Ballistic imaging of sprays for large bore diesel engines

Paper in proceeding, 2020

Injector geometries of large marine two-stroke Diesel engines differ extensively from typically used configurations in Diesel engines. In typical applications, the injector orifices are arranged asymmetrically and employ multiple bores face in roughly the same direction. To enhance mixing, the orifices are also positioned off axis with respect to the central bore of the injector. Prior experimental work has shown that the spray plumes produced by this arrangement exhibit asymmetric propagation with respect to the nominal axis of each orifice. These spray deviations can lead to increases in fuel consumption, increased wear, and higher levels of emissions. In this work, time-gated ballistic imaging was applied to study the spray morphology in the near-nozzle region of marine fuel injection sprays. The sprays presented here were generated by a selection of transparent 0.75 mm diameter mono-hole nozzles with different levels of inlet radii produced by hydro-erosive grinding. Here the nozzle orifice was positioned orthogonal to the inlet and nominal axis of the injector to match the geometry common in large marine two-stroke diesel injectors. Time-gated imaging of the spray near the nozzle orifice was achieved using a colinear, two-color optical Kerr effect shutter system which allows the acquisition of single-shot images formed by high-quality (minimally scattered) source light. The time-gated spray images allow qualitative evaluation of the primary breakup region and positively identify spray edges and voids due to the contrast provided by the optical path length and time-gate interaction.