Flame Propagation in Dust/Air Mixtures Under Reduced Pressure Conditions

Industrial processes are often operated at conditions varying from atmospheric conditions. Safety relevant parameters normally used for hazard evaluation and classification of substances like combustible dusts are only valid within a very narrow range of pressure, temperature and gas composition. The development of dust explosions and flame propagation under reduced pressure conditions is poorly investigated. Standard laboratory equipment like the 20 l Siwek chamber does not allow investigations at very low pressures. An experimental device was developed for the investigations on flame propagation and ignition under reduced pressure conditions. Flame propagation was analysed by a video analysis system the actual flame speed was measured by optical sensors. Experiments have been carried out with lycopodium at dust concentrations of 100 g/m³, 200 g/m³ and 300 g/m³. Flame shape and velocity strongly differs to results at atmospheric conditions. Effects like buoyancy of hot gases during ignition and flame propagation are less strong that at atmospheric conditions. For the investigated dust concentrations flame velocity reaches speeds that are nearly an order of a magnitude higher than at ambient conditions. Results gained from these experiments are contributing to the setup of mathematical models for the description of gas explosions and ignition.