CNG 101 answers some of the basic questions about natural gas as a transportation fuel.
What is natural gas?
Natural gas primarily consists of methane (around 90%), with small amounts of ethane, propane and other gases. Methane is a simple gas molecule made up of one atom of carbon and four of hydrogen (CH4). It is lighter than air and burns almost completely, with by-products of combustion being carbon dioxide and water.
Why use natural gas as a fuel?
- Engine, urban, and greenhouse gas emissions are inherently lower than gasoline or diesel engines emissions.
- Natural gas decreases our reliance on foreign fuel sources (more 98% of the natural gas used in the United States comes from North America)
- Natural gas costs less per energy unit than gasoline or diesel.
How do you use natural gas as a transportation fuel?
Compressed Natural Gas or CNG is the most common form of natural gas used in vehicles. Natural gas is stored on the vehicles by being compressed to 3600 psi.
Who provides the natural gas?
The local utility (Oklahoma Natural Gas) provides the natural gas, which is piped to the location where the gas will be compressed before being dispensed into the vehicles.
What kinds of vehicles use natural gas?
Natural gas vehicles are available in all classes of gasoline and diesel vehicles.
Are your CNG conversions dedicated or bi-fuel vehicles?
We provide vehicles that are bi-fuel, meaning they can run on either gasoline or natural gas.
How do you fuel a natural gas vehicle?
It is similar to the way you fuel any car or truck. The dispenser looks about the same, but the nozzle is different. We can easily educate you on how to fill a CNG vehicle. Because natural gas is under pressure, the storage systems must be designed so that no fuel escapes when the vehicle is being fueled. Natural gas nozzles lock onto the receptacles, and form a leak-free seal, similar to the coupling on an air compressor nozzle. The receptacles are designed so that when the nozzle is removed the gas is prevented from escaping.
How is the fuel stored in the vehicle?
Most NGVs operate on compressed natural gas so the fuel takes up less space. CNG is stored on board vehicles under high-pressure (3,600+ pounds per square inch) in tube-shaped cylinders that are attached to the rear, top or undercarriage of the vehicle. The cylinders meet very rigorous safety standards. They are made of high-strength materials designed to withstand impact, puncture and, in the case of fire, their pressure relief devices (PRDs) provide a controlled venting of the gas rather than letting the pressure build up in the tank.
Natural gas may also be stored on-board in the form of liquefied natural gas or LNG. To become LNG, natural gas must be cooled to –260 degrees Fahrenheit. The biggest advantage of LNG over CNG is space requirements. LNG requires only 30 percent of the space of CNG to store the same amount of energy. In order to keep the LNG cold, LNG is stored on-board vehicles in thermal storage tanks.
How long does it take to fuel a natural gas vehicle?
There are basically two types of fueling equipment for CNG vehicles: fast-fill and time-fill. In fast-fill, the combination of a large compressor coupled with a high-pressure storage tank system, called a cascade, fills the tank in about the same amount of time it takes to fuel a comparable gasoline or diesel vehicle.
A time-fill system does not have a storage system and has a much smaller, and less expensive compressor. It typically refuels CNG vehicles overnight at a rate of about one gallon per hour. Time fill works for vehicles that remain idle overnight, such as refuse trucks and school buses.
There are also home refueling options for individuals that own a CNG powered vehicle and are looking for the convenience of being able to fuel at home. The units connect to a residential gas line and typically hang on a garage wall. These systems can fuel a single vehicle at the rate of slightly more than one gallon per hour.
Are natural gas vehicles safe?
Absolutely! Compressed natural gas is stored on board vehicles in tanks that meet the most stringent safety standards in the world. Some of the tests that these tanks must pass are the drop test, the bonfire test and gunshot test.