The effect of using additive manufactured nozzle plugs on the ignition process

The selection of the nozzle plug and the appropriate quantity of an incendiary composition is an important step in modelling the ignition process of a solid propellant motor. The aim of the research discussed in this paper was to develop a nozzle plug which promotes adequate pressure in the combustor, while ensuring safety and simplicity of installation on the nozzle. The widespread availability of 3D printing technology has significantly simplified and reduced the cost of fabricating complex geometries. The authors designed and tested more than a dozen different snap-on nozzle plugs in order to investigate the effects of the material, the direction of printing, the shape and numer of snaps, the smoothness of the printed surface, the composition of the incendiary composition and the use of an additional hold-down feature. Tests were carried out on two test rigs equipped with features imitating a rocket motor nozzle, pressure measurement, temperature measurement, and a propellant fixture. The tests showed that the printed nozzle plugs only allow effective ignition of the solid propellant with additional attachment features applied and an incendiary composition in the form of a mixture of black powder and smokeless powder. The research used a low-smoke propellant based on poly(glycidyl azide) for fuel and ammonium perchlorate as the oxidizer with the addition of octogen.