Supercritical CO_2 power cycles for fossil energy power generation will likely employ oxy-combustion at very high pressures, possibly exceeding 300 bar. At these high pressures, a direct fired oxy-combustor is more likely to behave like a rocket engine than any type of conventional gas turbine combustor. Issues such as injector design, wall heat transfer and combustion dynamics may play a challenging role in combustor design. Computational Fluid Dynamics (CFD) modeling will not only be useful, but may be a necessity in the combustor design process. To accurately model turbulent reacting flows, combustion sub-models appropriate for the conditions of interest as defined by the turbulent time and length scales as well as chemical kinetic time scales are necessary. This paper presents a comparison of various turbulence-chemistry interaction modeling approaches on a canonical, single injector, direct-fired sCO_2 combustor. Large Eddy Simulation is used to model the turbulent combustion process with varying levels of injector oxygen concentration while comparing the effect of the combustion sub-model on CO emissions and flame shape. While experimental data is not yet available to validate the simulations, the sensitivity of CO production and flame shape can be studied as a function of combustion modeling approach and oxygen concentration in an effort to better understand how to approach combustion modeling at these unique conditions.
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