What is the formula for calculating combustion efficiency?

The formula for calculating combustion efficiency focuses on the relationship between carbon dioxide (CO2) emissions and the total products of combustion, specifically carbon monoxide (CO) and CO2. In this context, the correct answer reflects the understanding that combustion efficiency increases as more CO2 is produced compared to CO.

When combusting fuel, an efficient combustion process will ideally produce a higher proportion of CO2 and a lower proportion of CO, indicating that the fuel is being burned completely. The formula CO2/(CO + CO2) measures this relationship by comparing the total CO2 produced to the sum of CO and CO2. This reflects the total output of the combustion process, allowing a clear assessment of how efficiently the fuel was utilized.

A higher value from this calculation signifies that combustion is occurring more completely, leading to higher efficiency. Thus, the correct choice accurately represents the standard method to evaluate combustion efficiency in terms of the output gases.