Application of a Nonadiabatic Flamelet/Progress-Variable Approach to Large-Eddy Simulation of H2/O2 Combustion Under a Pressurized Condition

A new nonadiabatic procedure of the flamelet/progress-variable approach (NA-FPV approach) is proposed, and the validity is assessed by performing a large eddy simulation (LES) employing the NA-FPV approach for an H2/O2 combustion field in a single element coaxial combustor under a pressurized condition. The results show that the LES employing the NA-FPV approach can successfully predict the heat flux and capture the effects of heat loss through the cooled walls on the combustion characteristics. This procedure is quite useful especially for the numerical simulations of combustion fields with high temperatures, where there remain reactive radicals (e.g., OH, CH) with high concentrations, such as pressurized combustion, supercritical combustion, and oxygen combustion.

Fluid-Structure Interaction in Combustion System of a Gas Turbine—Effect of Liner Vibrations

Prediction of mutual interaction between flow, combustion, acoustic, and vibration phenomena occurring in a combustion chamber is crucial for the reliable operation of any combustion device. In this paper, this is studied with application to the combustion chamber of a gas turbine. Very dangerous for the integrity of a gas turbine structure can be the coupling between unsteady heat release by the flame, acoustic wave propagation, and liner vibrations. This can lead to a closed-loop feedback system resulting in mechanical failure of the combustor liner due to fatigue and fatal damage to the turbine. Experimental and numerical investigations of the process are performed on a pressurized laboratory-scale combustor. To take into account interaction between reacting flow, acoustics, and vibrations of a liner, the computational fluid dynamics (CFD) and computational structural dynamics (CSD) calculations are combined into one calculation process using a partitioning technique. Computed pressure fluctuations inside the combustion chamber and associated liner vibrations are validated with experiments performed at the state-of-the-art pressurized combustion setup. Three liner structures with different thicknesses are studied. The numerical results agree well with the experimental data. The research shows that the combustion instabilities can be amplified by vibrating walls. The modeling approach discussed in this paper allows to decrease the risk of the gas turbine failure by prediction, for given operating conditions, of the hazardous frequency at which the thermoacoustic instabilities appear.

Novel Burner Concept for Premixed Surface-Stabilized Combustion

Surface-stabilized combustion is credited with high burning rates, extended lean flammability limits, wide modulation range and other advantages. This makes it an attractive technology for compact low-emission combustors. The experimental gas turbine surface burners reported to this date are produced from compressed and sintered Fe-Cr-Al fiber mats. The authors have developed a new concept of surface burner fabricated by braiding ceramic cords around a ceramic frame. This simple method produces a basket-type surface suitable for stabilizing lean premixed flames over a broad range of operating conditions. The use of ceramics extends possibilities for operation at very high inlet temperatures with reduced risks of material sintering and oxidation. This paper presents test results with an experimental burner on a pressurized combustion rig with optical access. The experiments were performed under the following conditions: inlet temperatures of 22–740 C, pressures of 1–3 bar, thermal power between 4 kWTh and 32 kWTh and equivalence ratios of 0.28–0.95. Measurements of flue gas composition and pressure drop are also reported in the paper. The operating window for low-NOx and low-CO combustion is analyzed. With the demonstrated performance, the burner could cover the operating envelope of a 3 kWe recuperated micro turbine [1]–[2] with no pilot and no staging. This would also limit NOx to <40 ppm @ 0% O2 within the micro turbine load range of 100% to 50%.

Next Generation Oxy-Fired Systems: Potential for Energy Efficiency Improvement Through Pressurization

Oxy-fired combustion has been identified as a key technology needed for greenhouse gas mitigation because it is capable of producing a concentrated CO2 stream suitable for sequestration. This technology as applied to pulverized coal systems has recently been brought to a near-commercial status with several key world-wide demonstrations. A barrier to its adoption has been the large additional auxiliary power required for oxygen production and CO2 compression which results in low overall system efficiency. There have been various strategies proposed to address these efficiency issues. A very promising concept is the use of pressurized combustion in order to increase the system efficiency. The use of pressure increases the power requirement of the air separation system. However, pressurization increases the boiler and steam side efficiencies while decreasing the power requirement for the CO2 compression system. The use of pressure will also affect the performance and size of each piece of equipment within the system. This paper describes the efficiency benefit of using pressure as compared with a baseline ambient pressure oxy-fired system and a typical air-fired system. The technical aspects of various system layouts are presented, the overall efficiency is evaluated and the merits of specific configurations are discussed. Design issues of equipment associated with the fuel supply, furnace, ash removal, heat transfer and flame moderation systems are presented.