Effect of Velocity Slip on the Burning Rate of Fuel Particles

Abstract

The burning rate of fuel particles often is limited by the rate at which gaseous reactants can diffuse to the particle surface. Under such conditions, the diffusion limitation can be reduced by letting the particle slip with respect to the surrounding gas. The relationship between slip velocity and increase in the burning rate is analyzed taking into account both the decreasing particle size during combustion and the tendency of viscous drag to reduce slip. Four slip-producing flows are explored: shock waves, flow accelerations, flow oscillations (turbulence), and standing waves. Benefits are computed for a range of typical conditions. The results indicate that only small reductions in burning time can be expected for particle sizes suitable for flight applications.