Octane rating reference — what is the octane number assigned to normal heptane (C7H16)? In the octane number scale used for petrol knock resistance, normal heptane is assigned which reference value?

Introduction / Context:
Octane number quantifies the knock resistance of petrol in spark-ignition engines. It is defined by comparing a test fuel's knock behavior to blends of two reference hydrocarbons: iso-octane and n-heptane. Understanding the endpoints of this scale is essential for interpreting fuel labels like RON and MON.

Given Data / Assumptions:

• Standard CFR test engine procedure.
• Reference hydrocarbons are iso-octane (2,2,4-trimethylpentane) and normal heptane.
• Linear scale between the references by volume.

Concept / Approach:
On the octane scale, iso-octane is assigned a value of 100 for excellent knock resistance, while normal heptane is assigned 0 for very poor knock resistance. A test petrol's octane number equals the percentage by volume of iso-octane in a blend with n-heptane that matches the knock of the fuel under standard conditions.

Step-by-Step Solution:
Identify the octane scale endpoints.Recall: iso-octane = 100, n-heptane = 0.Therefore, the octane number of normal heptane is 0.

Verification / Alternative check:
Fuel testing protocols consistently define these endpoints; pump ratings (RON/MON) derive from this same reference concept.

Why Other Options Are Wrong:
50 would indicate a blend equally split by volume with iso-octane. 100 is the rating for iso-octane, not heptane. 120 exceeds the reference scale and refers to performance numbers or boosted effective indices, not the basic octane scale.

Common Pitfalls:
Confusing octane number (knock resistance) with energy content or cetane number (diesel ignition quality).

Final Answer:
0