Phases of Combustion
Authored By: D. Kennard, K. McPherson
The main phases of the combustion reaction are:
- Pre-ignition is the heat absorbing phase of combustion where heat is applied to fuel resulting in vaporization of water and other substances providing the gases that sustain flames in the next phase of combustion.
- Flaming combustion is a phase of combustion where heat is released. This phase is the most efficient phase of combustion producing the least amount of smoke per unit of fuel consumed. The products of flaming combustion are primarily carbon dioxide and water vapor.
- Smoldering combustion is the least efficient phase of combustion and produces the most smoke. This phase lacks flame, and is associated with conditions where oxygen is limited – either by char of fuels (particularly those with large surface to volume ratios) or by tightly packed fuels like duff and organic soils or in wet fuels.
- Glowing combustion is the phase of combustion when only embers are visible. During this phase, there is no longer enough energy to create visible smoke.
- Extinction either occurs when fire goes out after the available fuel is consumed or there is insufficient heat produced by oxidation in previous stages to vaporize moisture from unburned fuel. The fuel moisture, surrounding air or inorganic materials absorb and reduce the heat from combustion and this results in the fire extinction process (DeBano et al. 1998).
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