Experimental study of spray-formation processes in twin-fluid jet-in-crossflow at jet-engine operating conditions

Jet-in-crossflow;Cross-flow;Transverse jet;Twin-fluid;Airblast;Air-assist;Spray;Penetration;Trajectory;Fuel-injection;Jet-engine;Atomization regime;Experimental study;Shadowgraph;High pressure;High Weber number

Tan, Zu Puayen ; Zinn, Ben T. Jagoda, Jechiel Setizman, Jerry Genzale, Caroline Lubarsky, Eugene Aerospace Engineering ; Zinn, Ben T.

University:Georgia Institute of Technology

Department:Aerospace Engineering

关键词: Jet-in-crossflow;    Cross-flow;    Transverse jet;    Twin-fluid;    Airblast;    Air-assist;    Spray;    Penetration;    Trajectory;    Fuel-injection;    Jet-engine;    Atomization regime;    Experimental study;    Shadowgraph;    High pressure;    High Weber number;   

Others  :  https://smartech.gatech.edu/bitstream/1853/58214/1/TAN-DISSERTATION-2017.pdf

美国|英语

来源: SMARTech Repository

【 摘 要 】

The jet-in-crossflow (JICF) fuel-injection technique is widely applied in modern jet-engine fuel-air mixers to provide rapid fuel atomization and mixing. However, the “Classical” JICF places large amounts of fuel into the initial jet/spray’s recirculation zone and the wall boundary-layer, both of which can risk flashback and fuel-coking on the wall, particularly for next-generation jet-engines that will operate at increasingly higher pressures and temperatures. Twin-Fluid (TF) JICF, where streams of air are co-injected with the fuel jet into the crossflow, is being considered as a way to mitigate the Classical-JICF’s shortcomings. However, the TF-JICF is a nascent fuel-injection technique that is not well understood, especially at the high operating pressures of jet-engines. This dissertation reports an experimental investigation of TF-JICF where liquid Jet-A fuel was co-injected with pressurized nitrogen into a crossflow of air. The developed fuel sprays were characterized using shadowgraphy. The fuel-to-crossflow momentum-flux ratios were varied from J=5-40, the air-nozzles pressure-drops were varied from dP=0-150% of crossflow pressure, and the crossflow Weber numbers were varied from Wecf=175-1050. These operating conditions allowed us to obtain a dataset that is both comparable with near-atmospheric studies of TF-JICF in the literature and applicable to jet-engines. The results show that TF-JICF can be classified into four spray-formation regimes (i.e., Classical-JICF, Air-Assist JICF, Airblast JICF and Airblast Spray-in-Crossflow), each containing a unique set of spray characteristics and mechanisms. In the Air-Assist regime that spans dP≈3-13%, the injected air formed a protective air-sheath around the initial fuel jet, which inhibited the development of Rayleigh-Taylor waves and surface-shearing (i.e., disturbances created by the crossflow), thus reducing the near-wall fuel concentrations. Applying higher levels of dP transitioned the spray into the Airblast JICF regime, where the intensified fuel-air impingement and shearing generated new disturbances on the jet. These generally caused the near-wall regions to become repopulated with fuel droplets (i.e., counter-productive towards mitigating flashback and wall-coking). When dP was higher than 100%, the jet became completely atomized by air prior to encountering the crossflow, producing an “Airblast Spray-in-Crossflow”. The resulting spray-plume’s penetration became related to the combination of the fuel and air’s momentum-fluxes, where increasing dP caused increasing separation between the spray-plume and test-channel wall. This reduces the near-wall fuel concentrations and is beneficial towards fuel-air mixer design, although the required levels of dP for this regime is likely too high for practical jet-engine operation.