  Direct fired supercritical CO2 (sCO2) power cycles allow for the combustion
of gaseous fuels under oxyfuel conditions with inherent carbon capture. As the
CO2 is captured intrinsically, the efficiency penalty of capture on the overall
plant is small, meaning that power plants achieve a similar efficiency to
traditional fossil fuel power plants without carbon capture and storage.
However, at high pressures and in large dilutions of CO2, combustion mechanisms
are poorly understood. Therefore, in this paper sensitivity and quantitative
analysis of four established chemical kinetic mechanisms have been employed to
determine the most important reactions and the best performing mechanisms over
a range of different conditions. CH3O2 chemistry was identified as a pivotal
mechanism component for modelling methane combustion above 200 atm. The
University of Sheffield (UoS) sCO2 mechanism created in the present work better
models the ignition delay time (IDT) of high-pressure combustion in a large
dilution of CO2. Quantitative analysis showed that the UoS sCO2 mechanism was
the best fit to the greatest number of IDT datasets and had the lowest average
absolute error value, thus indicating a superior performance compared to the
four existing chemical kinetic mechanisms, well-validated for lower pressure
conditions.
