CFD Simulation of Oil Jets for Piston Cooling Applications Comparing the Level Set and the Volume of Fluid Method

A new CFD simulation model and methodology for oil jet piston cooling has been developed using the modern level set approach. In contrast to the widely used volume of fluid (VOF) method, the level set approach explicitly tracks the interface surface between oil and air, using an additional field equation. The method has been extensively tested on two- and three-dimensional examples using results from literature for comparison. Furthermore, several applications of oil jet piston cooling on Ford engines have been investigated and demonstrated. For example, three-dimensional simulations of piston cooling nozzle jets on a diesel engine have been calculated and compared to test-rig measurements. Laminar jets, as well as jets with droplets and fully atomized jets, have been simulated using realistic material properties, surface tension, and gravity. Simulations of cooling jets on the undercrown of a gasoline piston and on a moving piston with a cooling gallery have been investigated and compared to test-rig measurements. Results of a VOF model with the CFD software STAR-CCM+ used in the Ford CAE workflow have been compared to the new level set method. Despite using different computational approaches (level set versus volume of fluid method), the results are similar for laminar jets. Differences occur for semi-turbulent and atomized oil jets with many droplets, which need highly resolved meshes. All in all, the modern CFD tools are a powerful way for investigating active cooling strategies for pistons in order to improve the efficiency of internal combustion engines and to reduce emissions.