Morocco is one of the richest countries with olive tree. Annually, about 675,000 t of Olive Cake are produced and injected which leads to damaging the environment especially the groundwater as well as the water table itself. To remedy this problem, and because olive cake has a high caloric value, the idea of this paper comes to valorize this waste through the Stirling engine in order to produce clean energy with low greenhouse emissions.To fulfill this purpose, the impact of the particle size of pulverized olive cake (OC) on the flow behavior and combustion parameters in a 3D vertical chamber was investigated. The spherical OC particles are injected through two injectors perpendicularly to the air inlet jets. Two particle sizes are chosen to conduct this study (PS1, PS2). The numerical approach is based on Reynolds averaged Navier–Stokes (RANS) method using the realizable k–ε turbulence model. For gas phase a non-premixed combustion model is used, and for the discrete second phase a Lagrangian approach is chosen. Temperature distribution, flow topology, velocity contours, and species concentrations profiles in the burner are obtained for the two cases. Results show that the first case particle size gives optimal results and is more suitable for this study. Keywords: Particle size, Pulverized, Olive cake, Combustion, Stirling, Emissions