Deflagration
Definition and meaning of Deflagration in chemistry.
Deflagration is a rapid combustion reaction in which a flame front propagates through a fuel by transferring heat to adjacent unreacted material, moving at subsonic speed relative to the unburned substance.
In more detail
Because the reaction advances through conduction, convection, and radiation of heat rather than through a shock wave, deflagration travels at typical speeds from centimeters per second up to a few hundred meters per second, well below the speed of sound in the unreacted material. This distinguishes it from detonation, in which a supersonic shock wave compresses and ignites the fuel almost instantaneously, producing far higher pressures and more destructive overpressure effects. Deflagration is the mode of burning seen in ordinary flames, burning propellants, and most accidental fires or dust explosions, and its rate strongly depends on pressure, temperature, and fuel-oxidizer mixing. Under confinement or turbulence, a deflagration can sometimes accelerate and transition into a detonation (deflagration-to-detonation transition, DDT).
Key facts
| Field | Physical Chemistry |
|---|---|
| Propagation mechanism | Heat conduction/convection into unreacted fuel |
| Typical speed | Subsonic (mm/s to ~hundreds of m/s) |
| Contrast | Detonation (supersonic, shock-driven) |
Gunpowder burning in an open firework fuse undergoes deflagration: the flame front moves through the powder train at a controlled subsonic rate, unlike the near-instantaneous detonation of a high explosive such as TNT.
Frequently asked questions
Is deflagration the same as an explosion?
Not necessarily. Deflagration is a combustion mechanism; it can occur as an ordinary flame or, if confined or fast enough, produce an explosion. It is distinguished from detonation, which is always a shock-driven explosive process.
Can a deflagration become a detonation?
Yes. In confined or turbulent conditions, flame acceleration can trigger a deflagration-to-detonation transition (DDT), converting subsonic burning into a supersonic shock-driven detonation.