Large eddy simulations of staged pressurized oxy-combustion

Oxy-fuel combustion is one of the popular methods for reducing carbon dioxide emissions from fossil fuel combustion systems. However, a large amount of flue gas recycle is required in oxy-fuel combustion to control the heat flux by lowering the flame temperature, but this poses a significant efficiency burden on the process. In non-premixed oxy-gas combustion systems, the high radiative heat flux results from the large soot volume fraction. One of the ways to control the radiative heat flux is to reduce the soot volume fraction, without compromising on the flame temperature. To do so, the inert can be strategically distributed between oxidizer and fuel to change the stoichiometric mixture fraction, Zst, of the flame, which has been shown to reduce soot and radiative heat flux. In this study, Large Eddy Simulations (LES) is used to further characterize this suppression of soot inception. The experimental reactor at Washington University in St. Louis is modeled for methane combustion, and mixture fraction maps are generated to provide the flame structure, which has a strong influence on soot inception within the reactor. The mixture fraction maps are obtained by extracting the corresponding data from arbitrary lines across the turbulent flame for different Zst values at the inlet. The important parameters affecting soot inception, such as the C/O ratio and the temperature limits for soot formation, are calculated by means of a simple model. Parametric studies have been performed and variances over space and time are calculated.