afterflame

Afterflame is a term used primarily in combustion science to describe a secondary flame that persists after the main flame front has passed through a region. In many hydrocarbon flames, behind the primary flame zone a trailing, less intense flame can continue due to heat feedback and slow secondary reactions. This lingering flame, or afterflame, can appear as a tailing glow behind the main visible flame.

Mechanism and detection: Afterflame arises when residual heat and reactive intermediates sustain combustion in areas where fresh reactants remain or where mixing is incomplete. It is commonly observed in diffusion flames and in certain premixed flames under lean or rich conditions, and its intensity depends on fuel type, pressure, temperature, and flow geometry. Researchers often monitor afterflame using high-speed imaging and chemiluminescence of OH, CH, and other radicals to study extended reaction zones and heat release.

Impact and applications: The presence of afterflame affects flame stability, heat distribution, and pollutant formation such as NOx, by extending the flame zone. In industrial burners, engines, and gas turbines, designers account for post-flame combustion to optimize efficiency and safety. It can also challenge flame sensing and control systems due to lingering emissions after the main flame appears to be extinguished.

Other uses: Outside science, the term has occasionally been used in literature or branding as a metaphor or naming element, though such usage is not standardized. See also: afterglow, tail flame, residual combustion.