ABSTRAKT

This paper discusses the influence of Mg addition on boron dust-air clouds ignition. Analysis of this phenomena basis on experimental and theoretical data.
The mathematical model is restricted to quasi-steady approximation. It has been assumed that any temperature gradients (in gas, in solid/liquid phase) have been neglected. The influence of total mass concentration, initial gas temperature, particle size, pressure and content of Mg in percent on the ignition has been studied.
Experiments have been carried out with different binary mixtures in which content of Mg varied from 5 to 25% (by weight) and a total mass concentration (B+Mg, C_Σ) varied from 0,05 to 0,60 kg/m³. The powders was dispersed into the reaction chamber by means of compressed air impulse. The formation time of dust air clouds was less than 20 m·sec. The gas temperature within reaction vessel varied in the range 800−1650 K. The critical ignition temperatures and delay times of binary (B+Mg) dust-air mixtures is measured.
From theoretical and experimental analysis it is shown that the addition of Mg in boron powder decrease a critical ignition temperature by 50−100 K and delay time up two orders.
The increase of magnesium percent content in binary systems have a dual effect on the process: firstly, the velocity of heat-generation increases in the beginning of the ignition; secondly, the conditions of boron cloud ignition have become worse due to the decrease of boron mass concentration and oxygen depletion. Competition of these factors stipulate the optimal addition when the ignition temperature of mixtures B+Mg has a minimum.