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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Much attention has recently been given to high-efficiency cooling of pistons in internal combustion engines by cooling channels because of improved thermal efficiency. Cooling a piston efficiently requires a grasp of the gas-liquid multiphase flow state. However, because the magnitude and direction of the inertial force applied to the piston change depending on the crank angle, the flow field in the cooling channel that forms a complex gas-liquid multiphase flow remains a problem. Therefore, we developed a rig test apparatus simulating the reciprocating motion of a piston and visualized internal flows in a clear acrylic channel using a high-speed camera. This paper examines the effects of the Reynolds number of the oil jet and oscillation frequency of the reciprocating motion on flow characteristics in a right circular cylindrical channel. The Reynolds number and oscillation frequency were tested in the ranges 1000 to 2500 and 0 to 8.33 Hz, respectively. We found that the oil flow pattern in the channel forms the complex air-oil multiphase flow via air entrainment caused by the collision between the oil jet and the channel oil at the inlet. The gas phase area ratio in the channel increases with increasing Reynolds number, but its fluctuation is dominated by oscillation frequency. The fluctuation of the gas phase center of gravity becomes larger because of increases in inertial force with increases in oscillation frequency. The average bubble diameter in the channel decreases with increasing Reynolds number and oscillation frequency. We found that bubbles of small diameter are generated because the interfacial fluctuation of the oil jet increases as the jet goes downstream.