The present work aims to study numerically the cooling system in car engines to ensure the piston thermo-mechanical resistance. Most engines use an oil jet cooling system coupled with "cocktail shaking" to extract heat from the piston. This cooling method brings into play a two-phase incompressible turbulent flow in a mobile environment, because of motion of pistons in the cylinder. The need for a more effective cooling involves an accurate understanding of the physical mechanisms. The idea is to support the engine design process to account for advanced technologies to improve turbine or engine performances, burn less filet and generate less green house gas. In the present work, a numerical model dedicated to the simulation at small scale of oil/air two-phase flows and related heat transfers is proposed to characterize the cooling of engine elements under fragmented jet impact. Large Eddy Simulations of an impinging liquid jet onto a heated semi-hemispherical target were run and the numerical results were compared with experimental data. The mixed-scale model (P. Sagaut, Large Eddy Simulation for Incompressible Flows, Springer, 2000) and the Wall Adapting Local Eddy (WALE) model (Nicoud and Ducros, Flow, Turbulence and Combustion, vol. 62, pp. 183-200, 1999) were evaluated. The best results were obtained using the WALE approach, the mixed-scale model being too dissipative near solid walls. Then cocktail shaking in simplified piston geometries is presented to illustrate the interest of the global simulation approach.