An experimental evidence of steadily-rotating overdriven detonation

Abstract

This experimental work reports on detonation behaviors in a curved chamber without inner wall after diffraction of a Chapman-Jouguet (CJ) detonation from a straight channel tangent to the chamber outer wall. The upper and lower faces of the chamber receive either soot foils for recording the history of the transmission dynamics, or optical windows for schlieren high-speed visualizations. Tests were carried out with the stoichiometric propane-oxygen mixture at initial temperature 1 T 0 = 288 K and initial pressures ranging between 8 kPa and 15 kPa. The primary observation is the existence of an initial pressure range (8 kPa-12 kPa) for which, after diffraction transients, a Mach detonation can rotate normal to the outer wall with a constant angular velocity such that the normal front velocity at the wall is larger than the CJ value. The height of the Mach front decreases and its tangential velocity increases with increasing initial pressure. This over-driven detonation results from the irregular reflection of the initially-oblique front as the outer wall tilts with respect to the front, similarly to shock propagation in a continuouslyconverging channel. The Mach triple-point moves away from the wall and stabilizes its trajectory parallel to the wall. This Mach front shows detonation cells parallel to the wall with a constant mean width very small compared to that on the initial CJ front. A detonation can thus smoothly propagate in a curved chamber without center body, though the Mach front does not sweep the entire equivalent cross-section of the chamber. These observations are consistent with experimental results for RDE chambers without center body, or with linearly-increasing cross sections, that show improved properties of rotating detonation, compared to chambers with constant cross sections. This supports the interest of further studies on the hollow-chamber configuration of RDEs.

Dynamics of detonation transmission and propagation in a curved chamber: a numerical and experimental analysis

“…5 and 6 are attained during propagation as a regular reflection, whereas the transition from regular-to-Mach detonation is accompanied by a decrease in the front propagation speed. For p 0 = 15 kPa, the final wave structure ("S-shape") is overdriven and accelerates linearly for t ≥ 200 µs reaching an average normalized propagation speed of D end /D CJ ∼ 1.16; this observation is in line with our previous findings using a stoichiometric propane-oxygen mixture [9]. For p 0 = 26 kPa, the velocity signal ends shortly after the deceleration period due to the arrival of the wave to the end of the curved section.…”

“…Adapted from Ref. [9]. diffracts in a larger volume bounded by a 80-mm radius outer wall and a small 30-mm radius inner wall.…”

“…The combustion products finally expand inside a large vessel which is separated from the curved chamber by a 18-µm Mylar foil (Mylar 1). More details on the experimental apparatus and procedure are given in [9,10].…”

“…Promising RDE geometries are the hollow and semi-hollow configurations in which the internal wall of the combustor is fully or partially removed, resulting in larger specific impulse, pressure and rotation frequencies, e.g., [5]. Literature includes experimental, numerical and theoretical studies on detonation propagation inside annular RDEs [6,7,8], curved channels/chambers of constant and varying widths [9,10,11,12,13,14,15,16], wedges and bends [17], and U-bend tubes [18]. Loss-of-coolant accidents in nuclear reactors may result in significant releases of hydrogen and the generation of flammable atmospheres that accumulate between the containment and the curved reactor building [19].…”

“…Recently, this geometry was experimentally studied using a stoichiometric propane-oxygen mixture [9,10]. Its primary finding is a steadily rotating overdriven detonation wave along the outer wall of the chamber, whose distinguishing features are: (i) a Mach wave; (ii) a quasi-steady rotation velocity;…”