A model with a moving flame front is proposed for the combustion of a carbon particle, taking into account the effect of CO oxidizing in the boundary layer around the particle. Using this model, the continuous transition of the effective combustion product from CO2 under the ignition condition to CO under the condition of diffusion control has been successfully realized. Good agreement was obtained with the experimental measurements of Young and Niksa; such agreement could not be obtained using the customary single-film model. (c) 2005 The Combustion Institute. Published by Elsevier Inc. All rights reserved.