ID 252

Ballistic Imaging of Sprays for Large Bore Diesel Engines

 

Abstract:

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 cylinder wear, and higher levels of harmful emissions. In this work, time-gated ballistic imaging was applied to study the spray morphology in concert with in-nozzle flow effects imaged by nanosecond shadowgraphy. 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 approximate the geometry common in large marine two‐stroke diesel injectors. Time-gated imaging of the primary breakup area of the spray emerging from the nozzles was achieved using a collinear, two-color optical Kerr effect shutter system which allows the acquisition of ultrashort (~120 fs) single-shot images formed by high-quality (minimally scattered) source light. The single shot spray images and coordinated shadowgraphy of internal flow allow qualitative evaluation of the primary breakup region and the effects of cavitation in-nozzle flow.