Static pressure distribution inside the swirl spray

The transient static pressure of the air located along the centerline of the spray from a DISI pressure swirl injector was measured for different injection pressures, fuel temperatures and injection durations. The drop in the pressure at the centerline was found to be mainly attributed to the swirling liquid and enhanced with the swirling velocity manifested by the injection pressure. With increasing the injection duration, the pressure was found to be continuously dropped, although the measured swirling momentum of the liquid reaches an asymptotic value and remains constant until the needle starts to close. This implies that the pressure at the centerline of a transient spray does not reach its asymptotic value which corresponds to the case of a continuously injected spray. At higher fuel temperature, the air pressure at the centerline increases and can reach a value more than atmospheric pressure due to the sudden evaporation of the fuel after been released underneath the needle. This high air pressure pushes the main stream of the spray to the radial direction resulting in a larger nozzle spray angle which is soon collapsed after a short distance due to the severe expansion of the air and enhanced swirling motion. The link between the pressure drop across the spray and liquid film profile for different operating conditions was presented using a simple analytical model. The injector was then modified to eliminate the pressure drop at the center line to have a robust spray that has limited variation with the operating condition and can be used in spray guided gasoline direct injection system. By cutting the nozzle to have a tapered nozzle with an angle less than the flow angle the opened hollow cone shape along the spray streamlines was formed. This shape assists in equalizing the pressure between the centerline and outer part of spray envelop. The results showed that there is a potential from tapered nozzle spray to be independent of the operating conditions without much sacrifice of the atomization quality.