Ignition of disperse systems during stage processes on their surface

The possibility of moderating the conditions for ignition of a solid combustible that has a difficultly penetrable oxide coating on its surface is illustrated by solution of the problem of ignition of a gas suspension of boron particles in an oxygen–water vapor mixture as an example. The decrease in the ignition temperature of this combustible is reached owing to an active gaseous reagent capable of reacting with an oxide film and transforming it to the products which having no blocking properties. The calculation has shown that if the B$_2$O$_3$ film which hinders particle ignition is removed only as a result of its evaporation, the ignition temperatures of the particles are high. Gasification of the oxide significantly accelerates the removal of the film, which causes a decrease in ignition temperatures compared to a dry medium. The experiment has supported the validity of the calculation. The effect is manifested the stronger the higher the reaction surface of the reacting system. The critical condition for ignition of a gas mixture of particles is obtained from analysis of the stationary solutions of a system of equations on the stability to small perturbations. It is shown that the optimum ratio of the oxidizing components at which the minimum ignition temperature of the suspension occurs exists.