A numerical method of modeling oil jet piston cooling

To meet stringent emission regulations and high power requirements, peak cylinder pressures and specific power of petrol engines have increased dramatically in recent years, resulting in higher thermal loading of in-cylinder components such as pistons. To keep maximum temperatures securely below an acceptable limit, modern engine pistons are oil cooled.

An oil jet, injected from a nozzle tube on the crankcase, impinges on the underside of the piston and achieves effective temperature control. On the one hand this cooling concept can ensure the required durability and reliability of pistons. On the other it can help to gain efficiency and decrease fuel consumption by reducing piston cooling at part load. These high requirements for the cooling concept need an exact analysis of thermal boundary conditions and their influence on the piston temperature.

Using the commercial CFD code STAR-CCM+, a numerical approach to calculate oil jet piston cooling has been developed. This includes macro controlled transient piston motion with mesh morphing and replacement of the compressed grid at predefined piston positions. The oil flow and heat transfer distribution on the undercrown has been simulated by a VOF (volume of fluid) multiphase model.

Finally, a stationary model with adapted gravitational forces has been developed and compared with the original simulation and experimental data to reduce calculation time and complexity.

Johannes Lutz
Speaker Company: 
BMW Group