Final answer:
Excess primary air in an atmospheric burner leads to a reduced flame temperature because the combustion process becomes too lean, making it less efficient, and in extreme cases, can result in the flame being extinguished.
Step-by-step explanation:
If an atmospheric burner is supplied with too much primary air, the result may be a reduced flame temperature. Providing an excess of primary air can cause the mixing of fuel and oxidizer to become too lean, leading to lower temperatures and possible flame instability or even flameout. Whereas incomplete combustion and excessive soot formation usually result from insufficient oxygen, in this case, the excess air thins out the fuel concentration to a point where the combustion process can cool down and become less efficient.
Proper combustion requires a precise mix of fuel and air. If the ratio skews too much towards air, as with excess primary air, the energy release during combustion is spread over a larger mass of matter, which reduces the overall temperature of the combustion process. In extreme cases, the flame may be too cool to sustain combustion and could be extinguished.