Photodissociation as a method to increase the ignition volume

• Published in: Combustion and flame 2022-10, Vol.244, p.112222, Article 112222
• Main Authors: Kobtsev, V.D., Kostritsa, S.A., Pelevkin, A.V., Smirnov, V.V., Titova, N.S., Torokhov, S.A., Volkov, S.Yu
• Format: Article
• Language: English
• Subjects: Combustion; Experiment; Hydrogen-oxygen mixture; Laser-induced ignition; Modeling; Photo-dissociation
• ISSN: 0010-2180; 1556-2921
• DOI: 10.1016/j.combustflame.2022.112222

Experimental and numerical studies of the ignition and combustion of an H2-O2 mixture (ϕ=1.5, T0=713 K, P0=1 atm) initiated by the radiation of the pulsed excimer ArF-laser with the wavelength of λ=193.3 nm, leading to the dissociation of O2 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 of f = 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 Ep=20 mJ with f = 20 cm and Ep=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 H2O2 mixture depends on focusing and at considered mixture conditions is equal to Ep∼5 mJ when using lens with focal length of f = 20 cm. At f = 50 cm, the minimal pulse energy increases to Ep∼20 mJ. However, the minimal mass fraction of laser-produced O atoms, at which the H2O2 mixture ignites at T = 700 K, does not depend on focusing and is equal to YO∼0.001.