CNG

Basic components of a CNG vehicle

1. Filler valve
The valve is used to fill the vehicle's pressure tank with natural gas at CNG fuel stations. The filler valve can be located in the engine compartment (the usual solution for converted automobiles), near the gas tank inlet, or separately in a different place.

There are two filling methods - the "Italian" system (used chiefly in Italy) and the NGV 1 system (used in other European countries).

NGV 1 inlet:

near the gas tank inlet

in the engine compartment

in a separate location

2. Pressure tank + multi-valve
Most tanks for pressurized natural gas have a volume of 70-100 liters and are fitted with a multi-valve for safe and reliable operation. The multi-valve functions as an operating device, which closes the pressure tank when the ignition is turned off and controls the amount of gas flowing from the vessel, and as a safety mechanism, which automatically shuts off gas flow if the piping system is damaged (pressure falls) and releases gas from the vessel if the pressure exceeds a certain value or if a heat sensor detects a fire.
Pressure tanks are usually made of steel, but an increasing number of lightweight tanks made from aluminum or composite materials, as strong as steel but weighing up to three times less, have recently appeared on the market.
While most converted cars have a CNG tank installed in the trunk, vehicles designed for the use of natural gas have a pressure tank below the chassis or in another suitable location.
Most buses have CNG bottles in the luggage compartment or on the roof (low-profile buses).

Automobiles - examples of locations of pressurized vessels:

in the trunk

under the chassis

3. Connecting high-pressure pipe
During the filling process, the pipe brings natural gas from the filling valve to the pressurized vessel. Conversely, while the vehicle is in the natural gas mode, the pipe delivers gas from the bottle to the regulator.

4. Pressure gauge (optional)
The pressure gauge shows the pressure in the high-pressure section of the gas system (pressure tank, connecting pipe).

5. Gas pressure regulator
The regulator reduces the high pressure of gas to the desired level. It includes a closing valve. The regulator is located in the engine compartment, where it is connected to the internal cooling circuit from which it takes heat.

Vehicles with direct gas injection feature:

6. Electronic injectors
Injectors are devices that control the injection of gas into the intake manifolds of individual cylinders. They work sequentially, which means that natural gas is injected separately to each cylinder.

7. Injection rail
The injection rail is part of the injectors and brings natural gas from the pressure regulator to individual injectors.

CNG FIAT Multipla / injection rail

Skoda Fabia / injection rail

Vehicles with central gas mixing feature:

6. Stepper
Based on signals sent by the control unit, the stepper continually adjusts the quantity of gas entering the mixing system to ensure optimal power, fuel consumption, and emissions.

7. Mixer
The mixer mixes the fuel (natural gas) with air to create an explosive mixture. It has the same function as a carburetor or a fuel injection system in vehicles powered by gasoline.

8. Electronic control unit
The unit ensures correct operation of a vehicle powered by natural gas by working together with the gasoline control unit and supplying natural gas according to operating modes and signals sent from the engine.

9. Natural gas/gasoline switch and fuel gauge
The switch and the fuel gauge are located on the dashboard in front of the driver; in mass produced CNG vehicles, they are incorporated into the dashboard. By switching from gasoline to natural gas, the supply of gasoline is stopped, and the gas intake from the regulator is opened. Gas regulation starts depending on information sent by the lambda sensor and the natural gas fuel gauge is activated.

10. Catalytic converter and lambda sensor
The lambda sensor analyzes the composition of exhaust fumes and sends information to the electronic control unit, which adjusts the supply of natural gas.

Diagram of an automobile powered by compressed natural gas