Theoretical analysis on deflagration-to-detonation transition

Abstract

The study on deflagration-to-detonation transition (DDT) is very important because this mechanism has relevance to safety issues in industries, where combustible premixed gases are in general use.However, the quantitative prediction of DDT is one of the major unsolved problems in combustion and detonation theory to date. In this paper, the DDT process is studied theoretically and the critical condition is given by a concise theoretical expression. The results show that a deflagration wave propagating with about 60% Chapman-Jouguet (C-J) detonation velocity is a critical condition. This velocity is the maximum propagating velocity of a deflagration wave and almost equal to the sound speed of combustion products. When this critical conation is reached, a C-J detonation is triggered immediately. This is the quantitative criteria of the DDT process.It is generally known that combustion waves propagating in a premixed detonable mixture can be classified into two modes, either deflagration or detonation. The detonation wave is initiated by two ways, one is direct initiation, and the other is deflagration-to-detonation transition (DDT). The direct detonation initiation needs extremely high ignition energy supplied to the premixed detonable mixture. Once the detonation is initiated directly, it will propagate self-sustainable with a Chapman-Jouguet (C-J) detonation velocity.Most of the detonation initiation is imitated by the DDT process. The flame is ignited by a small amount of energy at the initial stage and then the flame front is accelerated by natural or artificial reasons from laminar flame with velocities at the level of some meters per second to turbulent flame with speeds at the level of a hundred meters per second. Under certain critical conditions, the DDT process can occur and the C-J detonation is triggered immediately. There is a critical threshold inherent in the DDT process. Sufficient evidence from the previous studies

Effects of heat loss and viscosity friction at walls on flame acceleration and deflagration to detonation transition*

“…Kagan et al [19] have used the reaction model of n = 2 to investigate the transition from a flame to a detonation in a channel. The studies [4,17,28] indicated that DDT is more likely to occur when the reaction level of n = 2 is considered, while it takes long time and distance for monomolecular reaction kinetics (n = 1). The present reaction model is valid for DDT because this study pays more attention to the physical mechanism, and the chemistry mechanism is relatively weak.…”