Radulescu Gasdynamics Laboratory

Experimental Investigation of Detonation Re-initiation Mechanisms following a Mach Reflection of a Quenched Detonation by Rohit Ranjan Bhattacharjee Detonation waves are supersonic combustion waves that have a multi-shock front structure followed by a spatially non-uniform reaction zone. During propagation, a decoupled shock-flame complex is periodically re-initiated into an overdriven detonation following a transient Mach reflection process. Past researchers have identified mechanisms that can increase combustion rates and cause localized hotspot re-ignition behind the Mach shock. But due to the small length scales and stochastic behaviour of detonation waves, the important mechanisms that can lead to re-initiation into a detonation requires further clarification.  If a detonation is allowed to diffract behind an obstacle, it can quench to form a decoupled shock-flame complex and if allowed to form a Mach reflection, re-initiation of a detonation can occur. The use of t...

The sequence of images illustrates the dynamics of cellular detonations.  The mixture is stoichiometric methane-oxygen, at an initial pressure of 3.5 kPa.  The detonation wave runs from left to right.  After the collision of triple points, the non-reacted gas accumulated behind the weak lead shock seperates from the lead front as a large pocket.  This pocket contains non-reacted gas.  The pocket is thinned out from the edges within a cell cycle.  The absence of notable gas dynamic events upon the pocket reaction (strong pressure waves) is indicative of diffusion assisted combustion. The slip lines emanating from the triple points, separating burnt and unburnt gas, develop Kelvin-Helmholtz instability.  This is characterized by the formation of whirls and resulting filamentary structure of the reaction zone interface.  These slip lines terminate with a jet pointing towards the Mach shock. Further analysis of the flow-field can be found in ...

On May 31, Philippe Julien from McGill's Alternative Fuels Laboratory came to our lab with a few toy balloons and a balloon inflation rig equipped with a retractable ignition sting. We put to the test our large scale 2m-by-2m shadowgraph system to visualize methane and hydrogen-air flames.  The flow evolution is visualized with a Phantom V1210 camera. In hydrogen-air, the flame exhibited the characteristic cellular structure. Batman begins! In methane, the larger flame thickness prevents hydrodynamic instabilities for curved flames.   Hats off, methane!