What is a Flame?
A flame is the visible, gaseous part of a fire. It is produced during combustion, a high-temperature chemical reaction between a fuel (like wood or gas) and an oxidant, usually oxygen from the air. The light and heat we see and feel from a flame are the result of this rapid, self-sustaining reaction releasing energy.
Section 2: The Structure of a Flame
A simple flame, like from a candle, has distinct zones. The innermost, dark zone contains unburnt gas. The middle, luminous yellow zone is where glowing soot particles from incomplete combustion are visible. The outermost, faint blue zone is where combustion is most complete. The teardrop shape of a flame is caused by gravity, as hot, less dense gases rise.
Section 3: A Practical Example
Consider a lit candle. The heat from the wick melts the wax, which acts as the fuel. This liquid wax is drawn up the wick by capillary action and vaporizes into a gas. This gas then reacts with oxygen in the surrounding air. This combustion reaction is what produces the visible flame, releasing both light and heat.
Section 4: Why Flames Have Different Colors
A flame's color depends on its temperature and the substances being burned. Incomplete combustion of carbon-based fuels produces tiny solid particles of soot that glow bright yellow or orange, a process called incandescence. Complete combustion produces enough energy to excite gas molecules, which then emit light at specific wavelengths, often appearing blue. Different chemical elements also produce distinct colors when burned, a principle used in fireworks.