The paper is devoted to the study of peculiarities of flame dynamics in ultra-lean hydrogen-air mixtures in terrestrial gravity conditions. By means of numerical methods, it is shown that gas-dynamical flows, which develop due to buoyancy force exerted on hot combustion products, play a crucial role on the overall ultra-lean flame dynamics from the earliest stage after ignition and up to large-scale motion of the developed flame. Immediately after ignition convective flows determine the flame kernel stability. It is shown that despite the superadiabatic temperature of the flame products that is considered as one of the main stability factors of the ultra-lean flames in microgravity conditions the influence of convective flows on the ultra-lean flames in terrestrial gravity conditions can alter flammability limits from that measured in microgravity. On the other hand, the propagation dynamics of the stable flame kernels is also mainly determined by the buoyancy forces. Rising velocity of the flame kernel in the ultra-lean mixture occurs to be much greater than burning velocity and correlates well with estimations obtained for the bubble rising in liquid. Apart from the upward rising, the developed flame is shown to be expanding laterally so the complex large-scale flame structure is observed which could be a possible hazard of explosion and fire for many industrial environments.

International Seminar on Fire and Explosion Hazards (9; 2019; Saint Petersburg, Russia). Proceedings of the Ninth International Seminar on Fire and Explosion Hazards [Электронный ресурс]. Vol. 2: 21-26 April 2019, Saint Petersburg, Russia / Peter the Great St. Petersburg Polytechnic University, Autonomous Non-Profit Organization "Fire and Explosion Safety", Gefest Holding Ltd ; [edited by A. Snegirev [et al.]. — Электрон. текстовые дан. (1 файл : 98,7 Мб). — Saint Petersburg, 2019. — Загл. с титул. экрана. — Свободный доступ из сети Интернет (чтение, печать, копирование). — Adobe Acrobat Reader 7.0. — <URL:http://elib.spbstu.ru/dl/2/k19-97.pdf>. — <URL:http://doi.org/10.18720/SPBPU/2/k19-97>.