EFFECT OF CAVITATION IN CIRCULAR NOZZLE AND ELLIPTICAL NOZZLES ON THE SPRAY CHARACTERISTIC

The fuel spray characteristic is one of the most important factors to improve combustion performance. Fuel spray characteristics are affected by the internal flow of liquid in the nozzle. Cavitation is a major factor that influences internal flow. In order to investigate the effects of cavitation phenomena in a circular nozzle and elliptical nozzles, all of the test nozzles in this study were made of transparent acrylic for visualization. The cross-sectional areas of all nozzles were approximately the same, based on a 3 mm diameter circular nozzle. The aspect ratios (a/b) of elliptical nozzles were 2 and 3, respectively. The internal flow in the test nozzle and the external flow were visualized and analyzed by using the images captured from the charge-coupled device (CCD) camera to investigate the effects of cavitation on the liquid jet under various injection pressures. The discharge coefficient tended to decrease with increasing pressure. The cavitation in elliptical nozzles was generated at a lower Reynolds number than the circular nozzle. Elliptical nozzles had a lower discharge coefficient than the circular nozzle at the same Reynolds number. The cavitation length at the major axis plane was longer than that of the minor axis plane in elliptical nozzles. The spray angle was increased with injection pressure. The spray angle in the elliptical nozzles was larger than in the circular nozzles.