Põlemisfront

Põlemisfront, in Estonian, refers to the flame front or combustion front—the moving boundary that separates burned gases from unburned fuel–oxidizer mixture in a combustion process. It is the region where chemical reactions occur rapidly, releasing heat and causing a sharp rise in temperature and changes in chemical species.

In premixed flames, the front is often described as a thin, nearly planar surface in laminar conditions, though it becomes highly wrinkled and corrugated in turbulent flows. The front's thickness ranges from submillimeter in highly flame-stabilized conditions to several millimeters in slower or diffusion-limited cases. The speed at which the front propagates into the unburned gas is the laminar burning velocity, and can vary from a few cm/s to several m/s depending on fuel, oxidizer, and pressure.

Two main propagation regimes are recognized: deflagration, in which heat and radical species diffuse into the fresh mixture and the front moves subsonically; and detonation, in which a shock wave drives an extremely thin reaction zone at supersonic speeds. In turbulent flames, the front becomes highly intricate, and its local orientation and speed are influenced by flow structures and turbulence.

Methods to study the Põlemisfront include optical diagnostics such as Schlieren imaging and planar laser-induced fluorescence, as well as computational simulations solving conservation equations for mass, momentum, energy, and chemical species.

Understanding the behavior of the Põlemisfront is essential for the design of safe and efficient combustion devices, including engines and burners, as well as for fire safety and risk assessment in industry and energy systems.