Auto-ignition and DDT driven by shock wave – Boundary layer interaction in oxyhydrogen mixture

Detonation research started just at the beginning of 1880s, but its generation mechanism is still a mystery and has not been explained in details yet. Many experimental research in the early 1900s reported that detonation is generated by a transition from deflagration, later known as deflagration-to-detonation transition (DDT). A high performance laser allowing to see a detailed phenomenon was developed later. However, even with nowadays experimental techniques a detailed view on detonation initiation cannot be provided.The present work shows for the first time in details that shock wave – boundary layer interactions are the key for an auto-ignition in the boundary layer in a smooth tube. From that process of the auto-ignition a new flame is developed and propagate along the wall with a sound speed, turns into a fast flame, and trigger DDT finally. The most important factors for the process of the auto-ignition in the boundary layer are thermodynamic interactions in the boundary layer and the induction time.

► Shock wave – boundary layer interaction drives an ignition in the boundary layer.
► Thermodynamic interactions and induction time are the most important.
► A new flame is developed from the ignition and propagates along the wall.
► That flame is a fast flame, because its speed is more than the local sound speed.
► We can observe DDT and detonation.