Three dimensional CFD analyses of cooling DI Diesel engine pistons using oil jets 2019-01-0154
The combustion process in the internal combustion engine leads to heat fluxes on the chamber walls. Under high combustion heat fluxes, while the coolant can be applied aggressively to maintain the block and head temperatures, it becomes relatively more difficult to maintain safe piston temperatures. While, the motivation for engine downsizing, turbocharging and optimizing the combustion process is to improve fuel economy, the side effect is one of greater heat fluxes on the piston. Piston cooling jets using engine lubrication oil are being increasingly used to meet piston temperature requirements.
This paper reports on a three-dimensional computational fluid dynamics (CFD) analysis of DI Diesel engine piston cooling using oil jets supplied from the main oil gallery. The combustion heat flux on the piston surface is obtained from an in-cylinder CFD model and is input to the current analysis as a boundary condition. The present model consists of two separate models 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 loosely coupled to a steady state piston model. The piston motion is rigorously accounted for. The predictions show good agreement with measurements. The model results help to quantify the inventory of heat transfer rates through various cooling paths including the oil jet. A comparison of designs becomes possible using such a model. The heat load on the oil and its temperature rise due to piston cooling can be predicted. This information will be needed for oil life and oil cooler sizing. In summary, the proposed model will become an additional valuable tool in the tool box of the analyst while guiding the design and development of the engine.