Impact Ignition of Liquid Propellants

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Abstract : The report describes a preliminary study of the impact ignition of liquid propellants. In one experimental set up, two dimensional cavities were shocked and the cavity collapse studied by both high-speed framing and streak photography. Cavities in water and liquid propellant (LCP 1846) were studied. Cavity sizes were in the range 1 - 7 mm and shock strengths in the range up to 1.5 GPa were used. The cavities were observed to involute and produce a high speed jet which crossed the cavity and impacted the downstream wall sending a shock into the surrounding material. The gas in the cavity was heated by rapid compression achieving temperatures sufficient to cause gas luminescence. Finally, the jet penetrated the downstream wall of the cavity to form a pair of vortices which travelled downstream with the flow. Jet velocities up to ca. 500 m s-1 were observed. A more general discussion of cavity collapse and the initiation of explosion is presented in Appendix 1 (Bourne and Field 1991, Proc. Roy.Soc. 435, 423-435). In the second series of experiments, drop-weight impacts were performed on layers of propellant of various geometries using a transparent anvil apparatus. This experimental set-up allows high-speed photographic recording of the event. The drop weight had a mass of 5 kg and was dropped from a height of 1.3 m. No ignition events were observed. Flow velocities of up to about 200 m s-1 were observed. Of particular interest was the production of filaments of cavities in the impacted layers.