Abstract
The high efficiency cooling of pistons in internal combustion engines by oil jets has recently received widespread attention. To date, curved circular oil jet nozzles have been commonly employed. However, although liquid jets from straight circular nozzles have been studied, there are few reports regarding the characteristics of liquid jets injected by curved circular nozzles. The present work therefore examined the characteristics of oil jets, such as jet width and interfacial fluctuations, following injection via either a 90° curved circular nozzle or straight circular nozzle into a stationary atmosphere. Oil jet parameters were assessed at Reynolds numbers from 1000 to 3000 and the jet interfaces were visualized using a background illumination method in conjunction with a high-speed camera. The oil jet injected from the curved nozzle exhibits more complex behavior compared with that from the straight nozzle. The cross section of the jet from the curved nozzle perpendicular to the direction of movement gradually expanded from a circular shape to an elliptical shape in the downstream direction. The side corresponding to the long diameter of this elliptical jet shape was also observed to switch depending on the Reynolds number. At the inner and outer side interfaces, the outer side interface became larger than the inner side interface at the Reynolds number of 1500 or less. However, the inner side interface became greater than the outer side interface at the Reynolds number of 2000 or more. The effects of the velocity distribution following the bend in the curved nozzle on oil jet behavior were examined by stereoscopic particle image velocimetry. The nozzle internal flow evidently generated movement from the outer side toward the inner side at the Reynolds number of 2000, while flow toward the inner side was dominant when the Reynolds number was 2500.
