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This paper reports the effect of changing the location of axial swirl vanes on premix combustion dynamics. Tests are conducted in a specially designed single-injector combustor operating at a pressure of 7.5 atmospheres and an inlet air temperature of 588K (600F). All of the tests are conducted using natural gas as the fuel. The air velocity and equivalence ratio are varied over an operating map for four different axial swirl vane positions in the premix nozzle. In contrast to earlier studies reported from this combustor, the fuel injection location is fixed. The results confirm the importance of the convective fuel time lag for the different swirl vane locations, but also show that changing the vane location at a fixed time lag can significantly affect the magnitude of the combustion oscillations.

Researchers at West Virginia University are working with the U.S. Department of Energy, National Energy Technology Laboratory (NETL) to study the effects of particulate deposition on turbine film cooling in a high pressure and high temperature environment. To simulate deposition on the pressure side of an Integrated Gasification Combined Cycle (IGCC) turbine first stage vane, angled film-cooled test articles with thermal barrier coatings (TBC) are subjected to accelerated deposition at a pressure of approximately 4 atm and a gas temperature of 1100°C. Two different test article geometries were designed, with angles of 10° and 20° to the mainstream flow. Both geometries have straight-cooling holes oriented at a 30° angle to the hot-side surface. A high pressure seeding system was used to generate a particulate concentration of approximately 33.3 ppmw. Particle concentrations of 0.02 ppmw exist in the IGCC hot gas path. An accelerated simulation method was developed to simulate deposition that would occur in 10000 hr of engine operation. Preliminary tests were performed at 4 atm and 1100 °C to validate the deposition process. The results showed more deposition on the 20° test article than the 10° test articles; however no substantial deposition developed on either test article. A lumped mass analysis showed that the fly ash particles dropped below the theoretical sticking temperature as they approached the test article. Deposition was analyzed non-destructively through visual observation and scanning with a scanning laser microscope. Based on the initial test run results, a detailed plan was created to increase the operating temperature of the rig and allow two 3-hour tests to be performed on each of the test articles. Non-destructive testing will be used before, in between and after the runs to examine the evolution of the deposition growth. Following the final run, destructive testing will be used to examine the chemical composition of the deposits and their potential interaction with the TBC. Preliminary work will lead to a future study the would enhance the understanding of particle deposition evolution and examine the effects of deposition on film cooling by performing the tests in a high-pressure and high-temperature environment that is similar to the high-pressure combustion exhaust gas environment of the first stage region in IGCC turbines.

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Combustion dynamics (or combustion oscillations) have emerged as a significant consideration in the development of low-emission gas turbines. To date, the effect of premix fuel nozzle geometry on combustion dynamics has not been well-documented. This paper presents experimental stability data from several different fuel nozzle geometries (i.e., changing the axial position of fuel injection in the premixer, and considering simultaneous injection from two axial positions). Tests are conducted in a can-style combustor designed specifically to study combustion dynamics. The operating pressure is fixed at 7.5 atmospheres and the inlet air temperature is fixed at 588K (600F). Tests are conducted with a nominal heat input of 1MWth (3MBTUH). Equivalence ratio and nozzle reference velocity are varied over the ranges typical of premix combustor design. The fuel is natural gas. Results show that observed dynamics can be understood from a time-lag model for oscillations, but the presence of multiple acoustic modes in this combustor makes it difficult to achieve stable combustion by simply re-locating the point of fuel injection. In contrast, reduced oscillating pressure amplitude was observed at most test conditions using simultaneous fuel injection from two axial positions.

This paper describes the evaluation of an alternative combustion approach to achieve low emissions for a wide range of fuel types. This approach combines the potential advantages of a staged rich-burn, quick-mix, lean-burn (RQL) combustor with the revolutionary trapped vortex combustor (TVC) concept. Although RQL combustors have been proposed for low-Btu fuels, this paper considers the application of an RQL combustor for high-Btu natural gas applications. This paper will describe the RQL/TVC concept and experimental results conducted at 10 atm (1013 kPa or 147 psia) and an inlet-air temperature of 644 K (700°F). The results from a simple network reactor model using detailed kinetics are compared to the experimental observations. Neglecting mixing limitations, the simplified model suggests that NOx and CO performance below 10 parts per million could be achieved in an RQL approach. The CO levels predicted by the model are reasonably close to the experimental results over a wide range of operating conditions. The predicted NOx levels are reasonably close for some operating conditions; however, as the rich-stage equivalence ratio increases, the discrepancy between the experiment and the model increases. Mixing limitations are critical in any RQL combustor, and the mixing limitations for this RQL/TVC design are discussed.

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