CNG Systems 1 — Questions and Answers

Question 1: What does CNG stand for?

Colored Natural Gas
Compression and Gas
Compressed Natural Gas (Correct answer)
Combustible Natural Gas

Correct answer: Compressed Natural Gas

CNG is an acronym that stands for Compressed Natural Gas. It is a fossil fuel substitute for gasoline (petrol), diesel, or propane fuel, used in internal combustion engines. Natural gas is compressed to less than 1% of its volume at standard atmospheric pressure.

Question 2: Which gas does CNG contain?

Butane
Methane (Correct answer)
Oxygen
Carbon Monoxide

Correct answer: Methane

Compressed Natural Gas (CNG) is primarily composed of methane (CH4). Methane is the simplest hydrocarbon and the main component of natural gas, making it the primary fuel source when natural gas is used in its compressed form.

Question 3: What does the shut-off valve at the compressed natural gas cylinder serve as?

To cut the gas flow from tank to lines. (Correct answer)
To stop the air from entering the intake.
To cut the gas from entering the intake.
To cut the gas flow from lines to the regulator.

Correct answer: To cut the gas flow from tank to lines.

The shut-off valve at the compressed natural gas cylinder is a critical safety component. Its primary function is to manually or automatically cut off the flow of gas from the high-pressure storage tank to the vehicle's fuel lines, preventing gas leakage or uncontrolled release in case of an emergency or during maintenance.

Question 4: What is the required rated service pressure for fuel supply cylinders?

At least 2400 psig at 30°F
At least 2400 psig at 70°F (Correct answer)
At least 2500 psig at 70°F
None of the above.

Correct answer: At least 2400 psig at 70°F

Fuel supply cylinders for Compressed Natural Gas (CNG) must be designed to withstand high pressures safely. The required rated service pressure is at least 2400 psig (pounds per square inch gauge) at a temperature of 70°F (21°C) to ensure structural integrity and prevent rupture under normal operating conditions.

Question 5: What must be used when venting CNG into the atmosphere?

A transfer hose
A pressure-filled pipe
A vent pipe or stack (Correct answer)
All of the above.

Correct answer: A vent pipe or stack

When venting Compressed Natural Gas (CNG) into the atmosphere, a vent pipe or stack must be used. This safety measure ensures that the gas is discharged upwards and away from ignition sources, personnel, and enclosed spaces, allowing for safe dispersion and preventing the accumulation of flammable gas at ground level.

Question 6: What must underground piping be protected from?

Erosion
Oxidation
Corrosion (Correct answer)
Combustion

Correct answer: Corrosion

Underground piping in CNG systems must be protected from corrosion. Soil conditions, moisture, and electrochemical reactions can degrade pipe materials over time, leading to leaks and safety hazards. Protective coatings, cathodic protection, and appropriate pipe materials are used to prevent corrosion.

Question 7: For safety, CNG equipment must not be located _____________.

equipment can be placed anywhere
near a refueling connector
near uncoated threaded socket welded joints
within 6 feet or directly beneath the electric transmission line (Correct answer)

Correct answer: within 6 feet or directly beneath the electric transmission line

For safety, CNG equipment must not be located within 6 feet or directly beneath an electric transmission line. This regulation prevents potential hazards such as electrical arcing, which could ignite the natural gas, or damage to the gas equipment from falling power lines. Maintaining a safe distance from electrical infrastructure is crucial.

Question 8: CNG compression, storage, and dispensing must be _______________.

located and conducted outdoors (Correct answer)
spaced no more than 4 feet apart
checked for valve service ratings
None of the above.

Correct answer: located and conducted outdoors

CNG compression, storage, and dispensing operations are required to be located and conducted outdoors. This is a critical safety measure to ensure adequate ventilation, preventing the accumulation of potentially flammable gas in enclosed spaces and minimizing the risk of explosion or fire in case of a leak.

Question 9: All pipe fittings in CNG systems must be made of forged steel and stamped with ________.

5,995 psi or greater
6,000 psi or greater (Correct answer)
4,995 psi or greater
None of the above.

Correct answer: 6,000 psi or greater

All pipe fittings in Compressed Natural Gas (CNG) systems are subjected to very high pressures, necessitating robust construction. They must be made of forged steel and stamped with a pressure rating of 6,000 psi or greater to ensure they can safely withstand the operational pressures without failure.

Question 10: What is a cascade storage system?

A downstream
A DOT standard
A type of fuel system
A method of storing gas in multiple cylinders or tanks. (Correct answer)

Correct answer: A method of storing gas in multiple cylinders or tanks.

A cascade storage system is a method used in CNG fueling stations to store natural gas in multiple cylinders or tanks at different pressure levels. This allows for efficient dispensing by sequentially drawing gas from tanks with progressively lower pressures, optimizing the filling process for vehicles.

Question 11: Which of the following materials is commonly used for the construction of high-pressure fuel storage cylinders in compressed natural gas (CNG) vehicles?

Steel (Correct answer)
Glass
Plastic
Aluminum

Correct answer: Steel

Steel is commonly used for high-pressure CNG fuel storage cylinders due to its exceptional strength and durability. It can withstand the immense internal pressures (typically 3,000-3,600 psi) required to store natural gas in a compressed state safely. While other materials like aluminum can be used, steel offers a robust and cost-effective solution for the demanding safety requirements of vehicle fuel tanks.

CNG Systems 1

What does CNG stand for?