CNG Systems 3

Question 1

A CNG technician notices the fuel gauge reads empty but the pressure gauge shows 200 psi. What is the most likely explanation?

Accepted Answer

Gas remains but at too low a pressure for practical use

Answer

At 200 psi there is still some CNG in the cylinders, but it is below the pressure needed for reliable engine operation and represents near-empty.

Question 2

Which CNG system component is responsible for metering the correct amount of gas into the engine's intake?

Accepted Answer

Gas injectors or mixer

Answer

Gas injectors (in sequential systems) or a mixer (in single-point systems) meter CNG into the intake airstream for combustion.

Question 3

What is the purpose of the manual shutoff valve on a CNG cylinder?

Accepted Answer

To allow manual isolation of gas flow for service or emergency

Answer

The manual shutoff valve lets technicians or emergency responders manually stop gas flow from the cylinder for safety or maintenance.

Question 4

What type of sensor is used to detect CNG leaks inside a vehicle enclosure?

Accepted Answer

Methane or combustible gas sensor

Answer

Methane sensors or combustible gas detectors are used to detect CNG leaks because methane (CH4) is the primary component of natural gas.

Question 5

During a fast-fill at a public CNG station, why may the displayed fuel gauge reading drop shortly after fueling ends?

Accepted Answer

Gas cools and contracts after the fast-fill heat of compression dissipates

Answer

Fast-fill compresses gas rapidly, raising its temperature and pressure; as the gas cools to ambient temperature, pressure and the gauge reading drop slightly.

(CNG) Compressed Natural Gas Practice Test

(CNG) Compressed Natural Gas Practice Test

CNG Systems 3