What does 'excess air' refer to in a combustion process?

In a combustion process, 'excess air' refers to the amount of air supplied beyond that necessary for complete combustion. This means that there is more air available than is required to fully burn the fuel. The presence of excess air ensures that all the fuel is adequately combusted, which can help in reducing the formation of carbon monoxide and other harmful emissions. Additionally, it can also help in stabilizing the flame and controlling the combustion process.

Using an appropriate amount of excess air is crucial for efficiency. Too little air can lead to incomplete combustion and production of pollutants, whereas too much can waste energy and also dilute the heat output. Therefore, a careful balance is necessary in any combustion process, but the defining characteristic of 'excess air' is that it is indeed the amount of air beyond what is strictly necessary for the combustion of the fuel being used.