In conjunction with a program to develop low-emissions ground power and aircraft auxiliary power units, the NASA Glenn Research Center designed and built a facility to test fuel reformer concepts capable of providing 10-kWe power. NASA is investigating jet and diesel fuel reforming as a viable mechanism to generate hydrogen for solid oxide fuel cell (SOFC) operation. Jet-A and diesel fuels are being considered for fuel cell applications because they are relatively safe to handle, have high energy density, and have existing infrastructure.
In fuel reformation, a hydrogen-rich flow of syngas necessary for SOFC operation is created by catalytic reaction when a well-mixed, high-temperature flow of fuel, air, and sometimes steam impacts a catalyst. Three types of reforming processes are possible for fuels: catalytic partial oxidation (CPOX), autothermal reforming (ATR), and steam reforming (SR), depending on the amounts of steam and air used. Because reformer catalysts suffer degradation due to the buildup of carbon deposits and inadequate feed mixing and vaporization, nonuniform temperature distributions can result. A fuel injector system that fully vaporizes and mixes the reactants is critical to achieving optimal reforming performance.
A special feature of the NASA fuel reformer facility is an optically accessible test section (see the photograph), that allows researchers to obtain flow measurements to assess fuel injector mixing prior to entering the reformer. Diagnostics include flow-field visualization and quantitative measurements of velocity, fuel, and species distribution. Two methods are (1) particle image velocimetry (PIV) to acquire two-dimensional velocity field measurements and (2) Raman spectroscopy to determine the chemical species distribution across the flow field. The schematic drawing shows the region within the quartz cylinder that is probed by these methods.
Left: Optically accessible test section that includes the fuel injector-mixer concept being examined atop the quartz cylinder through which the mixing measurements are conducted. The fuel injector is mounted vertically with the flow downward. Right: Particle image velocimetry (PIV) laser sheet orientation and measurement region along with Raman sampling locations. Dimensions are in millimeters. SVM, swirl venturi mixer.
The following schematic drawing shows a NASA-concept injector-mixer configuration. This swirl venturi mixer (SVM) concept provided a testbed for the parametric study of simple fluid elements whose combination leads to complex flow structure. These design elements include air/steam swirler angle, venturi throat size (diameter and length), and diffuser length and angle.
Major fluidic components of the SVM. Flow passes from top to bottom.
The graphs are examples of PIV and Raman results that show differences in species and velocity profiles. The Raman results show the differences between fuel loading for the same injector under two reforming processes and two flow rates. A flat, symmetric fuel profile is desired. The PIV results show distinct differences in velocity for different configurations of the SVM at the same flow conditions, with only one showing the desired uniform velocity profile across the flow field. This demonstrates that minor changes in fuel injector-mixer components can produce large differences in flow structure. These tests and others help to screen for the most suitable injector for a given reformer application and provide a database to help researchers understand the important parameters in injector design.
Species profiles for one fuel injector configuration using two ATR and CPOX flow conditions.
Resultant two-dimensional velocity profiles for three fuel injector configurations at the same ATR flow conditions. Flow passes from top to bottom.
In addition to NASA concepts, Glenn has investigated several fuel atomization and mixing concepts using the new test facility in conjunction with private industry and the Department of Energy. These concepts include a gas-assisted simplex, a fuel-siphoning impingement injector, fuel preheating injection, piezoelectric injection, and fuel spray and venturis.
Adrian, R.J.: Twenty Years of Particle Image Velocimetry. Exp. Fluids, vol. 39, no. 2, 2005, pp. 159-169. Hicks, Y.; Locke, R.; and Yen, C.: Optical Evaluation of Fuel Injection and Mixing Processes in a 10 kW Fuel Reformer. AIAA-2006-2975, 2006.
Song, C.S.: Fuel Processing for Low-Temperature and High-Temperature Fuel Cells--Challenges, and Opportunities for Sustainable Development in the 21st Century. Catalysis Today, vol. 77, nos. 1-2, 2002, pp. 17-49.
Tacina, Robert, et al.: Experimental Performance of a Swirl-Venturi Fuel Mixer for a Fuel Cell Reformer. ASME Paper GT2006-90772, 2006, pp. 617-627.
Find out more about this research:
Glenn’s Combustion Branch:
http://www.grc.nasa.gov/WWW/combustion/
Advanced laser-based diagnostics for combustor research:
http://www.grc.nasa.gov/WWW/OptInstr/AdvancedLaserDiag.html
Last updated: December 14, 2007
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