A combustor apparatus is provided, comprising a mixing arrangement for mixing a carbonaceous fuel with enriched oxygen and a working fluid to form a fuel mixture. A combustion chamber is at least partially defined by a transpiration member. The transpiration member is at least partially surrounded by a pressure containment member. The combustion chamber has opposed inlet and outlet portions. The inlet portion of the combustion chamber is configured to receive the fuel mixture for the fuel mixture to be combusted at a combustion temperature. The combustion chamber is further configured to direct the resulting combustion product toward the outlet portion. The transpiration member directs a transpiration substance therethrough toward the combustion chamber for buffering interaction between the combustion product and the transpiration member. Associated systems, apparatuses, and methods are also provided.