FLAME PROPAGATION THROUGH TURBULENT COMBUSTIBLE DUST/AIR MIXTURES (TWO-PHASE, SPHERICAL BOMB, BURNING VELOCITY)

The propagation of turbulent dust/air flames has been studied experimentally. Measurements of the burning velocity have been made in a 0.95 m('3) spherical chamber using the constant volume bomb technique. Mixture concentration was constantly monitored before the explosion by an optical dust probe and turbulence was created by six symmetrically located inlet jets. The turbulence level inside the chamber was adjusted by the inlet jet velocities. Steady state conditions were established before simultaneous isolation and ignition.;The maximum pressure and rate of pressure rise data showed general agreement with other sources (K(,ST) = 71 bar sec('-1) m). The ratio of turbulent to laminar burning velocity was found to correlate well with both the ratio of r.m.s. turbulent fluctuation velocity to laminar burning velocity ratio (obtained by interpolation of data to zero turbulence intensity) and Reynolds number. The data for two dust concentrations showed a linear relationship for the quantities mentioned. An optical probe was used to measure flame thickness which showed a range from 15-80 cm, increasing with both turbulence intensity and dust concentration.;Measurements and calculations strongly suggest that the propagation of the flame, for high turbulence levels, is controlled by turbulent exchange, whereas for low turbulence intensities it is probably controlled by radiation, which causes prior pyrolysis, and most of the combustibles burn in the gas phase.;Burning velocities of 45-100 cm/sec and 70-330 cm/sec were obtained for mixed grain dust and cornstarch respectively for controlled moisture, particle size distribution, and turbulence level (1.5-4.2 m/sec-r.m.s.) for a dust concentration range of 50-1300 gm/m('3).