Dynamic behavior of flowing particles in combustion environment

A new method for measuring the dynamic behavior of a single particle in combustion conditions has been developed. In this method, a particle is suspended in an electric field where various forces (gravity, free convection, forced convection, and photophoretic forces) are applied to it, normal to each other. An electro-optical system serves as a controller that views the particle's position and retains it at a fixed position by adjusting the electric forces at three coordinates. The controller continuously measures the changes in the forces. Measurements of the force balance for reacting and nonreacting 150-μm particles when all forces mentioned previously imposed on the particle were carried out. The particle was irradiated horizontally by a CO₂ laser beam, and flow was imposed from the top, side, and bottom of the particle. Flow velocity was in the range 0-0.3 m/s, and the particle temperature varied in the range 500-1000 K. The drag force due to forced convection was found to increase linearly with the particle's temperature, likewise the free-convection force. The photophoretic force, however, increased very strongly with temperature. Gas flow strongly affected free convection: for coflow and cross-flow (in respect to free convection flow), the free-convection force decreased with the flow velocity. However, for the counterflow, it first increased with the flow velocity, reached a maximum, and rapidly decreased with velocity. All forces measured were in the same order of magnitude (0.1-1 with respect to gravity), thus changes in their value during combustion can affect the dynamic behavior of the particle.