Experimental Study of Combustion Characteristics of Micron-Sized Aluminum Particles and Liquid Water

Abstract

Experiments have been performed to explore the combustion behaviors of spherical micron-sized aluminum ($\mu$ Al) particles and liquid water for Al particle sizes in the range of $3.5–25\mu \mathrm{m}$ . The ignition of quasi-homogeneous $\mu$ Al/water mixtures was successfully implemented by employing a novel ignition method, and self-sustained flame propagation was obtained in the mixtures over a broad range of fuel-equivalence ratio $\varphi$ . The burning rates, flammability limits, and thermal structure of the propagating flame were determined. The combustion products were also analyzed. For the particle sizes considered, the burning rates were found to first increase and then decrease as $\varphi$ increased, with the maximum values occurring at $\varphi =1.7–2.0$ and substantially lower than nano-$\mathrm{Al}/{\mathrm{H}}_2\mathrm{O}$ mixtures. The dependence of the burning rate on particle size follows a power law, $r_b\sim D^{-0.18}$ , indicating that the reaction process of $\mu \mathrm{Al}$ and water is kinetically controlled. Base on the experimental observations, a simplified flame propagation model was developed to provide insight into the effects of particle size and equivalence ratio. Combustion product analyses revealed that Al residues increased as $\varphi$ was further increased from 0.7, and the combustion efficiency of aluminum decreased accordingly.