What defines complete combustion?

Complete combustion is defined as a process where all of the fuel is burned fully, ideally in the presence of enough oxygen or air to allow the fuel to react completely. When there is an excess of theoretical air, the combustion process ensures that all fuel is converted to carbon dioxide and water, leaving no unburned fuel.

This scenario maximizes the efficiency and energy output of the combustion process, as it eliminates any waste that might occur from incomplete combustion. In contrast, incomplete combustion could leave some fuel unburned or result in the production of carbon monoxide and soot, which can be harmful and wasteful. Using theoretical air ensures that the combustion is calculated based on the stoichiometric amounts required for complete burning, while having excess air guarantees that all fuel gets burned efficiently.