Pressure Loads on Duct Wall for DDT Processes

In analyzing the effects of an explosion in any confined duct, it is important to see the difference between ideal detonation modes and a special case of DDT. Ideal detonation is characterized by a known level and type of Pc-j loads accompanying the detonation following C-J surfaces and P occurring at a closed-end reflection [48-50]. The related information is given in Tables 7.1, 7.2,7.5 and Figs. 7.4 and 7.5. 

The DDT case is not trivial and needs additional explanations. The combustion wave propagation along the duct causes compression of the un-reacted fresh mixture ahead of the flame. A boosting blast may result in the abrupt formation of a detonation in that part of the duct occupied by the initial gas. The over-compressed detonation wave of DIDc-j 1 can propagate through the mixture from the epicenter of the secondary explosion. Even a simple reflection of such a wave is able to increase the pressure level F3 (Figs. 7.4, 7.5). The potential of an 

5 - shock-compressed initial mixture 6 - pressure rise or shock front 

In the first case (Fig. 8.14a), the DDT occurs near the closed-end, the process follows the slow compression of the initial mixture, no noticeable motion of the mixture ahead of the flame front is observed. At the average pressure rise, heat perturbations (or hot spots) are anticipated in the compressed gas. These hot spots interact and form the center of a secondary fuel-air explosion/detonation. Such a phenomenon is the characteristic of ICE strong mode, which is known as engine knock . 

8 Shock-Free and Spontaneous Initiation of Explosive Regimes 

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