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
What is the purpose of a thermally activated pressure relief device (PRD) on a CNG cylinder?
Answer: Vent gas safely if cylinder temperature rises dangerously high to prevent rupture
The PRD is designed to vent CNG safely when the cylinder is exposed to fire or extreme heat, relieving pressure before the cylinder can rupture catastrophically.
According to US standards, what is the typical maximum working pressure for a CNG vehicle fuel system?
Answer: 3,600 psi (248 bar)
US CNG vehicle fuel systems are designed for a maximum working pressure of 3,600 psi (248 bar), which is also the standard delivery pressure at US fast-fill CNG stations.
A Type 4 CNG cylinder is constructed from:
Answer: Thermoplastic liner with full carbon-fiber composite overwrap
Type 4 cylinders use a thermoplastic polymer liner fully wrapped with carbon-fiber composite, making them the lightest option available but requiring special inspection procedures.
What is the standard service life of most CNG fuel storage cylinders used in US vehicles?
Answer: 20–25 years from manufacture date
Most CNG cylinders certified to FMVSS 304 or NGV-2 standards carry a rated service life of 20 to 25 years from the date of manufacture, after which they must be permanently removed from service.
The electrically operated solenoid valve in a CNG fuel system is typically located:
Answer: At or near the cylinder outlet to shut off fuel flow when the engine is off
The solenoid valve sits at or near the cylinder valve outlet and closes automatically when the ignition is off, isolating high-pressure gas if a downstream leak occurs.
CNG engines typically benefit from engine oil with which specific characteristic?
Answer: Low ash (low SAPS) formulation to reduce deposits and protect the exhaust catalyst
CNG engines require low-ash (low SAPS) oils because excess ash can foul hardened valve seats and contaminate catalytic converters, which are especially sensitive in clean-burning CNG applications.
Visual inspection of a CNG cylinder before use should specifically check for:
Answer: Dents, cuts, abrasions, bulges, or signs of heat or fire damage
Operators must inspect cylinders for physical damage including dents, gouges, abrasions, bulges, and heat damage, as any of these conditions can compromise structural integrity.