Light-duty natural gas vehicles perform and function much like gasoline-powered vehicles with spark-ignited engines. A CNG fuel system transfers high-pressure natural gas from the vehicle’s storage tank to the engine compartment where pressure is reduced to the operating pressure of the engine's fuel-management system. An LNG fuel system holds natural gas at cryogenic temperatures (~ -260 deg F) as a low-pressure (5-100 psi) liquefied natural gas. When required, LNG is vaporized into a gaseous state and sent to the engine compartment near the operating pressure of the engine's fuel-management system. With both CNG and LNG, the natural gas is injected into the engine intake air the same way gasoline is injected into a gasoline-fueled engine.
The engine functions the same way as a gasoline engine where the fuel-air mixture is compressed during the piston upstroke cycle and ignited by a spark plug where the expanding gases produce mechanical energy in the form of rotational forces that propel the vehicle. The description in the paragraph is the same for dedicated natural gas systems and bi-fuel natural gas systems. The difference between these two fuel systems is that the bi-fuel system can be switched between CNG-only and gasoline-only fuel supply where a dedicated systems runs on natural gas only without the ability to switch to another fuel.
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