Laminar burning velocity measurements of stabilized aluminum dust flames

The laminar burning velocity of a stabilized dust flame is experimentally investigated in the present work. The dust used was aluminum powder with an average particle diameter of approximately 5 microns. Dust flames, in comparison to gas flames, are thicker and brighter, may be influenced by radiation heat transfer, respond differently to heat losses, and are influenced by the particular flow configuration due to the particle's inertia. With the apparent sensitivity to a specific experimental apparatus, the introduction of a fundamental flame speed or burning velocity may be problematic for dust combustion. The present work investigates to what degree burning velocities obtained from Bunsen dust flames depend on experimental conditions (i.e. flow rate and nozzle diameter). The current experimental apparatus permits the stabilization of aluminum-air dust flames using conical nozzles and the accurate measurement of dust concentration. Experimental results show that burning velocities in aluminum-air suspensions increase considerably with the increase in flow rate but decrease with the increase in nozzle diameter. Theoretical estimations show that radiation heat transfer effects are small and cannot explain the observed experimental trends. The present analysis of dust flames shows that the observed effects are primarily the result of flame curvature and of larger flame thickness as compared to gas flames.