Orifice plates with large blockage ratios (BR=0.691, 0.826, 0.923 and 0.962) are placed in the entrance of the detonation transmission to investigate the artificially large-scale perturbations on the detonation propagation mechanism. Obstacles create large perturbations, thereby generating flow instability to affect the detonation transmission. In this study, stoichiometric methane-oxygen is examined because it has a wide application in the industry; therefore, its safety concerns must be addressed. Furthermore, the methane-oxygen mixture is characterized by a highly irregular cellular detonation front, and it is the representative of those potentially combustible mixtures used in practical aerospace application. Velocity behaviors after the detonation passes through the obstacles with different BR near the critical condition are analyzed; particular attention is paid to the cases for which BR is larger than 0.9 (i.e., 0.923 and 0.962), and the results are also compared with relatively smaller BR cases (BR=0.691 and 0.826). The effect of the diffraction, shock reflection and detonation instability on the propagation of detonation is examined. Finally, the analysis of critical length scale between the cell size (lambda/d) and BR when the detonation fails or succeeds as it passes the obstacles is also performed, this work aims to explore the mechanism of critical perturbation scale on the detonation propagation. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.