Ignition of stoichiometric hydrogen-oxygen by water hammer

Abstract

The potential of water hammer events for igniting hydrogen-oxygen mixtures was examined in an experimental study. Compression waves simulating water-hammer events were created by projectile impact on a piston in a water-filled pipe terminated by a test section filled with gas. Triangular wave forms with peak pressures up to 50 MPa propagated through the piping system and compressed the gas in the test section. Experiments were carried out with both air and hydrogen-oxygen gas mixtures using high-speed video of the transparent test section, dynamic pressure and spectroscopic measurements to examine the motion of the water-gas interface and determine ignition thresholds. The impulsive acceleration of the water-gas interface and deceleration created by the compression of the gas resulted in Richtmyer-Meshkov and Rayleigh-Taylor instabilities that grew to create large distortions of the initially planar and horizontal water-gas interface. The gas layer was compressed in volume by up to a factor of 50 and the gas pressures increased to as high as 20 MPa within 2 to 4 ms. The distortion of the water surface during compression resulted in a significant increase in interfacial area and ultimately, creation of a two-phase mixture of water and compressed gas. Some ignition events were observed, but the dispersion and mixing of water with the gas almost completely suppressed the pressure rise during the ignition transient. Only by eliminating the instability of the water interface with a solid disk between the water and gas were we able to observe consistent ignition with significant pressure rises associated with the combustion.

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