Photodissociation as a method to increase the ignition volume

Experimental and numerical studies of the ignition and combustion of an H-2 -O-2 mixture (phi= 1.5, T-0 = 713 K, P-0 = 1 atm) initiated by the radiation of the pulsed excimer ArF-laser with the wavelength of lambda= 193.3 nm, leading to the dissociation of O-2 molecules, have been carried out. The possibility of increasing the ignition region by changing the focusing of laser beam was demonstrated. When a lens with focus length off = 20 cm is used, the ignition region is close to spherical, and the flame propagation mode is realized. When a lens with f = 50 cm is employed, the ignition region substantially extends along the laser beam. Due to the propagation of the ignition wave in the longitudinal direction in this case, the combustion front velocity turned out to be much higher in the longitudinal direction than in the radial one. When the mixture ignites at different focusing at the identical time (at the energy in the pulse E-p = 20 mJ with f = 20 cm and E-p = 75 mJ with f = 50 cm), the volume of the ignition region turned out to be ~ 16 times larger when using a long-focus lens. At the same time, the pulse energy is only 3.75 times higher. The minimal pulse energy required for the ignition of the H-2 -O-2 mixture depends on focusing and at considered mixture conditions is equal to E-p ~5 mJ when using lens with focal length of f = 20 cm. At f = 50 cm, the minimal pulse energy increases to E-p ~20 mJ. However, the minimal mass fraction of laser-produced O atoms, at which the H-2 -O-2 mixture ignites at T = 700 K, does not depend on focusing and is equal to Y-0~ 0.001. (C) 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

Experimental and numerical studies were conducted on the ignition and combustion of an H-2 -O-2 mixture initiated by a pulsed excimer ArF-laser. It was demonstrated that the ignition region can be increased by changing the focusing of the laser beam. The shape of the ignition region and the combustion front velocity vary with different lens focal lengths.