This study reports 3D numerical simulations of the ignition and the propagation of grassland fires. The mathematical model consists in solving the conservation equations governing the behavior of the coupled system formed by the vegetation and the ambient atmosphere. Based on a finite volume discretization, the computation code is parallelized using OpenMP directives and had been the subject of numerous validations. the model was previously tested on small scale in case of homogeneous litter fires; in this study it is proposed to test it on larger scale in case of grassland fires. the results are in fairly agreement with experimental data, with predictions of operational empirical-models developed in Australia (MK5) and in the USA (BEHAVE), as well as with predictions of physical models (FIRETEC, WFDS, FireStar2D). The comparison with the literature is based on the estimation of the rate of fire spread (ROS) and the analysis of the fire-front shape.