In this investigation, the dynamic detonation parameters for stoichiometric acetylene-oxygen mixtures diluted with varying amount of argon are measured and analyzed. The experimental results show that the critical tube diameter and the critical energy for direct initiation of spherical detonations increase with the increase of argon dilution. The scaling behavior between the critical tube diameter dc and the detonation cell size λ as well as the critical direct initiation energy Ec is systematically studied with the effect of argon dilution. The present results again validate that the relation dc = 13λ holds for 0% -30% argon diluted mixtures and breaks down when argon dilution increases up to 40%. It is found that the explosion length scaling of Ro ~ 26λ becomes also invalid when the mixture contains approximately this same amount of argon dilution or more. This critical argon dilution is indeed close to that found from experiments in porous-walled tubes by which exhibit a distinct transition in the failure mechanism. Cell size analysis in literature also indicates that the cellular detonation front starts to become more regular (or stable) when the argon dilution reaches more than 40 -50%.Regardless of the degree of argon dilution or mixture sensitivity, the phenomenological model developed from the surface energy concept by Lee, which provides a relation that links the critical tube diameter and the critical energy remains valid. The present experimental results also follow qualitatively the observation from chemical kinetic and detonation instability analyses.

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