The remaining air needed for complete combustion besides primary air. This is the air surrounding the flames outside the burner ports.

Air that is mixed with a fuel while it is burning.

Air for combustion supplied to the furnace to supplement the primary air.

Combustion air externally supplied to a burner flame at the point of combustion.

Air that is pumped to the pollution-control devices to promote chemical reactions that reduce exhaust gas pollutants.

large surplus of air that cools the hot sections of a gas turbine engine to lower temperatures.