1 Characterization of Nano- and Micron-Sized Aluminum Particles Burning in Dump Combustor

Combustion performance of nano- and micro-sized aluminum particle additives was characterized and compared in dump combustor experiments. The nominal sizes of the aluminum particles used in the combustion experiments were 50-nm and 2-µm, respectively. The combustor featured a rearward-facing step for flame holding and an ethylene-oxygen pilot igniter placed at four step heights upstream of the dump plane. The combustor was operated with premixed ethylene-air at combustor velocities between 40 and 70 m/sec, and equivalence ratios between 0.5 and 0.7. The particles were introduced into the combustor as secondary fuel injection of particle-laden ethylene with aluminum particle loadings ranging between 4 % and 15 % of the total fuel mass flow rate. The particle dispersion and combustion behaviors for each case were characterized using planar Mie-scattering visualization and narrow-band emissions measurements. Also, the resulting pressure and temperature profiles were measured and compared against the baseline case where no particles were added. While particle dispersion characteristics appeared different between nano- and micro-sized aluminums, the particles in both cases reacted inside the combustor producing higher thermal output and higher momentum flux. The effects of particle burning on exit flow temperature and dynamic pressure were, however, significantly different between the two cases. While nano-sized particles readily contributed to the thermal output resulting in higher temperature profiles than the baseline case profiles, relatively slow burning of micro-sized particles caused the resulting temperature profiles to be initially even lower than the baseline profiles. The results suggest that micro-sized aluminum particles would be ineffective for high-speed combustors. On the other hand, nano-sized aluminum particles were shown to effectively enhance the volumetric heat release resulting in increased performance. The exit dynamic pressure profiles showed clear increase in momentum flux associated with nano-particle combustion. I