Deflagration detonation transition

A deflagration-detonation transition was first observed in 1985 in a large-scale experiment with an acetylene-air mixture (Moen et al. 1985). More recent investigations (McKay et al. 1988 and Moen et al. 1989) showing that initiation of detonation in a fuel-air mixture by a burning, turbulent, gas jet is possible, provided the jet is large enough. Early indications are that the diameter of the jet must exceed five times the critical tube diameter, that is approximately 65 times the cell size. 

An overall statement concerning the deflagration - detonation transition (DDT) was made within the frame of the PNP gas cloud program saying that the mechanisms and flame acceleration are qualitatively understood, however, they cannot be described on a quantitative basis, a statement that is, in principle, still valid today [6, 30, 41], although computational efforts are progressing tremendously. 

A deflagration may turn into a detonation, especially if it propagates through a pipe. Such a process is called Deflagration-Detonation-Transition (DDT). Research has not yet totally clarified its characteristics (cf. [20, 21]). 

Therefore, it is possible to observe the spatial orientation and displacement of the heat release fronts (combustion, deflagration, detonation) and their reciprocal transformation (deflagration/detonation transition, detonation quenching). It is important to find an answer to the question what optical recording systems and in what combination with the known ways of measurements are applicable for solving the assigned problems ... 

U. Behrens, G. Langer, M. Stock, I. Wirkner-Bott, Deflagration-detonation transition in hydrogen -i- air -t steam mixtures. Nucl. Eng. Design 130(1), 43-50 (1991)... 

Deflagration to Detonation Transition A reaction front that starts out with velocities below the speed of sound and subsequently accelerates to velocities higher than the speed of sound in the unreacted material is said to have undergone a Deflagration to Detonation Transition. The possibility of transition is enhanced by confinement/turbulence generators in the path of the reaction front. 

An in-line detonation flame arrester must be used whenever there is a possibility of a detonation occurring. This is always a strong possibility in vent manifold (vapor collection) systems, where long pipe runs provide sufficient run-up distances for a deflagration-to-detonation transition to occur. Figure 3-3 shows the installation of in-line arresters of the detonation type in a vent manifold system. 

Pipeline deflagrations and detonations can be initiated by varions ignition sonrces. The flame proceeds from a slow flame throngh a faster accelerating tnrbnlent flame to a point where a shock wave forms and a detonation transition occnrs, resnlting in an overdriven detonation (see Fignre 4-3). A stable (steady state) detonation follows after the peak overdriven detonation pressnre snbsides. 

Deflagration-to-Detonation Transition (DDT) The transition phenomenon resulting from the acceleration of a deflagration flame to detonation via flame-generated turbulent flow and compressive heating... 

Although the status of many 3D codes makes it possible to carry out detailed scenario calculations, further work is needed. This is particularly so for 1) development and verification of the porosity/distributed resistance model for explosion propagation in high density obstacle fields 2) improvement of the turbulent combustion model, and 3) development of a model for deflagration to detonation transition. More data are needed to enable verification of the model in high density geometries. This is particularly needed for onshore process plant geometries. 

VI. Preparation VII. Detonation Characteristics VIII. Thermal Decomposition IX. Combustion DDT (deflagration-to-detonation transition) X. References. The major emphasis will be placed on Sections VII, VIII and IX... 

Detonation in SP is initiated by shock or by DDT (deflagration to detonation transition). Let us first examine shock initiation, ie, initiation by in-contact or close-by detonation of HE... 

In 1957, a flame propagating in a long tube under conditions resulting in a deflagration to detonation transition (DDT) was given the name "tulip" by Salamandra et al. [7]. This term was subsequently commonly applied in detonation studies to describe this typical shape [8,9]. Figure 5.3.2 shows a few... 

Lee, J.H., Knystautas, R., and Freiman, A., High speed turbulent deflagrations and transition to detonation in Hj-air mixtures. Combust. Flame, 56,227,1984. 

A deflagration can also evolve into a detonation. This is called a deflagration to detonation transition (DDT). The transition is particularly common in pipes but unlikely in vessels or open spaces. In a piping system energy from a deflagration can feed forward to the pressure wave, resulting in an increase in the adiabatic pressure rise. The pressure builds and results in a full detonation. 

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