In this study, the dynamic detonation parameters, namely, the critical tube diameter and critical energy for direct initiation, of C2H2/N2O/Ar mixtures were measured at various initial conditions. Using chemical kinetics with the Konnov mechanism and experimental measured data, a simple correlation to evaluate the critical tube diameter of C2H2/N2O/Ar detonation is developed, given by d(c) = 594.8 phi(0.623) (1 - X-Ar)(0.2176) (p/p(o))(-0.0246) Delta(i) which is applicable for stoichiometric mixtures with initial pressures ranging from 50 to 130 kPa, equivalence ratios from 0.625 to 2.5 and stoichiometric mixtures with maximum percentage of argon dilution up to 50% at the atmospheric pressure. By combining this correlation function with a theoretical model based on a simple work done concept, the critical energy for direct blast initiation can be predicted; and the theoretical predictions are found to be in good agreement with the critical energy measured experimentally. To assess the detonation sensitivity, the critical energy results for direct initiation of detonation in C2H2/N2O/Ar mixtures are compared with those in H-2/N2O/Ar mixtures [Zhang et al., Int. J. Hydrogen Energy 39 (2011) 5707-5716]. The results indicate that C2H2/N2O/Ar is more sensitive than H-2/N2O/Ar at the same initial conditions. This is also supported qualitatively by the chemical kinetic calculation which shows that the ZND induction length scale for C2H2/N2O/Ar is relatively smaller than that of H-2/N2O/Ar mixture. Lastly, the effect of the oxidizer on the detonation sensitivity is studied by comparing the critical energy between C2H2/N2O/Ar and C2H2/O-2/Ar mixture. It is found that a higher energy is required to successfully initiate a spherical detonation in C2H2/N2O/Ar than in C2H2/O-2/Ar mixtures and equivalently, the results agree qualitatively with the ZND induction length analysis. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.