Burning Velocity for the Compacted Mixture of Ti-Al System Just after the Spontaneous Ignition

Abstract

Burning velocity just after the spontaneous ignition has been examined not only experimentally but also theoretically, relevant to the Self-propagating High-temperature Synthesis (SHS) process, for Ti-Al system. By varying mixture ratio, degree of dilution, and compact and particle sizes, not only the spontaneous ignition temperature, determined from the inflection-point of the temporal variations of the surface temperature, but also the burning velocity, defined as the normal component to the flame surface, has been measured. It is found that the burning velocity just after the spontaneous ignition first increases and then decreases with increasing mixture ratio, due to an increase and a decrease, respectively, in the heat of combustion, that it decreases with increasing degree of dilution, due to a decrease in the heat of combustion, and that it increases with increasing size ratio, defined as a ratio of compact and particle sizes, due to an increase in the reaction surface per unit spatial volume in the compacted mixture. Experimental comparisons with theoretical results have also been conducted and a fair degree of agreement is demonstrated, indicating that the formulation used has captured the essential features of the SHS flame propagation that passes through the compacted mixture. Since this kind of particle size effect, especially, relevant to the flame propagation after the spontaneous ignition, has not been captured in the previous studies, its elucidation can be considered not only notable but also useful, especially, in manipulating combustion process in materials synthesis.