Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction products.
At a certain point in the combustion reaction, called the ignition point, flames are produced. The flame is the visible portion of the fire. Flames consist primarily of carbon dioxide, water vapor, oxygen and nitrogen. If hot enough, the gases may become ionized to produce plasma. Depending on the substances alight, and any impurities outside, the color of the flame and the fire's intensity will be different.
A burning candle
Bushman starting a fire in Namibia
A coal-fired power station in China
The balanced chemical equation for the combustion of methane, a hydrocarbon
Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion does not always result in fire, because a flame is only visible when substances undergoing combustion vaporize, but when it does, a flame is a characteristic indicator of the reaction. While activation energy must be supplied to initiate combustion, the heat from a flame may provide enough energy to make the reaction self-sustaining. The study of combustion is known as combustion science.
The flames caused as a result of a fuel undergoing combustion (burning)
Air pollution abatement equipment provides combustion control for industrial processes.
The combustion of methane, a hydrocarbon
Colourized gray-scale composite image of the individual frames from a video of a backlit fuel droplet burning in microgravity