CFD Simulation of Oil Jet Piston Cooling Applied to Pistons with Cooling Gallery

Efficient cooling of pistons with oil jets can avoid engine failures due to exceeded piston temperatures of thermally high-loaded combustion engines and can contribute to fuel consumption savings. To reduce expensive and time-consuming engine testing during product development, computational fluid dynamics (CFD) simulations help to quantify the piston cooling performance and provide detailed insights into the complex interactions between oil, air, and piston already in the design phase. The durability of new piston design approaches, such as integrated advanced cooling galleries or highly resistant materials like steel, can be evaluated including the use of alternative fuels, such as compressed natural gas (CNG), hydrogen, alcohols, or e-fuels. A new CFD simulation methodology for oil-jet piston cooling has been developed to investigate the cooling efficiency considering various piston cooling geometries and operational parameters. Method, software, and tools were already available from a former common research project of Ford and RWTH Aachen University where the level set and volume of fluid methods have been compared. Several applications of oil-jet piston cooling have been investigated on Ford engines. One example describes a gallery cooled CNG piston for a gas engine to resist the increased thermal load of the methane combustion. Another application considers a steel piston for a diesel engine with enlarged cross-sections within the cooling gallery to handle higher metal temperatures coming along with steel to avoid oil coking. For both examples, various engine speeds and oil-jet volume flow rates have been investigated. Results for each case are the transient oil flow including the oil filling process of the cooling gallery, the oil filling ratio, and the total heat transfer. Overall, the analyses show that modern CFD tools are a powerful way for investigating active cooling strategies for pistons to improve the efficiency of internal combustion engines and to reduce emissions.