BRHS /
Phenomenology of flame acceleration and deflagration to detonation transitionThe sequence of events leading to detonation in a tube containing explosive gases can be summarized as follows:
![]() Figure 1a. The development of detonation in stoichiometric H2-O2 mixture initially at normal temperature and pressure, showing the generation of pressure waves ahead of the accelerating flame. ![]() Figure 1b. The onset of retonation. For both photographs spark ignition by discharging 1.0 mJ. Electrodes located at closed end of 25 x 37 mm cross-section tube (Oppenheim et al., 1963). Streak schlieren photographs. The forward-mowing wave was studied using wall imprints of the detonation process, an example of which is shown in Fig. 3. The characteristic fish-scale pattern, which corresponds to inception of the forward shock, is a distinguished feature of a self-sustained detonation front. There are generally four different modes of transition process observed and classified, based on the location of the onset of an “explosion in an explosion”: between flame and shock front (Fig.4a), at the flame front (Fig.4b), at shock front (Fig.4c) and at the contact discontinuity (Fig.4d). The oset of detonation depends on the particular pattern of shock fronts created by the accelerating flame. The process of DDT is unreproducible in its detailed sequence of events. DDT refers to the phenomena where the critical conditions for the onset of detonation are established by the combustion process itself without external energy source. There are several ways by which the conditions necessary for transition can be achieved. These include:
![]() Figure 2. Flash schlieren photograph of the onset of retonation in a stoichiometric H2-O2 mixture initially at normal temperature and pressure at an instant marked by A on streak schlieren photo (Fig.1)(Oppenheim et al., 1963). ![]() Figure 3. Wall imprints of the transition process. ![]() Figure 4. Various modes of DDT observed in 2H2+O2 mixture; a) onset occurring between flame and shock, b) onset occurring at flame front, c) onset occurring at shock front, d) onset occurring at contact discontinuity. (Urtiew and Oppenheim, 1966). << Coherent deflagrations in a system enclosure-atmosphere and the role of external explosions | Content | Effect of chemical composition, pressure, temperature, geometry, system physical scale, non-uniformity (SWACER) and presence of venting >> |