FLUID In the literature: contested

Can turbulence alone turn an unconfined premixed flame into detonation?

In plain words

A flame (deflagration, burning that spreads slower than sound) usually needs walls or obstacles to build up into a detonation. Simulations suggest that strong turbulence alone can do it in open space; does this happen in real gas mixtures, and by what route?

Precise statement

For a premixed fuel-air flame (for example stoichiometric H2-air or CH4-air) in homogeneous isotropic turbulence with no walls or obstacles, determine whether deflagration-to-detonation transition (DDT) occurs, and the threshold in turbulent intensity $u'/S_L$ and integral scale $L/\delta_L$ ($S_L$ laminar flame speed, $\delta_L$ laminar flame thickness). Test the proposed route in which the turbulent flame speed exceeds the Chapman-Jouguet deflagration speed (the fastest steady deflagration allowed by conservation laws), so pressure builds up in the flame brush and forms shocks that trigger detonation. An answer is a verified criterion for unconfined DDT as a function of mixture and turbulence.

What would settle it

Experiments with turbulent premixed flames free of walls and obstacles that observe or exclude DDT at controlled $u'/S_{L}$ and $L$, matched by fully resolved simulations with detailed chemistry.

Status in the literature

Unverified note

Simulations published in 2019 support the route in which the turbulent flame speed exceeds the Chapman-Jouguet deflagration speed; channel experiments up to 2025 are consistent with it, but no test free of walls and obstacles exists, and only a few mixtures have been tested.