Zeldovich spontaneous wave

A Zeldovich spontaneous wave, also known as the Zeldovich gradient mechanism, is a theoretical type of reaction wave that can occur in a reacting substance, such as a gas mixture, where the initial temperature varies across different locations.^[1] This variation in temperature creates gradients that cause different parts of the substance to react at slightly different times, driving the wave's propagation. Unlike typical combustion waves, such as subsonic deflagrations and supersonic detonations, it's characterized by the absence of interactions between different parts of the substance, such as those caused by pressure changes or heat transfer.

Introduced by Yakov Zeldovich in 1980^[2] building on his earlier research,^[3] this concept is often cited to explain the yet-unsolved problem of deflagration to detonation transition (DDT),^[4][5][6][7] where a slow-moving subsonic flame (deflagration) accelerates to a supersonic detonation. Essentially, the Zeldovich spontaneous wave helps explain how a reaction can spread solely due to initial temperature differences, independent of factors like heat conduction or sound speed (provided the initial temperature gradients are small). While it simplifies real-world conditions by neglecting gas dynamic effects, it offers valuable insights into the fundamental mechanisms of rapid reactions. The wave's behavior is dependent on the initial temperature distribution.