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The rise of fuel injector pressures in diesel engines has generally increased internal flow problems in the injector tip, particularly, the formation of cavitation vapor bubbles. These can not only impact spray formation, but their subsequent collapse can lead to cavitation erosion damage, affecting engine component life and performance. In this work, internal flow and spray phenomena are investigated for a multi-hole diesel fuel injector tip via flow visualization experiments and computational simulations of the flow injection event.
A multi-hole transparent quartz injector tip mated with a production injector body enables internal flow to be investigated for rail pressures up to 1000 bar. Effects of internal flow geometry, ambient (back) pressure, and rail pressure on the locations of vapor clouds and bubble inception are quantified via analysis of relatively high-speed (110kHz) imaging throughout needle opening, quasi-steady injection, and needle closing events.
Measured quantities from experiments, including local cavitation vapor probability and volume fraction are compared with computational simulations to enhance understanding of complex observed internal flow phenomena and to validate model predictions. Simulations employing volume-of-fluid (VOF) interface tracking and a homogeneous relaxation model (HRM) with fixed mesh refinement are also used to examine the effects of real geometry (as determined by high-resolution x-ray tomography) on internal flow predictions. Overall, this work represents a considerable effort to develop tools that will aid the design of robust hardware and spray combustion processes for injection pressures exceeding 2500 bar.
