VIS camera studies of the combustion process of pyrotechnic retarders of NGP-76 underwater fifle grenades

The study presents the combustion process of the multi-segment, low-gas pyrotechnic column of the warhead retarder of the NGP-76 underwater rifle grenade, designed to combat divers with an underwater shock wave. The combustion process, i.e. process from the ignition of the first segment of the retarder to the completion of combustion of its last segment, was recorded with a VIS camera filming at 30 frames per second. The rapid, short combustion of these outermost segments containing zirconium and Pb₃O₄ (minium) was accompanied by a blinding plume of brightly glowing particles of zirconium dioxide and lead vapor. The combustion of the middle segments formed from the MGS-54 pyrotechnic mixture containing BaCrO₄, KClO₄ and Sb₂S₅, determining the duration of the delay, i.e. the delay produced by the retarder, was much slower and longer than that of the outermost segments. During the combustion of each MGS-54 segment, the combustion front took the form of a flat section in the initial part of the segment, i.e. in the area of higher density, while in the further part of the segment (with lower density) the shape of the front became irregular. At the MGS-54 segment boundary, the combustion front halted briefly. Behind the combustion front, a conical tail of luminous solid combustion products became clearly visible at the MGS-54 segment boundary. The gaseous combustion products of the MGS-54 segments, formed in small amounts and revealed as white plumes, were probably KCl vapor and/or sulfur dioxide. After combustion, the retarder column of the MGS-54 segments was green in color due to the presence of chromium compounds, possibly Ba(CrO₂)².