Detonation diffraction from circular tubes to cones

Abstract

An experimental study of the detonation diffraction from 26- and 52-mm inner diameter tubes to cones of various angles α in stoichiometric acetylene/oxygen mixture allowed us to determine critical conditions for diffraction and to detail the mechanisms involved. All soot-foil records show that critical transmission is due to super-detonation propagating transversally in shocked gas before the decoupled flame front. However, at large cone angles (α > 40∘), super-detonation originates at the axis of the flow and propagates tangentially to the cone wall (this situation is close to detonation transmission to a space and a half-space). At smaller angles (i.e. α < 40∘), on the opposite, super-detonation originates at the cone wall and propagates toward the axis. In addition the soot plates often give some evidence that, during escape of detonation products from the tube, a Mach disk is formed at a distance of about one tube diameter from the tube exit. Numerical two-dimensional simulations of detonation diffraction favorably agree with the observations.