Described are sub-scale tests that successfully demonstrate active feedback control as a means of suppressing damaging combustion oscillations in natural-gas-fueled, lean-premix combustors. The control approach is to damp the oscillations by suitably modulating an auxiliary flow of fuel injected near the flame. The control system incorporates state observer software that can ascertain the frequency, amplitude, and phase of the dominant modes of combustion oscillation, and a sub-scale fuel flow modulator that responds to frequencies well above 1 kHz. The demonstration was conducted on a test combustor that could sustain acoustically coupled combustion instabilities at preheat and pressurization conditions approaching those of gas-turbine engine operation. With the control system inactive, two separate instabilities occurred with combined amplitudes of pressure oscillations exceeding 70 kPa (10 psi). The active control system produced four-fold overall reduction in these amplitudes. With the exception of an explainable control response limitation at one frequency, this reduction represented a major milestone in the implementation of active control. [S0742-4795(00)00702-X]
Described are sub-scale tests that successfully demonstrate active feedback control as a means of suppressing damaging combustion oscillations in natural-gas-fueled, lean-premix combustors. The control approach is to damp the oscillations by suitably modulating an auxiliary flow of fuel injected near the flame. The control system incorporates state observer software that can ascertain the frequency, amplitude, and phase of the dominant modes of combustion oscillation, and a sub-scale fuel flow modulator that responds to frequencies well above 1 kHz.The demonstration was conducted on a test combustor that could sustain acoustically coupled combustion instabilities at preheat and pressurization conditions approaching those of gas-turbine engine operation. With the control system inactive, two separate instabilities occurred with combined amplitudes of pressure oscillations exceeding 70 kPa (10 psi). The active control system produced four-fold overall reduction in these amplitudes. With the exception of an explainable control response limitation at one frequency, this reduction represented a major milestone in the implementation of active control.
This study seeks to design the aerodynamic features a first stage vane for a 100 MW class supercritical CO2 Brayton cycle turbomachine. For a turbine inlet temperature of 1350 K, the recuperated configuration is found to provide the highest cycle efficiency, and the corresponding cycle parameters are then used to design the turbine stages. A 6-stage turbine is selected and the first stage is designed following a one-dimensional mean line approach. Initial mean line turbomachine parameters (work coefficient and flow coefficient) are selected to provide high thermodynamic efficiency and simple radial equilibrium equation principles. Turning loss correlations are utilized to define and optimize hub and casing velocity triangle parameters. Typical turbomachinery characteristic parameters are used to compare the carbon dioxide turbine with typical air combustion turbines. Detailed aerodynamic analysis is performed on a complete three-dimensional model of the vane flow field using a commercial computational fluid dynamics code, STAR-CCM+. Actual properties of the working fluid are input to the model from the REFPROP database provided by the US National Institute of Standards and Technology (NIST). The detailed flow field is computed, from which aerodynamic loss coefficients are calculated. The computer model confirms that the design is successful in turning supercritical carbon dioxide at the prescribed angle and pressure. However, results of the real fluid simulation show that aerodynamic losses caused the stage efficiency to be about 4% below the design target.
This paper focuses on unconventional thermodynamic cycles and their applications in alternative energy. It looks into these promising advancements, beginning with the exploration of trends in cost, efficiency, and the adoption of various sources of power. By studying historical trends, conventional means of obtaining energy are seen to be currently increasing in efficiency in smaller and smaller increments. The second part of our study is the application of alternative configurations of the Brayton cycle. In particular, this paper analyzes a closed-cycle turbine with supercritical carbon dioxide as the working fluid. Beginning with a simple cycle calculation, this study adapts the cycle and explores the benefit of recuperated and combined cycle systems. A parametric study was also created, comparing the efficiency versus the specific power of each cycle. Consideration of supercritical carbon dioxide as the working fluid in turbomachine cycles may demonstrate an economic advantage in the global market. This paper provides a perspective on the feasibility of these developments for realistic applications in industry. Also important to feasibility, it assesses trends in the cost of power generated by each cycle and energy source. With this information, choices may be made on which cycle is more economically promising in today’s market. The results of this study provide a clear indication of relative efficiencies. These efficiencies, in turn, determines the optimal design direction for a particular supercritical carbon dioxide cycle. In addition, the results provide insight into the effect of this technology on the cost and efficiency of concentrated solar power production.
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