Comparisons of Computed and Measured Hollow-Cone Sprays in an Engine

A second effort is reported to reproduce the distribution of fuel from a pulsating hollow-cone liquid-only poppet injector measured by the planar exciplex technique within the head cup of a motored ported single-cylinder engine operated at 1600 rpm with high swirl and a squish ratio of 75%. The injector, cup and cylinder were coaxial. The engine flowfield without injection had previously been characterized by LDV and PIV and so had been the injector and its spray in constant pressure environments. In a previous effort, the injector was assume to generate drop and the computed collapse of the spray was found to be too slow. In this work, the injector is assumed to generate liquid sheets that change shape and produce drops from their leading edges and surfaces as they propagate through the gas. The intact length (also the breakup length) of the sheets was extrapolated from the measurements in constant pressure environments and simple correlations were used for the Sauter Mean Diameters of the drops formed by the two mechanisms. With liquid sheets, the collapse of the spray is found to be too fast initially and correct afterward. Best agreement with the measured liquid fuel distribution is found by assuming that drops are generated at small injector openings and sheets at larger openings. But the most important general conclusion is that, for this type of injector, the spatial and temporal evolution of the entire spray is a very sensitive function of the initial sizes and trajectories of the drops that are generated at and near the injector. Current knowledge, models and measuring techniques are inadequate to predict the evolution of such sprays.