When the top flame vent is lit, oxygen flows in from the bottom vent, causing the flame to move downward, burning against the direction of the oxygen flow. The charcoal makers control the size of the flame by adjusting the ventilation; they seal up the vent that the flame reaches and then block the flame vent, until they see blue smoke emerging, which signals that it's time to cool down and await the kiln to be opened.
After listening, Xiulote mentally simulated the specific burning process. Generally, the charcoal near the flame vent should be overburned, with the best quality in the middle, and the areas near the ventilation holes likely underburned.
A moment later, he looked at the anxious charcoal maker leader and calmly inquired.
"How much charcoal is produced from this pile of wood? Can high-quality charcoal make up half of it?"