Engines and Fuels 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 Engines and Fuels flashcards as text
Which NFPA code specifically governs vehicular natural gas fuel systems in the United States?
Answer: NFPA 52 (Vehicular Natural Gas Fuel Systems Code)
NFPA 52 is the primary US standard covering design, installation, operation, and maintenance of CNG and LNG fuel systems on vehicles.
An excess flow valve (EFV) in a CNG fuel system is designed to:
Answer: Automatically restrict or stop flow if downstream flow exceeds a safe rate, indicating a major leak or line break
An EFV automatically closes or restricts flow when it detects a flow rate exceeding normal operation, indicating a ruptured downstream line or fitting, thereby limiting dangerous fuel release.
CNG vehicle engine performance at high altitude is reduced primarily because:
Answer: Lower air density reduces the mass of oxygen available per intake charge, reducing combustion energy
Like all naturally aspirated engines, CNG engines lose power at altitude because thinner air contains less oxygen per intake cycle, reducing the fuel-air mixture's combustion energy.
Which US federal regulation establishes the safety standards for CNG fuel containers installed in motor vehicles?
Answer: FMVSS 304 (49 CFR Part 571.304)
Federal Motor Vehicle Safety Standard 304 (FMVSS 304), found in 49 CFR Part 571.304, specifies the minimum performance and test requirements for CNG fuel containers used in motor vehicles.
Why must CNG vehicles generally be stored in well-ventilated above-grade facilities rather than below-grade (underground) garages?
Answer: CNG is lighter than air and can accumulate near ceilings, where underground facilities often lack adequate overhead ventilation
Methane is lighter than air and rises, so a CNG leak in an underground or poorly ventilated enclosed garage can accumulate near the ceiling, creating a potentially explosive atmosphere.
CNG is generally considered to have a fire safety advantage over liquid gasoline in vehicle accidents because:
Answer: CNG disperses rapidly upward into the atmosphere rather than pooling as a flammable liquid on the ground
Unlike gasoline, which pools on the ground and spreads fire across large surfaces, a CNG leak rises and disperses rapidly into the atmosphere, significantly reducing the risk of sustained ground-level fire.
After a CNG vehicle is involved in a collision, which action should be taken FIRST before any repairs or towing?
Answer: Shut off the CNG cylinder manual valve(s) and verify there is no gas leak
After any collision, the CNG cylinder manual valve(s) must be closed immediately to isolate the high-pressure fuel supply and eliminate the risk of gas feeding a fire or creating an asphyxiation hazard.