Condensed combustion products of aluminized propellants. 1. A technique for investigating the evolution of disperse-phase particles

This paper describes a technique for investigating the evolution of the condensed combustion products of metallized propellants. The technique involves freezing the combustion products of a propellant sample at different distances from the burning surface by mixing with a cocurrent cold flow of an inert diluent gas, followed by collecting the particles in metal sieves and in an aerosol filter. The technique allows one to determine particles sizes from 1.2 $\mu$m to maximum as well as to establish the content of neat aluminum in particles at pressures up to 80 atm. The site of freezing is set by varying the length of the guard tube which prevents the flame from contacting with the diluent gas flow. The procedures and results of the particle-size and chemical analyses are described. Apart from changes in the mass distribution of particles in size, the evolution of the particles, as they depart from the burning surface, is characterized by a dependence of the mass fraction of aluminum in particles on the reaction time which involves the residence times in the guard tube and in the zone of the initial mixing of the flow of combustion products with the cocurrent flow of the diluent gas.