Illuminating kerosene quality: As the molecular weight (ring size/condensation) of aromatics in kerosene increases, how does its smoking tendency in wick or lamp burners change?

Introduction:
Smoking tendency is a key measure for illuminating kerosene and aviation kerosene (smoke point). Heavier, more condensed aromatics tend to produce soot and smoke during diffusion flame combustion. The question probes how increasing aromatic molecular weight affects smoking behaviour.

Given Data / Assumptions:

• Fuel: kerosene-range hydrocarbons.
• Change: increasing molecular weight/condensation of aromatics (more rings, higher boiling point).
• Context: wick/lamps and combustors where smoke point matters.

Concept / Approach:
Aromatics favour soot formation due to ring structures and lower hydrogen-to-carbon ratio. As molecular weight and ring condensation increase (e.g., polynuclear aromatics), soot precursors increase, causing more smoke and a lower measured smoke point. Therefore, greater aromatic molecular weight worsens smoke characteristics.

Step-by-Step Solution:

Verification / Alternative check:
Standard kerosene specifications emphasise smoke point; higher heavy-aromatic content correlates with lower smoke point (i.e., worse smoking tendency).

Why Other Options Are Wrong:

• Decreases/Remains same/Unpredictable/Vanishing: Contradict established combustion trends for aromatic-rich fuels.

Common Pitfalls:
Assuming higher molecular weight always improves combustion; for aromatics, it typically increases sooting.

Final Answer:
Increases