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 does the Wobbe Index measure in the context of CNG fuel quality?
Answer: The interchangeability and energy delivery rate of the gas relative to a standard
The Wobbe Index measures the energy flow rate through a given orifice, used to assess whether a gas blend will deliver equivalent power to a reference gas.
Which component connects the vehicle's CNG fuel system to the refueling nozzle at the station?
Answer: NGV1 or NGV2 receptacle (fill valve)
The NGV1 receptacle (light-duty) or NGV2 (heavy-duty) is the standardized fill valve on the vehicle that accepts the refueling nozzle.
A CNG cylinder passes its visual inspection but has exceeded its mandatory service life. What action must be taken?
Answer: Remove it from service and render it permanently unusable
Regardless of visual condition, a CNG cylinder that has reached its expiration date must be removed from service and destroyed per regulatory requirements.
What is the purpose of the thermal PRD (pressure relief device) vent tube on a vehicle-mounted CNG cylinder?
Answer: To direct vented gas away from the vehicle body and toward a safe location
The vent tube directs gas released from the PRD away from enclosed spaces, fuel lines, and ignition sources to prevent accumulation and ignition hazards.
Which of the following CNG system components is MOST likely to cause a rich-running condition if it fails in the open position?
Answer: A CNG injector stuck open
An injector stuck open delivers continuous fuel to that cylinder, creating an excessively rich air-fuel mixture, misfires, and potential catalyst damage.
In a multi-cylinder CNG storage system, what is the purpose of interconnecting the cylinders with a manifold?
Answer: To equalize pressure across all cylinders and draw fuel as a single unified supply
The manifold links all cylinders so they equalize pressure and the engine draws from the combined supply as though it were one large tank.
What safety precaution is MOST important before performing any maintenance that requires disconnecting CNG fuel lines?
Answer: Closing the manual cylinder shutoff valve and depressurizing the lines
Always close the manual shutoff valve and bleed residual pressure from the fuel lines before disconnecting any fittings to prevent gas release and ignition risk.