Final answer:
Excess air is the term for the surplus oxygen in the combustion chamber beyond what is required for complete combustion, aimed at reducing harmful by-products and ensuring fuel is fully burned.
Step-by-step explanation:
The air that passes through the combustion chamber in excess of that which is required for complete combustion is called excess air. In an ideal combustion process, fuel would react with oxygen to produce only carbon dioxide and water. However, real-life combustion often involves a surplus of air to ensure that all the fuel is burned completely. This excess air helps in minimizing the production of harmful by-products such as carbon monoxide, particulates, and soot that occur in incomplete combustion. For instance, in automobiles, the catalytic converter uses this excess air to convert residual hydrocarbons and carbon monoxide into less harmful substances like carbon dioxide and water vapor. Nonetheless, the presence of excess air can result in energy loss, as not all the heat generated can be utilized, some being lost with the exhaust gases.