How to verify the difference of different parts of candle flame with matchsticks

Place a matchstick horizontally on the flame (in the middle and lower part of the flame, so that the matchstick contacts the outer flame, the inner flame and the center of the flame at the same time), and take out the matchstick after one or two seconds. You will see that the part of the matchstick that touches the external flame turns black obviously, indicating that the external flame has the highest temperature.

This experiment is used a lot, but recent research shows that the conclusion that the external flame temperature is the highest is incorrect, and the internal flame temperature is the highest. So why is the blackening most obvious where the matchstick touches the external flame? Because C+O2→ (ignites) CO2, the outer flame is in full contact with oxygen, so the matchstick at the outer flame burns fully and turns black most obviously.