Cellular Structures Imaged in the Detonation Front of Pure Liquid Nitromethane

We developed a tabletop compression microscope, which uses laser driven flyer plates to generate 4-ns duration planar shocks in tiny cuvettes filled with the high explosive nitromethane. When the flyer velocity is 4.0 km/s, a detonation forms at a pressure of 19 GPa and a velocity of 6.25 µm/ns. We implemented a high-speed high-resolution camera in combination with photon Doppler velocimetry to watch how the reaction zone develops on the nanoscale. We captured, for the first time in pure liquid nitromethane, micron-scale structures, known as cellular structures in the detonation front. These cells are caused by a superdetonation, a shock traveling in a precompressed medium, that forms behind the shock front after a short delay. The superdetonation will collide with the original shock front and reflect transverse waves into the reacting material behind it. These waves bounce between the backwards traveling shock from the superdetonation and the shock front creating a complex reactive flow with a convoluted shock front. Applying the size of the cells measured in the front to known theory allows us to measure the reaction zone length.