deflagratie

Deflagration, known in Dutch as deflagratie, is a mode of combustion in which a flame front propagates into the unburned fuel–air mixture at subsonic speeds, slower than the local speed of sound. The propagation is sustained primarily by heat transfer and molecular diffusion from the burned gas to the unburned region, rather than by a shock wave. As a result, the pressure rise during a deflagration is typically moderate, though rapid deflagrations can still produce dangerous transient overpressures.

By contrast, detonation involves a shock wave that pre-compresses and heats the unburned mixture, triggering combustion in a near-instantaneous reaction. Detonation propagates at much higher, often supersonic, speeds and generally generates larger overpressures and more destructive effects. Deflagration can, under certain conditions, accelerate and transition to detonation in a process known as deflagration-to-detonation transition (DDT). This is more likely in confined spaces with turbulence, obstacles, and particular mixture properties.

Factors influencing deflagration include the fuel–air ratio, initial temperature and pressure, confinement, and the level of turbulence. The phenomenon is relevant to industrial safety (gas leaks, chemical plants, mining), propulsion research, and engine technology. In spark-ignition engines, for example, the combustion process begins as a subsonic deflagration that gradually heats and expands the mixture; in heavy or poorly controlled mixtures, the flame can intensify toward faster, potentially detonation-like behavior. Understanding deflagration helps in designing safer facilities, evaluating explosion risks, and choosing appropriate mitigation strategies.