A combustor for a gas turbine system, the combustor comprising: a combustor liner defining a combustion region including a primary combustion zone and a secondary combustion zone downstream from the primary combustion zone; a flow sleeve (144, 147, 344A, 344B) surrounding at least part of the combustor liner, the flow sleeve (144, 147, 344A, 344B) including a plurality of cooling openings (150, 350) therein to: direct a flow of first air at a first pressure from a first air source to cool an outer surface (182, 437) of the combustor liner, and create a flow of second air at a second, lower pressure than the first pressure in an annulus between the combustor liner and the flow sleeve (144, 147, 344A, 344B); a first fuel nozzle positioned at the primary combustion zone; a second fuel nozzle positioned at the secondary combustion zone; and a fuel source configured to deliver a first fuel to each of the first and second fuel nozzles (170, 172), wherein the first and second fuel nozzles (170, 172) produce a premixture of the first air flow and the first fuel, and produce a mixture of the premixture and the second air flow, prior to introducing the mixture to a respective primary or secondary combustion zone, characterized in that the first and second fuel nozzles (170, 172) each include: a first annular wall defining a first passage in fluid communication with the second air flow; a second wall defining a first plenum in fluid communication with the first air source; a third wall defining a second plenum in fluid communication with the fuel source to create a flow of the first fuel therein, wherein the third wall is at least partially surrounded by the second wall; and a mixing conduit extending through the second plenum and fluidly connecting the first plenum) and the first passage the mixing conduit defining at least one injection hole in fluid communication with the second plenum. a combustor liner defining a combustion region including a primary combustion zone and a secondary combustion zone downstream from the primary combustion zone; a flow sleeve (144, 147, 344A, 344B) surrounding at least part of the combustor liner, the flow sleeve (144, 147, 344A, 344B) including a plurality of cooling openings (150, 350) therein to: direct a flow of first air at a first pressure from a first air source to cool an outer surface (182, 437) of the combustor liner, and create a flow of second air at a second, lower pressure than the first pressure in an annulus between the combustor liner and the flow sleeve (144, 147, 344A, 344B); a first fuel nozzle positioned at the primary combustion zone; a second fuel nozzle positioned at the secondary combustion zone; and a fuel source configured to deliver a first fuel to each of the first and second fuel nozzles (170, 172), wherein the first and second fuel nozzles (170, 172) produce a premixture of the first air flow and the first fuel, and produce a mixture of the premixture and the second air flow, prior to introducing the mixture to a respective primary or secondary combustion zone, characterized in that the first and second fuel nozzles (170, 172) each include: a first annular wall defining a first passage in fluid communication with the second air flow; a second wall defining a first plenum in fluid communication with the first air source; a third wall defining a second plenum in fluid communication with the fuel source to create a flow of the first fuel therein, wherein the third wall is at least partially surrounded by the second wall; and a mixing conduit extending through the second plenum and fluidly connecting the first plenum) and the first passage the mixing conduit defining at least one injection hole in fluid communication with the second plenum. a first annular wall defining a first passage in fluid communication with the second air flow; a second wall defining a first plenum in fluid communication with the first air source; a third wall defining a second plenum in fluid communication with the fuel source to create a flow of the first fuel therein, wherein the third wall is at least partially surrounded by the second wall; and a mixing conduit extending through the second plenum and fluidly connecting the first plenum) and the first passage the mixing conduit defining at least one injection hole in fluid communication with the second plenum.