Apparatus and method for burning a lean, premixed fuel/air mixture with low NOx emission

Apparatus for burning a gaseous fuel with low NOx and low HC emission in free air at substantially atmospheric pressure to generate hot combustion products, the apparatus comprising:

• premixing means for premixing air with the fuel to provide a lean fuel/air mixture having a fuel/air equivalency ratio of less than unity;
• a nozzle including an internal bore having an exit, the lean fuel/air mixture passing in a stream through the internal bore towards the exit and burning adjacent thereto, the stream having a direction of flow, the internal bore having a bore width in a plane perpendicular to the direction of flow;
• and
• a blunt annular flame stabilizer means, mounted in the stream of the lean fuel/air mixture spaced from the internal bore by between about 0.5 mm and about 15% of the bore width in the plane, and having a height in the direction of flow of between about 0.3 mm and 10 mm, for dividing the stream of the fuel/air mixture into an outer portion and an inner portion having substantially similar flow velocities, the blunt annular flame stabilizer means having sufficient width in the plane for the annular flame stabilizer means to create downstream eddies in both the inner portion and the outer portion of the fuel/air mixture, the eddies recirculating a portion of the hot combustion products into the stream of the fuel/air mixture to continuously re-ignite the fuel/air mixture.

A method of burning a lean fuel/air mixture with low NOx and low HC emission in free air at substantially atmospheric pressure to generate hot combustion products, the method comprising steps of:

• providing a lean fuel/air mixture having a fuel/air equivalency ratio of less than unity;
• directing the lean fuel/air mixture in a stream, the stream having a direction of flow, and an extent in a plane perpendicular to the direction of flow;
• providing a blunt, substantially annular flame stabilizer having a length in the direction of flow of between about 0.3 mm and about 10 mm;
• mounting the annular flame stabilizer in the stream of the fuel/air mixture to divide the stream into an outer portion and an inner portion having substantially similar flow velocities, the annular flame stabilizer dividing the fuel/air mixture at a point inset from the extent of the stream by between about 0.5 mm and about 15% of the extent of the stream in the plane, and dividing the stream over a width sufficient to create recirculating eddies in both the outer portion and the inner portion of the stream of the fuel/air mixture;
• and
• igniting the stream of the lean fuel/air mixture at the eddies, whereafter the eddies recirculate a portion of the hot combustion products into the stream to continuously re-ignite the fuel/air mixture.

Apparatus for burning a gaseous fuel with low NOx and low HC emission to generate hot combustion products, the apparatus comprising:

• premixing means for premixing air with the fuel to provide a lean fuel/air mixture having a fuel/air equivalency ratio of less than unity;
• a nozzle having an internal bore wherethrough the lean fuel/air mixture passes in a stream, the stream having a direction of flow, the internal bore including an exit, and having a bore width in a plane perpendicular to the direction of flow;
• and
• a blunt annular flame stabilizer means, mounted in the stream of the lean fuel/air mixture in the internal bore spaced from the internal bore by between about 0.5 mm and about 15% of the bore width in the plane, having a height in the direction of flow of between about 0.3 mm and 10 mm, and including a downstream face substantially flush with the exit, for dividing the stream of the fuel/air mixture into an outer portion and an inner portion having substantially similar flow velocities, the annular flame stabilizer means having a width in the plane sufficient to create downstream eddies in both the outer portion and the inner portion of the fuel/air mixture, the eddies recirculating a portion of the hot combustion products into the stream to continuously re-ignite the fuel/air mixture.