Reaktionsfront

Reaktionsfront, or reaction front, is the moving boundary between regions where a chemical reaction has occurred and where it has not. It forms when transport processes such as diffusion or convection supply reactants to a localized zone where rapid chemistry takes place. The front often has a characteristic speed and thickness.

In reaction-diffusion models, concentrations follow equations of the form ∂t u = D ∇^2 u + R(u), with D a diffusion coefficient and R(u) the local reaction term. The front is a finite-width zone that propagates with a speed set by diffusion and the kinetics. In Fisher–KPP–type kinetics, the minimal front speed is 2 sqrt(D r) for the standard f(u) = r u (1−u) model, and the thickness scales roughly as sqrt(D/r). Fronts can be classified as pulled or pushed, depending on whether the leading edge or the nonlinear interior dynamics control the propagation.

Reaktionsfronts occur in combustion (premixed flames), autocatalytic or catalytic chemical systems, and certain polymerization and porous-media processes. The concept is also used in theoretical biology as an analogue for the spread of traits or populations, described by reaction-diffusion equations.

Observing fronts typically involves imaging concentration fields or heat release, while real systems may include convection, turbulence, and temperature gradients that alter front structure and speed. See also reaction-diffusion system; Fisher-KPP equation; combustion theory.