Kerosene quality control: “Char value” is the mass of charred deposition on a standard wick after burning kerosene for 24 hours at a fixed rate. For good-quality kerosene, the char value should be less than approximately how many mg per kg of kerosene?

Introduction / Context:
The char value test assesses kerosene cleanliness and tendency to form deposits during wicking combustion (e.g., lamps). Low char formation indicates better burning performance and less fouling of the wick and chimney.

Given Data / Assumptions:

• Standard wick lamp test over a 24-hour period.
• Mass of char reported as mg per kg of kerosene.
• Seeking the conventional maximum acceptable limit for good-quality fuel.

Concept / Approach:
Acceptable kerosene grades exhibit very low char deposition. Practical specifications commonly cite an upper limit near 20 mg/kg. Values like 100 or 500 mg/kg would represent poor burning quality with significant deposit formation.

Step-by-Step Solution:

Verification / Alternative check:
Historical lamp oil and illuminating kerosene specs align around this magnitude for acceptable char value.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing soot/char aesthetic observations with the standardized mass-based metric.

Final Answer:
20