Temperature measurements and high-speed photography of micron-sized aluminum particles burning in methane flat-flame exhaust

This work seeks to investigate the ignition and burning of micron-sized aluminum particles using nonintrusive temperature measurements and high-speed photography. First, the detected emission spectra were used to deduce the particle temperature according to Planck's laws, and the emissivity dependence on the wavelength was determined. Second, the ratio pyrometer method using a Nikon digital camera was developed to specify the two-dimensional temperature profile. These two methods were preliminarily validated through a B-type thermocouple of known temperature. Further, aluminum particles with controlled sizes of approximately 45 and 125 µm were injected as a well-dispersed stream or discrete single particles, respectively, into the hydrocarbon combustion exhaust with controlled gas temperature and compositions. The temperature evolutions of 45 µm aluminum particles derived from the camera pyrometer are in reasonable agreement with the numerical results predicted by a previously developed model. Regarding 125 µm particles, the temperature contour shows a sharp temperature increase and flame expansion during ignition. It can be attributed to the transition from surface reaction to more vigorous combustion in the vapor phase, which was visualized by a high-speed camera equipped with a long-distance microscopic lens. In this work, the camera pyrometer has demonstrated the capability of measuring the average projected particle temperature and characterizing the combustion process of micron-sized aluminum particles, with promising simplicity and economy.