In this paper, detonability limits in two-dimensional annular channels are investigated. Since the channelheights are small in comparison to the tube diameter, curvature effects can be neglected and the annularchannels can be considered to be essentially two-dimensional. Mixtures that are highly diluted with argonare used since previous investigations seem to indicate that detonations in such mixtures are "stable” inthat cellular instabilities play minor roles on the propagation of the detonation. For stable detonationswhere the ZND structure is valid, boundary layer effects can be modeled as a flow divergence term inthe conservation of mass equation following the pioneering work of Fay [J.A. Fay, Phys. Fluids 2(3)(1959) 283–289]. Expansion due to flow divergence in the reaction zone results in a velocity deficit. Thereexists a maximum deficit when an eigenvalue detonation velocity can no longer be found, which can betaken as the onset of the detonability limits. Experimentally, it was found that unlike "unstable” detonations,the detonability limits for "stable” detonations are well-defined. No unstable near-limit phenomena(e.g., galloping detonations) was observed. Good agreement is found between the theoretical predictionsand the experimentally obtained velocity deficits and limits in the two channel heights of 2.2 and6.9 mm for hydrogen–oxygen and acetylene–oxygen mixtures diluted with over 50% argon. It may be concludedthat at least for these special mixtures where the detonation is "stable,” the failure mechanism is dueto flow divergence caused by the negative displacement thickness of the boundary layer behind the leadingshock front of the detonation wave.
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