Investigations On the Influence of Different Inert Gases On the Laminar Flame Propagation in Lycopodium/Air Mixtures

The laminar flame velocity is a key parameter in the description of explosions. The determination of the flame velocity (laminar or turbulent) of dust/air flames is relatively complex due to the characteristics of dusts in general. In context of investigations on the limiting oxygen concentration of different powders, the influence of the oxygen concentration and different inert gases on the laminar flame propagation in lycopodium/air mixtures was investigated. In the course of this study, an existing apparatus for the determination of the flame velocity was adapted for the measurement of the laminar flame speed. The apparatus mainly consists of a vertical duct with a diameter of 140mm that is split in three main sections. The dust input system lies in the head section of the apparatus and is realized by a small conveyor screw. The bottom section of the apparatus houses the electrical spark ignition system and a gas inlet system. The gas inlet creates a steady flow of chosen gas mixture to act against the sinking of the particles. The flame propagation is detected by IR photodiodes along the 2m long main section of the apparatus. The dust concentration is measured by light extinction. The determination of the flame velocity was carried out at dust concentrations of 50g/m³, 100g/m³ and 150g/m³ as well as around the lower explosion level of lycopodium. The oxygen concentration was varied in steps of 2%Vol. from 21%Vol. down to the limit where no ignition could be achieved. To investigate the influence of the inert gas on the flame propagation carbon dioxide and nitrogen were used as inert gases. The results of the recent studies are used for further studies on the limiting oxygen concentration of different dusts and the validation of a new CFD model for the simulation of dust explosions in large vessels.