Deflagrating

Deflagrating refers to the rapid combustion process that propagates through a fuel–air mixture or along a surface at subsonic speeds with respect to the local speed of sound. In deflagration, the flame front advances mainly by heat transfer through conduction and convection and by diffusion of reactive species, rather than by a shock wave. As a result, the pressure rise behind the flame is typically modest and the burning velocity remains well below the sonic limit of the mixture.

Deflagration is distinct from detonation, where a supersonic shock front drives the chemical reaction and produces a much larger and sharper pressure rise. The deflagration front can be laminar, with a predictable flame speed set by chemical kinetics and diffusion, or turbulent, where mixing and surface area enhancement accelerate the apparent flame speed.

A safety and engineering concern is the potential for deflagration to transition to detonation (deflagration-to-detonation transition, DDT) under certain conditions of confinement, geometry, and turbulence. DDT is particularly relevant in confined spaces containing flammable gases, vapors, or dusts and is a focus of hazard analysis and mitigation efforts.

Common contexts involve hydrocarbon-air mixtures, hydrogen-air mixtures, and dust explosions in industrial settings. Mitigation strategies include inerting, ventilation, flame arresters, fuel–oxidizer segregation, and rapid quenching. The term deflagrating is often used to describe the process of undergoing deflagration, though most discussions focus on deflagration as a mode of combustion.