Internal and near nozzle flow characteristics in an enlarged model of an outwards opening pintle-type gasoline injector

Abstract

The internal nozzle and near the nozzle exit flows of an enlarged transparent model of an outwards opening injector were investigated for different flow rates and needle lifts under steady state flow conditions. A high resolution CCD camera, high speed video camera and an LDV system were employed to visualize the nozzle flow and quantify the tangential velocity characteristics. The images of the internal flow between the valve seat and the square cross-section end of the needle guide revealed the presence of four separated jet flows and four pairs of counterrotating vortices with each pair bounded in-between two adjacent jets. The counterrotating vortices are highly unstable with a circumferential oscillatory motion which was transmitted to the spray outside the nozzle with almost the same frequency. The dominant circumferential frequencies at the nozzle exit were identified by FFT analysis of the tangential velocities. A linear relationship exists between the dominant frequencies and the flow Reynolds number based on injection velocity and needle lift. Magnified images of the flow just outside the nozzle exit showed formation of interconnecting streamwise strings on the liquid film as soon as it emerges from the annular exit passage. The interspacing between the strings was found to be linearly related to injection velocity and almost independent of the needle lift.

Internal Flow and Spray Characteristics of Pintle-Type Outwards Opening Piezo Injectors for Gasoline Direct-Injection Engines

“…However, the results showed that up to a flow rate of 1.3 l/s the spray surface was always rough independent of valve lift. Observation of the spray in the new enlarged cavitating model showed a different structure to that observed in the non-cavitating injector [16]. A small sample of the results, presented in Figure 8, clearly show the complex nature of the spray with its many jet like strings which suggests that, apart from ambient effects on the emerging spray, there have to be changes in the flow structure within the annular nozzle passage.…”

“…The steady flow rig, which was similar to that presented in [3,16], comprises two pumps, connected to the model injector at its inlet and outlet to provide the maximum pressure difference across the injector, a supply tank and an ultrasonic flow meter as shown in Figure 2. The large-scale model injector, made from acrylic (Perspex), is geometrically similar to the real size injector but 23.3 times larger.…”

“…The injector is an outwards opening piezo injector with a converging-diverging nozzle flow passage close to its exit and a small parallel section in-between where the nozzle seat is as shown in Figure 4; this configuration is referred to as the cavitating nozzle and has an overall nominal cone angle of 90º. The main difference between this design and that used in [16] is the outer surface profile of the needle which has triple angles in the cavitating model and a single angle in the non-cavitating one where the divergence section at the nozzle exit is parallel. In order to prevent image distortion of the nozzle flow due to the strong curvature of the cartridge outer surface, a flat window of 10mm width and 20 mm length (to insure complete viewing of the nozzle seat region) was machined and inserted at the outside surface of the cartridge as shown in Figure 4.…”

“…The experimental investigation of [16] aimed at identifying the origin of this string-type spray structure by visualising the internal nozzle and the near-nozzle exit flows of an enlarged transparent model of an outwards opening noncavitating injector. The results show a very complex flow in the region above the nozzle seat with four separated jet flows originating from the square cross-section of the needle guide and four pairs of counter-rotating vortices, each pair confined between two adjacent jets.…”

“…The present work is the continuation of the experimental study in [16] but in a cavitating nozzle geometry and its main objective is the characterisation of the internal nozzle flow and, in particular, the formation of the flow filaments near the nozzle exit. The internal flow was visualised and monitored with pulsed and continuous light sources, a high-resolution CCD camera and a high-speed video recorder.…”