Natural Gas

Natural gas is a mixture of hydrocarbons—mainly methane— and is produced either from gas wells or in conjunction with crude oil production. It can be stored onboard a vehicle as compressed natural gas (CNG) or as liquefied natural gas (LNG), though CNG is more common. It is one of the cleanest burning and least expensive alternative fuels, offering a number of advantages over gasoline. Air exhaust emissions from natural gas vehicles are much lower than those from gasoline-powered vehicles. For example, for heavy-duty and medium-duty applications, natural gas engines reduce CO and particulate matter emissions by up to 90% relative to commercial diesel engines. However, fueling a vehicle with CNG, a high-pressure gas, requires that the engine be modified to change how the fuel is injected into the cylinders. Natural gas vehicles also require about four times the fuel tank volume to provide the same driving range as gasoline vehicles. Because the high-pressure holding tanks require periodic inspection and certification, natural gas is often used in fleets with centralized storage and refueling centers, where specially trained personnel can service the vehicles. As of 2005, almost 150,000 heavy-duty vehicles used natural gas as a fuel.

Visual source: http://www.evworld.com/archives/testdrives/carpicts/gmcng-dia.gif

How is natural gas produced: Gas streams produced from reservoirs contain natural gas, liquids, and other materials. Natural gas (methane) can also come from landfill gas and water/sewage treatment. First, the gas is separated from free liquids such as crude oil, hydrocarbon condensate, water, and contaminants. The separated gas is further processed to meet specified requirements. For example, a dehydration plant controls water content, a gas processing plant removes certain hydrocarbon components to hydrocarbon dewpoint specifications; and a gas sweetening plant removes hydrogen sulfide and other sulfur compounds (when present).

Sources:

• The Natural Gas Vehicle Coalition
• The DOE’s Alternative Fuels Data Center
• The Auto Alliance
• Price comparisons between CNG and other alternative fuels