Direct-fired supercritical power cycles, operating on natural gas or syngas from coal gasification, have been proposed as future energy technologies which exhibit 100% carbon capture at a price competitive with existing fossil fuel technologies. In this work, ignition delay times (IDTs) of hydrogen, syngas, and methane were measured in a high concentration of CO2 bath gas at 20 bar of pressure. Measured datasets studied were compared with chemical kinetic simulations using AramcoMech 2.0 and the University of Sheffield supercritical CO2 (UoS sCO2) chemical kinetic mechanisms. The UoS sCO2 mechanism was recently developed to model IDTs of methane, hydrogen, and syngas in CO2 bath gas. The performance of both mechanisms was evaluated quantitively by comparing the average absolute error between the simulated and experimental IDTs, which showed UoS sCO2 2.0 as the superior mechanism for modeling IDTs in CO2 bath gas.