Impacts of alternative combustion diluents and hydrogen addition on a swirl-stabilized flame related to gas turbine application
Abstract: The global energy tendency leads to increasing attention on clean combustion technologies in order to eliminate adverse impacts on the environment. The utilization of oxyfuel combustion (CO2 acts as the only combustion dilution), flame diluents, and hydrogen fuel in gas turbine combustion provides a promising solution to reduce combustion pollutant emissions. However, alteration in chemical and physical properties of combustion reactants may lead to new combustion behaviors which must be understood so that a safe and smooth gas turbine operation can be achieved.This doctoral thesis presented an experimental study based on a swirl-stabilized gas turbine model combustor under the atmospheric pressure. In addition, chemical kinetics calculations were conducted using CHEMKIN software in order to achieve a comprehensive understanding of combustion process. The primary objectives are to study the impacts caused by alteration of combustion dilution and hydrogen addition on flame LBO limits, stabilization, CO emission performance, as well as the features of combustion dynamics. Due to the use of quartz liner, the primary flame reaction zone can be investigated by using optical measurement methods or direct observation. Flame LBO limits were identified by gradually turning down equivalence ratio until flame physically disappears in the combustor. Combustion emissions (O2, CO, and CO2) were monitored by using a water-cooled emission probe which was mounted at the location close to the combustor exit. Time-averaged CH chemiluminescence was recorded to identify flame shapes and anchored locations. The inverse Abel transform was adopted to reconstruct CH distribution on the combustor symmetry plane. Broadband chemiluminescence was used to study flame oscillation phenomenon prior to LBO limits. A 2-dimensional high-speed PIV (particle image velocimetry) system was used to investigate the flow field in the combustor with a frequency of 2 kHz. Both the time-averaged and instantaneous velocity field were studied. The snapshot method of POD (proper orthogonal decomposition) was applied to the dataset of the measured velocity fields. FFT analysis was used to study the prominent frequency for dynamics phenomena.Experimental results showed that LBO limits and flame stabilization depended on many factors such as fuel, combustor inlet temperature, as well as combustion dilutions. Addition of combustion dilution resulted in a smaller operation region for low CO combustion. This negative impact can be counteracted by improving combustor inlet temperature and the addition of hydrogen. The broadband chemiluminescence indicated that dilution addition did not significantly affect the frequency of combustion oscillation. PIV measurement results showed that hydrogen addition enhanced the velocity in the combustor. PVC (precessing vortex core) was identified by using snapshot POD. Suppression effects of combustion on PVC were observed based on POD and FFT analysis.
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