G2 Gas Fitter Practice Exam

What is the theoretical gas to air ratio necessary to achieve perfect combustion with an atmospheric natural gas burner?

1. 1 part of natural gas to 5 parts of air

2. 1 part of natural gas to 8 parts of air

3. 1 part of natural gas to 10 parts of air

4. 1 part of natural gas to 12 parts of air

The correct answer is: 1 part of natural gas to 10 parts of air

In perfect combustion, the fuel and air mix should allow for complete oxidation of the fuel without any excess air or unburned fuel. For natural gas (primarily methane), the stoichiometric ratio—that is, the precise amount of air needed to fully combust with the given amount of gas—is typically about 1 part of natural gas to 10 parts of air. This ratio ensures that all of the methane is converted to carbon dioxide and water, resulting in efficient energy production. The combustion process does not only depend on the gas composition but also on conditions such as pressure and temperature, which can affect the efficiency of combustion. A ratio of 1 to 10 signifies that when 1 volume of natural gas is burnt, it requires 10 volumes of air, which reflects ideal combustion. Deviating from this ratio results in either incomplete combustion (excess fuel) or reduced efficiency (excess air). The other options suggest different proportions, which would lead either to excess fuel that doesn't combust completely or excess air, which can lower the flame temperature and reduce the efficiency of the burner. Understanding this ratio is essential for achieving optimal performance with gas appliances.