FACILITY × Brigham Young University × Fall 1995
LABORATORY-SCALE GAS TURBINE COMBUSTOR
The laboratory-scale gas turbine combustor (LSGTC) available in the Combustion Laboratory at BYU (provided to the BYU Combustion Laboratory by the Wright Laboratory, Wright-Patterson Air Force Base) has been used to investigate the combustion characteristics of several fuel injectors in a combustor configuration that closely simulates the characteristics of a real gas turbine combustor (Sturgess, et al., 1992). A schematic of the LSGTC is presented in Figure 1.
This burner has the capability of incorporating a wide variety of different injectors, and has been operated on propane, natural gas, and ethanol. The ethanol has been used to simulate combustion characteristics of a liquid fuel sprayed into the combustion chamber, but avoids the sooting of the quartz windows that would accompany the operation of the burner with Jet-A fuel. The LSGTC allows the combustion characteristics to be investigated in a simple geometry where various diagnostic measurements (primarily laser-based optical measurements) can be more easily made. In an actual gas turbine combustor, additional combustion and cooling air is often added to the combustor downstream of the actual fuel injector. This adds an additional complexity to the flow and combustion characteristics of the burner. Side plates with provision for air injection are available, and have been used to simulate downstream air injection. To date, however, laser diagnostics of the near flame zone are all that have been made.
The combustion chamber, shown in Figure 1, has been designed to be nearly axisymmetric and incorporate quartz windows to allow optical diagnostics to be made. The combustor cross-section is square with generously filleted corners to minimize secondary flow development. The hydraulic diameter is 150 mm. This box-section combustor with corner fillets allows reasonable optical access while providing a cross section that approximates a two-dimensional axisymmetric cross section. The bluff body provides a recirculation region which can stabilize the flame. Optical windows of fused quartz are provided on the four flat sides for a downstream length of 490 mm. The combustor overall length to hydraulic diameter ratio is 4.9, and the exit blockage is 45 percent by means of an orifice plate. The only air addition in this configuration is through the dome. The combustor is mounted on a 240 mm length spool piece containing a mounting pad for the fuel injector flange. The combustor and spool piece are situated on an inlet air conditioning section, also shown in Figure 1. Reactants are supplied at ambient temperature and pressure. Ignition is by means of a removable torch-ignitor. This combustion chamber allows the combustion characteristics of a practical injector to be investigated in a simple geometry where various diagnostic measurements can be made.
NON-PREMIXED AND PREMIXED FUEL INJECTORS
Coaxial Jet Injector - Three different injector configurations have been tested in the LSGTC to data. The first was a simple coaxial jet of air (ca 40 mm diameter) that surrounded a central fuel jet (ca 29 mm diameter). Air and fuel velocities used in this coaxial jet configuration are about 100 m/s and 30 m/s respectively, depending on total air flow rate and overall fuel equivalence ratio being tested.
Practical High Swirl Jet Engine Injector - The second injector tested in the LSGTC is a high-swirl (HS) practical injector from a Pratt-Whitney Aircraft Company, Inc. aeroengine. This injector, which is shown schematically in Figure 2, has a nominal swirl number (based on vane angle) of 1.41.
The total air passage effective area is 0.176 in2, with an outer to inner flow split of 2.8. The outer swirler vane angle is 55 degrees while the inner swirler vane angle is 70 degrees. The injector is mounted in a plain bulkhead dome containing insert jets angled at 12.5 degrees into the flame, and radially outwards flowing film cooling jets. This arrangement closely simulates that of an engine combustor. The total effective air flow area of the dome, excluding the fuel injector, is 0.160 in2. This injector has been operated successfully with both gaseous propane, and liquid ethanol fuels.
Premixed Natural Gas, High Swirl, Injector - The third injector, shown schematically in Figure 3, has been designed to burn premixed gaseous fuels in a burner that closely simulates the combustor of a lean premixed natural gas fueled gas turbine that would be used in an electric power generation station.
The burner shown uses swirl to stabilize the flame. Three different levels of swirl are available, low (SN = 0.43), medium (SN = 0.74) and high (SN = 1.29). The burner has also been designed to incorporate flame arrestors in the injector to prevent flashback into the premixed fuel air mixture. The premixed injector has been successfully operated with gaseous propane, and natural gas fuels at all three swirl levels and over a wide range of fuel equivalence ratios between the lean and rich flammability limits for the respective fuel being tested.
The nature of the LSGTC facility is such that new injector configurations can be easily incorporated into the combustion chamber, and laser diagnostic measurements made. Laser diagnostic instruments available for use in this burner include a two-color laser Doppler anemometer (LDA) for velocity measurement, a coherent anti-Stokes Raman spectrometer (CARS) for temperature and limited species concentration measurements, and a planar, laser induced fluorescence (PLIF) for 2-D imaging of combustion intermediates in the flame. This provides the BYU Combustion Laboratory with a unique measurement capability.