A Transient, 3-Dimensional Multiphase CFD/Heat Transfer and Experimental Study of Oil Jet Cooled Engine Pistons

This paper reports on a novel three-dimensional computational fluid dynamics (CFD) and heat transfer coupled methodology for analyzing piston cooling using oil jets. The method primarily consists of models of the fluid and the solid domains that are thermally coupled to one another. One of the models is a crank angle transient, three-dimensional, multiphase, volume of fluid (VOF) CFD model of the fluid behind the reciprocating piston consisting of the piston jet and crankcase gases. This model is coupled to a piston solid model. The piston motion and heat transfer from the piston to the liner are rigorously accounted for. The combustion heat flux on the piston surface was an input to the current analysis as a boundary condition. All simulations were performed using the commercial CFD software Simerics MP+.

The developed method is applied to three DI Diesel engine pistons, one piston without a cooling gallery and two pistons with cooling galleries. Jet orientations aligned and non-aligned with piston motion directions were both simulated. All temperature predictions from the simulation were validated against experimental measurements. The simulation methodology was demonstrated to have the capability to consistently predict the temperature inside the pistons to within < 15C. In addition, it was also demonstrated that the methodology is general enough to be applied to any piston design including gallery cooled designs with straight and/or tilted jets. As oil jet cooled pistons become increasingly common due to higher efficiency engine development, this piston cooling simulation methodology can be now used as a predictive and valuable tool in the tool box of the analyst while guiding the design and development of the engine.