Electrical oscillations in combustion of magnesium particles in a constant electric field

For a magnesium particle (6 mm in diameter)burning in air, electrical oscillations in the measuring circuit were found at a threshold intensity of the external constant electric field of 30 kV/m. Spectral analysis of the oscillations revealed low-frequency (5 kHz) and high-frequency (25 kHz) oscillation modes. It is shown that low-frequency electrical oscillations are due to variations in the density of the positive space charge of submicron MgO particles between the metal particle surface and the negatively charged plate of the capacitor. High-frequency oscillations are caused by modulation of the dielectric permittivity of the medium in the chemical condensation zone of the magnesium particle. The cause of the modulation is instability in the condensation zone of the burning particle, which is manifested in the excitation of longitudinal oscillations of the MgO particles (dust acoustic waves) propagating in the thermionic plasma of magnesium combustion products. The occurrence of the dust acoustic waves is due to streaming instability caused by differences in the drift velocities of charge carriers in the electric field.