Normal cetane (n-cetane) used in diesel knock rating Which statement(s) about normal cetane are correct?

Introduction / Context:
Diesel fuel ignition quality is characterized by the cetane number scale. The reference fuels for this scale include normal-cetane at the high-reactivity end and alpha-methylnaphthalene (historically) or heptamethylnonane (modern) at the low-reactivity end. Understanding what “cetane” is helps interpret diesel ignition behavior.

Given Data / Assumptions:

• Normal cetane denotes n-hexadecane.
• It is used as a primary reference fuel for the cetane number determination.
• Straight-chain paraffins typically have high cetane numbers (short ignition delay).

Concept / Approach:

In the cetane rating method, a test diesel’s ignition delay is matched to that of a blend of reference fuels. n-Hexadecane, with excellent ignition quality, is assigned cetane number 100. Its long, straight-chain structure enhances reactivity, explaining its role as the “good” end of the scale. Therefore, all listed statements about normal cetane are correct.

Step-by-Step Solution:

Verification / Alternative check:

Engine test standards for cetane number routinely cite n-hexadecane as the 100-point reference, with low-reactivity reference adjusted in modern practice (e.g., HMN).

Why Other Options Are Wrong:

Options restricting correctness to subsets ignore that all three statements are simultaneously true.

Common Pitfalls:

Confusing octane (SI knock resistance) with cetane (CI ignition quality); they measure different phenomena.

Final Answer:

all of the above