In this paper we study the transient heat conduction in a piston of a diesel engine, subjected to a periodic boundary condition on the surface in contact with the combustion gases. The heat transfer coefficient at the top surface was modeled taking into account the temperature and pressure inside the combustion chamber. Such instantaneous pressure was measured using a special probe for an engine operating with several blends of diesel and biodiesel, and the temperature was obtained through a First Law analysis. The physical properties, including the cetane number were evaluated experimentally for all diesel/biodiesel blends used in this work. An elliptic scheme of numerical grid generation was used, so that the irregular shaped piston in the physical domain was transformed into a cylinder in a computational domain. The timewise variations of the temperature of several points in the piston were examined for different piston materials and various load conditions. (C) 2010 Elsevier Ltd. All rights reserved.