Gas Fitter Practice Test

What is the ultimate CO2 level for natural gas if excess air temperature is below 65 F?

1. 9.9%

2. 12.9%

3. 8.9%

4. 11.9%

The correct answer is: 11.9%

The ultimate CO2 level for natural gas when the excess air temperature is below 65°F is 11.9%. This value is based on the stoichiometric relationship of combustion and the complete combustion characteristics of natural gas. When the combustion process occurs at lower temperatures, there is a tendency for the gas to produce a higher concentration of carbon dioxide due to the more efficient combustion process. Understanding combustion efficiency is essential here. At cooler temperatures, combustion may not be as complete, leading to the production of more CO2 as opposed to unburned hydrocarbons or pollutants. In this case, the combustion of natural gas produces water vapor and carbon dioxide, and maintaining the CO2 level at 11.9% indicates optimal combustion efficiency given the lower excess air conditions. Therefore, knowing how temperature and excess air affect combustion helps one understand why 11.9% is the appropriate CO2 level under the specified conditions.