Why excess air is required to burn a fuel completely

Excess air is supplied to the combustion process to ensure each fuel molecule is completely surrounded by sufficient combustion air. As a burner tune-up improves the rate at which mixing occurs, the amount of excess air required can be reduced.

Explanation:

Excess air is supplied to the combustion process to ensure each fuel molecule is completely surrounded by sufficient combustion air. As a burner tune-up improves the rate at which mixing occurs, the amount of excess air required can be reduced.

excess air is required to ensure adequate mixing of fuel and air, avoid smoke, minimize sg in Coal burning, and to ensure maximum steam output.