What does a yellow flame indicate in gas combustion?

A yellow flame in gas combustion is an indication of insufficient combustion, often due to a lack of air mixing properly with the gas. When combustion is insufficient, it typically means that there is not enough oxygen to facilitate the complete burning of the fuel. As a result, the flame can produce carbon particles that give it a yellow color, indicating that the fuel is not burning cleanly.

In contrast, complete combustion produces a blue flame, signifying that the gas is burning efficiently with the appropriate amount of air. An optimal gas-air mixture would also produce a blue flame due to effective burning, while low fuel consumption does not directly relate to the color of the flame. Therefore, a yellow flame is a clear and observable sign of inadequate air supply and inefficiency in the combustion process.