Study on combustion oscillation characteristics of micron aluminum particles

Aluminum (Al) particles are regarded as general addictive into solid propellants not only as an extra energy source but also as a metallic damping-carrier on combustion instability. It is possible that the stability in propellant can be improved through partial Al substitution. However, knowledge of unsteady combustion characteristics of Al particles has been insufficient. In order to explore the unsteady combustion and attenuation characteristics of Al particle, a methane micro-combustor is designed. The acoustic oscillation of combustor is found to be excited, regardless of the Al particles mass of diameter. Moreover, the effects of 1) particle size and 2) mass are examined in detail. The burning of micro-sized Al particles in present experiment is attributed to melt dispersion mechanism. The rupture time is in the range of 2.18 ms to 2.81 ms for Al particles with mean diameter of 10 μm, 20 μm and 30 μm. With the increasing of particle size, the sound level of high-frequency oscillation increases from 65 dB to 85 dB. However, the attenuation effect for high-frequency oscillation is weakened for larger particle size. Finally, it is found that the pressure growth rate can be dramatically increased from 1000 Pa/s to 11,000 Pa/s and the peak amplitude of high frequency oscillation is augmented, as the Al particles mass ratio is increased. The present research sheds lights on an effective evaluation of unsteady Al combustion by considering particles parameters.