COMBUSTION HEAD FOR A LOW NOx LIQUID FUEL BURNER

Abstract

A combustion head for a burner provided with a nozzle for atomizing a liquid fuel; the head has a first body adapted to receive a primary comburent flow and having a frontal wall arranged to produce a swirl in the primary comburent flow; and a second body adapted to receive a secondary comburent flow, to convey it towards a combustion chamber and to produce a swirl therein; a duct and an intermediate body which define a channel, adapted to feed a tertiary comburent flow into the combustion chamber and having a tapered end profile which converges towards the first body and the second body; and a frontal surface of the intermediate body substantially lies on the plane defined by the frontal wall of the first body.

1 . A combustion head ( 1 ) for a fuel burner, which comprises a central duct fed with a liquid fuel, having a longitudinal symmetry axis (X), and is provided, at one end, with a nozzle for the atomization of said liquid fuel into a combustion chamber (CC); the combustion head comprises:
 a first body having a cylindrical extension and coaxial to the longitudinal symmetry axis (X); the first body being mounted on the central duct to receive at an inlet thereof a primary flow (F 1 ) of comburent and to convey the primary flow (F 1 ) towards the nozzle, the first body having a frontal wall provided with a plurality of spaced apart peripheral indentations suited to produce a swirl in said primary flow (F 1 ) of comburent; and   a second body having a cylindrical extension and coaxial to the longitudinal symmetry axis (X); the second body being mounted on the first body so as to receive at an inlet thereof a secondary flow (F 2 ) of comburent and to convey the secondary flow (F 2 ) towards the combustion chamber (CC), the second body having a plurality of openings which are suited to produce a swirl in said secondary flow (F 2 ) of comburent;   a swirl regulation assembly to control the swirl produced in said primary flow (F 1 ) of comburent and in said secondary flow (F 2 ) of comburent; the swirl regulation assembly comprising a duct positioned coaxially to the longitudinal symmetry axis (X) and externally of the second body with the interposition of an intermediate body there between that is also coaxial to the longitudinal symmetry axis (X); the duct and the intermediate body defining a channel (C 1 ) there between through which a tertiary flow (F 3 ) of comburent is fed into the combustion chamber (CC);   the intermediate body including a frontal surface positioned substantially on a plane defined by a frontal wall of the first body, so that the nozzle is positioned directly facing the combustion chamber (CC); and, at an end section of the swirl regulation assembly adjacent the combustion chamber (CC), the channel (C 1 ) has a tapered profile which converges towards the first body and the second body.   
     
     
         2 . The combustion head according to  claim 1 , wherein the end section the channel (C 1 ) is defined by a front portion of the duct, which is shaped as a truncated cone coaxial to the longitudinal symmetry axis (X) and faces a truncated cone-shaped surface of the intermediate element, which is also coaxial to the longitudinal symmetry axis (X). 
     
     
         3 . The combustion head according to  claim 1 , wherein the duct is movable with respect to the intermediate body between a position of maximal closure, corresponding to a tertiary flow (F 3 ) of comburent with a minimum flow rate, preferably equal to zero, and a position of minimum closure, corresponding to a tertiary flow (F 3 ) of comburent with a maximum flow rate. 
     
     
         4 . The combustion head according to  claim 3 , wherein the duct comprises a plurality of internal projections, which are distributed about the longitudinal symmetry axis (X); the projections being in contact with and, when in use, slide on an external surface of the intermediate body, so as to allow a translation motion of the duct with respect to the intermediate body between the position of maximal closure and the position of minimum closure. 
     
     
         5 . The combustion head according to  claim 1 , wherein the intermediate body has a rear surface shaped as a truncated cone, is coaxial to the longitudinal symmetry axis (X), and is tapered towards the first body; the rear surface being suited to increase the average axial speed of the primary flow (F 1 ) of comburent and of the secondary flow (F 2 ) of comburent at the inlet of the first body and of the second body, respectively. 
     
     
         6 . The combustion head according to  claim 1 , wherein the frontal wall is provided with a through hole that is coaxial to the longitudinal symmetry axis (X). 
     
     
         7 . The combustion head according to  claim 6 , wherein a cylindrical lateral wall of said first body is free of through holes and the primary flow (F 1 ) of comburent at the outlet of the first body is only divided into a primary swirled comburent flow and a primary axial comburent flow. 
     
     
         8 . The combustion head according to  claim 1 , wherein each indentation has a pair of facing lateral walls that are inclined by a first angle (α) with respect to a plane defined by a front flat surface of the frontal wall. 
     
     
         9 . The combustion head according to  claim 8 , wherein the first angle (α) ranges between 42° and 48°. 
     
     
         10 . The combustion head according to  claim 1 , wherein each of the plurality of openings is defined by a pair of facing lateral walls that are inclined by a second angle (β) with respect to a plane defined by a rear flat surface of the second body. 
     
     
         11 . The combustion head according to  claim 8 , wherein the second angle (β) ranges between 42° and 48°. 
     
     
         12 . The combustion head according to  claim 10 , wherein the second body comprises a front portion and a rear portion with the front and rear portions both being cylindrical in shape and positioned coaxially to the longitudinal symmetry axis (X), but having different diameters; the plurality of openings being located in the rear portion. 
     
     
         13 . A liquid fuel burner provided with a combustion head comprising:
 a first body having a cylindrical extension and coaxial to the longitudinal symmetry axis (X); the first body being mounted on the central duct to receive at an inlet thereof a primary flow (F 1 ) of comburent and to convey the primary flow (F 1 ) towards the nozzle, the first body having a frontal wall provided with a plurality of spaced apart peripheral indentations suited to produce a swirl in said primary flow (F 1 ) of comburent; and   a second body having a cylindrical extension and coaxial to the longitudinal symmetry axis (X); the second body being mounted on the first body so as to receive at an inlet thereof a secondary flow (F 2 ) of comburent and to convey the secondary flow (F 2 ) towards the combustion chamber (CC), the second body having a plurality of openings which are suited to produce a swirl in said secondary flow (F 2 ) of comburent;   a swirl regulation assembly to control the swirl produced in said primary flow (F 1 ) of comburent and in said secondary flow (F 2 ) of comburent; the swirl regulation assembly comprising a duct positioned coaxially to the longitudinal symmetry axis (X) and externally of the second body with the interposition of an intermediate body there between that is also coaxial to the longitudinal symmetry axis (X); the duct and the intermediate body defining a channel (C 1 ) there between through which a tertiary flow (F 3 ) of comburent is fed into the combustion chamber (CC);   the intermediate body including a frontal surface positioned substantially on a plane defined by a frontal wall of the first body, so that the nozzle is positioned directly facing the combustion chamber (CC); and, at an end section of the swirl regulation assembly adjacent the combustion chamber (CC), the channel (C 1 ) has a tapered profile which converges towards the first body and the second body.   
     
     
         14 . The combustion head according to  claim 8 , wherein the first angle (α) is preferably equal to 45°. 
     
     
         15 . The combustion head according to  claim 10 , wherein the second angle (β) is preferably equal to 45°.