In recent years, especially in high-performance spark-ignition engines, the thermal stress of pistons has gradually increased due to the implementation of various technologies, aimed at meeting emission reduction and specific power increase requirements. If the heat is not properly dissipated, cracking and plastic deformation of the material as well as formation of hot spots triggering pre-ignition in the combustion chamber mixture can occur. This last aspect is even more true considering innovative fuels such as hydrogen. To overcome these problems, one or more jets of oil are directed towards the piston under-crown region, impacting at high speed. This technique ensures immediate cooling and allows the engine performance to be increased without compromising the useful life.
In order to optimize the oil jet effectiveness, 3D-CFD can be proficiently adopted. In this regard, the aim of this work is to define a robust numerical methodology able to simulate oil jet impingement and piston thermal field. In particular, a 3D-CFD Volume-of-Fluid (VoF) simulation is used to numerically assess the oil jet impact and provide a map of heat transfer coefficients, which, in turn, is adopted in a 3D-CHT model to estimate the piston thermal field.
The proposed methodology is validated against experimental data on a high-performance engine piston. In particular, a pair of oil jets is investigated and the resulting heat transfer coefficient map is exploited to obtain the thermal field of the piston, which is finally compared to the available experimental temperature measurements. The results show that the predicted temperatures agree with the experimental data within an error lower than 2.5%.