Diagrams for compressed natural gas vehicles are available on the Alternative Fuels Data Center website. Cars of Change also has compressed natural gas diagrams on display.
To follow a compressed natural gas vehicle diagram, start from the natural gas fill valve. When the vehicle is filled with fuel, the fuel travels to high pressure cylinders, and it exits the cylinders and enters the engine's manual shut-off valve. Natural gas goes through a high-pressure fuel line and into the engine compartment, where it goes into a regulator that lowers the pressure of the gas. The solenoid valve brings the gas from the regulator to the fuel injector, where it mixes with air from the carburetor and goes to the engine's combustion chambers. There, it is burnt and produces enough power to run the vehicle.
Several types of natural gas vehicles follow this diagram. Dedicated vehicles run only on compressed natural gas. Bi-fuel vehicles are able to accommodate both compressed natural gas and gasoline thanks to separate fueling systems. Dual-fuel vehicles run on natural gas but depend on diesel fuel to ignite the engine.
Dedicated and bi-fuel vehicles include passenger vehicles. Dual-fuel vehicles are used commercially. Dedicated vehicles have considerably lower emissions than other vehicles using natural gas, and they have the advantage of more available space, as they are not as heavy. However, compressed natural gas vehicles of any type do not have the range of gasoline powered vehicles, as gas has a much lower energy density.