Left: Nine-point LDI configuration tested at Glenn. The viewpoint is aft looking upstream. Right: Relative spatial positioning of the air swirler, fuel nozzle, and converging-diverging venturi for each injector element.
Lean direct injection, conceived at the NASA Glenn Research Center, is representative of a new generation of turbine engine combustor injector concepts designed to rapidly mix air and fuel to create a stable combustion zone within a short distance from the injector in order to reduce the emission of oxides of nitrogen (NOx). This injector concept was chosen as the primary test case for validating the National Combustion Code (NCC). To begin building a validation database, Glenn researchers tested a nine-point injector in anonsite flame tube combustor facility. The experimental hardware was the baseline nine-injector array shown in the view looking upstream in the preceding photograph. Each injector element was the lean direct injector (LDI) shown in the preceding illustration below.
The nine-point injector was mounted in the optically accessible flame tube shown in the following illustration. A laser sheet passed through the top window. Cameras on each side imaged fluorescence (for planar laser-induced fluorescence (PLIF) measurements) or particle fields (for particle image velocimetry (PIV) or planar-light-scattering (PLS) measurements). The laser sheet and imaging apparatus were moved across the flow to gather data over the entire optically accessible volume. For PIV measurements, data also were gathered with the laser sheet passing through the side windows and the camera on top. Using appropriate laser wavelengths and filters, both hydroxyl radical (OH) and fuel PLIF were measured. For the PIV measurements, a high-pressure seeder seeded the flow with 0.3-μm-diameter aluminum oxide particles. Pairs of particle field images were used to determine the velocity field.
Optically accessible flame tube and the relative orientation of the laser sheet and intensified charge-coupled device (ICCD) cameras to the test rig for a vertically applied laser sheet.
Three-dimensional species image maps showing the distribution of total fuel, OH, and liquid fuel were derived from PLIF and PLS data. Examples of these data are in the following images, which show views of fuel PLIF (left), OH PLIF (center), and PLS from fuel droplets (right) 7.5-mm downstream from the injector. The black circles indicate the position and diameter of each LDI venturi diffuser. The view is constrained by the window size so that only the central injector element is fully in view.
End views 7.5 mm from the injector exit plane showing the species pattern of total fuel (left), OH (center), and liquid fuel (right). The field of view is the central 46- by 46-mm area. Each species is scaled independently. Top: Inlet conditions: temperature, 617 K; pressure, 1030 kPa; equivalence ratio, 0.38. Bottom: Inlet conditions: temperature, 822 K; pressure, 1723 kPa; equivalence ratio, 0.41.
In these images, we can see ringlike structures, particularly in the OH images; these give an indication of the size and position of the flame front at this location. Comparing the fuel PLIF (from liquid and vapor) and PLS (from liquid) images tells us whether the fuel is mostly liquid or vapor. In the top set of images, a significant portion of the fuel is in the liquid phase; whereas in the bottom set of images, which were acquired at a higher temperature, the fuel is almost completely vaporized.
As an example of the PIV results, the final figures compare experimentally and computationally derived axial air velocities under nonfueled, nonreacting conditions 6-mm downstream from the injector. The computations were obtained using a Reynolds averaged Navier-Stokes simulation. The square overlay on the computational result shows the region accessible by our PIV measurements. A comparison shows that the overall velocity field structure is similar. Finer experimental PIV grid spacing would likely bring out the fine structure observed in the computational results and improve the comparison.
Axial air velocities 6-mm downstream of the injector exit plane. Left: Experimental PIV results. Inlet conditions: temperature, 617 K; pressure, 1030 kPa. Right: Computation. Inlet conditions: temperature, 822 K; pressure, 2740 kPa.
Davoudzadeh, Farhad; Liu, Nan-Suey; and Moder, Jeffrey P.: Investigation of Swirling Air Flows Generated by Axial Swirlers in a Flame Tube. ASME Paper GT-2006-91300, 2006, pp. 891-902.
Tacina, Robert, et al.: Sector Tests of a Low-NOx, Lean-Direct-Injection: Multipoint Integrated Module Combustor Concept. ASME Paper GT-2002-30089, 2002, pp. 533-544.
Tacina, R.; Mao, C.; and Wey, C.: Experimental Investigation of a Multiplex Fuel Injector Module for Low Emission Combustors. AIAA-2003-0827, 2003.
Tacina, R.; Lee, P.; and Wey, C.: A Lean-Direct-Injection Combustor Using a 9 Point Swirl-Venturi Fuel Injector. XVII International Symposium on Air Breathing Engines (ISABE), ISABE-2005-1106, Munich,Germany, 2005.
Find out more about this research:
Glenn’s Optical Instrumentation & NDE Branch: http://www.grc.nasa.gov/WWW/OptInstr/AdvancedLaserDiag.htmlGlenn contacts:
Dr. Yolanda R. Hicks, 216-433-3410, Yolanda.R.Hicks@nasa.gov
Robert C. Anderson, 216-433-3643, Robert.C.Anderson@nasa.gov,
ASRC Corporation contact: Dr. Randy J. Locke, 216-433-6110, Randy.J.Locke@nasa.gov
Authors:
Robert C. Anderson, Dr. Yolanda R. Hicks, Dr. Randy J. Locke, and Changlie Wey
Headquarters program office:
Aeronautics Research Mission Directorate
Program/projects:
Subsonic Fixed Wing
Last updated: December 14, 2007
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