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Abstract
The methodological aspects and the potentials of a quantitative imaging technique, suitable for the analysis of the condensed phases fields of diesel sprays in isothermal and burning conditions are described. The technique is based on the simultaneous detection of two polarized components of light scattered by the liquid fuel and/or the carbonaceous material present in a pulsed laser sheet, which crosses a diesel spray injected into a high pressure, high temperature environment. A couple of digital images are recorded: the first one is the pattern of the vertically polarized scattered light and it is used as descriptor of the scatterers concentration; the second one is the pattern of the ratio between two polarized components and it is used as descriptor or the scatterers characteristics
Some representative images of these quantities are reported for preignition and post-ignition conditions. The level and the type of randomness of the condensed phases are very different for the two conditions. In the first case the fuel spray is always compact with statistically uniform properties in the central part of the spray. Only in the very diluted peripheral part the spray presents spatial random characteristics due to the effective interactions with the environment. On the opposite in the post-ignition conditions both fuel and soot are randomly distributed on the whole spray section
The presence of the soot inside the spray in the form of many isolated structures or of large single connected regions suggests that it is originated by pyrolitic processes. The soot formation, active on randomly distributed fuel packets, can occur either in the central part of the spray or in the periphery. In this latter case the soot is then convected toward the interior region.