2012 Volume 7 Issue 4 Pages 693-706
Burning velocity just after spontaneous ignition has been examined not only experimentally but also theoretically, as related to a Self-propagating High-temperature Synthesis (SHS) process, for a Ti-Al system. After varying the mixture ratio, the degree of dilution, and the compact and particle sizes, the spontaneous ignition temperature, which is determined from the inflection-point of the temporal variations of the surface temperature, was measured. The burning velocity, which is defined as the normal component to the flame surface, has also been measured. It was found that the burning velocity just after spontaneous ignition first increases, and then decreases with an increase in the mixture ratio, which is due to an increase and a decrease respectively, in the heat of combustion. The burning velocity also decreases with an increase in the degree of dilution, which is due to a decrease in the heat of combustion. In addition, the burning velocity increases with increasing size ratio, defined as the ratio of compact and particle sizes, as a result of 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 has been demonstrated, indicating that the formulation used has captured the essential features of SHS flame propagation as it passes through the compacted mixture. Since this kind of particle size effect, which is specifically relevant to flame propagation after spontaneous ignition, has not yet been captured in previous studies, its elucidation can be considered both notable and useful, especially while manipulating the combustion process during materials synthesis.
