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It is well established that spray characteristics from automotive injectors depend on, among other factors, whether cavitation arises in the injector nozzle. Bulk cavitation, which refers to the cavitation development distant from walls and thus far from the streamline curvature associated with salient points on a wall, has not been thoroughly investigated experimentally in injector nozzles. Consequently, it is not clear what is causing this phenomenon. The research objective of this study was to visualize cavitation in three different injector models (designated as Type A, Type B, and Type C) and quantify the liquid flow field in relation to the bulk cavitation phenomenon. In all models, bulk cavitation was present. We expected this bulk cavitation to be associated with a swirling flow with its axis parallel to that of the nozzle. However, liquid velocity measurements obtained through particle image velocimetry (PIV) demonstrated the absence of a swirling flow structure in the mean flow field just upstream of the nozzle exit, at a plane normal to the hypothetical axis of the injector. Consequently, we applied proper orthogonal decomposition (POD) to analyze the instantaneous liquid velocity data records in order to capture the dominant coherent structures potentially related to cavitation. It was found that the most energetic mode of the liquid flow field corresponded to the expected instantaneous swirling flow structure when bulk cavitation was present in the flow. [ABSTRACT FROM AUTHOR]

Spray characterization in a novel twin-jet airblast injector is reported in this paper with the focus on the study of the effect of injector air swirl on droplet characteristics and dispersion behavior. The operational principle of the injector is based on achieving atomization of two liquid jets, injected in a radially opposite direction from a central hub by high-speed annular swirling cross-stream flow of air. Liquid jet atomization within model atomizers and the resulting spray study have not gained much attention in spite of its practical importance, for example, in lean premixed prevaporized combustors. In the present work, droplet size and three-component velocity measurements are measured in the above injector using the phase Doppler particle analyzer technique. Air velocity without liquid injection is also obtained using the laser Doppler velocimetry technique. For given inlet air and liquid mass flow rates, experiments are conducted in the absence and presence of annular air swirl corresponding to swirl number, S = 0 and 0.74, respectively. The addition of air swirl is found to dramatically affect the spray topology and also the measured spray characteristics as the droplet size reduces significantly downstream of the injector exit, which is explained. Droplet dispersion is studied by evaluating droplet size velocity correlation and also droplet Stokes number. The results not only provide insight into the physics behind improved atomization due to air swirl, but also demonstrate the ability of the novel injector to achieve atomization quality and high spray dispersion over a wide operating range. [ABSTRACT FROM AUTHOR]

In this work, we investigate the atomization and spray characteristics of a novel rotary atomizer with micro-channel grooves, using optical diagnostics. Micro-jets emanate from the grooves provided in the rotating injector. The spiraling liquid jets interact with the surrounding high-speed swirling air flow, resulting in the creation of a well-dispersed fine spray. Attention is focused on the effects of air swirler orientation with respect to that of injector rotation. Accordingly, the co- and counter-swirl cases are investigated. The primary jet breakup process is visualized using back-lit illumination technique, which also provides the measurement of jet breakup length. The jet break-up modes are identified for different air swirl strength and orientation and injector rotational speed. The size, number density and velocity components of the spray droplets are measured using PDPA technique at different axial and radial locations. Air velocity is also measured (in the absence of liquid injection) using the LDV technique. In addition, Laser Sheet Imaging (LSI) is employed to investigate the overall spray structure. Results show that the droplet size significantly reduces when air swirl strength or injector rotational speed is increased. Though not much difference is observed in the characteristic droplet size between the co- and counter-swirl cases, the droplet size distribution is narrower and droplet dispersion is improved for the latter. The current findings demonstrate the potential of the rotary injector to dynamically control the spray characteristics as per requirement. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the mechanism of breakup of a transversely injected liquid jet due to swirling cross-stream flow of air in a model airblast injector. The focus is especially on examining the differences in the jet atomization in the absence and presence of air swirl within the injector. Multi-directional imaging of the liquid jet core is achieved by application of the Optical Connectivity (OC) technique for simultaneous visualization of the jet core from the side- and front-view. In addition, visualization of the jet core from the bottom view is also possible. Apart from the jet penetration and breakup length (obtained from the side-view image), the present technique facilitates measurement of jet width and spread rate (from the corresponding front-view image) at the same time. The airblast injector is operated for a wide range of operating conditions. The results highlight significant influence of swirling the air flow on the jet breakup morphology as well as primary breakup parameters. The measurements provided some new insight into the physics of the primary atomization within an atomizer, where the air flow is confined, in contrast to the widely studied jet-in-crossflow in wind-tunnels. In the present case, prior to its breakup into ligaments and droplets, the liquid jet undergoes jet-to-sheet transformation. Also, the liquid sheet deflects in the direction of air swirl and disintegrates in a complex manner. The addition of swirl to the air flow leads to reduction in the mean jet breakup parameters, while the fluctuations are higher. • The influence of swirling crossflow air on liquid jet atomization within an injector is studied. • A multi-directional fluorescence imaging technique is employed to visualize the jet core. • The jet penetration/breakup length and jet width/spreading angle are measured. • Significant influence of air swirl on the primary jet breakup parameters is identified. • Jet-to-sheet transformation occurs prior to jet breakup into ligaments and droplets. [ABSTRACT FROM AUTHOR]