What is meant by excess air?

Excess air refers to the additional air that is supplied to a combustion process beyond what is theoretically required for complete combustion of the fuel. In a perfect combustion scenario, all fuel would react with a precise amount of air to convert it entirely into carbon dioxide, water vapor, and other byproducts. However, practical combustion systems often introduce excess air to ensure that any variations in fuel quality, moisture content, or other factors do not lead to incomplete combustion. This extra air helps to reduce emissions of carbon monoxide and unburned hydrocarbons, ensuring more thorough combustion and better efficiency in the system.

Understanding excess air is crucial because it affects the overall efficiency of burning processes and impacts emissions; too much excess air can lead to wasted energy and increased heating costs, while too little can lead to incomplete combustion and harmful emissions.