The presence of excess air in combustion systems primarily results in:

The presence of excess air in combustion systems primarily results in fuel wastage because excess air dilutes the concentration of fuel in the combustion chamber. When more air is present than what is necessary for complete combustion, not all of the fuel is utilized effectively. This inefficiency leads to unburned fuel being expelled in the exhaust, which is essentially wasted.

In combustion processes, there is an optimal air-to-fuel ratio that enables complete combustion, maximizing energy output and minimizing emissions. When there is excess air, it creates a cooler flame and lower flame temperature, as the added air absorbs energy that would otherwise contribute to heating the fuel. Therefore, while choices like optimal combustion and reduced emissions indicate improved efficiency, they do not correspond to the scenario of excess air, which inherently causes fuel wastage and inefficiency.