2021 年 16 巻 2 号 p. JFST0011
In general, technical methods for improving the thermal efficiency of an engine increase the heat load on peripheral components. Recently, a piston cooling gallery equipped with a flow path has been developed. The engine oil is supplied an oil jet from the nozzle, which is placed under the piston to the piston gallery entrance hall. The nozzle of the oil jet is curved to minimize its size, and the jet interface between ambient air and oil fluctuates near the nozzle exit owing to the shape. Few studies have investigated the behavior of oil jets ejecting from curved pipes. We therefore investigated the flow in two nozzles having a basic bend of 90° with radii of curvature of 15 and 60 mm. Our results clarify the effect of internal flow on the ejecting oil jet behavior. Silicone oil was used as the working fluid. The kinematic viscosity of the silicone oil at 298 K was similar to that of engine oil at 353 K. The behavior of the oil jet was investigated by visualization using background light. A light-emitting-diode displacement meter was installed to measure the jet width. We found that the width of the oil jet increased on the downstream side with large fluctuation of the interface under the condition of a small radius of curvature and large Reynolds number. Furthermore, we time-synchronously measured flow in the nozzle, two-dimensional two-component time-resolved particle image velocimetry, and visualization of the jet. The Reynolds number was set from 1000 to 3000, which is close to that of the engine oil jet. The oil flow velocity in the nozzle fluctuated in the radial direction. The fluctuation became strong under the condition of a small radius and large Reynolds number. The fluctuation propagation speed calculated from the correlation coefficient was as high as the flow speed itself. Furthermore, the jet interface fluctuation speed in the flow direction was as high as the fluctuation propagation speed in the nozzle. Our results demonstrate that the cause of the interface fluctuation is the fluctuation propagation of flow in the nozzle.