CNG Systems 2

Question 1

What is the primary function of the high-pressure regulator in a CNG fuel system?

Accepted Answer

Reduce storage pressure to a usable level for the engine

Answer

The high-pressure regulator steps down CNG from storage pressure (up to 3,600 psi) to an intermediate or low pressure the engine can use.

Question 2

Which component prevents CNG from flowing back from the fuel rail into the storage cylinders?

Accepted Answer

Check valve

Answer

A check valve allows fuel flow in only one direction, preventing backflow from the fuel rail toward the cylinders.

Question 3

On a bi-fuel CNG vehicle, what determines which fuel the engine uses when both fuels are available?

Accepted Answer

The engine control module (ECM) or driver selection switch

Answer

On bi-fuel vehicles, the ECM or a manual driver switch controls which fuel system (CNG or gasoline) is active.

Question 4

What does a pressure relief device (PRD) on a CNG cylinder do in a fire scenario?

Accepted Answer

Vents gas to prevent cylinder rupture from excessive heat

Answer

A PRD is thermally activated and vents CNG safely to atmosphere to prevent catastrophic cylinder failure when exposed to fire.

Question 5

Which material is commonly used for CNG storage cylinders (Type 3) due to its strength-to-weight ratio?

Accepted Answer

Aluminum liner with carbon fiber overwrap

Answer

Type 3 cylinders use an aluminum liner fully wrapped with carbon fiber or glass fiber composite for high strength at reduced weight.

(CNG) Compressed Natural Gas Practice Test