Air that passes through an appliance in excess of that required for complete combustion is called what?

The term for air that passes through an appliance in excess of that which is necessary for complete combustion is known as "excess air." This concept is crucial in combustion systems since maintaining the correct air-to-fuel ratio is essential for achieving efficient combustion, minimizing pollutants, and maximizing energy output.

Excess air refers specifically to the portion of air that goes beyond the stoichiometric requirement for combustion, meaning it is not needed for the ideal reaction of fuel and air. While some air is essential for complete combustion to ensure all the fuel is burned, excess air ensures that there is a buffer to avoid incomplete combustion, which can lead to the production of carbon monoxide and other harmful byproducts.

The role of excess air is also significant in ensuring that the combustion process can be monitored and adjusted, which can improve efficiency and reduce emissions. Adjusting the amount of excess air can help in fine-tuning the combustion process for optimal performance while also providing necessary safety margins.

The other options—primary air, secondary air, and residual air—refer to specific types or conditions of air used in combustion, but do not accurately describe the concept of air that exceeds the requirement for complete combustion.