Smoke point as an indicator of kerosene burning quality: A test sample shows a smoke point of 15 mm. Removal of which hydrocarbon family would typically raise the smoke point to about 25 mm (cleaner flame)?

Introduction / Context:
The smoke point test measures the maximum flame height without smoking and is a practical indicator of kerosene and aviation turbine fuel burning quality. Hydrocarbon type strongly influences sooting propensity.

Given Data / Assumptions:

• Initial smoke point: 15 mm.
• After selective component removal, smoke point rises to ~25 mm.
• Hydrocarbon families: paraffins, olefins, aromatics, naphthenes.

Concept / Approach:
Aromatics have high sooting tendency due to ring structures that promote soot precursor formation (polycyclic aromatic growth). Reducing aromatic content improves flame luminosity and increases smoke point. Paraffins and naphthenes generally have higher smoke points; olefins are intermediate and can form gums but are less dominant in smoke point reduction than aromatics.

Step-by-Step Solution:
Identify the most sooting family → aromatics.Hypothesis → remove aromatics → decrease soot → higher smoke point.Observation matches: smoke point rises from 15 mm to ~25 mm.

Verification / Alternative check:
ASTM fuel property correlations and refinery practice confirm that aromatics reduction (via reformate management, hydroprocessing, or extraction) raises smoke point and improves burning quality.

Why Other Options Are Wrong:

• Normal paraffins: already high smoke point; removing them would worsen, not improve.
• Olefins: affect stability/gum more than smoke point; impact smaller than aromatics.
• Naphthenes: moderate sooting; not the main culprit.

Common Pitfalls:
Confusing smoke point with octane/cetane; it specifically reflects sooting behavior in diffusion flames.

Final Answer:
Aromatics