ANCHORAGE OF LAMINAR FLAME OF FUEL-GAS

Abstract: The aim of this invention is to provide a method and apparatuses to make possible the proper combustion in very compact combustion systems in all operating conditions connected with the capacity modulation or/and the use of limit gases. This aim is reached by applying the method so that, in a combustion system, a premixed, atmospheric or forced burner form the fuel-gas air mixture, from almost stoichiometric to strongly hyperstoichiometric, which outflows from at least one flame opening (7) with velocity and modalities such as to obtain a substantially laminar flow and average velocity in all operating higher than the combustion velocity of the mixture in said condition, at least for a distance equal to that of at least one fluids dynamic obstacle (12) which is immerged in said jet, down stream the flame opening/s (7). Said obstacle (12) is always completely detached from said opening/s (7), having such shape and dimensions to create down stream a stagnation zone, anchorage of the flame (19) in all operating conditions. The flow field down stream and on the side of the obstacle (12) is almost laminar with progressively slightly divergent fluids threads, to obtain a flame (19), from laminar to wrinkled, at the beginning ignited from a specific device, characterised by a large surface and very low thickness anchored to the obstacle (12) at least in some points.

Description: DESCRIPTION Anchorage of laminar flame of fuel-gas FIELD OF THE INVENTION The present invention relates to gaseous fuel combustion systems either natural or forced draft and in particular to a method and apparatuses in accomplishment of same, for controlling the outflow of the air-gas mixture through the flame openings of burners, totally or partially premixed, to obtain: a stable flame, detached from the flame openings area, low emissions, in the most wide field of burner capacity modulation required in practice, even in feeding conditions with limit gases, in a so simple and practical way to be used also for apparatus with capacity of only few k W . The gas combustion system is the assembly of the burner, with the combustion chamber, the heat exchanger, the means for the circulation of air and exhausts, if existing, as well as the control apparatus with its sensors; more elements of the assembly can form a sole body therefore a distinction only possible for functions. The gas combustion systems are the main functional assembly of domestic and industrial appliances as central heating boilers, water heaters, of two main types: instantaneous and storage water heater, room heater and furnaces, gas cookers etc.. For burner it is understood the functional assembly of the parts which create the mixture of air and fuel-gas and make possible the outflowing of them in the combustion chamber through the flame openings. The invention applies in particular to fuel-gas combustion systems, where the mixture, foπned by air, said primary air, and fuel gas (hereafter simply said mixture) is by approx. stoichiometric to strongly hyperstoichiometric (0.95 < λ < 1.6, where λ is the ratio between air actually present in the mixture and the air existing in the stoichiometric mixture of the same gas in the same conditions); flow in combustion chamber, out from the flame openings of the burners with substantially laminar flow, having an out flow velocity between 0.2 and 4.0 meter per second, and generates a lamellar flame, means of big surface and minimum thickness (magnitude order of a millimetre),this means that the ratio surface thickness is well over a value of ten, substantially detached from the area occupied by the flame openings; the flame front, that is the surface where the combustion starts, coincides with the flame itself being the combustion monostadium for the presence of all the necessary oxygen since the ignition and is from laminar to wrinkled. The invention applies to combustion systems with gas atmospheric burners but also with forced burners, where the air gas mixture is obtained, in the wanted flow and composition, with the help of auxiliary means (for example fans, or compressors) both types operate either with the presence of secondary air (called partially pre-mixed burners) or with only primary air (called totally pre-mixed burners). In all types of burners the mixture outflows from the flame openings with a velocity fairly higher to the flame speed so as to avoid that the flame adheres to the opening itself (flame substantially detached). In the combustion chamber the mixture ignited, at least initially, by suitable ignition devices, forms the flame which is kept in stability conditions from a sort of anchorage system, acting at least in some points. Opening configurations, in particular slots obtained in thin thickness sheet, so close to create an almost homogeneous sole jet of mixture are considered single flame openings. The front of flame is recognisable because it emits in the visible, even if the specific maximum emission due to OH and CH ions is respectively in the wavelength between 305 and 320 mm and around 431.5 and 438 mm. BACKGROUND OF THE INVENTION The apparatuses of the kind disclosed in the preamble of the claims arise when the burner capacity is modulating down therefore the mixture exit velocity reduce or when instead of the standard fuel-gas for which the apparatus is set, a fuel-gas from the same family as said standard fuel-gas but prone on flame blow-off or prone to flash back are fed. Specifically, the burner flame openings surface may attain critical temperature value, and in some other occasion, the flame may become unstable, resulting in poor combustion of fuel-gas. Generally said, the flame openings surface, which reach temperature up to 500°C, must be of costly materials and moreover the thermal stress reduces the possibility of flame openings design. In 1979 Kawamura T. carried on sperimental studies on a lamellar flame substantially detached from the area occupied by the flame openings using a burner designed for laboratory purpose, operating in free air, the outflow was forced through two parallel long slots punched in sheet metal . The PCT/IT 87/00079, of the same inventor, claims the following method: in an atmospheric burner, A) inside the burner it is sucked a quantity of primary air which is at least 80% of the air stoichiometrically necessary to the combustion; B) the secondary air, from the very first combustion steps, laps all sides of every single bladed small flame exiting from each group of slots foreseen on the burner diffuser, in such a way that the total air involved exceeds the stoichiomerical air value; C) the combustion starts and is completed within the bladed thickness of the flame, The burners considered are only atmospheric, the only foreseen burner 85 diffuser is in sheet metal with thickness of around 0.5 mm., the group of slots is defined "each group of slots being appropriately subdivided longitudinally into two subgroups of slots lying not so close together" to anchor the flame on the unpunched surface between subgroups of slots. 90 The PCT/IT 91/00056, perfecting the previous one, consider also the forced burners and the fully premixed burners with no need of secondary air, but it expects the sole use of sheet metal diffuser and of the sole anchorage of the flame on the flame openings surface. The anchorage zone reaches high temperatures particularly in limit 95 conditions, moreover the thermal stress, caused from temperature differences of 200-300°C in few millimetres, forces the use of costly materials and constrains special shape and arrangement of the slots which limits the specific capacity of said burner. Furthermore because the exit velocity is limited by the inefficacy of the flame anchorage, the 100 specific capacity of the burner itself is again limited. The difficulty of the anchorage of this type of flame impose also the introduction of more or less expensive regulation systems as per EP0606527A1 deposited on 16 August 1993. In other hyperstoichiometric burners the very low exit velocity of the mixture generates the flame in the 105 proximity of the flame openings surface therefore such surface is water cooled to maintain temperature compatible with not too expensive materials, but the water cooling system double the cost of the burner and the absence of flame anchorage leave the possibility of unstable conditions. 110 The PCT/GB 90/01485 Cafferty filed by BRAY BURNERS LIMITED consider a burner with a maximum primary aeration λ=0.7, "...enabling the issuance from the body of a curtain of said air-gas mixture, wall means adjacent the aperture means arranged so as to lie substantially parallel thereto and adjacent one side therefor..."; the invention doesn't 115 consider the hyperstoichiometric mixture with consequent flame of large surface and minimum thickness, doesn't consider the fluids dynamic obstacle immersed on the mixture flow and completely detached and down stream from the flame opening/s. Said invention doesn't solve the problems described previously particularly the 120 difficulty to maintain the flame stable and the level (50 ppm) of emissions reached, originated by the inadequate premixture, which is not acceptable. DISCLOSURE OF INVENTION The aim of this invention is to provide a method and apparatuses in 125 fulfilment of same, to eliminate the foresaid difficulties, to make possible the proper combustion in very compact combustion systems, even formed by a sole body, to reduce the emission to a very minimum, to maintain the temperature of the flame opening/s surface low to allow the use of steel, alluminium, and other unexpensive materials, all 130 previously described goals must be achieved in all operating conditions caused by the capacity modulation or/and the use of limit gases. The feasibility must be so simple, to be used also for combustion systems of capacity of only few hundred watt. This aim is reached by applying the method so that, in a combustion 135 system, a premixed, atmospheric or forced burner form the fuel-gas air mixture, from almost stoichiometric to strongly hyperstoichiometric, which outflows from at least one flame opening with velocity and modalities such as to obtain a substantially laminar flow and average velocity over 0.4 m/sec, in all operating conditions being the jet 140 velocity higher than the combustion velocity of the mixture in said condition, at least for a distance equal to that of at least one fluids dynamic obstacle which is immerged in said jet, down stream the flame opening/s. Said obstacle is always completely detached from said opening/s, having such shape and dimensions to create down stream a 145 stagnation zone, anchorage of the flame in all operating conditions. The flow field down stream and on the side of the obstacle is almost laminar with progressively slightly divergent fluids threads, to obtain a flame, from laminar to wrinkled, at the beginning ignited from a specific device, characterised by a large surface and very low thickness 150 anchored to the obstacle at least in some points and doesn't touch at all the flame openings surface. If the flame openings on the burner head are distributed near each other on a surface and enough homogeneity, the jets outflowing from different openings, join together after few to some ten mm. remaining 155 the jet velocity over the combustion velocity at the given conditions of mixture and temperature; in this case the fluids dynamic obstacle, no longer connected with the shape and arrangement of flame openings, may be a mesh net or, for instance, an assembly of parallel rods having center axes up to perpendicular to the axes of elongated openings. 160 If the flame openings are homogeneously distributed over a surface but spaced each other, the jets outflowing from different openings, don't join together before the jet velocity becomes equal to the combustion velocity at the given conditions of mixture and temperature; in this case the fluids dynamic obstacle must closely follow the shape of the 165 connected opening. Following the previously described criteria the body/s forming the obstacle need to have the center axe of the assembly or of the body in the center, or slightly out of the center (for instance when near the side walls of the combustion chamber) of the mixture jet in the observed 170 point. The distance obstacle-opening and its shape may vary along the opening length to follow flow-rate changes along said opening or to obtain particular flame shapes to comply to the heat exchanger. It is possible to define the position of the flame as the distance between the barycenter of the flame front and the surface of at least one flame 175 opening which generates this front, hereafter said quantity will be called flame distance. If the temperature, the aeration ratio λ, of the mixture remain stable but flow-rate decreases (the exit velocity decreases), the flame distance decreases and vice-versa if the flow rate increases. 180 The flame distance optimum value can generally be predetermined arbitrary constant, but can have different values according to the fueJ- gas flow rate; in any case, during the on periods on the combustion system, the instantaneous ratio, which is the detected flame distance/optimum flame distance, have the value -1- for the reached 185 conditions considered as optimum, values over 1 show the tendency to the flame blow-off increasing as the ratio increases, values under 1 show the tendency to overheat the burner head (means the flame openings zone) increasing as the ratio decreases. The instantaneous ratio: detected flame distance/optimum flame 190 distance, will be hereafter called flame ratio. To maintain the flame ratio near the optimum in all the operating conditions, the modification on the flame distance will cause a change of the cross section of the obstacle changing the flow conditions on the side of said obstacle and therefore shape of the flame. 195 Following the teaching of the Patent demand MI/96/A00058 of 23-03- 96 of the same inventor, the outflow cross-section of the flame opening/s is varied according to the flame ratio, between a minimum and a maximum cross-section, causing a flame ratio > 1 an outflow section increase and vice versa, so as to maintain the flame ratio around 200 a pre-fixed value, except for a different regulation during the transient periods, for example of starting, when needed. By adopting the flame ratio, or any variable quantity which follows the same variation law, as control-parameter for the variation of the outflow cross-section of the flame opening/s, it is possible to reduce at 205 the minimum the variation of the outflow velocity at the change of the burner capacity by maintaining the flame stable and the emissions reduced. For instance, the distance of a V shaped obstacle can be varied in such a way that the vertex of the V would enter the flame opening reducing 210 the open surface. By using any variant of the described method, the temperature of the outflow zone of the mixture remains within acceptable limits (even below 200 °C), at any flow condition of the burner, type of feeding gas, temperature of the inlet air and the flame remain stable, the 215 harmful emissions are reduced to minima values. BRIEF DESCRIPTION OF THE DRAWINGS In order to better understand the invention, its characteristic and the advantages it provides, few embodiments thereof are described hereinafter, by way of non limitative example and with the assistance of 220 the appended drawings, in which - Table 1/5 fig. 1 shows a combustion system with totally premixed forced burner, with the air-gas regulation and external obstacles with triangle cross section, fig. 2 shows a combustion system with totally premixed atmospheric burner, forced draught and external obstacles 225 with V shaped cross section. - Table 2/5 fig. 3 shows a combustion system with partially premixed atmospheric burner , natural draught, spaced flame openings with bimetallic V shaped external obstacles, fig. 4 shows a combustion system under natural draught, with partially premixed atmospheric 230 burner , with flame openings very close togehter, totally covering the burner head, the obstacle is a mesh net. -.Tav 3/5 fig. 5 shows a burner of the tubular type in longitudinal view with a single flame opening, with variation of the outflow cross section according to the temperature of the exit area of the flame openings fig. 235 6 shows a vertical cross section of the burner of fig. 5, fig. 7 shows a burner similar to that of fig. 5, fig. 8 and fig. 9 show two cross sections of the tubular burner of fig. 6 in different operating conditions. - Table 4/5 fig. 10, 11, 12, 13, 14, 15, 16 and 17 show different flame openings and their dispositions and correlation to external fluids 240 dynamic obstacles. - Table 5/5 fig. 15 shows a combustion system with atmospheric burner, forced draught, outflow velocity variation according to the flame ratio and or according to the fluel gas flow rate; fig.18 is a front view, fig.19 a side view, fig. 20 a cross section of a flame opening. 245 DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows, in vertical cross section, a combustion system 1 with a heat exchanger 2, a combustion chamber 3, a fan 4 for the air gas and exhausts circulation, put upstream the combustion chamber for which this is in over pressure compared to the outside of shell 5 representing 250 the body of the combustion system, which, in this case, is a water cooled alluminium casting, whose inferior part forms the burner head 6 and the burner body 8, inside which a distributor 8C is installed; flame openings 7B obtained from the alluminium casting have lips, are lengthened, perpendicularly to the drawing surface. On the center axe 255 of the jet out flowing from said openings 7B, inside the combustion chamber 3, at a distance, from the flame openings surface, which can reach ten time the width of said openings, according to the exit velocity, complanar with the outflowing jet, are disposed fluids dynamic obstacles 12A, made on small ceramic bars, with isosceles 260 triangle cross section, having sharpest edge upstream and a side perpendicular to the jet axe downstream; the width of the obstacles is of the same magnitude of the width of the openings, in this case between 2 and 4 mm., the hight of the lips of the openings can vary between 7 and 20 mm., in the length the openings are interrupted every 265 25-50 mm. The lamellar flame 19, ignited by a device not in the figure, generates and remains firmly anchored to triangle section obstacles 12 A, downstream of the flame openings 7B, becoming alike a flying carpet, wave shaped because the openings are each other spaced so to create separate outflowing jets joining together only after the 270 combustion for the expansion due to the reached temperature; a certain amount of exhaust gases is recycled from the doubled vortex foπned between two flame openings and sucked inside the mixture jet just down stream the openings edges. The fuel gas valve 11 and the fan 4 speed are operated by the process 275 controller 15 according to the signals transmitted by the ionisation current sensor 14 A. FIG. 2 shows, in vertical cross section a combustion system operating in forced draught with the fan 4 mounted downstream the heat exchanger 2 so the inside of the shell 5 is in depression compared to the outside. The burner, the body 8 of which is the bottom part of the shell 5, is a fully premixed atmospheric one, the air-fuel gas mixture is obtained in a Venturi type tube 10 from the fuel gas exiting the injector 23 and the air from outside the shell 5 entering the mouth 9. Under the vacuum created by the fan in the combustion chamber 3 with respect to the region outside the shell 5 the mixture is drawn through the Venturi 10 and the mixing chamber to the flame openings 7 A, better described in fig. 15, 16, obtained on the sheet metal, for example, of 0.4-0.6 mm thickness, of the burner head 6. The flame openings 7A, made of a row of slots each, where the slots are 0.5 to 0.75 mm. width and 5 to 15 mm. long, parallel to each other on the long side with center distance between 0.9 and 1.5 mm., rows are spaced centre to centre from 15 to 60 mm to obtain a flying carpet type lamellar flame 19 anchored to external obstacles 12B, made on stainless steel sheet metal, visible in V shaped cross section with upstream vertex and centreline of the V, perpendicular to the surface and in centre of the flame openings, parallel to the rows and distant to the slot surface from few to some ten mm according to the exit velocity of the mixture, V shaped obstacles of this type are better described in fig 7, 8, 9. The distance among flame openings and shape and position of the obstacles don't permit any recycling of exhaust gases, therefore the jets down stream the burner head surface suck only recycled air gas mixture. The lamellar flame covers the plan of the combustion chamber 3, lying at level of the optical sensor 14B. The process controller, not shown, varies the gas flow through the valve 11 , according to the heat request. The optical device 14B, based on photo sensor/s, transmits a signal corresponding to the detected position of the flame to the process controller, not shown, which compares said position to a pre-fixed one (flame ratio), in order to change the fan speed. FIG. 3 shows a natural draught combustion system 1 which employs a partially premixed atmospheric burner with body 8A of the extractable type, , the secondary air is introduced from the inlet openings 18 on the shell 5. Flame openings 7 A are formed of rows (perpendicularly lengthened to the drawing) of slots as in fig.2, 15, 16, punched on burner head 6; The external fluids dynamic obstacles have a V shaped cross section, as in fig.2, but made from bimetallic sheets cut and bent as described in fig.15, 16, 17. Being the centre distance among exits 7A big, the flame, ignited by a device not seen, divides itself in long separate V shaped lamellar flames 19A (perpendicularly lengthened to 320 the drawing), at the same time the secondary air, introduced through the apertures 18, is sucked from the mixture jets just down stream the flame opening increasing the λ of the mixture up to 30%. At the same time, the external bimetallic sheet V shaped obstacle, according to the temperature reached changes their cross section, 325 therefore changing the outflow velocity field so to favour the stability. For higher temperatures (continuous line) smaller cross section, the contrary (dashed line) for lower temperatures. The ignition is obtained from the heat element 14 and the flame presence is controlled by a tennocouple not shown. 330 FIG.4 show a natural draught combustion system with partially premixed atmospheric burner, without any specific process control. The burner head 6 is of perforated sheet metal having the circular holes diameter from 2 to 5 mm. and lips from 1.5 to 7 mm. high as better described in fig. 10, 1 1, uniformerly positioned on the burner head as in 335 fig. 11, so spaced each other to obtain a ratio open/total surface between 0.2 and 0.5 as to form a single substancially homogeneous mixture jet and to build a carpet shaped lamellar flame 19 anchored to a mesh net fluids dynamic obstacle 13 B, been the net made of wires of high nickel steel, covering more/over the complete flame openings 340 surface. Through calibrated passages 18 the outside and the inside of the shell 5 are in pression balance, secondary air inlets only at the maximum capacity, at the ignition some air goes out. The presence of flame is detected from a combined device 14 A, which is a ionisation current sensor also capable to cause the spark ignition. 345 FIG. 5 shows an atmospheric burner with tubular body 8A with a sole flame opening 7B between two lips, with an external fluids dynamics obstacle having a triangle cross section positioned with the central axis on centerplane of the burner at a distance from the flame opening edges up to 10 times the width of said flame opening with a cross dimension 350 of the same magnitude of said width, anchoring the large V shaped flame. The fluids dynamics obstacle, of triangle section ceramic rod, is supported on the extremities leaving the possibility of expansion. FIG. 6 shows the atmospheric burner of fig. 5 in vertical cross section to better understand the reciprocal dimension and position of the flame 355 opening in this particular case. FIG. 7 shows a tubular atmospheric burner with the body 8A forming a sole flame opening 7B with two mobile lips 7B2, which define the outflow cross section of it, moved by the deformation (temperature function of the flame opening edges) of two bimetallic sensors- 360 actuators 17. The lips 7B2-a position full line drawn and 7B2-b the dashed drawn one correspond to two different conditions of the flame opening temperature obviously higher the one corresponding to the dashed line, the same for the position 17-a and 17-b of the bimetallic arces; the cross section of the burner body 8 A is similar to that of fig.5 365 but the external obstacle have a V shaped cross section 12B. FIG. 8 and 9, show the vertical cross sections of the tubolar burner of fig. 7 in the two different operating conditions, shown there with lines dashed and continuos for the same conditions represented there. FIG. 10 shows, on plan view from the top, round holes having an 370 external lip around, punched on sheet metal, arranged in groups of three holes in line, the groups parallel and so near to each other, forming a row which is one flame opening 7C, in fact the mixture exiting from all the slots of a row foπn a sole jet, the three rows shown have center distance as in fig. 3 to obtain separate V shaped flames; 375 dimensions of the holes are as defined in fig. 4. The projection of external trilobate elongated obstacles 12D are shown with dashed lines. FIG. 11 shows, on plan view from the top, round holes having an external lip around, punched on sheet metal as those shown in fig.10 disposed regularly and close together, with a ratio open /total surface 380 around 30%, jets outflowing from the flame openings are separate and join together around the level of the trilobate obstacles 12D, but because in this case the center distance of said external fluids dynamic obstacles (projection is shown in dashed line), is big enough, a flame shaped alike a wave flying carpet is obtained, similar to that of fig. 1 385 obtained with a different lay out of flame openings and obstacles. This fact demonstrate that when jets of air-gas mixture exiting from different flame openings join together before the external obstacle and maintain, there, a velocity higher than the combustion velocity for that mixture in that condition, the shape and position can be indipendent 390 from that of the flame openings; the obstacles my assume various forms, parallel alongated rods, trilobe shaped 12D as here, V shaped 12B, triangular 12 A, also round, nets of different construction and design as the mesh net 13B of fig. 4 and the laid on small rods 13C of fig. 14. 395 FIG.12 shows the vertical section of two aligned elongated openings so close together that a sole obstacle , in this case a bimetallic V shaped one, can be used if the vertex is near the flame openings surface. Also the flame and the wall design is visible. FIG. 13 shows an enlarged plan view of the burner head in a first level 400 where are visible slots parallel each other combined in groups of three and four, these said groups (the flame openings) been distributed in a check pattern to obtain a flying carpet shape lamellar flame 19 in the second level the external obstacle is visible formed of a net 13C made of parallel ceramic rods in one direction and wires perpendicularly, 405 covering the combustion chamber plan FIG. 14 shows the vertical section corresponding with the application of fig. 13 where the reciprocal position of openings, obstacle and flame are visible. FIG. 15 shows the vertical section.C-C of fig. 16 where the reciprocal 410 position of openings, obstacle and flame are visible. FIG. 16 is a top view in two levels, of a part of the burner's head 6 of fig.3, two flame openings are represented, made of a row each of parallel slots having width from 0.5 to 0.75 and length from 5 to 15 mm. adjacent on the long side, spaced centre to centre from 0.9 to 1.5 415 mm., the external bimetallic obstacle 12C V shaped is visible on the left side on the second level. FIG. 17 show the plan view of part of a sheet metal rectangle with alternate parallel cuts which bent would form the V shaped obstacle of fig.3, 12, 15, 16, the cuts are foreseen to preventing arc formed bending 420 of the obstacle caused by the temperature distribution during the heating periods of the combustion system, if the sides of the V are longer than some mm. and the total length of the obstacle more than about 100 mm. FIG.18 shows a forced draught combustion system, the burner, the 425 body 8A of which is bottom part of the shell 5, is atmospheric, the air- fuel gas mixture is obtained in a Venturi type tube 10 from the fuel gas exiting the injector 23 and the air from outside the shell 5 entering the mouth 9. An optical device 14B is used to detect the flame ratio as to permit to 430 the controller 15 the variation of the outflow velocity of the mixture according to said flame ratio using a step by step motor 25 moving up and down the obstacles 13A through an eccentric 28 as better described in fig 19 and 20. The flame openings 7B, lips formed, are lengthened, perpendicularly to the drawing surface; on the center axe of 435 the jet out flowing from said openings 7B, inside the combustion chamber 3, at a variable distance, from the flame openings surface, parallel to the openings, are disposed (displaced) fluids dynamic obstacles, V shaped, supported by a ceramic rod each, made of stainless steel sheet metal; the openings and the obstacles have the 440 same length . The lamellar flame 19, ignited by a device not in the figure, generates and remains firmly anchored to obstacles 12B, downstream of the flame openings 7B becoming alike a wave shaped flying carpet because the opening are each other spaced about five times the openings width. No recirculation of exhaust gases is foreseen 445 because the openings are too close to each other. FIG. 19 shows the vertical section A-A of fig. 18, looks clear how the eccentric 28 moved by the motor 25 can push down the obstacles 12A against the springs 30 actuating the desidered changes of the cross section of the flame openings 7B visible in fig. 18 and 20. 450 FIG. 20 shows a vertical section of lips fonned flame opening 7B with movable obstacle 12B which modify the outflow cross-section of the flame opening and therefore the outflow velocity, according to the flame ratio, between a minimum and a maximum cross-section, causing a flame ratio > 1 an outflow section increase and vice versa, so as to 455 maintain the flame 19A distance around a pre-fixed value, except for a different regulation during the transient periods, for example of starting, when needed. Two position of the ostacle and that correlate of the flame, are shown, with dashed line 12B-a the one for smaller outflow cross-section continuos line 12B-b those for higher.

Claims: 460 CLAIMS 1 . the method so that, in a gaseous fuel combustion system with either natural or forced draft, a- a premixed, atmospheric or forced burner form the fuel-gas air mixture, from almost stoichiometric to strongly hyperstoichiometric, 465 b-the mixture outflows from at least one flame opening with velocity and modalities such as to obtain a substantially laminar flow and average velocity over 0.4 m/sec, characterised by the fact that: c-an almost homogeneous sole jet of mixture is exiting from each flame 470 opening, inside which, immediately down stream said opening, the gaseous content of the volume surrounding the jet is sucked and mixed, d- at least one fluids dynamic obstacle is immerged in the outflowing jet, down stream at least one flame opening, detached from said opening, . in a position where the fuel-gas air mixture jet velocity 475 remains over the combustion velocity at any operating condition, e- caused from the shape and dimensions of the obstacle, down stream this fluids dynamic obstacle a stagnation zone is created, f- a flow field almost laminar with progressively divergent fluids threads is generated down stream and on the side of the obstacle, 480 g-a laminar to wrinkled flame, at the beginning ignited by a specific device, is generated and anchored in all operating conditions, at least in some points, by the vortexes connected to the stagnation zone. 2-. method as per claim 1 characterised by the fact that , the gaseous content from the volume surrounding the jet sucked, immediately down 485 stream the flame opening, inside said jet, is mainly recycled air-gas mixture. 3-. method as per claim 1 characterised by the fact that , the gaseous content from the volume surrounding the jet sucked, immediately down stream the flame opening, inside said jet is mainly secondary air. 490 4-. method as per claim 1 characterised by the fact that , the gaseous content sucked, immediately down stream the flame opening, inside the jet from the volume surrounding said jet is mainly recycled exhaust gases. 5- method as per one or more of claims 2, 3, 4, where the composition 495 of the gaseous content from the volume surrounding the jet sucked, immediately down stream the flame opening, inside said jet, is a mixture of secundary air and recycled exhaust gases in different ratio following different operating conditions. 6- premixed, atmospheric or forced burner, acting the method as per 500 one or more of claims 1 , 2, 3, 4, 5, forming a fuel-gas air mixture, from almost stoichiometric to strongly hyperstoichiometric, which outflows from at least one flame opening with velocity and modalities such as to obtain a substantially laminar flow and average velocity over 0.4 m/sec, characterised by the fact that: the outflow surface of flame 505 opening/s is such that, in all operating conditions, the out flowing jet velocity remains hiher than the combustion velocity of the mixture in said condition, at least for a distance equal to that of at least one fluids dynamic obstacle which is immerged in the jet, down stream the flame opening/s. Said obstacle is always completely detached from said 510 opening/s, having such shape and dimensions to create down stream a stagnation zone, anchorage of the flame in all operating conditions. The flame openings shape, the obstacle shape and distance, are such and so combined to obtain a flow field down stream and on the side of the obstacle almost laminar with progressively slightly divergent fluids 515 threads, conditions to have a flame, from laminar to wrinkled, at the beginning ignited from a specific device, characterised by a large surface and very low thickness positioned down stream and anchored to the obstacle at least in some points, flame which doesn't touch at all the flame openings surface. 520 7- burner head as per claim 6 characterised by the fact that the external fluids dynamic obstacle/s is/are made of material heat resistant over 500°C. 8- burner head as per claim 6 or 7 characterised by the fact that the flame openings and connected fluids dynamic external obstacles are so 525 close each other and disposed in such an homogeneous way to obtain a sole flame covering all the surface engaged from the flame openings. 9- burner head as per claim 6 or 7 or 8 characterised by the fact that the external obstacle is a mesh net regularly distributed over the entire surface of the flame opening/s. 530 10- burner head as per claim 9 characterised by the fact that the mesh net obstacle follows the shape of the flame opening/s surface. 11- burner head as per claim 6 or 7 or 8 characterised by the fact that the obstacle is made of rods regularly distributed over the entire surface of the flame opening/s. 535 12- burner head as per claim 6 or 7 characterised by the fact that the obstacle strictly connected with the flame opening/s follow the shape of said flame opening 13- burner head as per claim 12 characterised by the fact that the obstacle/s have in all points axis of symmetry in the center axis of the 540 mixture outflowing jet in that point. 14- burner head as per claim 12 characterised by the fact that a sole elongated body act as obstacle for up to three elongated flame openings, very close together on the long side, having in all points axis of symmetry in the center axis of the mixture outflowing jet in that 545 point. 15- fluids dynamic external obstacle following the method of claims from 1 to 5 characterised by the fact that the cross section of the fluids dynamic obstacle has an edge even sharp up stream to divide the mixture jet without generating any stagnation. 550 16- fluids dynamic external obstacle following claim 15 characterised by the fact that the cross section of the fluids dynamic obstacle has three edges 17- fluids dynamic external obstacle following the claim 16 characterised by the fact that the cross section of the fluids dynamic 555 obstacle is V shaped and the vertex up stream. 18- method as per one or more of claims 1, 2, 3, 4, characterised by the fact that any variation of the form and or position of the flame cause a change of the cross section of the external fluids dynamic sutch to tende to reestablish the previous conditions. 560 19- method as per claim 18 characterised by the fact that any increase of the flame distance cause a increase of the transversal dimension of the obstacle cross section, the opposite for a reduction. 20- fluids dynamic external obstacle following claim 15 and the method claim 19 characterised by the fact that the obstacle is an elongated 565 sealed bulb, filled of expansible fluid. 21 - fluids dynamic external obstacle following claim 20 with a rounded V with vertex up stream cross section. 22- fluids dynamic external obstacle following claim 15 and the method claim 19 characterised by the fact that the obstacle is a V shaped 570 bimetallic sheet metal rod. 23- method as per one or more of claims 1, 2, 3, - , characterised by the fact that any variation of the flame ratio cause a change of the cross section of the flame opening, a flame ratio > 1 increasing the cross section, decreasing by flame ratio < 1 between a mimmum and a 575 maximum cross section coinciding with the minimum and the maximum of burner capacity. 24- burner head as method claim 23 characterised by the fact that the movement of the external fluids dynamic obstacle/s changes the cross section of the flame opening/s. 580 25- frilly premixed burner head as per method claim 2 characterised by the fact that the flame openings are so close together that the gaseous content from the volume surrounding the jet sucked, immediately down stream the flame opening, inside said jet, is mainly recycled air-gas mixture. 585 26- fully premixed burner head as per method claim 4 characterised by the fact that the flame openings are so spaced together that the gaseous content from the volume surrounding the jet sucked, immediately down stream the flame opening, inside said jet, is mainly recycled exhaust gases. 590 26- partially premixed burner head as per method claim 3 characterised by the fact that the flame openings are so spaced together and so disposed to facilitate the flow of secondary air in between flame openings that the gaseous content from the volume surrounding the jet sucked, immediately down stream the flame opening, inside said jet, is 595 mainly secondary air

Inventors: SEBASTIANI ENRICO, SEBASTIANI, ENRICO
Applicants: SEBASTIANI ENRICO, SEBASTIANI, ENRICO
Application year: 1997
Main classification: F23D14
IPC codes: F23D14