Wednesday, September 16, 2009

How Natural Gas Vehicles Work

Light-duty natural gas vehicles work much like gasoline-powered vehicles with spark-ignited engines. This schematic shows basic CNG fuel system components.

CNG enters the vehicle through the natural gas fill valve (A) and flows into high-pressure cylinders (B). When the engine requires natural gas, the gas leaves the cylinders and passes through the master manual shut-off valve (C). The gas travels through the high-pressure fuel line (D) and enters the engine compartment. Gas enters the regulator (E), which reduces the gas pressure used for storage (up to 3,600 psi) to the required vehicle fuel injection system pressure. The natural gas solenoid valve (F) allows natural gas to pass from the regulator into the gas mixer or fuel injectors. The solenoid valve shuts off the natural gas when the engine is not running. Natural gas mixed with air flows down through the carburetor or fuel-injection system (G) and enters the engine combustion chambers where it is burned to produce power, just like gasoline.

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. See Development of the High-Pressure Direct-Injection ISX G Natural Gas Engine.

Heavy-duty engines can also burn diesel and natural gas in a dual-fuel system. See City of Los Angeles Bureau of Sanitation LNG Heavy-Duty Trucks.

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