Experimental observations of flame acceleration and transition to detonation following shock-flame interaction

TLDR

Experiments perturb laminar flame bubbles with incident and reflected shock waves, and the coupled waves are analyzed via a generalized Hugoniot approach, suggesting that thermal auto‑ignition chemistry may also contribute before detonation. Flame acceleration closely coupled to the reflected shock wave leads to detonation at higher incident shock velocities, with combustion fronts resembling turbulent flames yet not due to classical turbulence, indicating that chemi‑acoustic interactions and gas‑dynamic effects drive the observed combustion enhancement.

Abstract

Observations are presented from experiments where laminar flame bubbles were perturbed successively by incident and reflected shock waves. Significant flame acceleration was observed in many instances, with the flame closely coupled to the reflected shock wave. The coupled waves are interpreted using a generalized Hugoniot analysis. As the incident shock velocity increased, detonation emerged near the highly convolved reaction zone. Prior to detonation the external visual attributes of the combustion fronts appear identical to turbulent combustion. However, they cannot be due to classical isotropic turbulence. The overall conclusion is that the observed enhancement of combustion is driven by chemi-acoustic interactions and related gas-dynamic effects. An analysis of the prevailing thermodynamic states suggests that thermal auto-ignition chemistry could also play a significant role prior to the onset of detonation.