Classification of detonation length scales and post-shock states through spatio-temporal velocity fields

The ability to predict and control detonation waves is of significant interest to several fields, including high-speed propulsion, industrial safety, and astrophysics. Understanding multidimensional detonation behavior requires identifying a characteristic length scale of a detonation, one of which is the cell width (or cell length). This study aims to validate the use of spatio-temporal velocity fields of the leading shock (i.e., velocity maps) as a method of measuring cell structure data through a series of experiments of stoichiometric methane–oxygen mixtures with varying levels of nitrogen dilution in a thin channel. Velocity maps were extracted from megahertz shadowgraphy, and the cell sizes measured from the velocity maps, soot foils, and shadowgraphy images were compared and showed good agreement. The agreement between diagnostics validated velocity maps as a method of measuring cellular length scales. The velocity maps were then used to compute the post-shock state of the detonation, and high-resolution spatio-temporal pressure and temperature fields of the von Neumann state were created for the first time. These von Neumann maps contain the same cell structure data that velocity maps do and also provide the local post-shock dynamics of a non-uniform shock.