WO2007134580A1

WO2007134580A1 - Flame modelling

Info

Publication number: WO2007134580A1
Application number: PCT/DE2007/000895
Authority: WO
Inventors: Ulrich Dreizler; Daniel Dreizler
Original assignee: Ulrich Dreizler
Priority date: 2006-05-19
Filing date: 2007-05-16
Publication date: 2007-11-29

Abstract

Proposed is a method for the combustion of liquid and/or gaseous fuels, and a fan burner for carrying out said method, in which an envelope flame which delivers the actual firing power is arranged around a core flame, wherein at least the core flame can be modelled in terms of its size and shape such that it, in particular on account of a variable configuration, generates an inner, internal waste gas recirculation situated in the interior of the envelope flame.

Description

flames modeling

State of the art

The invention is based on a method or a device for carrying out this method according to the preamble of claim 1 or of claim 11.

A fundamental problem in the combustion of liquid or gaseous fuels via such methods, or devices consists in the formation or design of the flame on the one hand to save fuel the best possible effective heat transfer from the flame to the heat transfer material, such as water, eg , B. within a boiler, and on the other hand by the design or training of the flame to meet the increasingly stringent requirements for the detoxification of the exhaust gas.

It is known in generic methods and devices for exhaust gas detoxification, a partial recycling of exhaust gases in the Root of the flame during the combustion process perform (EP 0 347 834, Dreizier), whereby the combustion temperature and thus the proportion of toxic NO _x in the total exhaust gas of the combustion process is reduced. In order to achieve this, in the known burner head and corresponding methods on which the flame-shaping combustion tube or the adjoining flame tube, radial openings exist for the recirculation of exhaust gas, this recirculation is still supported by projecting into the flame webs. Exhaust gas recirculation is required both outside the flame and down to the root to achieve the desired NO _x reduction.

In another known generic but only for heating oil firing system (EP 0 913 631 A2, Weishaupt), are also attributed to nitrogen oxide reduction exhaust gases in the flame are around a central atomizer around with its own ignition device to achieve a homogeneous distribution of fuel Air and exhaust additional atomizing nozzles evenly spaced, as well as otherwise known in many ways by the prior art. Although only a correspondingly relatively small proportion of the fuel consumed is omitted on the central atomizer nozzle for their task as a pilot or Zündflammdüse, here is the problem of recirculation of exhaust gas to the combustion air of all nozzles, what in hardly effective way an annular disk jam body around the central nozzle and is provided between the nozzles arranged around it.

Since the heat transfer from the flame on the separation of the heat transfer material serving wall of a boiler z. T. on Radiation, but essentially based on convection, must also be considered in the design and training of the flame of this. Especially in processes or devices of the generic type, the nuclear flame hardly contributes to the convection. However, this nuclear flame is for the ongoing ignition of the fuel-air mixture of Hüllflamme of considerable importance, since in particular because of the decisive for a good efficiency turbulence of the fuel-air mixture, a tearing of the flame must be considered. For this reason, a central flame forming central fuel nozzles are provided in the above-mentioned known burner heads. However, in these generic burners through the flame tube and the fuel supply the fuel distribution to the core flame and the shell always fixed by the design, so that for a change in performance of the burner always also simultaneously the fuel supply to the core flame and envelope flame changes and this with the same fuel distribution. With increasing performance and with correspondingly increasing energy demand, the unusable proportion of the firing, namely the nuclear flame, thus increases proportionately. In addition, the thereby increasing volume of the core flame obstructs the recirculation, in particular to the inner part of the flame, which inevitably leads again to higher No _x - shares in the exhaust gas.

In another known burner head (EP 0 857 915; ELCO) is achieved by a centrally arranged atomizing nozzle for liquid fuels and arranged around these gas nozzles, in conjunction with the recirculation of exhaust gas conveying guide devices in a flame tube, that the flame front only in one forms a certain distance from the combustion head in the combustion chamber. This is intended to ensure that the radially supplied exhaust gas reaches the root of the flame in order to achieve the above-mentioned advantages in the combustion process there as well. Since this, of course, a greater risk of tearing the flame, it is also proposed there in addition to the local stabilization of the spaced flame to use a working with gaseous fuels support burner, which should ensure a continuity of the combustion process despite the central Ölzerstäuberdüse.

In another known combustion device (EP 0 478 305; Hitachi), which primarily serves as a premix burner for gas turbines and in which gas nozzles are arranged centrally symmetrically, a flow resistance is arranged in each case in the flow of combustion air and fuel gas, thereby "essentially" combustion gas Although cooling of the center of the respective flame and thus a reduction of the NO _x content are achieved thereby, but at the cost of a great effort bezgl. Design and arrangement of this centrally located in the flame flow resistance, In addition, there are considerable problems with regard to the flame stability of this combustion device.

Object of the invention

The invention has for its object a method, or to develop a device for carrying out this method of the generic type, with recirculation of exhaust gas and without additional means projecting into the flame. This object is achieved by the method according to the invention according to the main claim and the burner head according to the invention according to claim 10.

Advantages of the invention

The inventive method or the burner head according to the invention has over the described prior art has the advantage that the central flame or flame, in particular for fuel economy in size, regardless of the surrounding envelope flame, adjustable and thus modeled. This can be done by centrally one or two fuel nozzles are available, of which even one is switched off or by the amount of fuel supplied is changed. In any case, as a result of this intervention in the flame, at least the core flame can be modeled so small in the longitudinal section that a NO _x -reducing internal recirculation of its exhaust gas occurs in the region of this central flame. The invention relates not only to pure oil burners or gas burners, but also combined burners for oil and gas. Without the function of the nuclear flame is lost as a pilot or pilot flame, according to the invention is not usable energy from the flame center acceptable. This is done by gradual or continuous reduction of the core flame, while the overall flame and thus the ratio of the core flame to the envelope flame can be modeled as desired. This is often found in the prior art continuous Nachzünden the main flame through the nuclear flame is also in solutions according to the invention of extraordinary importance, both for avoiding the Vibrations with noise, as well as due to a delayed Nachzündens by the main flame itself. In the invention, the saving of fuel primarily in that the actually used heat output emanates from the arranged at the edge of main flames of the envelope flame and not from the nuclear flame, according to the invention independent is changeable by the envelope flame. Even with the one known burner head (EP 0 857 915, Elco) it can be seen that the introduction of recirculated exhaust gases to the flame center is a problem and that a lack of flame stability can only be recovered by introducing a higher proportion of fuel gas into the center of the flame ,

In one of the above-mentioned known oil firing systems (EP 0 913 631 A2, Weishaupt) exhaust gas recirculation to the central pilot flame or to the flame interior is not possible by the use of a combustion air not additionally circularly swirling and no swirl generating annular disk jam body, but also not at all sought , In addition, the central atomizing nozzle and the outer nozzles are always applied simultaneously with the same fuel pressure, which depends on the desired performance of the overall flame. The nozzles can only be operated together and synchronously.

According to an advantageous embodiment of the method according to the invention, the change of the fuel supply takes place at least to the core flame in stages. Here, the one stage may be formed by fuel oil and the other stage by gas as fuel. By switching on the supplementary firing level or switching it off, the core flame can be adjusted accordingly be modelable. This tap-change can be done regardless of whether each stage in turn can be changed in their performance. It is only known (EP 0 857 915 B1) to support a nuclear flame by a supporting flame, if necessary, without, however, contributing to its modeling. On the contrary, it can be assumed that such a supporting flame promotes a subsequent ignition of the main flame, but additionally introduces heating energy in the middle of the flame and this stimulates the pollutant formation of the nitrogen oxides NO _x .

According to an additional embodiment of the invention, the change of the supply of the fuel to the core flame is continuous, wherein it is also continuously modelable. The core flame can thereby be cool and free of flow, so that even there an internal recirculation of the exhaust gases in the envelope flame is possible, whereby NO _x emissions are reduced.

According to an additional embodiment of the invention relating to the method, a central recirculation of exhaust gas can be achieved via the fuel supply to the core flame in relation to that of the envelope flame, as a result of which the core flame can be controlled or the flame shape can be modeled. The size ratio of envelope flame to core flame has a natural influence on the exhaust gas side of the core flame and corresponding to the exhaust gas recirculation concerned.

According to an advantageous embodiment of the invention as a fan burner serves as a central nozzle Ölzerstäuberdüse, wherein the supplied via an oil pump under pressure fuel oil via a solenoid valve or needle shut-off and is absteuerbar. In this embodiment, a fuel oil version given an oil flow regulator can be arranged downstream of the oil pump, in particular in the return of the fuel oil line and downstream of the branch to the central nozzle and it can be arranged in the fuel lines to the nozzles, regardless of whether it is oil or gas nozzles, solenoid valves which serve according to a predetermined program for the formation of an optimum combustion, but above all also for the creation of a semi-hollow core flame with internal Abeasrezirkulation.

drawing

Several embodiments of the invention are illustrated in the drawings and described in more detail below.

It shows, each greatly simplified:

Figure 1 is a gas burner in longitudinal section.

Figure 2 is an oil burner in longitudinal section.

3 shows an oil burner with 2-stage nuclear flame in longitudinal section.

4 shows an oil-gas combination burner in longitudinal section.

5 shows a hydraulic circuit diagram for a burner according to FIG. 2 or FIG. 4 and FIG 6 shows a hydraulic circuit diagram for a burner according to FIG. 3.

Description of the Ausführangsbeispiele

As shown in FIG. 1 very greatly simplified and shown in longitudinal section in a gas burner 1 in a cross-sectional plane 2 a plurality of gas nozzles 3 arranged in a circle, by the operation of the gas burner, an annular envelope or main flame 4 is formed, which in their performance needs , For example, a boiler, is adjusted. Centrally located between these outer gas nozzles 3, a gas nozzle 5 is arranged to form a core flame 6, which is correspondingly surrounded during operation of the gas burner 1 by the outer or enveloping flame 4. This nuclear flame serves on the one hand in case of failure or disturbances of the envelope 4 to their reignition and on the other hand for supplementary power control. At very low power requirements, it can even serve as a replacement for the envelope 4, but it is much smaller in each case. The gas supply to the external gas nozzles 3 via a gas line 7, which is controlled outside the gas burner via a controllable gas valve 8. The central gas nozzle 5 is supplied via a gas line 9 with gas, which is controlled by a controllable gas valve 10.

In this gas burner 1 according to the invention the envelope flame is adjusted according to the required power, via the gas valve 8. In this case, all the gas nozzles 3 are supplied simultaneously with gas, the invention does not exclude that this gas quantity control via the gas valve 8 during operation is changeable, for example, in adaptation to the actual actual heat demand. However, the core flame 6 is changeable via the gas valve 10 according to a predetermined program. In any case, however, due to its arrangement, the core flame can be modeled within the larger enveloping flame 4 enveloping it in such a way that an inwardly cooler flame is produced in the direction of flow, which in turn leads to internal recirculation of the exhaust gas forming in this core flame. It is decisive that during the operation of this nuclear flame in her an exhaust-detoxifying NO _x - reducing recirculation of exhaust gas takes place, without affecting the enveloping, easily working outside with exhaust gas recirculation envelope, ie without additional, the envelope or main flame impairing construction elements.

In Fig. 2 is also very much simplified and in longitudinal section an oil burner 11 is shown, which operates in principle to solve the invention as the gas burner of Fig. 1. About a number of circularly arranged Ölzerstäubungsdüsen 12 is a required power bringing envelope 13th within which a core flame 15 formed via a central nozzle 14 is arranged. The fuel supply to the nozzles 12 via oil lines 16, which are controlled by a solenoid valve 17, so that from an oil pump 18 from an oil tank 19 all fuel nozzles 12 are supplied simultaneously and under the same pressure with fuel oil. To the central nozzle 14 performs an oil line 20 which is controllable via a control valve 21 and which is also supplied by the pump 18 with fuel oil. The control valve 21 operates, as not shown here but the embodiment of FIG. 5 removable, with a Ölzerstäuberdüsen 30 is generated, wherein what is shown overlapping in the drawing and not individually recognizable for the fuel, gas nozzles 29 and Ölzerstäuberdüsen 30 side by side but also on a circle around the Ölzerstäuberdüse 27 of the core flame 26 are arranged. The lances 31 of the Ölzerstäuberdüsen 30 thus do not pass through the gas supply pipes 32 of the gas nozzles 29 but next to it. The gas supply pipes 32 branch off from a central gas distribution pipe 33, into which a gas supply pipe 34 opens. The leading to the central Ölzerstäuberdüse lance 35 is correspondingly arranged coaxially with the gas distribution pipe 33 and slidable in the axial direction, in particular to be able to adjust the position of the root of the core flame 26.

According to the invention, this combination burner 25 can operate either as a pure oil burner, in which the envelope flame 28 is formed by spraying fuel oil through the Ölzerstäuberdüsen 30 or the envelope flame 28 can be formed as a pure gas flame through the gas nozzles 29 gas supplied, and not least by the Combination of oil and gas for maximum simmer performance. The core flame 26, however, is achieved only via the Ölzerstäuberdüse 27, wherein the pressure, or the amount of the Ölzerstäuberdüse 27 supplied fuel oil determines the variable size of the core flame 26. Depending on the size of the core flame 26, but also depending on spray angle of the Ölzerstäuberdüse 27, 26 forms an open zone 36 on the exhaust side of this flame 26, which causes an internal recirculation of exhaust gas due to the flame forming this negative pressure in the center of the core flame 26 and thus on the one hand achieved a corresponding detoxification of the exhaust gases of NO _x and on the other hand a certain cooling of the core flame 26, which benefits the entire firing efficiency.

In Fig. 5 is a hydraulic circuit diagram for an oil burner is shown, as it is shown as an embodiment in Fig. 2 and Fig. 4 as a combination burner. Therefore, the same reference numerals are used for the corresponding articles shown in Fig. 5 as in Fig. 2. The equipment shown in the hydraulic circuit diagram operates as follows. The fuel oil is conveyed from the oil tank 19 via the oil pump 18 in a main line 37, wherein the adjusting pressure in the main line 37 via a pressure gauge 38 is measured and controlled by oil pressure switch for maximum pressure 39 and minimum pressure 40. When deviating from a desired pressure range of the oil burner 11 is turned off. Downstream of this control point, a main solenoid valve 41 is arranged in the main line 37 in order to interrupt the oil supply, if necessary. In the usual way, the oil pump 18 has a suction line 42 and a return line 43.

From the main line 37 branches to the central nozzle 14 leading oil line 20, wherein the injected via the central nozzle 14 oil amount is controlled on the one hand via an arranged in the oil line downstream of the central oil quantity regulator 44, or via the control valve 21, which the oil line 20 directly to a return line 45 opens up, which leads back to the oil tank 19, so that when the valve 21 is closed in the firing breaks the promotion to the central nozzle 14 is interrupted. The amount of oil quantity regulator 44 controlling the quantity to be injected via the central nozzle 14 is controlled by a servomotor 46 in the course of a program. The pressure upstream of the oil quantity regulator 44 is via a pressure gauge 47 Volume controller together to thereby model the core flame 15 according to a program. Here, too, applies to the embodiment of FIG. 1 described interaction of enveloping flame and nuclear flame.

3 is also an oil burner 11, in which only in contrast to the embodiment of FIG. 2, the core flame 22 is formed in two stages, namely over a first stage forming Ölzerstäuberdüse 23 and a second provided for a second stage of the core flame 22 Ölzerstäuberdüse 24. The supply of at least one of these Ölzerstäuberdüsen 23 or 24 via a not-shown solenoid valve, as well as the embodiment of FIG. 6 removable, while the other Ölzerstäuberdüse for a first Stage can be supplied together with the Ölzerstäuberdüsen 12 with fuel oil. In this way, depending on the program, a minimal nuclear flame can be generated and after connection of the second Ölzerstäuberdüse a maximum nuclear flame. The advantage would be mainly in the saving of a quantity control device in the supply of the central nozzle for a multi-stage operation of the central flame.

In the fourth embodiment shown in Fig. 4 is a so-called combination burner 25, which is greatly reduced and shown in longitudinal section. In a combi burner both gas and oil is burned as fuel, the combination can be done in a variety of ways. In the example shown, the core flame 26 is generated by fuel oil and an oil atomizer nozzle 27, while the main flame or envelope flame 28 via a combination of gas nozzles 29 and controlled to control in the oil line 20 in front of the central nozzle 14 required for the core flame oil pressure. The oil line 20 opens downstream of the oil quantity regulator 44 in the return line 45th

From the main line 37, the oil line 16 branches off, which is controlled by the solenoid valve 17 and to the individual - here four - Ölzerstäubungsdüsen 12 leads. If the solenoid valve 17 is opened, the hydraulically actuated needle shut-off valves 65, which are arranged at the entrance to the burner lances 31, open automatically under oil pressure. The return lines of these enveloping enveloping flame causing Ölzerstäubungsdüsen 12 open into a return line 48, in which an oil flow regulator 49 is arranged for adjusting the enveloping flame forming injecting amount of oil, wherein the adjustment via a servo motor 50 takes place. Again, it may be so that the amount of oil to be injected is changeable according to a changing power requirement - but it is also conceivable that a certain power should be maintained and the amount of oil to be injected is adjusted. Upstream of this oil quantity regulator 49, the pressure in the oil line 48 is controlled via an oil pressure gauge 51, while downstream of the oil quantity regulator 49, a pressure switch 52 monitors the pressure in the return line 45 of both oil lines 20 and 48. In the return line 45 also two solenoid valves 53 are arranged, which are closed at burner standstill. An electrolessly opening solenoid valve 66 ensures in the burner standstill for pressure equalization via the safety return 67 and can safely reduce pressure peaks in the closed hydraulic system when heated. Using this hydraulic circuit diagram can be achieved using a predetermined electrical program, which detects both the magnets of the solenoid valves and the actuators of the oil flow regulator, a very favorable flame quality, in which a larger envelope flame available. is with a smaller core flame and achieving recirculation of the exhaust gas at the smaller core flame.

In Fig. 6 is a hydraulic circuit diagram for an oil burner is shown, as shown as an embodiment in Fig. 3. Again, therefore, the same reference numerals are used for the corresponding objects shown in Fig. 6 as in Fig. 3, as far as it concerns objects taken from there. Here, too, fuel oil is pumped under pressure into a distributor 54 via an oil pump 18 from an oil tank 19 and a main line 37, in which main line 37 the main solenoid valve 41 for connecting and disconnecting the distributor block 54 is arranged. The pressure in the main line 37, or the manifold block 54 can be checked via a pressure gauge 55. The manifold block 54 is also connected to two pressure switches, namely a maximum pressure switch 56 and a minimum pressure switch 57. This ensures that the pressure in the manifold block 54 will be sufficient for those required for firing.

From the distributor block 54, a pressure line 59 controlled via a solenoid valve 58 leads to a distributor block 60, from which the oil lines 16 leading to the oil atomizing nozzles 12 branch off. Thus, the main or envelope flame is switched on or off via the solenoid valve 58. In the nozzles 12 also hydraulically actuated spring-loaded shut-off valves are arranged, open only under appropriate overpressure of the supplied fuel oil.

From the manifold block 54, two additional pressure lines 61 and 62 lead to the oil atomizing nozzles 23 and 24 to form a two-stage core flame. The first stage is controlled via a solenoid valve 63 in the oil line 61, while the second stage via a solenoid valve 64 in the oil line 62 is switchable. The function of this hydraulic plan shown in Fig. 6 is explained in the rest with the description of FIG.

All in the description, the following claims and the drawings illustrated features may be essential to the invention both individually and in any combination.

LIST OF REFERENCE NUMBERS

1 gas burner

2 cross-sectional plane

3 gas nozzles

4 envelope (outer flame)

5 gas nozzle

6 nuclear flame

7 gas line

8 gas valve

9 gas line

10 gas valve

11 oil burners

12 oil atomizing nozzle

13 envelope flame

14 central nozzle

15 nuclear flame

16 oil pipes

17 solenoid valve

18 oil pump

19 oil tank

20 oil line

21 control valve

22 nuclear flame

23 Oil atomizer nozzle

24 oil atomizer nozzle

25 combination burners

26 nuclear flame

27 Oil atomizer nozzle

28 envelope Gas nozzles Oil atomizing nozzles Lances Gas supply pipes Gas distribution pipe Gas supply pipe Lance Zone with internal recirculation Main line Pressure gauge Oil pressure switch Maximum pressure Oil pressure switch Main solenoid valve Suction line Return line Oil flow regulator Return line Actuator Pressure gauge Return line Oil volume control Actuator Oil pressure gauge Pressure switch Solenoid valves Manifold Pressure gauge Maximum pressure switch Minimum pressure switch Solenoid valve Pressure line Manifold block Oil line Oil line Solenoid valve Solenoid valve Hydraulic needle shut-off valve Normally open solenoid valve Safety return

Claims

claims

1. A method for burning liquid and / or gaseous fuels while supplying combustion air and with or without recirculated exhaust gas,

- With at least one with respect to a flame chamber (flame tube) largely centrally arranged, via a central fuel nozzle (5, 14, 23, 24) (gas or oil) and one of these fuel nozzle associated air mixing device of the combustion air supply formed core flame (6, 15, 22, 26),

with an envelope flame (4, 13, 28) formed around this core flame at a distance via a plurality of external fuel nozzles (3, 12, 29, 30) (gas or oil) and an air mixing device of the combustion air supply assigned to these nozzles

with control of the fuel supply to the nozzles, characterized

during combustion operation, the fuel and / or combustion air supply to the core flame or to the envelope flame can be changed independently of one another,

- That by such a change, the size ratio of the flames is mutually changeable and

- That thereby at least the nuclear flame can be modeled by variable design.

2. The method according to claim 1, characterized in that the change of the fuel supply at least to the core flame (22) takes place in stages, so that the core flame can be modeled in stages (Figures 3 and 6).

3. The method according to claim 1, characterized in that the change of the fuel supply to the core flame (6, 15) (Fig. 1, 2, 4 and 5) continuously (continuously), so that the core flame is continuously modeled.

4. The method according to any one of the preceding claims, characterized in that via the fuel supply to the core flame in proportion to that of the envelope flame, a central recirculation of exhaust gas can be achieved.

5. The method according to any one of the preceding claims, characterized in that in the recirculation of the core flame cooling in the range of the flame root can be achieved.

6. The method according to any one of the preceding claims, characterized in that the control of the fuel supply to the core flame is independent of that to the envelope flame.

7. The method according to claim 6, characterized in that the envelope flame is adjustable to a continuous power, however, on the other hand, the fuel supply to the core flame during operation is changed in opposite directions.

8. The method according to any one of the preceding claims, characterized that the recirculation of the nuclear flame is effected on its exhaust side due to the size ratio of envelope flame to core flame.

9. The method according to any one of claims 2 to 8, characterized in that the core flame is formed by means of at least two independently supplied with a fuel or different fuels nozzles (Fig. 3 and 6).

10. Blower burner (1, 11, 25) for liquid and / or gaseous fuels, for use on a flame chamber having a boiler and / or serving for fuel air mixture and flame forming flame tube, with a plurality of to form a Hüllflamme (4, 13, 28) , further out in the flame tube and preferably circularly arranged fuel nozzles (outer nozzles)

(3, 12, 29, 30) (oil or gas), with at least one fuel line (7, 16, 31, 32) to the outer nozzles, with at least one within the arrangement of

Outer nozzles for forming a core flame (6, 15, 22,

26) arranged largely centrally

Central fuel nozzle (5, 14, 23, 24) (central nozzle) (oil or gas), with one leading from the outer nozzles

Fuel line (7, 16, 31, 32) independent

Fuel line (9, 20, 35, 61, 62) to the central nozzle and with independent control devices (valves 8, 10, 17, 21, 41, 53, 63, 64, 66) in the fuel line leading to the central nozzle and the outer nozzles, in particular for carrying out the method according to one of claims 1 to 9, characterized in that serve as control devices valves, which are in particular electrically (magnetically) and / or hydraulically actuated according to a predetermined program.

11. fan burner according to claim 10, characterized in that as a central nozzle Ölzerstäuberdüse (14, 27) and that via an oil pump (18) under pressure (39, 40) subsidized fuel oil via a solenoid valve or control valve (21) and is deductible.

12. Blower burner according to claim 11, characterized in that in the fuel line downstream of the oil pump (18) an oil quantity regulator (44) is arranged.

13. fan burner according to claim 12, characterized in that the oil quantity regulator (44) in a return (45) of the oil pump (18) downstream of the branch to the central nozzle (14) is arranged.

14. Blower burner according to one of claims 10 to 13, characterized in that oil atomizing nozzles (12, 30) and / or gas nozzles (3, 29) are provided for forming the envelope flame (4, 13, 28).

15. Blower burner according to claim 14, characterized in that in the fuel lines to the gas nozzles for controlling the fuel supply at least one solenoid valve is arranged.

16. fan burner according to one of claims 10 to 15, characterized in that two central nozzles are provided with independent fuel lines to form a gradable core flame and that one of these central nozzles via a valve disposed in the fuel line valve is controllable.