Plant Operation Practice Test

How much air is approximately needed to burn 1 pound of fuel?

1. 5 pounds of air

2. 10 pounds of air

3. 15 pounds of air

4. 20 pounds of air

The correct answer is: 15 pounds of air

To determine the amount of air required to burn 1 pound of fuel, it is essential to consider the stoichiometry of combustion reactions, particularly for hydrocarbons, which are common in fuels. The process of combustion requires a specific ratio of fuel to oxygen to ensure complete combustion. For typical hydrocarbons, the general rule of thumb is that about 15 pounds of air are needed to completely combust 1 pound of fuel. This figure takes into account that air is composed of approximately 21% oxygen and 79% nitrogen, meaning that there is significantly more air needed than fuel due to the dilution of oxygen in the atmosphere. This 15-to-1 ratio reflects the average conditions found in combustion processes in engines, burners, and other appliances where fuel is burned. Considering factors such as efficiency, type of fuel, and combustion conditions might adjust the exact ratios in practical scenarios, but the approximation remains valid for many typical combustion systems. The other options do not align with this standard ratio found in combustion science. While 5, 10, and 20 pounds of air may represent different combustion scenarios or theoretical calculations, they do not accurately reflect this widely accepted approximation for the combustion of 1 pound of fuel in most cases.