Systems Flashcards
7 cards from real CNG practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Systems flashcards as text
What is the primary function of the high-pressure regulator in a CNG fuel system?
Answer: Reduce storage pressure to a usable level for the engine
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.
Which component prevents CNG from flowing back from the fuel rail into the storage cylinders?
Answer: Check valve
A check valve allows fuel flow in only one direction, preventing backflow from the fuel rail toward the cylinders.
On a bi-fuel CNG vehicle, what determines which fuel the engine uses when both fuels are available?
Answer: The engine control module (ECM) or driver selection switch
On bi-fuel vehicles, the ECM or a manual driver switch controls which fuel system (CNG or gasoline) is active.
What does a pressure relief device (PRD) on a CNG cylinder do in a fire scenario?
Answer: Vents gas to prevent cylinder rupture from excessive heat
A PRD is thermally activated and vents CNG safely to atmosphere to prevent catastrophic cylinder failure when exposed to fire.
Which material is commonly used for CNG storage cylinders (Type 3) due to its strength-to-weight ratio?
Answer: Aluminum liner with carbon fiber overwrap
Type 3 cylinders use an aluminum liner fully wrapped with carbon fiber or glass fiber composite for high strength at reduced weight.
What is the standard maximum operating pressure for most CNG vehicle storage systems in the United States?
Answer: 3,600 psi
U.S. CNG vehicle systems are designed for a maximum operating pressure of 3,600 psi (248 bar) at 70°F.
What happens to CNG system pressure when the ambient temperature drops significantly in cold weather?
Answer: Pressure decreases
Gas pressure drops with temperature according to the ideal gas law, so cold weather reduces the pressure reading in CNG tanks.