Why Compressed Natural Gas?
Gasoline powered vehicles produce oxides of nitrogen (NOx) that when combined with volatile organic compounds(V0C's ) which are produced by trees naturally, will react with sunlight in the lower atmosphere to form ozone, a primary constituent of smog. CNG powered vehicles are clean - they emit 85% less NOx, 70% less reactive hydrocarbons, and 74% less carbon monoxide than similar gasoline powered vehicles. The use of CNG-fueled vehicles significantly reduces emissions of ozone precursors. In 1994, about 55,000 vehicles in the United States ran on compressed natural gas (CNG).
How does CNG work?
The common CNG vehicle fuels at pressures of either 3,000 or 3,600 pounds per square inch (psi) and stores its fuel in one or more cylinders located under the body or in the trunk of the vehicle. The filling valve is located in the same general area as that of the gasoline refueling receptacle. When the CNG leaves the storage tank, it travels through high-pressure fuel lines into one or more pressure regulators, where it is reduced to atmospheric pressure. Unlike gasoline, which must be vaporized before ignition, CNG is already gaseous when it enters the combustion chamber. When the intake valve opens, the gas enters the combustion chamber, where it is ignited to power the vehicle.
Advantages of using CNG
Current prices are between 70 and 99 cents per gasoline gallon equivalent.
It is safer to use than gasoline because it is lighter than air and if a leak occurs, it will dissipate rapidly into the atmosphere. Therefore, CNG poses no direct threat to land or water contamination in the case of a leak.
Natural gas has an ignition temperature of about 1200 degrees Fahrenheit. This is about 600 degrees higher than gasoline. CNG is flammable only in concentrations from 5.3 to 15 percent in air, so if a leak does occur, it is less likely to ignite than gasoline unless the leak happens in a confined space with no ventilation. Therefore, in terms of fires, CNG vehicles may be considered safer than gasoline vehicles.
When gasoline is injected into the combustion cylinder, it tends to wash away the lubricant on the cylinder wall thus causing greater friction between the moving parts. In a CNG vehicle, the fuel enters the combustion cylinder as a gas and has little effect on the lubricant on the cylinder walls, thus extending the life of the engine.
Engine maintenance cost can be reduced by extending time between oil changes because the particulate materials that are produced during the combustion cycle of gasoline engines and cause the engine oil to get dirty are not present in the CNG engine.
N.C. Division of Air Quality • Mailing Address: 1641 Mail Service Center, Raleigh, NC 27699-1641
Physical Address: 217 West Jones Street, Raleigh, NC 27603 • Phone: (919) 707-8400 Fax (919) 707-0718