Patent ID: 8607568

Claim:
A combustion system comprising: a first combustion chamber; a second combustion chamber positioned downstream of the first combustion chamber; and a pre-mixed, direct-injection secondary fuel nozzle extending through the first combustion chamber into the second combustion chamber, the pre-mixed, direct-injection secondary fuel nozzle, comprising: a mixing head comprising a plurality of mixing tubes; a first wall defining a fuel passage into the mixing tubes; a second wall positioned outward of the first wall wherein the first wall and the second wall define a combustion air passage into the mixing tubes, wherein the second wall comprises an upstream portion having a first diameter, a downstream portion having a second diameter that is larger than the first diameter, and a tapered portion having an increasing diameter from the upstream portion to the downstream portion, and wherein the downstream portion of the second wall surrounds the mixing head and is spaced apart from the mixing head to form a gap therebetween; a third wall positioned outward of the second wall, wherein the second wall and the third wall define a cooling air passage, wherein the third wall comprises a plurality of louvers and a plurality of apertures, and wherein the third wall is positioned about the upstream portion of the second wall and at least partially about the tapered portion of the second wall upstream of the mixing head; and a plurality of swirling vanes positioned in the gap between the mixing head and the second wall; a joint located at a downstream end of the third wall that joins the third wall to the tapered portion of the second wall upstream of the mixing head; and a plurality of cooling holes formed through the joint.