Typical quality of commercial diesel fuel: The usual cetane number range of diesel oil commonly available at retail pumps is approximately
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A20 to 25
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B25 to 30
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C30 to 40
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D40 to 55
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E60 to 80
Answer
Correct Answer: 40 to 55
Explanation
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:
Relate common standards (e.g., EN 590, ASTM D975) to real-world pump values.Identify the broad everyday band encompassing regular and premium diesel.Select the range that captures typical availability: 40 to 55.Therefore, choose 40 to 55.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