Influence of nozzle hole eccentricity on spray morphology

Abstract

Large marine two-stroke diesel engines have an injector geometry, which differs substantially from the configurations used in most other diesel engine applications, as the injector orifices are distributed in a highly non-symmetric fashion. In order to experimentally assess the impact of key features of such orifice arrangements on spray morphology, orifice eccentricity relative to the injector axis in particular, a dedicated test setup has been realised, including the development and application of tailor-made data processing routines. The high-speed camera recordings of the Mie-scattering data obtained simultaneously for two perpendicular views of single sample sprays have been analysed in terms of spray tip penetration and spray angle as well as with respect to the orientation of the spray. These analyses confirm the complex three-dimensional structure of sprays at such conditions: They are in fact far from rotationally symmetric – specifically when high levels of eccentricity apply – and the actual orientation of their axis in such cases clearly deviates from the nominal one, normally assumed to be in line with the orifice axis. These deflections are in the range of 10° and they apply not only in the direction of the eccentricity but also perpendicular to it. Additional effects arise from the geometric configuration of the central bore of the injector, upstream of the orifice, and when varying the injection pressure.In the case of high eccentricity, moreover, a clear pattern can be discerned in the initial evolution of the spray deflection: Starting from a slight deflection in the direction of the eccentricity, the spray axis moves first to its nominal direction and then gradually changes orientation again towards the level of stabilisation.