What happens to the cool and hot zones of a nonluminous flame when the air control valve is closed?

When the cool and hot zones of a non luminous flame’s air control valve is closed, the gas in which will be in placed as first and as it encounters air as it was in the mouth of the burner, there will be a presence of incomplete mixing, causing a combustion which would be incomplete and will also lead to a process that can’t be controlled, resulting to flame that is cool.