(10b) On the Occurrence of Flame Instabilities during Dust Explosions

The paper addresses two series of experiments where flame instabilities are affecting the course of dust explosions. The first series of experiments concern testing of isolation devices and especially explosion isolation flap valves preventing dust explosions from propagating from a vented process vessel into connected equipment. The vented process vessels vary in volume from 4.4 to 60 m³. When applying the isolation valve the reduced explosion pressures were considerably higher, up by a factor of 4.4. These experiments have been published before but the role of flame instabilities and especially the Raleigh-Taylor instability is not recognized. Understanding the occurrence and influence of flame instability processes is important to be able to predict the maximum reduced overpressures during vented dust explosions where the protected vessel is also provided with isolation devices.

The second series of experiments concern dust explosion experiments in a closed vessel of 55 m³. During these experiments acoustically driven flame instabilities were observed increasing combustion rates. The effects of acoustically driven flame instabilities were shown to decrease at higher dust concentrations and when applying rockwool to damp the acoustic waves.