Numerical results of a standoff microjet methane diffusion flame are further analyzed to elucidate the characteristic chemical structure of the flame near the extinction limit. Computed results indicate that the standoff behavior of the microjet diffusion flame is a consequence of flame quenching on the tube wall, followed by the sequence of accelerating fuel pyrolysis by heat conduction through the tube wall, producing intermediate radicals, initiating further reaction on the HO2 path near the tube wall, creating a hot zone in the quenching gap region, and finally forming a reaction kernel to hold the flame. (C) 2007 The Combustion Institute. Published by Elsevier Inc. All rights reserved.