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PhD Defense by
Advisor: Prof. Ben T. Zinn
2:00 PM, Wednesday, November 9, 2016
Montgomery Knight Building Room 317
Abstract
Jet-in-crossflow (JICF) fuel-injection is widely applied in modern jet-engines to provide rapid fuel-atomization and mixing. However, “classical” JICF places large amounts of fuel into the low-velocity region near the injector wall, which can cause flashback and fuel-coking on the wall. A nascent fuel-injection technique called Twin-Fluid (TF) JICF is being considered as a way to mitigate Classical-JICF’s shortcomings. In TF-JICF, air is co-injected around the fuel jet to modify its atomization and penetration characteristics. Designers expect TF-JICF to enhance the fuel’s penetration away from the wall (i.e., reduce near-wall fuel concentrations). However, the performance of TF-JICF is currently not well understood, especially at the high pressures found in jet-engines. This dissertation work addresses the knowledge gap by experimentally investigating a TF-JICF where liquid Jet-A fuel was co-injected with pressurized nitrogen into a crossflow of air. The crossflow and injection conditions were varied over wide ranges that cover those conditions reported in the available TF-JICF literature, as well as those expected for jet-engines. The resulting TF-JICF fuel sprays were imaged by shadowgraphy, and their penetrations, dispersions and atomization processes were analyzed.
For a fixed fuel flow-rate, different levels of air-injection velocities were found to cause different spray characteristics (see figure below). A mild injection of air inhibited the atomization of the initial fuel jet, thus reducing the near-wall fuel concentration and flashback/wall-coking risks. A very strong injection of air “propelled” the fuel very far away from the wall while also enhancing atomization. On the other hand, medium levels of air-injection were generally non-beneficial towards fuel-injector design. Four TF-JICF regimes were identified (i.e., Classical-JICF, Air-Assist JICF, Airblast JICF and Airblast Spray-in-Crossflow) based on these characteristics and their formation mechanisms.
