Be Prepared to Service Natural Gas Vehicles

Increase your awareness of this growing segment of fleet vehicles so you can meet your customers’ service needs.

Natural gas typically costs 30 percent to 60 percent less than diesel or gasoline.

Natural gas typically costs 30 percent to 60 percent less than diesel or gasoline.

Natural gas vehicles (NGVs) provide many benefits and have become a popular choice for fleets. NGVs are safe, economical, domestic, abundant and environmentally sound.

The use of NGVs has increased significantly in North America during the past 10 years. First, natural gas typically costs 30 percent to 60 percent less than diesel or gasoline. Second, natural gas produces clean exhaust emissions as opposed to gasoline and diesel exhaust. Finally, natural gas is a domestic fuel produced right here in the United States, reducing America’s dependence on foreign oil as well as impacting our trade deficit.

According to the International Association of Natural Gas Vehicles, there are more than 20 million NGVs worldwide. In the United States, the NGV count is approaching 200,000. The list of commercial fleets switching to NGVs is impressive and growing, and includes AT&T, United Parcel Service (UPS), Waste Manage­ment, Verizon and Ryder to name just a few.

As more NGVs are on the road, maintenance technicians who will service and repair these vehicles must be adequately trained on the properties and characteristics of the fuel itself, as well as the fuel system. Although NGVs have an excellent safety record, they are different from gasoline and diesel vehicles, and require different safety and service procedures.

What is natural gas and how does it work in vehicles?

Paul Pate, NGVi training manager, demonstrates how to use a depth gauge to assess damage on a CNG cylinder.

Paul Pate, NGVi training manager, demonstrates how to use a depth gauge to assess damage on a CNG cylinder.

Natural gas is formed from decaying organic matter deep below the earth’s surface. It is comprised of more than 90 percent methane with smaller amounts of ethane, propane, butane, carbon dioxide and other trace gases. It is odorless, colorless and tasteless. One of the main differences between natural gas and liquid fuels is that it is lighter than air. It rises and dissipates in the air when leaked, instead of pooling on the ground.

Natural gas as a transportation fuel is available in two forms: gaseous as compressed natural gas (CNG) and liquefied as liquefied natural gas (LNG). CNG is highly compressed and stored in high-pressure storage cylinders. It’s used extensively in all classes of vehicles including sedans, pickup trucks, medium- and heavy-duty trucks and buses. LNG is natural gas that has been liquefied by reducing its temperature to -260 degrees F at atmospheric pressure. It is mainly used as fuel in heavy-duty vehicle applications. NGVs are powered by the same gas that is used for home-heating, water-heating or cooking. All light-duty and many medium-duty NGVs use spark-ignited internal combustion engines that are either dedicated (run exclusively on natural gas), or bi-fuel (operate on either natural gas or gasoline). Most heavy-duty NGVs also use spark ignition. CNG vehicles require special onboard fuel storage cylinders, available in many sizes to meet various fuel storage needs. Today’s CNG systems operate at 3,600 pounds per square inch (psi).

Are NGVs safe?

Servicing NGVs requires technicians to be aware of safety procedures and repair practices that are unique to these vehicles.

Servicing NGVs requires technicians to be aware of safety procedures and repair practices that are unique to these vehicles.

Compared to gasoline and diesel vehicles, NGVs are among the safest vehicles in North America. According to a survey conducted by NGVAmerica, based on 8,331, NGVs that collectively traveled 178.3 million miles, the NGV vehicle injury rate was 37 percent lower than the gasoline fleet vehicle rate. Additionally, the collision rate for NGVs was 31 percent lower than the rate for gasoline fleet vehicles.

One of the main reasons NGVs have resulted in fewer passenger injuries and deaths is that fires are less likely to occur in collisions involving NGVs than those involving liquid fuels. This is due to the unique properties of natural gas and the integrity of the natural gas vehicle fuel delivery system.

Because CNG is lighter than air and will not pool on the ground when leaked or spilled, it dissipates rapidly into the atmosphere, reducing the likelihood of ignition. The ignition temperature of natural gas is approximately 1,080 F compared to 600 F for gasoline, which makes it more difficult to ignite. Natural gas has a narrow flammability range, and must be mixed with air in just the right proportion before it can ignite. It is only flammable when the fuel concentration in air is roughly between 5 percent and 15 percent. If the mixture is either more or less than those percentages, natural gas simply will not burn.

Another reason compressed natural gas vehicles are so safe is because unlike the gasoline or diesel fuel tanks, CNG is stored inside high-pressure cylinders manufactured to extremely rigorous federal standards, and made from much sturdier materials. According to these standards, all CNG fuel storage cylinders must be manufactured to withstand 2.25 times their nominal fill pressure, which is 3,600 psi at 70 F. This means that even a standard cylinder has a minimum burst pressure of 8,100 psi, which is far above the fuel delivery pressures of CNG fueling stations.

Proper CNG fuel system inspection requires visual inspection of the entire fuel system, not just cylinders.

Proper CNG fuel system inspection requires visual inspection of the entire fuel system, not just cylinders.

Also, NGV fuel systems are installed according to the National Fire Protection Association standard, NFPA-52: Vehicular Gaseous Fuel Systems Code. Among other things, this standard covers the types of onboard fuel storage cylinders installed on the vehicle as well as the safety factors required for all of the tubing and components that make up the high- and low-pressure components of the fuel system.

CNG cylinders are required to be produced and certified in accordance with National Highway Traffic Safety Adminis­tration (NHTSA) regulations. NHTSA requires that every CNG fuel system be inspected by a properly trained and qualified technician every 36 months or 36,000 miles, whichever comes first, and following any fire or vehicle collision exceeding 5 miles per hour.

Finally, all CNG cylinders have pressure-relief devices referred to as “PRDs,” which are designed to vent gas before any cylinder ruptures.

Why the need for NGV training?

The unique characteristics of natural gas, the rigorous safety standards, and confirmed solid safety record lead to the conclusion that NGVs are the safest vehicles on the road. Yet, it is important to remember that every fuel has hazards. Although liquid fuels such as gasoline or diesel are no exception, technicians have learned how to safely maintain and repair vehicles that operate on those fuels. The same is true for natural gas: to safely and correctly maintain NGVs, learning about the fuel and the vehicle technology first is crucial.

Because of their daily contact with natural gas vehicle systems and storage, maintenance technicians must have full knowledge of how these vehicles work. It is also imperative that they understand how to safely perform maintenance and repair of the entire natural gas system, including the high-pressure side, the unique components in the engine’s fuel and ignition system and the emissions system.

Servicing NGVs requires technicians to be aware of safety procedures and repair practices that are unique to these vehicles. Failure to understand how to diagnose technical problems with NGVs can reduce the safe operation of the vehicle and increase the risk of accident both in the shop and on the road.

In this new era when NGVs are becoming more and more popular, adequate training for vehicle technicians on the unique fuel systems and operating characteristics for NGVs is a must. For more information about NGV training, visit www.ngvi.com.