Carbon capture, utilization, and storage (CCUS) enables
carbon-neutral use of fossil-fuels and carbon-negative use of biofuels. One of the major challenges of CCUS is separating out the carbon dioxide from the exhaust gas stream. The Allam-Fetvedt cycle addresses this challenge by re-engineering gas turbine technology to produce a stream of pure carbon dioxide. To do this, the cycle uses oxycombustion of fuel, eliminating nitrogen from the combustion process. The cycle then mixes the combustion products with a stream of carbon dioxide, instead of the air used in conventional combustion turbines. After the water produced in the combustion process is removed, the cycle has a stream of almost-pure carbon dioxide that can be either used or sequestered. However, making this cycle works requires that the combustion take place in a stream of high-pressure carbon dioxide: effectively trying to light a match inside of a fire extinguisher. These challenges are compounded by the fact that combustion takes place at pressures where carbon dioxide is a supercritical fluid and does not behave as an ideal gas. Simulations using the PeleC exascale combustion code on the Summit and Eagle supercomputers show key aspects of the flame, including the temperature and velocity fields, pollutant formation, and reaction rates. These results can be used to accelerate the development and deployment of this technology.