CNG - Compressed Natural Gas Fuel System Components Questions and Answers

Question 1

Which of the following is the primary function of a thermally-activated Pressure Relief Device (PRD) on a CNG cylinder?

Accepted Answer

To safely vent the cylinder's contents in the event of a fire or high-temperature exposure.

Answer

A thermally-activated PRD is a critical safety component designed to open and release the gas from the cylinder if the temperature reaches a specific point (e.g., ~230°F), such as in a vehicle fire. This controlled venting prevents the cylinder pressure from rising to a level that could cause a rupture.

Question 2

A technician is servicing a CNG vehicle and notices that after turning the ignition off, the high-pressure fuel supply to the regulator is immediately cut off. Which component is responsible for this action?

Accepted Answer

The main fuel solenoid valve

Answer

The main fuel solenoid valve is an electronically controlled valve that opens to allow fuel flow when the ignition is on and the engine is running, and closes to stop the flow of high-pressure gas when the ignition is turned off.

Question 3

What is the primary purpose of the check valve located within the CNG fueling receptacle?

Accepted Answer

To prevent the backflow of gas from the vehicle's fuel system.

Answer

The check valve in the fueling receptacle is a one-way valve that allows high-pressure gas to flow into the vehicle's cylinders during fueling but prevents it from escaping back out through the receptacle once the fueling nozzle is removed.

Question 4

A technician needs to replace a damaged section of high-pressure fuel line between the CNG cylinder and the primary pressure regulator. Which material is most appropriate for this application?

Accepted Answer

Seamless stainless steel tubing

Answer

High-pressure fuel lines in a CNG system must be made from seamless stainless steel to safely withstand the extremely high pressures (up to 3,600 psi) and resist corrosion and vibration.

Question 5

The main pressure regulator in a CNG fuel system performs which critical function?

Accepted Answer

It reduces the high pressure from the storage cylinders to a much lower, usable pressure for the engine.

Answer

The primary function of the main pressure regulator is to reduce the storage cylinder pressure (e.g., 3,600 psi) down to a consistent and significantly lower operating pressure required by the engine's fuel injection system (e.g., around 125 psi).

(CNG) Compressed Natural Gas Practice Test

(CNG) Compressed Natural Gas Practice Test

CNG - Compressed Natural Gas Fuel System Components Questions and Answers