Abstract
A laser sheet imaging system was developed for the investigation of high-speed fuel sprays under a relatively low injection pressure (less than 1 MPa). A pulsed laser and high-resolution CCD cameras were used for the evaluation of the fuel injection system of a small IC engine. Large droplets were detected during the injection incident, with a variation in the scattered light pattern from one droplet to another. The light scattering pattern of individual droplets was investigated in order to study the interaction between the laser beam and large fluid droplets compared to the wavelength. A laser sheet, with a wide waist Gaussian profile, was used for illumination, so that the relative position of a droplet in the third dimension of the field of view (FOV) can be estimated from the 2D-image. Light scattering images were processed in order to closely investigate the structure of the fuel droplets, and the behaviour of the laser beam when encountering large droplets (0.2–1.4 mm). The Particle Image Velocimetry (PIV) method was applied on the double exposure spray images to calculate the droplet velocity distribution of the global spray, using a high temporal resolution (15 s).
Highlights
The fluid atomisation topic is of importance to a wide range of engineering applications, including internal combustion engines
It was empirically found that the ratio between a droplet radius and its image Displacement on Z-axis coefficients (DCs) coefficient is constant for all particles located within the central laser beam: Const = r μm DC
Reflections generated by the “edge” and “surface wave” phenomena become more dominant than the light corona generated by the light diffraction effect, especially at wide angles of observation
Summary
The fluid atomisation topic is of importance to a wide range of engineering applications, including internal combustion engines. Because of the low Weber number at the moment of fluid discharge, large fluid ligaments are produced during the fluid fragmentation process, which eventually turn into large droplets mostly concentrated in the central part of the spray jet Such droplets are produced by the atomiser during the very beginning stage of the injection incident, due to either the liquid remains inside the swirl chamber of the injector, or the fluid segments attached to the injector nozzle. In both cases, when an injection event occurs, large drops with a low radial velocity are released from the nozzle. Moving the view angle slightly towards the forward scattering direction (at approx. 80◦–85◦ instead of 90◦) was found to produce a clear image of the internal reflections in the fluid droplet
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