Diffusionflammor

Diffusionflammor are flames in which the fuel and the oxidizer are introduced separately and mix and react predominantly by diffusion at the flame surface, rather than being premixed before ignition. They are common in hydrocarbon flames, such as candles, oil lamps, and many industrial jet flames, where the fuel leaves a source and entraining air supplies the oxidizer.

In a diffusion flame, the reaction zone forms at the interface where fuel molecules and oxidizer molecules meet through diffusion. The flame can be laminar or turbulent, and its shape is influenced by the flow field and buoyancy. The color of diffusion flames often reflects soot formation: enriched, fuel-rich regions tend to emit a luminous yellow or orange glow due to incandescence of soot particles, while regions with more complete combustion can appear blue.

Key properties include the dependence on mixing rates and local equivalence ratio, which determine temperature distribution, flame length, and pollutant formation. Because combustion occurs where mixing happens, diffusion flames are sensitive to ambient conditions, air flow, and fuel jet characteristics. Soot and carbon monoxide formation are common concerns when the mixture is not optimally mixed and burned.

Diffusion flames are important for fundamental combustion research as simple models of mixing-controlled reactions. They also have practical relevance for safety devices and engines that operate with diffusion-like burning, such as candles, diesel sprays, and certain industrial burners.

See also: premixed flames, jet diffusion flames, soot formation, combustion modeling.