Final answer:
A long, yellow flame on an atmospheric burner is usually due to the incomplete combustion of carbon-based fuels, where carbon particles are emitted and heated, causing them to glow yellow.
Step-by-step explanation:
A long, yellow flame (or luminous/carbonizing flame) on an atmospheric burner is typically caused by the combustion of any carbon-based fuel (such as gas, diesel, or coal). During the process of combustion, incomplete burning can occur due to insufficient oxygen, which results in the production of soot or carbon particles. These particles get heated to high temperatures, causing them to glow and emit light, thus giving the flame its yellow color.
This phenomenon can be explained by high-temperature combustion of a fuel, where the molecules are heated so much that they glow. The yellow color indicates that the combustion process is not completely efficient, and significant carbon particles are being produced. This is often seen with the use of sulfur-based fuels like diesel and coal, or the presence of fumes from paints or solvents adding to the incomplete combustion process.