A method of operating a combustion burner to heat a furnace. Fuel and combustion air are supplied into a combustion zone and ignited. Additional combustion air is supplied into the atmosphere outside of the combustion zone. The amount of additional combustion air supplied outside of the combustion zone is decreased as a temperature of the atmosphere inside the furnace increases such that the content of nitrogen oxides (NOx), as corrected for 3% O.sub.2 (cNOx (3% O.sub.2)), in the gases generated by combustion of the fuel and the combustion air and emitted from the furnace maintained below a predetermined value.

A method of operating a combustion burner to heat a furnace. Fuel and combustion air are supplied into a combustion zone and ignited. Additional combustion air is supplied into the atmosphere outside of the combustion zone. The amount of additional combustion air supplied outside of the combustion zone is decreased as a temperature of the atmosphere inside the furnace increases such that the content of nitrogen oxides (NOx), as corrected for 3% O.sub.2 (cNOx (3% O.sub.2)), in the gases generated by combustion of the fuel and the combustion air and emitted from the furnace maintained below a predetermined value.

A method of forming a gas turbine engine component, the method including forming a plurality of cooling apertures in a preform structure of the component, the plurality of cooling apertures of the preform structure comprising a first cooling aperture and a second cooling aperture, wherein cross-sectional shapes of the first and second cooling apertures of the preform structure are different from one another, as measured in a same relative plane; and applying a coating to at least a portion of the preform structure to form the component, wherein a cross-sectional shape of the first and second cooling apertures of the component are approximately the same as one another, as measured in the same relative plane.

A method of forming a gas turbine engine component, the method including forming a plurality of cooling apertures in a preform structure of the component, the plurality of cooling apertures of the preform structure comprising a first cooling aperture and a second cooling aperture, wherein cross-sectional shapes of the first and second cooling apertures of the preform structure are different from one another, as measured in a same relative plane; and applying a coating to at least a portion of the preform structure to form the component, wherein a cross-sectional shape of the first and second cooling apertures of the component are approximately the same as one another, as measured in the same relative plane.

A supercritical CO.sub.2 boiler capable of realizing uniform combustion, corrosion resistance and coking resistance, and a boiler system are provided. The supercritical CO.sub.2 boiler includes a main combustion chamber, an upper furnace, a furnace arch and a flue, wherein a cross section of the main combustion chamber is circular or oval, or is of an N-sided shape, where N>4; at least four burner groups are disposed on the main combustion chamber, each group of burner nozzles corresponding to each burner group includes a recirculating air nozzle, a primary air nozzle and a secondary air nozzle; lateral recirculating air nozzles symmetrically distributed are respectively disposed at two sides of the primary air nozzle, the recirculating air nozzle and the lateral recirculating air nozzle are configured to feed recirculating flue gas or a mixed gas of the recirculating flue gas and secondary air into the main combustion chamber.

A supercritical CO.sub.2 boiler capable of realizing uniform combustion, corrosion resistance and coking resistance, and a boiler system are provided. The supercritical CO.sub.2 boiler includes a main combustion chamber, an upper furnace, a furnace arch and a flue, wherein a cross section of the main combustion chamber is circular or oval, or is of an N-sided shape, where N>4; at least four burner groups are disposed on the main combustion chamber, each group of burner nozzles corresponding to each burner group includes a recirculating air nozzle, a primary air nozzle and a secondary air nozzle; lateral recirculating air nozzles symmetrically distributed are respectively disposed at two sides of the primary air nozzle, the recirculating air nozzle and the lateral recirculating air nozzle are configured to feed recirculating flue gas or a mixed gas of the recirculating flue gas and secondary air into the main combustion chamber.

An inward-firing combustion burner, includes a burner casing configured to receive a fuel-air mixture at a burner inlet and to provide hot combustion gas at a burner output, a combustion substrate disposed within the burner casing, the substrate having a shape comprising at least a semi-cone or a flat surface or equivalent shape, having a substrate porosity defined by a plurality of pores, and having a substrate inner surface and a substrate outer surface, the substrate configured to receive the fuel-air mixture at the outer surface of the substrate, the fuel-air mixture passing through the pores at a mixture flow rate from the substrate outer surface toward the substrate inner surface, and the burner configured such that, in operation, the fuel-air mixture ignites near the plurality of pores to form a respective plurality of flamelets, each flamelet corresponding to one of the pores.

An inward-firing combustion burner, includes a burner casing configured to receive a fuel-air mixture at a burner inlet and to provide hot combustion gas at a burner output, a combustion substrate disposed within the burner casing, the substrate having a shape comprising at least a semi-cone or a flat surface or equivalent shape, having a substrate porosity defined by a plurality of pores, and having a substrate inner surface and a substrate outer surface, the substrate configured to receive the fuel-air mixture at the outer surface of the substrate, the fuel-air mixture passing through the pores at a mixture flow rate from the substrate outer surface toward the substrate inner surface, and the burner configured such that, in operation, the fuel-air mixture ignites near the plurality of pores to form a respective plurality of flamelets, each flamelet corresponding to one of the pores.

A method of forming a gas turbine engine component, the method including forming a plurality of cooling apertures in a preform structure of the component, the plurality of cooling apertures of the preform structure comprising a first cooling aperture and a second cooling aperture, wherein cross-sectional shapes of the first and second cooling apertures of the preform structure are different from one another, as measured in a same relative plane; and applying a coating to at least a portion of the preform structure to form the component, wherein a cross-sectional shape of the first and second cooling apertures of the component are approximately the same as one another, as measured in the same relative plane.

A method of forming a gas turbine engine component, the method including forming a plurality of cooling apertures in a preform structure of the component, the plurality of cooling apertures of the preform structure comprising a first cooling aperture and a second cooling aperture, wherein cross-sectional shapes of the first and second cooling apertures of the preform structure are different from one another, as measured in a same relative plane; and applying a coating to at least a portion of the preform structure to form the component, wherein a cross-sectional shape of the first and second cooling apertures of the component are approximately the same as one another, as measured in the same relative plane.