Flame propagation through dust clouds of carbon, coal, aluminium and magnesium in an environment of zero gravity

The mechanism and the rate of flame propagation through dust clouds of carbon, coal, aluminium and magnesium have been investigated. Any errors due to the upward buoyant motion of burnt gases and the downward settling velocity of dust particles were eliminated by conducting these experiments in a zero-gravity environment. A technique of flat-flame propagation was developed to measure the burning velocity accurately. The results show that the burning velocity is influenced by particle size, fuel transfer number, dust concentration, volatile matter (for coal), oxygen enrichment and heat loss by radiation from the burning fuel particles. A simple model to elucidate the structure and the mechanism of flame propagation is developed. Then expressions to predict the flame thickness and the burning velocity are derived. Attention is drawn to the similarity that exists between the mechanisms of flame propagation through dust clouds and through fuel mists. The importance of radiation heat loss is emphasized. It is shown that for a dust cloud of particle size 10 $\mu m$ of graphite or aluminium in oxygen, radiation loss from particles can reduce the burning velocity by as much as 40% or 25% respectively.