ASE - Automotive Service Excellence Practice Test (F1: Compressed Natural Gas (CNG) Vehicles) 1

Question 1

Which component in a CNG fuel system is responsible for reducing high-pressure fuel from the cylinder to a usable pressure for the engine?

Accepted Answer

Pressure regulator

Answer

The pressure regulator steps down high cylinder pressure (typically 3,000–3,600 psi) to the low operating pressure required by the fuel injectors, usually 3–10 psi depending on system design.

Question 2

A technician detects a natural gas odor around a CNG vehicle in an enclosed shop. What is the FIRST action that should be taken?

Accepted Answer

Immediately ventilate the area and move the vehicle outdoors

Answer

Natural gas is highly flammable and lighter than air, so it accumulates near the ceiling of enclosed spaces. The priority is to ventilate the area and remove the vehicle to eliminate ignition risk before any diagnostic work begins.

Question 3

What type of valve on a CNG cylinder automatically stops fuel flow if the downstream fuel line is severed or ruptures?

Accepted Answer

Excess flow valve

Answer

The excess flow valve is a safety device that automatically closes when fuel flow exceeds a predetermined rate, such as during a fuel line rupture, preventing uncontrolled fuel release.

Question 4

During inspection of a CNG vehicle, a technician finds a cylinder with visible deep gouges and abrasion damage on its surface. What is the correct procedure?

Accepted Answer

Remove the cylinder from service immediately

Answer

CNG cylinders with visible physical damage such as deep gouges, cuts, or abrasions must be removed from service immediately. Structural integrity cannot be confirmed without specialized non-destructive testing, and a compromised cylinder poses a serious burst hazard.

Question 5

What is the purpose of the Pressure Relief Device (PRD) installed on CNG fuel cylinders?

Accepted Answer

To vent cylinder pressure if the cylinder temperature rises dangerously, such as during a fire

Answer

The PRD is a thermally activated safety device that vents cylinder contents if exposed to high temperatures, such as in a vehicle fire. This controlled release prevents a catastrophic cylinder rupture (BLEVE).

ASE Practice Test

ASE Practice Test

ASE - Automotive Service Excellence Practice Test (F1: Compressed Natural Gas (CNG) Vehicles) 1