Fuel rating basics: In the octane number scale used for gasoline, what value is assigned to normal heptane (n-heptane)?

Introduction / Context:
Octane number quantifies the knock resistance of gasoline in spark-ignition engines. It is defined by comparing a test fuel to a blend of iso-octane and n-heptane under standardized conditions.

Given Data / Assumptions:

• Reference fuels: iso-octane and n-heptane.
• Scale anchors: iso-octane set high, n-heptane set low.
• Measurement methods: RON and MON (principles similar for the scale reference).

Concept / Approach:
By definition, iso-octane is assigned octane number 100 as the high-knock-resistance reference, and n-heptane is assigned octane number 0 as the low-resistance reference. Real fuels are compared to equivalent blends between these anchors.

Step-by-Step Solution:

Verification / Alternative check:
Standard fuel testing handbooks and ASTM methods state the same scale definition.

Why Other Options Are Wrong:

• 100: Assigned to iso-octane, not n-heptane.
• 70: Arbitrary; not a reference endpoint.
• Infinity: Not used in octane scaling.

Common Pitfalls:
Confusing cetane scale (diesel ignition quality) with octane; they are opposite in their performance meaning.

Final Answer:
0