4,447 research outputs found
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Spray characteristics of a multi-hole injector for direct-injection gasoline engines
The sprays from a high-pressure multi-hole nozzle injected into a constant-volume chamber have been visualized and quantified in terms of droplet velocity and diameter with a two-component phase Doppler anemometry (PDA) system at injection pressures up to 200 bar and chamber pressures varying from atmospheric to 12 bar. The flow characteristics within the injection system were quantified by means of a fuel injection equipment (FIE) one-dimensional model, providing the injection rate and the injection velocity in the presence of hole cavitation, by an in-house three-dimensional computational fluid dynamics (CFD) model providing the detailed flow distribution for various combinations of nozzle hole configurations, and by a fuel atomization model giving estimates of the droplet size very near to the nozzle exit. The overall spray angle relative to the axis of the injector was found to be almost independent of injection and chamber pressure, a significant advantage relative to swirl pressure atomizers. Temporal droplet velocities were found to increase sharply at the start of injection and then to remain unchanged during the main part of injection, before decreasing rapidly towards the end of injection. The spatial droplet velocity profiles were jet-like at all axial locations, with the local velocity maximum found at the centre of the jet. Within the measured range, the effect of injection pressure on droplet size was rather small while the increase in chamber pressure from atmospheric to 12 bar resulted in much smaller droplet velocities, by up to four-fold, and larger droplet sizes by up to 40 per cent
Computational fluid dynamics combustion analysis evaluation
This study involves the development of numerical modelling in spray combustion. These modelling efforts are mainly motivated to improve the computational efficiency in the stochastic particle tracking method as well as to incorporate the physical submodels of turbulence, combustion, vaporization, and dense spray effects. The present mathematical formulation and numerical methodologies can be casted in any time-marching pressure correction methodologies (PCM) such as FDNS code and MAST code. A sequence of validation cases involving steady burning sprays and transient evaporating sprays will be included
Impaction of spray droplets on leaves: influence of formulation and leaf character on shatter, bounce and adhesion
This paper combines experimental data with simple mathematical models to
investigate the influence of spray formulation type and leaf character
(wettability) on shatter, bounce and adhesion of droplets impacting with
cotton, rice and wheat leaves. Impaction criteria that allow for different
angles of the leaf surface and the droplet impact trajectory are presented;
their predictions are based on whether combinations of droplet size and
velocity lie above or below bounce and shatter boundaries. In the experimental
component, real leaves are used, with all their inherent natural variability.
Further, commercial agricultural spray nozzles are employed, resulting in a
range of droplet characteristics. Given this natural variability, there is
broad agreement between the data and predictions. As predicted, the shatter of
droplets was found to increase as droplet size and velocity increased, and the
surface became harder to wet. Bouncing of droplets occurred most frequently on
hard to wet surfaces with high surface tension mixtures. On the other hand, a
number of small droplets with low impact velocity were observed to bounce when
predicted to lie well within the adhering regime. We believe this discrepancy
between the predictions and experimental data could be due to air layer effects
that were not taken into account in the current bounce equations. Other
discrepancies between experiment and theory are thought to be due to the
current assumption of a dry impact surface, whereas, in practice, the leaf
surfaces became increasingly covered with fluid throughout the spray test runs.Comment: 19 pages, 6 figures, accepted for publication by Experiments in
Fluid
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Breaking the Rayleigh-Plateau instability limit using thermocavitation within a droplet
We report on the generation of liquid columns that extend far beyond the traditional Rayleigh-Plateau instability onset. The columns are driven by the acoustic pressure wave emitted after bubble collapse. A high-speed video imaging device, which records images at a rate of up to 105 fps, was employed to follow their dynamics. These bubbles, commonly termed thermocavitation bubbles, are generated by focusing a midpower (275 mW) continuous wavelength laser into a highly absorbing liquid droplet. A simple model of the propagation of the pressure wavefront emitted after the bubble collapse shows that focusing the pressure wave at the liquid-air interface drives the evolution of the liquid columns. Control over the aspect ratio of the liquid column is realized by adjusting the cavitation bubble's size, beam focus position, and droplet volume. © 2013 by Begell House, Inc
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