TECHNICAL PAPERS: Gas Turbines: Controls, Diagnostics, and Instrumentation

Development of a Temporally Modulated Fuel Injector With Controlled Spray Dynamics

[+] Author and Article Information
H. Chang, D. Nelson, C. Sipperley, C. Edwards

Thermosciences Division, Department of Mechanical Engineering, Stanford University, Stanford, CA 94305-3032

J. Eng. Gas Turbines Power 125(1), 284-291 (Dec 27, 2002) (8 pages) doi:10.1115/1.1496118 History: Received December 01, 2000; Revised March 01, 2001; Online December 27, 2002
Copyright © 2003 by ASME
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Spray modulation using a piezoelectric actuator upstream of a pressure-swirl atomizer. The image to the left (a) is of an underdeveloped water spray. The image to the right (b) is taken with the same average flow rate but using 6 kHz modulation. The left side of each image is a time-averaged exposure while the right is phase-locked to the modulation.
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Effect of piezoelectric modulation on Sauter mean diameter and mean drop velocity. Note the dependence of the drop size, speed, and trajectory on modulation frequency.
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Schematic of a spill-return nozzle (Lefebvre 10). While similar to a pressure-swirl atomizer, it includes a return flow path from the swirl chamber which permits the flow rate delivered to the combustor to be decoupled from the pressure drop across the atomizer.
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Sauter mean diameter (SMD) as a function of spilled fraction at fixed overall pressure drop (ΔPF) injecting into ambient pressure (PA) (Rizk and Lefebvre 10). Little effect is observed over a range of conditions approaching 90% turn down in fuel delivery.
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Spray patternation at full fuel delivery (zero spilled fraction) and with a turn down to 36% delivery (0.64 spilled fraction) (Rizk and Lefebvre 12). FN is the flow number of the nozzle.
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Integrated actuator/atomizer assembly. The voice coil is used to modulate the spill return flow rate by varying the position of the valve stem. An LVDT is used to provide a position feedback signal to the control system.
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Closed-loop response of the LEAD-compensated actuator system as a function of modulation frequency. Amplitude response remains flat to ∼1 kHz while stable performance is expected up to ∼2 kHz. (Dots: real experimental data/Solid line: simulations)
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Strobe-lighted images of overall spray structure with and without modulation. Without modulation a uniform spray field is evident. With modulation, light and dark bands appear, synchronized with the modulation frequency. These bands are advected downstream at the induced flow velocity.
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Laser-sheet images of the internal structure of the spray with and without modulation. Without modulation little internal structure is evident. With modulation, gas-phase vortical structures appear, made evident by preferential droplet transport. These cause the dense bands observed in the overall spray images of Fig. 8. As modulation frequency is increased, the scale of these structures decreases and their spatial frequency rises.
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Time-averaged phase Doppler data taken along a radius 19 mm downstream of the nozzle exit. Neither the mean droplet diameters nor the mean drop velocities are significantly altered by modulation.
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Phase-averaged droplet arrival rates and droplet mean diameters for 100 Hz modulation spray. Data taken at z=19 mm and (a) r=0 mm, (b) r=4.5 mm, (c) r=9 mm, (d) r=13 mm.
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Phase-averaged droplet arrival rates and droplet mean diameters for 400 Hz modulation spray. Data taken at z=19 mm and (a) r=0 mm, (b) r=4.5 mm, (c) r=9 mm, (d) r=13 mm.




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