Light-duty natural gas vehicles work much like gasoline-powered vehicles. In a CNG fuel system, high-pressure natural gas moves from the storage tank to the engine where its pressure is reduced to the engine’s required fuel injection system pressure. After the natural gas is injected into the engine, the fuel-air mixture is compressed and ignited by a spark plug. The expanding gases propel the vehicle.

Some heavy-duty vehicles use spark-ignited natural gas systems, but other systems exist as well. High-pressure direct injection engines burn natural gas in a compression-ignition (diesel) cycle. Heavy-duty engines also can burn diesel and natural gas in a dual-fuel system.