The change in a particle's morphology affects both its trajectory and its carbon consumption rate. For that reason, the present work studies the evolution of particle's morphology during the char conversion process. Particle-resolved transient CFD calculations were performed to estimate changes in particle density and volume. The complex physical and chemical processes taking place in the vicinity and the interior of the char particle were studied and discussed in detail for different process conditions and reaction regimes. The char conversion study confirmed the theoretical correlation between the char diameter and the char density exponent. New expressions were discovered for both exponents alpha and beta, depending on the effectiveness factor ri and the stage of carbon conversion XC. In addition, the Random Pore Model, which describes the development of the specific surface area of the particle, was extended to include an empirical correlation gamma, making it valid for different reaction regimes and operating conditions. (C) 2020 The Authors. Published by Elsevier Inc. on behalf of The Combustion Institute.