What is combustion?
Combustion is a chemical reaction that happens when a fuel (like gas or wood) burns with oxygen from the air. It releases heat and light.
Why do flames have blue and yellow parts? Different parts of a flame show how cleanly the fuel is burning. Two common colors you’ll see are blue and yellow.
Blue part
- Usually hotter and brighter.
- Occurs when there is plenty of oxygen so the fuel burns more completely.
- When burning cleanly, it mainly makes carbon dioxide (CO₂) and water (H₂O).
Yellow part
- Glows yellow because tiny soot particles get very hot and glow (incandescence).
- Common when there isn’t enough oxygen, so the fuel doesn’t burn completely.
- This part can look smoky and is usually cooler than the blue part.
Complete vs. incomplete combustion
- Complete combustion: fuel + plenty of oxygen → mostly carbon dioxide (CO₂) and water (H₂O). Often blue and very hot.
- Incomplete combustion: not enough oxygen → gives soot (carbon) or carbon monoxide (CO) and water. This often adds yellow, smoky color.
Why this matters
Seeing blue and yellow helps us guess how cleanly a flame is burning. A bright blue flame usually means a strong, clean burn. A yellow flame can mean incomplete burning and soot.
Safety note
Flames can be dangerous. Always learn about flames with a teacher or adult in a safe environment, and keep flammable materials away.