Study of Exothermic Processes in Shock Ignited Gases by the use of Laser Shear Interferometry

Abstract

Abstract The paper reports on the measurements of maximum exothermic power pulses attainable from a given chemical system. Experimental tests involved the use of a shock tube technique whereby the exothermic process of combustion was controlled by reflected shock, so that it occurred under virtually inviscid flow conditions, while the measurements were performed at a resolution commensurate with the actual rate of chemical reaction. Experimental observations were made by means of a novel method of laser shear interferometry—a cross-breed between holography and the conventional means for measuring refractive index fields, in that, on one hand, it was based on the exploitation of the phase coherence of the laser light beam, recording first a diffraction image of the wave fronts which, for the desired final result, had to be optically reconstructed, and, on the other, it yielded eventually either two-dimensional interferograms or schlieren photographs of the observed phenomena. Chemical systems treated in this manner comprised primarily of stoichiometric hydrogen-oxygen mixtures with 80 and 90 per cent argon, the experiments covered the full permissible range of initial thermodynamic conditions, with the scope being bounded on the lower side by the density limit resulting in illegibly small fringe shifts, and on the upper side by the onset of unstable detonation phenomena.