Methods of decreasing the CO 2 emissions of the internal combustion engine have been suggested. For example, an engine can be designed with a high compression ratio and/or a downsizing turbocharger. However, these methods generate high combustion temperatures that increase the heat load. The piston cooling gallery has been proposed as a system for cooling the engine piston. The piston cooling gallery is an oil flow path that is set internal to the piston. An oil jet injected from a nozzle placed under the piston flows into the piston cooling gallery through an entrance hall. It may thus be desirable to control the shape of the oil jet such that it is stable and straight. However, the interface of the ambient air and oil jet may have unstable waviness because of Kelvin-Helmholtz instability and/or Rayleigh-Taylor instability. In addition, we investigated the flow and found that the propagation of the flow speed fluctuation of the nozzle internal flow results in the waviness of the oil jet in a previous study. To further clarify the relationship between oil jet interface instability immediately after nozzle exit and flow in nozzle, this paper reports on two types of particle image velocimetry (PIV), namely twodimensional two-velocity-component PIV and two-dimensional three-velocity-component PIV, in addition to two-component and three-component snapshot proper orthogonal decompositions, and analyzes turbulence propagation adopting a cross-correlation method. We find a characteristic basis vector with large energy that propagates the fluctuation downstream under the condition that the interface between the oil jet and air has strong waviness.

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