Natural gas, or methane, comes in two common forms, liquefied natural gas (LNG) and compressed natural gas (CNG). CNG is a gaseous form of hydrocarbon of the methane series found in petroleum. Historically, natural gas has played a limited role as a transportation fuel in the United States. However, the total consumption of both LNG and CNG grew between 2005 and 2009.
CNG has experienced small but continuous growth in total consumption between 2007 and 2011. Resulting in an average annual percent increase of 4.6%.
The LNG growth rate between 2007 and 2011 is even smaller, recording an average annual percent increase of only 1.3%.
Natural gas is less expensive than gasoline. Natural gas for use in transport vehicles costs approximately 40 percent less than diesel fuel on an energy-equivalent basis and considering only existing taxes. Additionally, Natural gas is a viable fuel option for commercial fleets because of its low emissions of hydrocarbons, carbon monoxide, and other toxins. Since the gaseous fuel doesn’t need to be vaporized before entering the engine, CNG boosts cold weather starting because it enters the engine in a gaseous state.
However, natural gas has some disadvantages. Like electric-powered vehicles, natural gas-powered vehicles are more expensive than gasoline powered vehicles. CNG must be stored under pressure in heavy tanks, and the tanks are quite expensive. Also, to produce LNG, natural gas is purified and condensed into liquid by cooling to minus 260°F (-162°C). Because it must be kept at such cold temperatures, LNG is stored in double-wall, vacuum-insulated pressure vessels which are expensive as well.
Also, refueling can be inconvenient and takes a long time to complete. There are two types of natural gas refueling stations: “quick fill” and “time fill.” Compressor stations with “quick fill” capability can refuel in three to seven minutes, which is comparable to gasoline fill times. These types of stations are found at public stations and private onsite stations. A “time fill” station generally requires overnight to refuel, or from five to eight hours. 'Time fill' stations are generally found at private onsite locations and in homes and businesses.
In addition, the refueling infrastructure is limited. Currently there are 836 fueling stations for CNG and 38 fuel stations for LNG in the United States. Most are privately owned and are used for central refueling. Further, they are not distributed evenly: 24 percent (206) of the CNG facilities and 71 percent (27) of the LNG facilities are in California. Unless more natural gas vehicles enter the market, there will be little incentive to build more natural gas fueling infrastructure. Fortunately, the U.S. House of Representatives has passed a $150 million bill investing in improving natural gas vehicles and the infrastructure to refuel them. The 5-year program will have a budget of $30 million per year, for a total of $150 million.
Fleet managers that want more information on the availability and costs of natural gas fuel on a more local level should visit the U.S. Department of Energy’s Alternative Fuels Data Center. There fleet managers can find the DOE Alternative Fueling Station Locator and the Clean Cities Alternative Fuel Price Report. Additionally, the Alternative fuel’s Data Center allows fleet managers to view their state's incentives and laws related to alternative fuel and advanced vehicle use.