The visible, gaseous portion of the fire is called a flame (from Latin flamma). A very exothermic chemical reaction occurring in a narrow zone causes it. Very hot flames have enough ionized gaseous components with enough density to be classified as plasma.

When a lighter is held to a candle, the color and temperature of the flame depending on the type of fuel used in combustion, the supplied heat causes the candle wax’s fuel molecules to evaporate (If this process happens in an inert atmosphere without an oxidizer, it is called pyrolysis). In this condition, they may easily react with oxygen in the air, releasing enough heat in the exothermic process to evaporate even more fuel and maintain a continuous flame. The vaporized fuel molecules break down at the high temperature of the flame, generating different incomplete combustion products and free radicals, which subsequently react with each other and with the oxidizer in the next flame’s reaction (fire). A cold metal spoon may be used to explore all of the distinct aspects of a candle’s flame: Water vapor is the final product of combustion; yellow portions in the center are soot, and unburned wax is found right adjacent to the candlewick. When the flame has enough energy, it will excite the electrons in some of the transitory chemical intermediates, such as the methylidyne radical (CH) and diatomic carbon (C2), causing visible light to be emitted when these substances release their surplus energy (see spectrum below for an explanation of which specific radical species produce which specific colors). The average energy of the electromagnetic radiation emitted by a flame increases as the combustion temperature of the flame rises (assuming the flame contains tiny particles of unburned carbon or other material) (see Black body).

Several than oxygen, other oxidizers can be employed to create a flame. When hydrogen is burned in chlorine, a flame is produced, and gaseous hydrogen chloride (HCl) is released as a combustion product. Hydrazine plus nitrogen tetroxide, which is hypergolic and widely employed in rocket engines, is another of several potential chemical combinations. Fluoropolymers, such as magnesium/Teflon/Viton, can be utilized to deliver fluorine as an oxidant of metallic fuels.

The chemical dynamics of a flame are extremely complicated, including a huge number of chemical reactions and intermediate species, the majority of which are radicals. For example, the GRI-Mech chemical kinetics scheme employs 53 species and 325 elementary processes to explain biogas combustion.

There are several techniques for delivering the necessary combustion components to a flame. The flame develops where oxygen and fuel spread into one other in a diffusion flame. A premixed flame is one in which the oxygen and fuel have been mixed ahead of time, resulting in a different sort of flame. Candle flames (diffusion flames) work by evaporating the fuel, which rises in a laminar flow of hot gas, mixing with the oxygen in the air and combusting.

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