457 ISSN 1028-3358, Doklady Physics, 2016, Vol. 61, No. 9, pp. 457–462. © Pleiades Publishing, Ltd., 2016. Original Russian Text © V.V. Kozlov, G.R. Grek, O.P. Korobeinichev, Yu.A. Litvinenko, A.G. Shmakov, 2016, published in Doklady Akademii Nauk, 2016, Vol. 470, No. 2, pp. 166–171. Combustion of a High-Velocity Hydrogen Microjet Effluxing in Air V. V. Kozlov a *, G. R. Grek a , O. P. Korobeinichev b , Yu. A. Litvinenko a , and A. G. Shmakov b Presented by Academician V.A. Levin August 22, 2015 Received September 21, 2015 Abstract—This study is devoted to experimental investigation of hydrogen-combustion modes and the struc- ture of a diffusion f lame formed at a high-velocity eff lux of hydrogen in air through round apertures of various diameters. The efflux-velocity range of the hydrogen jet and the diameters of nozzle apertures at which the f lame is divided in two zones with laminar and turbulent f low are found. The zone with the laminar f low is a stabilizer of combustion of the flame as a whole, and in the zone with the turbulent flow the intense mixing of fuel with an oxidizer takes place. Combustion in these two zones can occur independently from each other, but the steadiest mode is observed only at the existence of the f lame in the laminar-f low zone. The knowledge obtained makes it possible to understand more deeply the features of modes of microjet combustion of hydro- gen promising for various combustion devices. DOI: 10.1134/S1028335816090068 The major energy sources nowadays the world over are combustible minerals—coal, oil, and natural gas, the share of which amounts to about 80% of all energy produced. Taking into account the rapid rates of industry growth, we hypothesize that the combustible mineral wealth will suffice for no more than for 50-100 years. The share of the use of alternative energy sources such as solar, wind, etc., amounts together with hydro- and nuclear power engineering to no more than 20%. Hydrogen power engineering has great prospects of development also due to the accessibility of the raw- material source, i.e., water, the stocks of which are almost unlimited, instead of only ecological purity. However, a number of important unsolved problems related to its properties and, first of all, to its fire- and explosion hazard inhibits the use of hydrogen as the energy carrier. It is possible to state the fact that hydro- gen power engineering is not widespread at present. Such technical problems as the methods of production of hydrogen and ways of its storage and transportation are still unsolved and are at the stage of experimental development and laboratory investigations. Special interest is raised by the process of combus- tion of hydrogen under its jet efflux from various types of torches, atomizers, nozzles, etc. In work with hydrogen, it is necessary to take into account con- stantly its high fire and explosion hazard. The physical and chemical aspects of hydrogen-jet combustion have been widely investigated all over the world both theoretically and experimentally. The great interest is due to the diffusion combustion of hydrogen in air from the viewpoint of both improving the f lame stabil- ity and decreasing harmful wastes of nitrogen oxides NO x into the atmosphere. In connection with this, there arises the problem of the possibility of affecting these processes with the help of various factors, for example, acoustic vibra- tions. In [1], the effect of acoustics on a decrease in NO x in the combustion products and on the stability of the elevated diffusion flame of the turbulent hydrogen jet flowing in air was investigated. The authors showed that the acoustic-frequency dependence of the NO x concentration in combustion products has a resonant character. The vortex formed at the acoustic action favored an increasing suction of air and elevated the degree of mixing of fuel with air. This effect resulted in a lower temperature in the combustion zone and, thus, reduced the NO x emission. In [2], the dynamic behav- ior of the diffusion turbulent f lame of hydrogen in the near region is investigated under the acoustic action on the resonant frequency of the air blast. The reso- nance frequency was chosen for the excitation of the air blast because of its ability to strengthen efficiently the acoustical amplitude and to decrease the NO x emission. From imposing acoustic pulsations at the MECHANICS a Khristianovich Institute of Theoretical and Applied Mechanics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630128 Russia b Voevodskii Institute of Chemical Kinetics and Combustion, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia *e-mail: kozlov@itam.nsc.ru