas concentration has reached its lower flammability limit (5% gas in air by volume). The red warning light and audible alarm located in the overhead console activate when a sensor detects gas fumes in concentrations above 50% LFL, and should allow ample time to utilize safety procedures. However, individuals with special needs should review the system with a professional safety engineer.

Alarm Procedure

Before operating the vehicle, the driver must be familiar with the procedures as shown on the interior sticker on the overhead panel (See Fig. 25.4 ) and the exterior sticker on the door (See Fig. 25.5 ).

Fig. 25.4, Interior Warning Sticker

Fig. 25.5, Exterior Warning Sticker

IMPORTANT: If an audible alarm activates, do not operate any electrical switch, including lights. Avoid causing sparks and stay away from arcing switches and equipment. Do not use a telephone, including cellular phones or any types of portable communication or electronic devices that have a battery.

If the vehicle is in motion when the audible alarm activates, bring it to a safe stop, shut down the engine, and exit the vehicle. Do not open the hood.

If outside the vehicle when the audible alarm activates, do not open the cab door or hood.

In the event of an audible alarm, immediately follow these procedures, as allowed by conditions:

Immediately shut off all engines. Extinguish any cigarettes, pilot lights, flames, or other sources of ignition in the area and adjacent areas.

Exit the vehicle leaving as many doors and windows open as possible, and move at least 30 feet away from vehicle. If the vehicle is parked, stay at lease 30 feet away until it is safe to do the following.

Manually close all fuel shutoff valves, including those on the LNG tank or CNG cylinders.

If the vehicle is indoors (as in a service shop), immediately open shop windows and doors to provide extra ventilation to the area. Do not start the engine or any other type of equipment until the gas leak is corrected and the area cleared of natural gas.

Evacuate the area.

After the area is cleared of natural gas and the alarm is no longer active, have the vehicle inspected by a qualified technician.

IMPORTANT: Do not consider the area clear until all alarm indicators are off, and the alarm panel light returns to green.

Sensors

Gas detection sensors are located on the cab overhead console (zone 1), in the engine compartment on the frontwall (zone 2), and in the sleeper, if equipped (zone 3). The sensors are located in high areas, where rising gas vapors will pass by or accumulate. On some vehicles, there is a sensor located under the cab floor (zone 4). Zone 4 is not used on DTNA vehicles.

If the system detects that one of the sensors has been disconnected or has malfunctioned, the sensor fault light for that zone will illuminate. A failed sensor may trigger and lock on an alarm. If this happens have a qualified technician troubleshoot the system and make appropriate repairs.

The sensors are sensitive to all hydrocarbon vapors. An alarm may be triggered by the use of chemicals such as cleaners, paint, polish, lacquer, gasoline, silicone, silicone spray, or other harsh chemicals. The sensors will also detect hydrogen fumes from an overcharged battery. If a sensor sends an alarm, but no gas fumes are present, check for recent use of chemicals or a battery charger.

NOTICE

Silicone-based chemicals and cleaners will permanently disable the sensors. When cleaning the vehicle, cover the sensors with a plastic covering. Keep the sensors covered until the area has been cleared of any cleaning fumes.

Harsh chemicals, including some high alcohol cotenant washer fluids, and extremely high temperatures may damage the sensor.

Puncture of or damage to the seal located inside the sensor housing will significantly shorten the sensor life.

Frequent exposure to high concentrations of gas will accelerate sensor deterioration.

Overhead Console

The overhead console consists of an alarm panel on the right side and the control module on the left side.

The alarm panel has a green light, a red light, a buzzer, and a sensor. See Fig. 25.6 . It is located within view from outside of the vehicle. The large green light is continuously illuminated during normal operating conditions.

Before entering the vehicle, always verify that the green light is illuminated. If the green light is not illuminated, do not enter the vehicle. Complete the alarm procedure previously outlined.

The alarm panel meets the California Highway Patrol Title 13-2008 and NFPA 52 2010 requirements. All drivers and technicians using it should be trained regarding the red and green lights, and the audible warning.

1. Green Light
2. Red Light
3. Sensor
4. Buzzer Alarm
5. Test Button
6. Sensor Fault Indicator Lights
7. Zone Numbers
8. Trace Leak Indicator Lights
9. Significant Leak Indicator Lights
10. Silence Engaged Light
11 Silence Button
12. Relay Reset Button
13. Relay Engaged Light
14. Power Indicator Light

Fig. 25.6, AMGaDS III Overhead Console

The control module, located on the center of the overhead console, contains the status lights and control buttons for the system. The areas that the sensors monitor are defined as Zone 1 (cab), Zone 2 (engine compartment), and Zone 3 (sleeper, if equipped). The control module has lights assigned to each zone that will illuminate if a sensor detects a trace level leak (between 20% and 30% LFL), a significant level leak (above 50% LFL), or if a sensor is disconnected or malfunctioning.

Trace Level: If either sensor detects gas fumes at a concentration greater than 20% to 30% LFL (1% gas in air by volume), the amber light next to the Trace indicator for that zone will flash. There is no buzzer alarm for a trace level detection, and the large green light on the alarm panel will remain illuminated.

Significant Level: If either sensor detects gas fumes at a concentration greater than 50% to 60% LFL (2.5% gas in air by volume), the small red light next to the SIGNIFICANT indicator for that zone will flash. After approximately 15 seconds, the large green light on the alarm panel will switch off, the red light will illuminate, and the buzzer will sound. All alarm indicators will remain on as long as fumes are detected.

Sensor Fault: If the system detects that either of the sensors has been disconnected or has malfunctioned, an amber light next to the Sensor Fault indicator for that zone will illuminate.

The control module also has buttons used to test or reset the the control module after an alarm. Red lights next to each button indicate when they are engaged.

Shutdown Reset: If an alarm has been activated and the Relay Engaged light is illuminated, the Shutdown Reset button will reset the internal relay. Press the Shutdown Reset button only after the gas has cleared, the buzzer has turned off, and the alarm panel light has returned to green.

Push To Silence: If an alarm has been activated, the Push To Silence button will silence the buzzer.

See Table 25.2 for the functions of all lights and buttons on the overhead console.

Testing

Daimler Trucks North America strongly recommends that all operators follow California Code of Regulations (CCR) inspection requirements, regardless of where the vehicle is operated. Per Title 13 CCR § 935 (2), gas detection systems should be tested three times per calendar year at equal intervals. The testing procedure should simulate the same operating environment in which the vehicle is used, with the same gaseous fuel.

Control Module Functions
Item	Display	Function	Action Required
Green Power Light	Illuminated	System is on.	None required.
Green Power Light	Unlit	Detection system is not functioning.	Ensure the batteries are connected and replace any blown fuses. If the gas detection system is still not functioning, replace the system immediately.
SIGNIFICANT Gas Concentration Lights	Red (illuminated)	Dangerous gas concentration detected.	Suspend vehicle operation immediately and follow alarm procedures.
Trace Gas Concentration Lights	Amber (flashing)	Minor gas concentration detected.	Suspend vehicle operation immediately and follow alarm procedures.
Sensor Fault Lights	Off	Sensor is functioning properly.	None required.
Sensor Fault Lights	On	Sensor has malfunctioned.	Replace the sensor immediately.
Shutdown Reset Button	—	Resets the system after an alarm activation.	Press to reset the system only after the gas has cleared, the buzzer has turned off, and the alarm panel light has returned to green.
Relay Engaged Light	On	Relay is engaged and test or alarm is being cleared.	Press the Shutdown Reset button.
Relay Engaged Light	Off	Normal condition.	None required.
Test Button	—	Tests the overhead console operation and circuitry.	Press and hold for one minute to to activate a test of all overhead console components.
Silence Button	—	Silences the alarm buzzer.	Press to silence the alarm buzzer.
Silence Engaged Light	On	Indicates the buzzer is active but silenced.	Suspend vehicle operation immediately and follow alarm procedures.
Silence Engaged Light	Off	Normal condition.	None required.

Table 25.2, Control Module Functions

Test results validating the performance of the gas detection system within the parameters established by the component manufacturer and NFPA 52 2010 should be maintained as a permanent part of the vehicle service records. Use of alcohol, propane, and other harsh liquids or gases are not acceptable methods for testing.

Always test the system and sensors after any component has been replaced, or if the vehicle has been involved in an accident or fire. Ensure that the gas detection system is wired directly to the battery.

It is recommended that the highest level of safety validation be utilized if there are multiple validation requirements in the state or locality where the vehicle is operated or domiciled.

Overhead Console Test

Press and hold the Push To Test button for one minute. The system will proceed with a self-diagnostic test that will include illumination of the Trace and Significant gas concentration lights, and the sensor fault lights. Verify the large red light and buzzer activate, and that all lights illuminate or flash to ensure that all bulbs are operational.

Sensor Test

The gas detection system sensors must be tested using qualified test gas, which can be purchased as part of a test kit. Testing with alcohol or heavy gases such as butane or propane does not satisfy CCR § 935 (2) or NFPA 52 regulations.

Expose each sensor to qualified test gas for at least 30 seconds. The system will proceed through the alarm procedure consistent with a significant leak and the buzzer will sound after approximately 15 seconds. If a sensor fails to respond after exposure to the test gas, replace the sensor.

Natural Gas Engine Starting

NOTE: Before starting the engine, read Chapter 4 for detailed information on how to read the instruments and Chapter 5 for detailed information on how to operate the controls. Read the operating instructions in the engine manufacturer's operation manual before starting the engine.

Before engine start-up, complete the engine pretrip and post-trip inspections and maintenance procedures in Chapter 21 .

Ensure the fuel shutoff valve is open.

Set the parking brake.

Ensure that the transmission shift control is in Neutral (N), Park (P), or the Park Brake (PB) position.

Without starting the engine, turn the ignition switch to the ON position ( Fig. 25.7 ). The electronic gauges on the instrumentation control unit (ICU) will complete a full sweep of their dials, the warning and indicator lights will illuminate, and the buzzer will sound for three seconds.

Fig. 25.7, Ignition Switch Positions

Turn the ignition switch to the START position.

Press down on the clutch pedal, if equipped, but do not press down on the accelerator pedal.

Release the key the moment the engine starts.

Bring the engine up to operating speed gradually as it warms up and develops stable oil pressure. If the vehicle has not been operated previously in a 24-hour period, allow the vehicle to idle for five minutes.

NOTICE

Do not rev the engine if the oil pressure gauge indicates no oil pressure. Shut down the engine within approximately ten seconds to avoid engine damage.

Check the oil pressure gauge for any drop in lubricating oil pressure or mechanical malfunction in the lubricating oil system.

Major Repairs and Replacement of Natural Gas Components

IMPORTANT: All repairs to natural gas system and components must be performed by certified technicians.

If a natural-gas-fueled vehicle is involved in an accident, remove the fuel tank or cylinders from service and have them inspected by a qualified technician. Replace any leaking or damaged fuel tanks/cylinders and fuel lines; repair or replace leaking or damaged fittings. Install parts and components in accordance with the manufacturer's instructions.