ASE Compressed Natural Gas (CNG) Vehicles 2

Question 1

What is the typical service pressure of a CNG fuel storage cylinder in a light-duty vehicle?

Accepted Answer

3,600 psi

Answer

Light-duty CNG cylinders are commonly rated for a service pressure of 3,600 psi (about 248 bar).

Question 2

Which component reduces high cylinder pressure to a usable pressure before the gas reaches the engine?

Accepted Answer

Fuel pressure regulator

Answer

A CNG pressure regulator (sometimes multi-stage) steps the high storage pressure down to injection pressure.

Question 3

A CNG cylinder has an expiration date stamped on it. Why must it be removed from service when expired?

Accepted Answer

The composite or steel structure can fatigue and fail under pressure over time

Answer

CNG cylinders have a finite service life because pressure cycling and material aging can compromise structural integrity.

Question 4

What odorant is added to CNG so leaks can be detected by smell?

Accepted Answer

Mercaptan

Answer

Mercaptan gives natural gas its characteristic 'rotten egg' odor for leak detection.

Question 5

Where does CNG tend to accumulate if it leaks inside an enclosed space?

Accepted Answer

Near the ceiling, because it is lighter than air

Answer

CNG (methane) is lighter than air, so it rises and collects at the highest points.

ASE Practice Test