Natural Gas is a hydrocarbon mixture predominantly composed of methane (CH4). Lesser components of this gaseous mixture include ethane, propane, butane, nitrogen, helium, carbon dioxide, hydrogen sulfide and water vapor, which are removed prior to use. It is a nontoxic, non-corrosive, non carcinogenic fuel with significantly less harmful tailpipe emissions.
A majority of natural gas is a fossil fuel that is drawn from wells or extracted in conjunction with crude oil production. Natural gas can also be mined from subsurface porous rock reservoirs through extraction processes, such as hydraulic fracturing. Natural gas from renewable sources (biogas) is an emerging fuel, produced from decaying organic materials (waste from plants, landfills, wastewater, and livestock).
Natural Gas is readily available to end-users through a utility pipeline, and exploration in the United States has led to the discovery of significant new natural gas reserves. In recent years, 80% to 90% of the natural gas used in the United States was domestically produced.
Commercial fleets have been utilizing natural gas for the last 50 years. Its low cost and stable pricing made it attractive during the 1970 Oil Embargo, and those benefits continue today. There are approximately 14.8 million natural gas vehicles (NGV) worldwide – about 112,000 in the U.S. This number continues to rise as original equipment manufacturers (OEM) – i.e. GM, Honda, etc – are producing more CNG vehicles (see below for a model list). NGV power, acceleration, fuel economy, range and cruise speed are comparable to gasoline or diesel vehicles.
Compressed Natural Gas (CNG):
CNG is produced by compressing natural gas to 1% of its volume at standard atmospheric pressure. It is stored and distributed in seal systems at pressures of 2900 to 3600 psi. CNG generally costs 20%-60% less than traditional petroleum fuels, and a growing number of vehicles that run on CNG are becoming available on the commercial market. Additionally, several models have EPA certified conversion kits.
There are two refueling systems for CNG vehicles: fast/quick-fill and time-fill. Quick-fill is equivalent to the time it takes to fill with gasoline, but pumps are more costly to install. Time-fill requires the vehicle to return to a central hub and be parked for several hours (i.e. overnight). This fueling system is less capital intensive and does ultimately put more fuel into the tank – making it ideal for high-mileage, centrally-fueled fleets that operate within a limited area. Refueling FAQ
Liquefied Natural Gas (LNG):
LNG is produced by purifying and cooling natural gas to -260oF. It results in higher energy densities at equivalent volumes – the energy density of LNG is 2.4 times that of CNG. This makes LNG easier to store and transport. The relatively high cost of production and transportation, coupled with the need for cryogenic storage tanks, are barriers to widespread use. Additionally, LNG must be kept cold, independent of pressure, to remain liquid. Despite storage in double-walled, vacuum insulated pressure vessels, heat leakage is inevitable - fuel will vaporize over time. This makes it best suited for the heavy-duty transportation market with continuous delivery routes, where the fuel does not sit in parked vehicles. A general rule of thumb is: 24 hrs without running = fuel loss.
LNG vehicles are refueled using low-temperature equipment and hoses. LNG vehicle fueling time is equivalent to gasoline or diesel vehicles.
Natural Gas Safety
CNG is a safe and reliable fuel option. However, to insure the integrity of a CNG system, a trained professional is needed to install the equipment safely and properly. If installed incorrectly, the tanks could abrade over time – leading to a tank failure. If you wish to convert your fleet or vehicle to natural gas, these systems need to be installed by someone trained and certified in high-pressure gas systems – including high pressure tanks. Conversions should also be done according to the National Fire Protection Association's Vehicular Fuel Systems Code (NFPA 52).
There are national safety standards for equipment (NGV2 for tanks and NGV3 for on-board equipment), and federal law requires that conversion systems being installed must meet EPA standards (which insure your vehicle emissions are lower). These standards are in place for your health and safety, and the health and the safety of the public. Unsafe, poor quality equipment (and even used equipment sold as new) is available for sale around the world. In these cases you get what you pay for - is it worth it?
The U.S. NGV industry is very proud of their safety record. Help maintain that record by doing your part. For more information on this critical issue visit SafeNGV.org
UCCC Natural Gas Vehicle Page
Alternative Fuel Data Center - Natural Gas
FuelEconomy.Gov - Natural Gas
America's Natural Gas Alliance
Natural Gas Vehicles for America
American Gas Association
American Clean Skies Foundation
International Association for Natural Gas Vehicles