Fuel System Components 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 Fuel System Components flashcards as text
Which CNG system component converts fuel system pressure data into an electrical signal readable by the ECM?
Answer: CNG pressure transducer
The CNG pressure transducer measures fuel line pressure and sends a voltage signal to the engine control module for fuel delivery calculations.
A CNG fuel rail is different from a gasoline fuel rail primarily because it:
Answer: Must withstand significantly higher working pressures
CNG fuel rails must handle pressures far exceeding gasoline systems (which run at 30–60 psi), so they are constructed from heavy-gauge steel or stainless steel rated for CNG service pressures.
What happens to a CNG regulator when the engine is not running and the system is pressurized?
Answer: It remains closed, preventing gas flow to the engine
Most CNG regulators are normally closed and only open when the engine is running and creates a vacuum signal or the solenoid is energized, preventing gas flow at shutdown.
The fueling receptacle (fill valve) on a CNG vehicle must comply with which connector standard in North America?
Answer: NGV1 (ANSI/CSA NGV1)
North American CNG vehicles use the NGV1 receptacle standard (ANSI/CSA NGV1) to ensure compatibility between vehicles and public or fleet fueling stations.
Why must CNG cylinders be stored and mounted with their pressure relief device (PRD) accessible?
Answer: So the PRD can vent gas to a safe area and be inspected
PRDs must be mounted so they vent in a safe direction away from ignition sources and so inspectors can verify the device is undamaged and unobstructed.
A two-stage CNG pressure regulator differs from a single-stage unit in that it:
Answer: Reduces pressure in two steps for more stable output at varying tank pressures
A two-stage regulator performs a first reduction from storage pressure to an intermediate level, then a second reduction to delivery pressure, providing more consistent output as cylinder pressure drops.
Which inspection interval is typically required for CNG high-pressure fuel lines and fittings on commercial vehicles?
Answer: Annually or per manufacturer's maintenance schedule
NFPA 52 and most OEM maintenance schedules require annual inspection of high-pressure lines and fittings for leaks, corrosion, abrasion, and secure mounting.