Interpreting a cetane number of 40 A diesel fuel with cetane number 40 has the same ignition quality as a volumetric blend of which two reference fuels in the specified proportions?

Introduction / Context:
The cetane number translates ignition delay into an equivalent mixture of two standard fuels in a calibrated test engine. This enables reproducible comparison between fuels across laboratories and time.

Given Data / Assumptions:

• Cetane number scale with cetane = 100 and alpha-methylnaphthalene = 0 as classic references.
• Linear interpolation of ignition quality between reference fuels by volume in the standardized method.

Concept / Approach:
A cetane number of 40 means that the test fuel has the same ignition delay as a blend containing 40% by volume cetane and 60% by volume alpha-methylnaphthalene. The higher the proportion of cetane, the better (shorter delay) the ignition quality. Thus the percentages numerically match the cetane number in the conventional interpretation.

Step-by-Step Solution:
Identify high and low references: cetane (100), alpha-methylnaphthalene (0).Match ignition delay to an equivalent blend.For CN = 40, the equivalent blend is 40% cetane + 60% alpha-methylnaphthalene.

Verification / Alternative check:
Standard diesel fuel testing procedures define the reading as the percentage of cetane by volume in the blend that matches ignition delay, confirming this interpretation.

Why Other Options Are Wrong:
Reversing the percentages would correspond to CN = 60. Petrol and diesel mixtures are unrelated to the cetane reference method.

Common Pitfalls:
Confusing the octane scale (iso-octane and n-heptane) with the cetane scale; they serve different engine types and properties.

Final Answer:
40% cetane and 60% alpha-methylnaphthalene