Abstract Developing a new generation of rocket engines based on detonation principles needs methods which ensure stability of operation including the onset of detonation wave after mild ignition. This aspect is crucial for ensuring safety of such engines. In the present paper the transition processes associated with flame acceleration and the onset of a detonation mode are under investigation. High-speed flame front photography has been performed during the deflagration of a premixed gas mixture in a long smooth tube. The evolution of flame front structure and shape has been determined, starting from the moment of deflagration initiation and ending with the occurrence of a local explosion leading to the formation of a detonation wave. Four characteristic flame propagation stages have been identified: the initial flame acceleration stage, followed by the apparent velocity deceleration stage, followed by the nearly constant propagation velocity stage, and finally the second acceleration stage, during which detonation is formed. The changes in process dynamics with a change in the initial pressure have been demonstrated. The behavior of flame front at the early stage of acceleration has been identified. The experimental findings are compared with the theoretical models available in the literature. At the initial stage of the accelerated propagation of flame extended along the channel walls — until deceleration — the velocity of the leading tip of the front is effectively described by the exponential relationship proposed by C. Clanet and G. Searby (1996). The most interesting and poorly studied, in the authors' opinion, stage of the deflagration-to-detonation transition process, the intensive repeated acceleration stage, during which flame shape changes abruptly, has been described in detail. The laminar burning velocity of the stoichiometric acetylene–oxygen mixture diluted with either nitrogen or argon at a reduced initial pressure (8–21 kPa) has been identified.
Highlights The FA and DDT in C2H2/O2 mixtures have been studied experimentally using high-speed imaging. Clear detailed high-quality images of the flame front are provided. Main stages of the FA and DDT have been identified and described. On the early stage the velocity of the flame front described by the exponential relationship. The laminar burning velocity at a reduced initial pressure has been determined.
Flame front dynamics, shape and structure on acceleration and deflagration-to-detonation transition
Acta Astronautica ; 204 ; 692-704
2022-10-06
13 pages
Aufsatz (Zeitschrift)
Elektronische Ressource
Englisch