Flame Propagation Regimes at Combustion of Lean Hydrogen-Air Mixtures in the Presence of Additives at Central Spark Initiation at Atmospheric Pressure
By means of high-speed color cinematography it is shown that the flames in lean Н2- air mixtures at an initial stage propagate symmetrically and the flame radius can be estimated from the frames of speed filming. It is shown that sufficiently strict calculation of cellular structure flame front of lean hydrogen mixes requires consideration of a 3D problem however thermal diffusion instabilities at the initial stage of combustion have no effect on the velocity of flame which can be estimated assuming unperturbed flame front in the range of 8%<H2<15%. It is shown that the analysis of experimental data on flame propagation in lean mixtures does not allow taking apart results of calculation by two-dimensional model with regard to convection and without convection. It is experimentally shown, that isobutene additives in quantities below a concentration limit (up to 1.5 %) tend to increase, and СО2 additives up to 15 % – to reduce the flame propagation velocity in lean Н2-air mixtures. The reasons for acceleration of combustion in the presence of hydrocarbon additive are considered. For lack of special conditions the processes of gasphase combustion occur under non-stationary currents, density and pressure fluctuations, i.e. have non-steady character [1-3]. For example a cellular combustion front is characteristic of lean hydrogen-air mixes, caused by thermal diffusion instability [3-5]. For the first time flame cells in combustion of lean H2-air mixes were observed in [6]. In [1,7] it was shown that flame cells in lean H2-air mixes can be obtained also in microgravity conditions, i.e. the gravity field isn't essential for occurrence of cellular flames. Investigations of flame propagation in lean H2-air mixes in narrow vertical pipes showed that flame propagation "upwards" is accompanied by the partial consumption of fuel; in this case the fuel content at concentration limit of flame propagation is less than that in a "downwards" direction [4,8]. In a 2D model of comb
