Combustion of Mechanically Alloyed Al∙Mg Powders in Products of a Hydrocarbon Flame

Abstract

Burn times and temperatures were measured optically for a set of mechanically alloyed Al·Mg powders injected into a laminar and a turbulent air-acetylene flame. Magnesium concentrations varied from 10 to 53 mole%; particle sizes were in the range of 1–50 μm. Emission from the burning particles at 700 nm, 800 nm, and 900 nm was captured using three filtered photomultiplier tubes. The burn times were correlated with particle sizes using measured statistical distributions for both times and sizes. The measured trends for burn times, t, as a function of particle size, d, for all alloys were approximated by a t = a·dn law, where the exponent n varied from 0.6 to 1. Shorter burn times were measured in more turbulent flows; respectively, the values of pre-exponent, a, decreased and exponent, n, increased slightly with an increased level of turbulence. An increase in Mg concentration led to longer burn times for the alloy particles for all flame conditions. For all compositions, alloy particles burned longer than similarly sized Al particles except for the alloy with the smallest concentration of Mg, Al0.9Mg0.1, for which particles less than ˜4 μm burned faster than similarly sized Al. This effect was observed for laminar and turbulent flames. The optically measured temperatures were lower for Al0.47Mg0.53 alloy (˜2400 K) compared to ˜2700–2800 K obtained for other alloys. Turbulent mixing resulted in a slight increase in the measured temperature.