Quasi-detonation

Quasi-detonation—flame propagates with the velocity between the sound speed in the combustion products and CJ value... 

From the practical point of view, the most important aspects of the accelerated flame phenomenon are with respect to the steady-state propagation of very highspeed flames, transition to detonation, and propagation of sub-CJ detonations (quasi-detonations). 

In the early studies [22,24,39] on propagation of detonation in very rough tubes, the steady propagation velocities as low as 50% of the normal CJ value have been observed. Such low-velocity detonations have been referred to as quasi-detonations [4]. 

The studies by Teodorczyk et al. [40-42] and Chan et al. [30] conclusively demonstrated that the mechanism of detonation initiation in quasi-detonation regime is owing to autoignition via shock reflections. These studies show that normal shock reflections from the obstacle, Mach reflection of the diffracted shock on the bottom... 

In the quasi-detonation regime, the continuous periodic detonation failure owing to diffraction by the obstacles and reinitiation by shock reflections constitutes the principal mechanism of propagation. 

Figure 8.4.10 shows two time sequences of schlieren photographs of quasi-detonation. In Figure 8.4.10a, detonation reinitiation occurs at the Mach stem on the bottom wall. However, prior to complete reinitiation of the decoupled wave by the upward-growing detonation, reflection and, subsequently, diffraction of the detonation occur again by encountering another obstacle. In the sixth frame of Figure 8.4.10a, the curved, diffracted, and reflected shock with a reaction zone close behind is clearly evident. However, as this cylindrical... 

Propagation of quasi-detonation in obstacle array in stoichiometric H2/O2 mixture (a) initial pressure 140 torr, detonation reinitiation via Mach reflection at the bottom wall (b) initial pressure 120 torr, detonation reinitiation by normal Mach stem reflection from the obstacle with subsequent enhancement via reflection from the top wall 6 ps between frames. (From Teodorczyk, A., Lee, J.H.S., and Knystautas, R., Prog. Astr. Aeron., 138,223,1990. With permission.)... 

Depending on the obstacle height and spacing, as well as on the vertical height of the channel, one or more of the above-described mechanisms can occur. However, the propagation mechanism comprises continuous reinitiation and attenuation by diffraction around the obstacles. This mechanism essentially is identical to that of a normal detonation, where reinitiation occurs when the transverse waves collide and the reinitiated wave fails between collisions. In quasi-detonations, the reinitiation is controlled by obstacles. In general, the obstacles and walls provide surfaces for the reflection and diffraction of shock and detonation waves. 

Propagation mechanism of quasi-detonations, Proc. Combust. Inst., 22,1723, 1988. 

Photographic study of the structure and propagation mechanisms of quasi-detonations in rough tubes. Prog. Astr. Aeron., 138, 223, 1990. 

Keywords Deflagration-to-detonation transition deflagration Quasi-detonation... 

Fast Deflagration and Quasi-Detonation in a Confined Volume... 

Quasi-detonation combustion regimes of mixtures with smaller H2 concentration (14%) in confined volumes were observed during large-scale experiments [14]. Again, this demonstrates the increase in dangerous blast probability with the growth of the mixture volume. 

Specific characteristics of the quasi-detonation process in hydrogenous mixtures were reported in an experiment with H2 + O2 combustion (0 = 0.4-1.6) carried out in a 124-mm diameter tube, 1,830-mm long, the tube was stuffed with steel or ceramic spheres of 19 and 38 mm diameters. 

Quasi-Detonation in Semi-Closed Encumbered Space... 

A correlation between HAM turbulent combustion velocities with forced three-dimensional agitation or local turbulence and the quasi-detonation regime data obtained in an encumbered space is of interest. It can be mentioned that local turbulence generation in a hydrogen + air mixture with less than 10% H2 does not noticeably affect the explosion for both turbulent and quasi-detonation combustions. This fact is obvious because it is based on the general physico-chemical nature of fast combustion regimes. 

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