Detonation dynamics visualization from megahertz imaging

Megahertz-rate imaging measurements are made in a non-premixed rotating detonation engine (RDE) and a premixed detonation tube. For the RDE, this includes 1 MHz broadband chemiluminescence imaging. The MHz-rate imaging enables high spatiotemporal resolution of the detonation propagation enabling optical emulation of the traditional soot foil technique used to measure detonation cell size. A key contribution of this work is that it represents the first direct experimental visualization of the cellular structure in an RDE. The detonation tube is used as a diagnostic development platform for the RDE, and measurements include 1 MHz particle image velocimetry and 10 MHz broadband chemiluminescence imaging. Vorticity in the detonation tube is between 50000 – 130000 s^-1 for up to 15 us after the passage of the detonation wave front. These high vorticity values along with poor premixing of some pockets upstream of the detonation may explain some of the post detonation burning in the RDE, where the vorticity rapidly mixes the unburned reactants in a hot environment leading to post wave fast deflagration. We discuss some of the challenges with time resolving detonation flows.