Low NOx burner and flow momentum enhancing device

A method of reducing NOx emissions from a burner apparatus comprising the steps of:

• a) delivering a combustion air stream comprising air or a mixture of air and fuel through an air flow passageway which is surrounded by a burner wall of the burner apparatus, the burner wall having a forward longitudinal end, the air flow passageway having a forward discharge opening at the forward longitudinal end of the burner wall, and the forward discharge opening having an internal diameter or width and
• b) causing a flow stream comprising all or a portion of the combustion air stream flowing through the air flow passageway to flow forwardly along and in contact with a surrounding exterior surface of a flow momentum enhancing device wherein (i) the flow momentum enhancing device has a longitudinal axis, (ii) the flow momentum enhancing device has a rearward longitudinal end which is positioned in the air flow passageway, at the forward discharge opening of the air flow passageway, or forwardly of the air flow passageway, (iii) the surrounding exterior surface has a maximum lateral outside diameter or width at a location which is rearward of the forward longitudinal end the flow momentum enhancing device and forward of the rearward longitudinal end of the flow momentum enhancing device, (iv) the surrounding exterior surface has an outside diameter or width at the forward longitudinal end of the flow momentum enhancing device which is less than the maximum lateral outside diameter or width such that, as the surrounding exterior surface extends forwardly from the location of the maximum lateral outside diameter or width, at least a forward longitudinal portion of the surrounding exterior surface converges inwardly, with respect to the longitudinal axis of the flow momentum enhancing device, as the surrounding exterior surface approaches the forward longitudinal end of the flow momentum enhancing device, and (v) the surrounding exterior surface has an outside diameter or width at the rearward longitudinal end of the flow momentum enhancing device which is less than the maximum lateral outside diameter or width,
• wherein, in step (b), the flow stream is caused to flow forwardly over and in contact with the maximum lateral outside diameter or width of the surrounding exterior surface and then forwardly along and in contact with the inwardly converging forward longitudinal portion of the surrounding exterior surface to create a reduced pressure region around at least a portion of the surrounding exterior surface and/or at the forward longitudinal end of the flow momentum enhancing device which draws inert products of combustion into the reduced pressure region and
• the maximum lateral outside diameter or width of the exterior surface of the flow momentum enhancing device is from 1.5 to 5 inches less than the internal diameter or width of the forward discharge opening of the air flow passageway.

A burner apparatus comprising:

• a burner wall having a forward longitudinal end;
• an air flow passageway, which extends through and is surrounded by the burner wall, for a combustion air stream comprising air or a mixture of air and fuel which travels through the air flow passageway, the air flow passageway having a forward discharge opening at the forward longitudinal end of the burner wall, and the forward discharge opening having an internal diameter or width;
• and
• a flow momentum enhancing device having a longitudinal axis, a rearward longitudinal end, a forward longitudinal end, and a surrounding exterior surface which extends from the rearward longitudinal end to the forward longitudinal end of the flow momentum enhancing device,
• the exterior surface of the flow momentum enhancing device having a maximum lateral outside diameter or width at a location which is rearward of the forward longitudinal end the flow momentum enhancing device,
• the exterior surface of the flow momentum enhancing device having an outside diameter or width at the forward longitudinal end of the flow momentum enhancing device which is less than the maximum lateral outside diameter or width,
• the rearward longitudinal end of the flow momentum enhancing device being positioned in the air flow passageway, at the forward discharge opening of the air flow passageway, or forwardly of the air flow passageway so that a flow path is defined outside of the flow momentum enhancing device for a flow path stream which comprises all or a portion of the combustion air stream which travels through the air flow passageway,
• wherein the flow path for the flow path stream travels over and in contact with the maximum lateral outside diameter or width of the exterior surface and then continues to travel along and in contact with the exterior surface from the location of the maximum lateral outside diameter or width to the forward longitudinal end of the flow momentum enhancing device such that, as the flow path for the flow path stream approaches the forward longitudinal end of the exterior surface, the exterior surface, and the flow path for the flow path stream traveling along and in contact with the exterior surface, converge inwardly with respect to the longitudinal axis of the flow momentum enhancing device,
• the burner apparatus further comprising a holding element for the flow momentum enhancing device which extends longitudinally through at least a portion of the air flow passageway to the rearward longitudinal end of the flow momentum enhancing device, and
• a mounting base secured to or rearwardly of the burner wall, the mounting base comprising a ring, to which a rearward longitudinal end of the holding element is attached, and a plurality of support arms which extend outwardly from the ring.

A burner apparatus comprising:

• a burner wall having a forward longitudinal end;
• an air flow passageway, which extends through and is surrounded by the burner wall, for a combustion air stream comprising air or a mixture of air and fuel which travels through the air flow passageway, the air flow passageway having a forward discharge opening at the forward longitudinal end of the burner wall;
• and
• a flow momentum enhancing device having a longitudinal axis, a rearward longitudinal end, a forward longitudinal end, and an interior passageway which extends longitudinally through the flow momentum enhancing device from the rearward longitudinal end to the forward longitudinal end of the flow momentum enhancing device,
• the flow momentum enhancing device further comprising a device wall which surrounds the interior passageway of the flow momentum enhancing device and extends from the rearward longitudinal end to the forward longitudinal end of the flow momentum enhancing device,
• the device wall having (i) an exterior surface which extends from the rearward longitudinal end to the forward longitudinal end of the flow momentum enhancing device and (ii) an interior surface, for the interior passageway, which extends from the rearward longitudinal end to the forward longitudinal end of the flow momentum enhancing device,
• the exterior surface of the device wall having a maximum lateral outside diameter or width at a location which is rearward of the forward longitudinal end of the flow momentum enhancing device,
• the exterior surface of the device wall having an outside diameter or width at the forward longitudinal end of the flow momentum enhancing device which is less than the maximum lateral outside diameter or width,
• the rearward longitudinal end of the flow momentum enhancing device being positioned in the air flow passageway, at the forward discharge opening of the air flow passageway, or forwardly of the air flow passageway,
• the interior passageway of the flow momentum enhancing device defining a flow path through the flow momentum enhancing device for a flow path stream which comprises all or a portion of the combustion air stream which travels through the air flow passageway, and
• as seen in a longitudinal cross-sectional view of the device wall, the device wall has a non-symmetrical wing airfoil shape.

A method of reducing NOx emissions from a burner apparatus comprising the steps of:

• a) delivering a combustion air stream comprising air or a mixture of air and fuel through an air flow passageway which is surrounded by a burner wall of the burner apparatus, the burner wall having a forward longitudinal end, the air flow passageway having a forward discharge opening at the forward longitudinal end of the burner wall, and the forward discharge opening having an internal diameter or width and
• b) causing a flow stream comprising all or a portion of the combustion air stream flowing through the air flow passageway to flow along and in contact with a surrounding exterior surface of a flow momentum enhancing device wherein (i) the flow momentum enhancing device has a longitudinal axis, (ii) the flow momentum enhancing device has a rearward longitudinal end which is positioned in the air flow passageway, at the forward discharge opening of the air flow passageway, or forwardly of the air flow passageway, (iii) the surrounding exterior surface has a maximum lateral outside diameter or width at a location which is rearward of the forward longitudinal end the flow momentum enhancing device, and (iv) the surrounding exterior surface has an outside diameter or width at the forward longitudinal end of the flow momentum enhancing device which is less than the maximum lateral outside diameter or width such that, as the surrounding exterior surface extends forwardly from the location of the maximum lateral outside diameter or width, at least a forward longitudinal portion of the surrounding exterior surface converges inwardly, with respect to the longitudinal axis of the flow momentum enhancing device, as the surrounding exterior surface approaches the forward longitudinal end of the flow momentum enhancing device,
• wherein, in step (b), the flow stream is caused to flow over and in contact with the maximum lateral outside diameter or width of the surrounding exterior surface and then along and in contact with the inwardly converging forward longitudinal portion of the surrounding exterior surface to create a reduced pressure region around at least a portion of the surrounding exterior surface and/or at the forward longitudinal end of the flow momentum enhancing device which draws inert products of combustion into the reduced pressure region,
• the flow stream is a first portion of the combustion air stream which travels through the air flow passageway,
• the method further comprises causing a second portion of the combustion air stream, different from the first portion, to flow through a longitudinal interior passageway of the flow momentum enhancing device which extends from the rearward longitudinal end to the forward longitudinal end of the flow momentum enhancing device,
• the flow momentum enhancing device comprises a wall of the device which surrounds the interior passageway of the flow momentum enhancing device and extends from the rearward longitudinal end to the forward longitudinal end of the flow momentum enhancing device,
• the wall of the device comprises an exterior surface which is the surrounding exterior surface of the flow momentum enhancing device,
• the wall of the device has an interior surface, for the interior passageway, which extends from the rearward longitudinal end to the forward longitudinal end of the flow momentum enhancing device, and
• as seen in a longitudinal cross-sectional view of the wall of the device, the wall of the device has a non-symmetrical wing airfoil shape.