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Effect of flow in the circular 90-degree curved nozzles on ejecting oil jet behavior IntroductionNational governments are making efforts to reduce CO2 emissions and thus global warming. In particular, governments in the European Union have established regulations for the emission of CO2 from vehicles having internal combustion engines. These regulations require any new vehicle to have an average CO2 emission below 95 g/km from 2021 (Schulz M. and Kourkoulas D., 2014). The thermal efficiency of the internal combustion engine must be increased to meet these regulations. As an example, an engine is designed with a high compression ratio (Yamakawa, M. et al. 2012) and/or using a downsizing turbocharger (Petitjean, D. et al. 2004) to increase thermal efficiency. Both methods increase the heat load

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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.

The objective of this study is to investigate experimentally the effect of pulsation frequency on the heat transfer characteristics and the mechanism of the pulsation flow, which is representative of the operating conditions of the engine exhaust flow. The experimental apparatus consists of a rotating disk with holes that converts steady hot air flow rate into a pulsating flow to exchange heat energy with external air. The fluid temperature is measured by thermocouples, and the wall temperature is measured by thermography. It is found that heat transfer enhancement due to pulsation does not occur at frequencies below 25 Hz, even though the velocity amplitude is large. In order to investigate the cause of this phenomenon, the flow field is measured by PIV(Particle Image Velocimetry) and the turbulent kinetic energy is evaluated. It is clarified that the turbulent kinetic energy near the wall is small at frequencies below 30 Hz, despite the large velocity amplitude. From the time series of velocity data, it was observed that the turbulence is extremely small during the acceleration phase of the fluid. As a result, the turbulent mixing during the acceleration phase is suppressed, and the time-averaged turbulent kinetic energy becomes small, which is thought to have suppressed heat transfer enhancement. This is the first attempt to experimentally link heat transfer and flow structure fluctuations in a pulsating flow, which is achieved by unsteady measurement of the flow field using PIV and calculation of the turbulent kinetic energy.