Near-limit propagation of gaseous detonations in narrow annular channels

Abstract

New results on the near-limit behaviors of gaseous detonations in thin annular channels are reported in this paper. The annular channels of thicknesses 3.2 mm and 5.9 mm are made by inserting smaller diameter tubes of 44.4 mm and 39.0 mm into a larger 50.8-mm diameter outer tube. The length of each annular channel is 2.0 m. Detonations are initiated in a steel driver tube where a small volume of a sensitive C2H2 + 2.5O2 mixture is used to facilitate detonation initiation. A 2-m length of circular tube with 50.8-mm diameter precedes the annular channel so that a steady Chapman-Jouguet (CJ) detonation is established prior to entering the annular channel. Four detonable mixtures of C2H2 + 2.5O2 + 85%Ar, C2H2 + 2.5O2 + 70%Ar, C3H8 + 5O2 and CH4 + 2O2 are used in the present study. Photodiodes spaced at 10 cm throughout the length of both annular channel and circular tube are used to measure the detonation velocity. In addition, smoked foils are inserted into the annular channel to monitor the cellular structure of the detonation wave. The results show that well within the limits the detonation wave propagates along the channel with a small local velocity fluctuation and an averaged global velocity can be deduced. The averaged detonation velocity has a small deficit of 5 -15% far from the limits and rapidly drops to 0.7VCJ -0.8VCJ when the onset of limit occurs. Subsequently, the fluctuation of local velocity also increases with decreasing initial pressure approaching the limit. No galloping detonations are observed for both stable and unstable mixtures in annular channels. The present study also confirms that single-headed spinning detonation occurs at the limit as in circular tube rather than the up and down "zig zag" mode in a two-dimensional rectangular channel.

Effects of inert gas jet on the transition from deflagration to detonation in a stoichiometric methane-oxygen mixture

“…In recent years, there is an increasing interest in developing detonation-based engines, such as Pulsed or Rotating Detonation Engines (PDEs or RDEs) for hypersonic propulsion applications [1][2][3]. One of the major challenges in designing these propulsive systems is the capability to initiate a detonation in a chamber of limited size [4][5][6], wherein the detonation propagation limits are a key as well as the fundamental problem for maintaining the propagation of detonations without failure to sustain their propulsion trust [7][8][9], this topic has been widely investigated as the detonations propagate though obstacles in recent years by Zhang et al [10][11][12] , Cao et al [13] and Gao et al [14][15][16].…”

On a stabilization mechanism for low-velocity detonations

“…Such losses arise when gaseous detonation propagates in small tubes (e.g., Zel'dovich et al (1987); Manzhalei (1992); Chan & Greig (1989); Camargo et al (2010)), narrow channels (e.g., Manzhalei (1998); Ishii & Monwar (2011); Gao et al (2016)), channels with obstructions (e.g. Lee et al (1984Lee et al ( , 1985; Teodorczyk et al (1989); Chan & Greig (1989); Teodorczyk et al (1991); Gao et al (2016)), packed beds of inert particles (e.g., Lyamin & Pinaev (1985); Lyamin et al (1991); Babkin et al (1991); Makris et al (1995); Babkin (2012)) or tubes with porous walls (Radulescu & Lee 2002). Friction with and heat transfer to the walls or obstacles (or the mass loss through the porous walls) decreases the velocity of detonation from its ideal value (i.e., there exists a velocity deficit).…”

“…Investigation into the propagation of detonation in the presence of momentum and heat losses began in the 1940s with the seminal work by Zel'dovich (1940) and then by Schelkin (1949). Such losses arise when gaseous detonation propagates in small tubes (e.g., Zel'dovich et al (1987); Manzhalei (1992); Chan & Greig (1989); Camargo et al (2010)), narrow channels (e.g., Manzhalei (1998); Ishii & Monwar (2011); Gao et al (2016)), channels with obstructions (e.g. Lee et al (1984Lee et al ( , 1985; Teodorczyk et al (1989); Chan & Greig (1989); Teodorczyk et al (1991); Gao et al (2016)), packed beds of inert particles (e.g., Lyamin & Pinaev (1985); Lyamin et al (1991); Babkin et al (1991); Makris et al (1995); Babkin (2012)) or tubes with porous walls (Radulescu & Lee 2002).…”