Compressed natural gas (CNG) is natural gas which has been compressed to around one percent of its original volume so that it can be used as a fuel source to power a vehicle. This alternative fuel is used in many regions of the world to power both dedicated vehicles which run on natural gas only and bi-fuel vehicles which run on natural gas and another fuel. Several auto manufacturers make natural gas vehicles or can do so by request, and companies which manufacture buses and other vehicles for commercial use often offer a compressed natural gas option.
This fuel consists mostly of methane, and can be harvested in a number of different ways. It is pumped into tanks which hold it in compression until it is needed. One of the biggest advantages to compressed natural gas is that it is cleaner burning than most other fuels, producing far fewer pollutants. It is also nontoxic and noncorrosive, and poses a low safety risk because it dissipates quickly in the event of a spill.
While this fuel can be flammable, it is only flammable under certain conditions. Usually it dissipates too quickly to be explosive, reducing safety risk for people who work with natural gas vehicles and for first responders who might be called upon to respond to accident with a CNG vehicle. The holding tanks are usually carefully structured and designed to make spills highly unlikely. CNG is also less hard on engines, reducing the amount of maintenance needed to keep a vehicle functioning well.
There are some disadvantages to using compressed natural gas as a fuel source. Energywise, vehicles cannot go as far on a single tank of CNG as they can on a tank of gasoline or diesel. As a result, this means that some vehicles may have added tanks to meet their energy needs, which adds to the weight of the vehicle, cutting down on efficiency. The extra tanks can also reduce the amount of room available in the vehicle.
This fuel can also be hard to obtain in some areas. If people have to drive a long distance to fuel up, the energy and environmental savings of compressed natural gas may not balance out. Difficulties with obtaining fuel can also be a problem for people on trips, as they may need to map out a route which ensures that they pass by stations which allow CNG refueling and this can put limitations on a trip.