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Toward a predictive understanding of low emission fuel-flexible distributed energy turbine systems

Using hydrogen derived from coal in power generation is one of the potential strategies being considered for eliminating CO2 emissions from combustion. In a two-stage gas combustor, injection of hydrogen into a secondary combustor provides an effective means for achieving a wide range of power settings. However, when additional hydrogen is injected into the exit stream of the first stage turbine, the mixture may autoignite. This uncontrolled autoignition event is undesirable as it leads to strong acoustic waves and high levels of nitrogen oxides (NOx). Since hydrogen was not a main fuel in the past, studies of hydrogen combustion under gas turbine environments have not been extensively carried out. Autoignition of hydrogen depends on pressure in a nonlinear fashion and is sensitive to the unique transport properties of the small hydrogen molecules, making prediction of autoignition a very challenging task. For both steady and transient flames, Large Eddy Simulation (LES) is essential for obtaining a fundamental understanding of flame stability mechanisms. As such, this work performs a LES study aimed at modeling and understanding 1) key stability mechanism(s) related to flame propagation and/or autoignition, and 2) the effect of pressure on hydrogen combustion over the range of 1 to 20 bar.