Typical quality of commercial diesel fuel: The usual cetane number range of diesel oil commonly available at retail pumps is approximately

Introduction / Context:
Cetane number indicates the ignition quality of diesel fuel—higher values correspond to shorter ignition delay and smoother combustion in compression-ignition engines. Knowing typical ranges assists in diagnosing cold-start issues, knock, and emissions in field conditions.

Given Data / Assumptions:

• Standard road diesel in many markets.
• Engines designed for CN around the mid-40s to low-50s.
• Premium or specialty diesels may vary, but the question targets “generally available”.

Concept / Approach:

Most on-road diesel specifications set minimum CN near 45–51 depending on jurisdiction and season. Practical retail fuels cluster roughly 40–55, ensuring reliable ignition without excessive advanced combustion phasing.

Step-by-Step Solution:

Verification / Alternative check:

OEM fuel recommendations and injector calibration maps are often built around CN in the mid-40s to ~50, corroborating this selection.

Why Other Options Are Wrong:

20–40 are too low for modern on-road fuels; 60–80 represents specialty high-cetane blends not commonly available at standard pumps.

Common Pitfalls:

Confusing research octane number (for SI engines) with cetane number; assuming premium diesel universally reaches extremely high CN values.

Final Answer:

40 to 55