Automotive fuels—CNG storage: Natural gas in a compressed natural gas (CNG) cylinder onboard a vehicle is typically stored at approximately what rated pressure at standard reference conditions?

Introduction / Context:

Compressed natural gas (CNG) vehicles store methane fuel in high-pressure cylinders. The nominal storage pressure defines cylinder design, filling protocols, safety devices, and refueling equipment. Many exam syllabi reference a standard nominal value used for classroom calculations and safety understanding.

Given Data / Assumptions:

• On-vehicle CNG cylinders rated for typical automotive service.
• Reference temperature around 15–20°C for nominal rated pressure.
• Familiarity with refueling station practices that may temporarily exceed nominal to compensate for cooling/settling.

Concept / Approach:

The commonly cited nominal storage pressure for automotive CNG cylinders is about 200 bar at reference temperature. While filling systems may reach ~200–220 bar depending on station and temperature to ensure usable capacity after temperature equalization, the textbook figure used for design familiarity is 200 bar. Higher values like 250–300 bar pertain to different standards or overfills not used as the typical classroom nominal.

Step-by-Step Solution:

Verification / Alternative check:

Automotive training materials and safety guides frequently quote 200 bar nominal; station fast-fill practices may list 200–220 bar compensated fills but do not change the nominal reference.

Why Other Options Are Wrong:

• 220 bar: possible as a compensated fill end-point; not the standard nominal reference in many curricula.
• 250, 300 bar: exceed typical passenger-vehicle cylinder nominal ratings for common systems.
• 150 bar: too low for full capacity and range expectations.

Common Pitfalls:

• Confusing nominal rated pressure with station delivery peaks or hot-soak equalized pressures.

Final Answer:

200 bar