Nano-aluminum flame spread with fingering combustion instabilities

Three consecutive modes of flame propagation were observed over a bed of nano-aluminum burning with a counter-flowing oxidizer of 20% oxygen and 80% argon by volume, each displaying significantly different characteristics. The first mode of propagation was the focus of this study and was examined within the critical Rayleigh and Peclet number regime where three-dimensional buoyancy effects were hindered and the fingering thermal-diffusive instability occurred. Fingering flame spread was observed and characterized for various Peclet numbers, top plate heights and particle sizes to gain a better understanding of the reaction mechanism associated with the combustion of nano-particles in close contact. Results indicate that the first mode of flame propagation over a bed of nano-aluminum has spread rates an order of magnitude greater than that of cellulose fuels. However, similar trends occur when varying the Peclet number and the height of the top plate. Furthermore, faster propagation speeds occur with smaller particles because of their increased specific surface area. The widths of the fingers grow and more of the surface is burned with increasing particle size due to the longer time scale available for lateral growth.