Patent Application
20170254533
The present invention relates to an innovative type of atmospheric gas burner for cooking tops, in particular household cooking tops, capable of producing an air-gas mixing with a stoichiometric titre or with a slight excess of air; a burner thus capable of producing fully premixed flames and possibly with excess of air.
By atmospheric burner it is meant a burner where the air-gas mixture is obtained by the effect of the gas supply pressure using the principle of the tube ejector of Venturi and without the aid of fans.
The ejectors (v.
In the tube ejector of Venturi (hereinafter simply “ejector”), the pressure energy of a motor fluid available at a nozzle located at the inlet of a Venturi tube with nozzle flow rate Q, and nozzle pressure Pm, is transformed into kinetic energy; the high-velocity jet coming out from the nozzle induces and drags an induced fluid flow at a lower pressure Pi which flows in at a flow rate regime Qi; both flows are conveyed within a pipe having section Athr (which is the Venturi groove) where they mix and recover part of the pressure; then the mixing continues in a diverging section (which is the Venturi diffuser) where additional kinetic energy is recovered in static pressure.
In this case, the pressure of the secondary Pi is the atmospheric pressure pa, the motor fluid with flow rate Qm is a fuel gas with flow rate Qgas and pressure pgas and the induced fluid with flow rate Qi is the combustion air with flow rate Qa and pressure pa; because of the very modest pressure variations that the gases are subject to while crossing the Venturi, they can be considered in incompressible regime.
The ideal length of the Venturi groove is comprised between 7 and 10 times its diameter D; the diffuser has a weak opening to recover pressure avoiding the stall (typically 2-3° half-open).
At the outlet of the diffuser, fuel gas and combustion air are, substantially fully mixed, with a flow rate of the mixture Qmix=Qgas+Qa and a pressure pmix.
Said stoichiometric mixture is an air-gas mixture where the air and gas masses are in a mixture ratio (mixture titre) equal to the exact stoichiometric ratio STC for a complete combustion of the gas without residual oxygen. A mixture rich in gas, that is to say with a mixture ratio<STC, i.e. with lack of air, is herein referred to as “rich” mixture. A mixture poor in gas, that is to say with a mixture ratio>STC, i.e. with excess of air, is herein referred to as “lean” mixture. For a complete combustion, in practice, a mixture with a slight excess of air in required compared to the STC ratio theoretically sufficient. Hereinafter, however, by “stoichiometric” titre mixture or “STC mixture” it is meant a mixture with the that minimum slight excess of air necessary to ensure the complete combustion.
Ejector efficiency ηej is herein defined as the ratio between the kinetic energy in the time unit of the mixture at the outlet of the diffuser, which is Emix=(Pmix−Pi)×Qmix, and the kinetic energy at the nozzle, which is Egas=(pgas−Pi)×Qgas.
That is, ηej=Emix/Egas=[(Pmix−Pi)×Qmix]/[pgas−Pi)×Qgas].
The geometry of Venturi is a determining element for the efficiency ηej of the ejector.
The greater is the efficiency ηej of the ejector the greater is the combustion air flow rate Qa that may be induced and if this was sufficient to obtain mixtures with a slight excess of air, the ejector burner would be independent from any supply of additional air.
This is possible in principle, if there are no dimensions limits, by accurately sizing, depending on the thermal power required, the diameter D and the length L20 of the Venturi groove and the length L30 and the angle of divergence B2 of the diffuser.
However, for burners for cooking tops, in particular household cooking tops, which provide for nominal powers of the various gas cookers (typically in number 4, 5 or 6) from 600÷800 W to 3 kW to arrive at 5 kW in the case of “special burners”, the geometrical and dimensional constraints of the cooking top and the operating parameters of the burners are absolutely incompatible with the ideal construction criteria for the ejectors with consequent dramatic drop of the efficiency to very few percentage points because the induced combustion air, called “primary air”, is not sufficient to obtain mixtures with STC titre that allow the complete combustion. The resulting drawbacks shall now be highlighted.
The most widespread, universally accepted and most traditional technical solution for making a gas burner of a cooking top 400, is that with the “vertical Venturi” (see
In this configuration, which can be considered the standard one, and henceforth designated as STD, the ejector is particularly inefficient mainly because of the leaks in the diffuser 115, which is radial, and the reduced longitudinal extension of the Venturi that is well far from the ideal shape and substantially coincides with the groove 114. ηej values in the range of 1% are frequent.
In substance, inside the ejector that draws primary air AIR11 a mixture too rich in fuel is obtained but still within the flammability range of the gas. The rich mixture exiting vertically from the groove 114, is conveyed through the radial diffuser 115 to the “slots” 117. From there the mixture exits with a titre that already allows the partial combustion and feeds the flames FLAME1; these recall by floating (that is, by natural circulation due to the difference in density) additional AIR21, called “secondary” essential for the completion of the chemical reaction of combustion.
The need for supply of secondary air in fact limits the power density of the flame which can only be composed of a discontinuous crown of flames or there would be lack of oxygen to the inner surface of the same crown. By excessively thickening the slots 117, the flames would not develop enough surface for interacting with the secondary air, resulting in excessive production of carbon monoxide (CO), or better of an unacceptably high value of the ratio [CO]/[CO2] in the fumes.
The slots 117 are essentially few tens of radial channels made with radial incisions on the body of the “flame spreader” 116 (or holes) and closed at the top by the “cap” 118 (an actual cover); thus the base of the flames has a centrifugal radial development as, moving away from the perimeter of the burner, the various “bulbs” of the crown of flames FLAME1 deviate upward in the direction of the bottom of the pot 404 due to floatation.
With the same nominal power, this type of STD architecture involves at least the dimensional drawbacks that is desirable to eliminate or at least mitigate.
In conclusion, with the STD configuration the vertical spaces are considerable and not only due to the component elements of the burner but also to the inevitable empty spaces that must be left around.
As for the modulation ratio Y obtainable from a STD burner, intended as the ratio between the maximum and minimum power that can be delivered with regular combustion, it depends on many factors, but first of all on the admissible range of speed of the mixture exiting from the slots 117. In fact, this must be comprised between a minimum speed Vmin below which there is backfire and a maximum speed Vmax above which there is the lift-off thereof.
According to rules well known to the men skilled in the art, Vmin and Vmax depend on the flame front speed Vf which in turn depends, among other things, also on the titre of the mixture which, in turn, as seen, is affected by the geometry of the burner. In conclusion, since the flame stability Vf is indirectly determined by the gas flow rate Qgas and the configuration of the burner, the modulation ratio Y achievable is strongly influenced by such factors
Typically, for the STD configuration Y is comprised between 3.5 and 4.5.
For higher modulation ratios Y, “special” burners are used provided with more than one ejector that separately supplies more than one crown of concentric flames; these burners, which have special geometrical features in order to cause secondary air to flow also to the innermost crowns of flame, are in fact multiple burners although often provided with a single special regulation valve that can turn on and modulate them in sequence.
Burners with horizontal or “linear” Venturi configuration, herein referred to as “LIN” (see
This configuration carries a Venturi with a completely linear development (Venturi groove 214 and diffuser 215 in axis) arranged horizontally parallel to the covering top (it should be noted that in the STD burner the diffuser 115 is instead radial). The linear diffuser 215 leads to a further mixing chamber 213 that occupies all the internal volume of the burner within which the mixing of primary air AIR12 with the fuel gas continues and completes.
This solution allows to obtain mixtures still rich compared to the stoichiometric titre, that is, with lack of air, but significantly leaner than those obtainable with the STD solution. Accordingly, also in this case the supply of secondary air AIR22 is necessary, but in a smaller amount compared to the secondary air AIR21 of the STD case. With the same nominal power of the burner, and thus of the diameter of the injector nozzle, therefore, AIR22<AIR21.
The slots 217 are made with over a hundred of small holes formed directly on the cap 218 with direction inclined towards the vertical of the pot. Shorter flames FLAME2, almost vertical, with an increased power density and a crown that is circumferentially continuous and radially less extended than the STD case may be obtained. In substance, the thermal exchange towards the pot improves, the contact times of the fumes with the surface of the same pot increase and it is possible to reduce the distance H02 between the base of the flames FLAME2 and the bottom of the pot 404.
All of these considerations result in a higher efficiency ηb of the burner.
As a confirmation of the absence of gas cookers with fully premix atmospheric burners, it is noted that the few examples of products with active supply of combustion air (referred to as “ventilated cooking tops”) are in fact limited to means for supplying only the secondary air in order to complete what remains a partially premixed combustion. The market is made from gas burners with partially premixed burners; no one has claimed the fully premixed ones so far.
Comparing directly the STD solution with the LIN solution,
Despite such strong adaptations, the maximum value of the modulation ratio for the LINs remains limited to Y≈3. This is due to the concurrence of two factors, both related to the combustion dynamics: the fact that the titre of the mixture obtained in the Venturi is closer to the STC titre, involves a greater flame speed Vf with greater risk of backfire; at the same time, simplifying, because the flames FLAME2 are shorter, for the fact that the combustion completes more quickly as it needs lower supply of secondary air, they are also more unstable and lift-off more easily than in the STD burner.
In a STD burner, changing the type of gas requires only changing the nozzle 111 as changing the cup 113 is either impossible for space reasons or is anyway useless because it would result in modest improvements of the efficiency ηej of the ejector. In a LIN burner, instead, in order to adapt it to all types of gas the replacement of the entire burner is necessary, because both the size of the Venturi and the morphology of the slots 217 on the cap 218 must be different for different classes of gas or the flame would be unstable.
The solutions with linear Venturi LIN currently on the market present, although in a slightly reduced form compared to the STD burners, all the limitations of a non-stoichiometric mixture (too rich) because inside the household cooking top, for the power required by each burner, there is not enough space for seating an ejector of optimised size to induce primary air AIR12 up to the stoichiometric titre. In any case, in addition to space limitations, the linear extension of the divergent diffuser 215 must in any case be truncated in order to be jointed to the mixing chamber 213, which in turn must be large enough to allow a complete mixing of AIR12 with the gas, otherwise there would be unevenness and instability of the flames FLAME2.
The main object of the present invention is to provide a new concept atmospheric burner of limited thickness suitable for use for cooking tops, household ones in particular, which eliminates at least in part the drawbacks listed above.
A further object of the present invention is to obtain, through said atmospheric burner, an air-gas mixture closer to the stoichiometric titre than what is allowed to LIN burners.
A further object of at least some variants of the present invention is to obtain, through said atmospheric burner, an air-gas mixture of a stoichiometric titre or leaner, which therefore does not require the supply of secondary air above the flame.
A further object, at least of some variants of the present invention is to obtain the previous results with said atmospheric burner of reduced plan dimensions with respect to a LIN burner of equal power.
A further object, at least of some variants of the present invention, is to obtain, modulation ratios Y higher than those possible today for cooking tops.
A further object, at least of some variants of the present invention, is to obtain better efficiencies ηb of the burner than those possible with the STD and LIN burners known today.
A further object, at least of some variants of the present invention, is to reduce the distance necessary today between the base of the flames and the bottom of the overlying pot.
A further object, at least of some variants of the present invention, is to be able to make burners of different power by using also a few modular elements that are mutually modular.
A further object of at least some variants of the present invention, is to allow a better aesthetic appearance of the cooking top.
Further features and advantages of the present invention shall be better highlighted by the following description of an atmospheric burner for cooking tops in accordance with the main claims, articulated in possible variants in accordance with the dependent claims and illustrated, by way of a non-limiting example, with the aid of the annexed drawing tables, wherein:
Unless otherwise specified, any possible spatial reference in this report such as the terms vertical/horizontal or lower/upper refers to the position in which the elements are located in operating conditions while spatial terms such as previous/subsequent, upstream/downstream should be understood with reference to the direction of circulation of the flows of airforms.
In
The following are indicated of the ejector 10: the Venturi 12, the converging section (or, simply, the “convergent”) 13 of opening semiangle B1 and length L10; the groove 14 of diameter D and length L20; the diverging section 15 (also referred to as simply “divergent 15” or “diffuser 15”) of opening semiangle B2 and length L30, the nozzle 11 at a distance L00 from the inlet of the groove 14. The nozzle 11 has section An; the groove 14 has section Ath.
Theoretical investigations, confirmed by experimental tests carried out by the applicant have shown, within the technical scope of atmospheric gas burners for cooking tops, that, as the diameter d of the nozzle 11 (see
As to the measures L10 (length of the convergent 13) and B1 (opening semiangle of the convergent 13), they are of little influence but it is better to provide a convergent 13 of elliptical profile, jointed at the inlet of the groove 14. The axis of the ejector 10, then, should be substantially rectilinear, a characteristic, the latter, which can be met almost completely in the invention and until the end of a first stretch of the diffuser 15 where by first stretch of the diffuser 15 it is meant that part of the diffuser 15 consecutive to the groove 14 and by second stretch it is meant the remaining part of the same diffuser 15 that, of course, ends where the section of the conduit that forms it ceases to increase.
As for the sections orthogonal to the axis of the ejector 10, in particular the sections orthogonal to the axis of the diffuser 15, they may also be of elliptical section or, in general, not axisymmetric. Accordingly, the opening semiangle B2 varies according to the main plane containing the axis of the same diffuser 15 whereon it is measured and then by opening semiangle B2 it is meant the maximum value that can be found along and about the axis of the diffuser 15.
An ejector 10 having the geometrical features just listed and herein referred to as optimal ejector 10.
By applying such criteria, a satisfactory value of ejector efficiency ηej, i.e. sufficient to form air-gas mixtures with titre >STC is obtained.
But the total length of a Venturi ejector 10 sized with the aforementioned criteria and sufficient to generate 1000 W, whatever the type of gas, can arrive at about 240 mm, a measure almost incompatible with the spaces available horizontally for each gas cooker of a cooking top; however, an ejector so dimensioned is not able, alone to meet the maximum power required in most of the gas cookers. Ensuring then 3 kW would result in a linear footprint of over 600 mm, a measure totally incompatible with the space available. This is actually the obstacle that the LIN burners face that therefore can not ensure efficiencies ηej of the ejector equal to those achievable in principle.
According to the invention, then, burners 300 of any power Wb provided for cooking tops 400 have a quantity Z≧1 of ejectors 310 that can all make their flows of mixture flow towards a single flame spreading cap 318 where:
It shall be specified that, at least with the features of the ejectors 310 just said, it is always possible, whatever the type of gas and supply pressure among those provided for a cooking top, to obtain from each ejector 310 a power Wej sufficient to make a burner of maximum power Wb not lower than those normally in use for cooking tops currently making use of a reasonably limited number Z of ejectors 310 (e.g. Z<=6).
Such geometry, offers many advantages compared to the prior art; e.g.:
In short, with ejectors 310 of geometry as described above, the flame spreading cap 318, may receive mixture with titre≧STC because each ejector 310 is sized for a maximum power Wej which is ≦ than the maximum power that can be obtained by keeping nej to values suitable for producing mixtures with titre≧STC and/or because along the route of the mixture, the entry of said complementary air is made possible to an extent at least sufficient to reach such a titre≧STC.
Preferably each of said plurality Z of ejectors 310 is sized for said Wej comprised between 40 and 1200 Watts with, even more preferably, the corresponding dimensional relationships above.
As to the possible confluence of two or more ejectors 310 towards a single flame spreading cap 318, and, in particular, to the fact that it may provide for a continuous and uniform arrangement of slots 317 substantially uniformly arranged, this is an advantage of the invention made possible by the fact that, when its teachings are applied to produce mixtures with titre≧STC, it is not necessary to provide more crowns of flames and relative adjacent spaces for the inflow of secondary air.
Preferably said plurality of ejectors 310 (see
With ref. to
The first rectilinear stretch 322 of the diffuser 315 of each ejector 310 guides the mixture flow according to a substantially horizontal direction until it reaches the conveying chamber 313 in which said flow enters tangentially lapping the circumferential wall 319 thereof.
The consecutive curvilinear stretch 323 of said diffuser 315 is capable of inducing in the mixture flow a spiral-wise pattern towards the central axis 324 of said conveying chamber 319.
According to a first basic version that is now described (see.
According to such variant, preferably the quantity Z of ejectors 310 is an even number; in that case, always preferably, at least the pairs of ejectors 310 which are axially symmetrical are sized for the same maximum power Wej.
With reference to
On the horizontal plane, in the circumferential direction, the flow of each Venturi 312 continues to expand also in the curvilinear stretch 323 converting part of the kinetic energy into pressure, until it mixes with the subsequent flow of the Venturi 312. A horizontal vortex is created which converts the quantity of linear motion of each ejector 310 into angular momentum of the stationary vortex, extending artificially the diverging stretch of the diffusers. In this way stoichiometric mixtures are obtained that from the periphery of the conveying chamber 313 converge towards the centre in the annular channel 327 with a tangential component of speed that increases as they approach the central axis 324. The same vortex maintains a pressure gradient in the radial direction such as to create a suitable depression at the centre of the conveying chamber 313. On the vertical plane, the converging-centripetal section of the annular channel 327 further accelerates the flow enhancing the radial gradient of pressure (and the corresponding depression at the centre of the horizontal vortex). In the proximity of the central axis 324 the centripetal-axial annular channel 327 creates a vertical stream which overlaps the horizontal vortex, this way, the mixture which leads to the diffusion chamber 328 expands in it with a centrifugal motion. This results in a second stationary vortex that has a toroidal shape. The diffusion chamber 328 has a suitable shape to allow said expansion and formation of a toroidal vortex; in particular sufficient volume for expansion, diameter greater than that of the annular channel 327 and height less than the diameter.
So, according to the version of the invention just described, the burner 300 is characterised by a geometry adapted to the formation of two stationary vortices: one substantially on the lying plane of the Venturis 312 and one subsequent, toroidal.
For this reason the burner 300 according to such first variant shall be also referred to as DVB (Double Vortex Burner) burner 300.
The annular channel 327 consists of a narrow section zone equivalent to a Venturi groove, wherein the mixture increases in speed and decreases in pressure; the diffusion chamber 328 equals the diffuser of a Venturi where the mixture slows down in speed and recovers pressure. In fact, downstream of the conveying chamber 313 a sort of circumferential Venturi is created which corresponds to the rules of the Bernoulli's theorem as a classic linear Venturi.
Any burner 300 according to the invention, has ejectors 310 capable of drawing primary air AIR13 in an amount sufficient to cause the mixture with STC titre to reach the flame spreading cap 318 and therefore without the need to leave between the bottom 404 of the pot and the top of the same flame spreading cap 318 the space required for the inflow of secondary air.
However, according to one useful variant of the DVB burner 300, the diffusion chamber 328, may be advantageously put into communication with the outside environment through an axial channel 329 inside the converging annular channel 327.
In this way, induced by the depression in the annular channel 327 and by the toroidal vortex, air herein referred to as “complementary” AIR13c may be recalled within the diffusion chamber 328, if the titre of the mixture coming from the annular channel 327 had titre<STC. In other words, according to such variant of the DVB burner 300, it is possible to size the ejectors 310 with efficiencies ηej insufficient to obtain the STC titre, for example due to space reasons, whilst, however, without the need for the supply of secondary air AIR23 above the flame spreading cap 318.
In conclusion, the primary air AIR13 and GAS coming from the tangential ejectors 310 continue to interact up to a perfect mixing already inside the conveying chamber 313 where the titre of the mixture can be STC and over, meaning that it is also possible to obtain mixtures with excess of air. The mixture (STC or lean) that spreads inside the diffusion chamber 328, however, may be further leaned (enriched with air AIR13c) depending on the structure of the axial channel 329.
In short, by comparing STD, LIN and DVB burners 300 we have:
AIR11<AIR12<AIR13; AIR21>AIR22>AIR23=0
The fact that secondary air AIR23 is not required allows to reduce the space H03 between flame spreading cap 318 and bottom of the pot 404 to the minimum necessary to allow the outflow of the mixture from the same flame spreading cap 318 and the inflow of the flue gases.
An advantageous aspect of the axial channel 329 (see.
Even more advantageously such valve 330 may be one-way and with adjustable preload.
In fact, if the valve 330 is one-way, it constitutes a safety element in case of:
Thanks to the intervention of the one-way valve 330 the dispersion of flammable mixture inside the cooking top is prevented.
The proposed DVB architecture offers countless technical, logistic and aesthetic advantages compared to the solutions available on the market.
The power Wb between a LIN burner and a DVB burner 300 with Z ejectors 310 being equal, the gas passage section of the single nozzle 211 of the LIN burner, of diameter d2, is equal to the sum of gas passage sections of the Z nozzles 311 of the DVB burner 300, of diameter d3, thus d32 =d22 /Z.
Imagining that the single ejector 219 of a LIN burner has its linear dimensions Li_LIN proportional to the homologous Li_DVB of each ejector 310, we have substantially Li_DVB2≅Li_LIN2/Z with clear space reduction of the burners on the cooking top.
The further less obvious advantages of the DVB architecture, compared to STD and LIN burners of equal power Wb are at least the following:
The DVB architecture compared to STD and LIN extends the contact time between gas and the primary and complementary air AIR13+AIR13c obtaining the maximum “goodness of mixing” desired for a fully “PREMIX” combustion.
In short:
L23/D3≧L22/D2>>L21/D1
Also for the DVB burner 300 the slots 317 actually consist of arrays of holes 317 sized around a millimeter or even incisions with appropriate depth and inclination formed on the cap 318. Compared to the LIN, however, it is possible to achieve even greater power density, by further limiting the radial extension of the “bed of flames” FLAME3. It should be noted how the flames FLAME3 can be oriented in any manner (also vertical or vertical/centripetal) and arranged in any manner without having to recall AIR23.
This characteristic is of fundamental importance as it allows to:
The flames FLAME3 due to combustion of the mixture with a least a completely uniform STC titre, along with the ability to handle even an excess of air, eliminate beforehand any risk of excessive production of [CO] (hence the ratio [CO]/[CO2] remains systematically below the minimum limits imposed by the regulation).
The average horizontal size Dp of the conveying chamber of the DVB burner 300 shown so far can not be reduced beyond a certain measure (typically Dp>10×D3) or there would be a sudden drop of the efficiency ρej. In fact, most of load (and efficiency) losses are located inside the horizontal vortex in the overlapping zone between the flows of two consecutive ejectors 310, where the ejector 310 that precedes interferes with the expansion of the ejector 310 that follows strongly limiting the effect of conversion of kinetic energy into static pressure.
To overcome this limitation, or to further increase the efficiency ηej the vertical space Dp being equal, deflectors 331 may be suitably inserted (see.
Basically, the blade array 331 starts at the engagement start point 335 of each diffuser 315 on the circumferential wall 319 of the conveying chamber 313 and continues towards the central axis 324 with a substantially spiral pattern. More exactly, and in more general terms, the blade array 331 is arranged along the zone 334 where the flows of two consecutive ejectors 310 come into contact. This blade array 331 has the task of guiding the air flow exiting from the preceding ejector 310 deviating it actively in a centripetal direction. The fluid flow of mixture is accelerated (with consequent decrease of the local static pressure) towards the centre of the horizontal vortex in a significantly greater manner than the homologous conveying chamber without deflectors 331; a greater spread of the flow exiting from the ejector 310 that follows is thus achieved. In practice, the second stretch 323 of each diffuser 315 is confined on three sides by solid outer, upper and lower walls 319, 325, 326 of the conveying chamber 313 and on the fourth side by a “fluid barrier” created by the flow accelerated by the preceding deflector 310.
These blade arrays 331, by virtue of their function of flow separators, are herein globally referred to as “Splitter” while “DVB-Splitter” the variant of DVB burner 300 provided with Splitter.
The operation of a DVB burner 300 or DVB-Splitter burner 300, or in any case of a burner 300 in which more ejectors 310 lead to sectors/manifolds 338 communicating with each other, poses the problem of the back flow of flammable mixture from the conveying chamber 313 towards the inner compartment 405 of the cooking top 400, passing through the Venturis 312 not supplied, if an adjustment is used, later referred to as “progressive”, where one or more ejectors 310 are disabled when the maximum deliverable power is not required.
This drawback can be advantageously addressed through the use of suitable low load loss non-return valves 340 or 342.
Such non-return valves 340 or 342 may be one-way valves 340 arranged, for example (see
Alternatively, such non-return valves 340 or 342 may be solenoid shut off valves 342 operated by the control knob of the burner 300 when this deactivates the corresponding ejector 310.
It is in fact evident that the one-way valves 340 may be easily operated by magnetic control; the version illustrated in
Alternatively (see
All variants indicated for such non-return valves 340 or 342 are provided only by way of example in order to show that they may consist in very simple devices.
In accordance to a second basic version, herein referred to as with “Separators” (see
Such sectors 338 as well as the corresponding consecutive conduits including corresponding Z “sectors of diffusion” 328 of the said diffusion chamber 328 are completely separated from each other up to the flame spreading cap 318.
In this way, since the interferences between two adjacent sectors 338, are completely avoided, each ejector 310 may be enabled separately without any axial-symmetry restriction (any Z, even odd) and the power modulation allows broad alternative options.
Preferably, such Z sectors 338 and subsequent conduits are obtained by providing a conveying chamber 313, an annular channel 327 and a diffusion chamber 328 shaped as described for the first main variant except that all such environments are divided into Z conduits by Z vertical partitions 339.
Preferably such vertical partitions 339 have a spiral-wise plan pattern so as to avoid as much as possible sudden changes in the direction of the flows of the mixture. Preferably such spiral-wise pattern follows the lines that the flows of mixture would take if the partitions 339 were absent.
It is still possible to provide an axial channel 329 from which complementary air AIR13c is drawn, divided as well by partitions in Z parts each communicating with a corresponding sector 338 that leads to the respective sector 328 of the diffusion chamber 328.
Advantageously, although not shown in the figures, the Z sectors 328 of the diffusion chamber 328 may have, in a plan view, concentric arrangement.
Advantageously, especially in such latter execution, the flame spreading cap 318 may be composed of one or more elements 318 separate from each other and each intended to cover only one or more of the Z sectors 328 in which the diffusion chamber 328 is divided into.
With such second basic version the risk of mixture “backflows” in the cooking top 400 is annulled and the non-return valves 340 or 342 are no longer required greatly simplifying the device.
On the other hand the intensity of the horizontal vortices decreases and the fluid-dynamic efficiency of the vortices in each of the isolated sectors 328 of the diffusion chamber 328 is worsened.
In short, having indicated the efficiencies ηej and ηb of burners of the DVB_SPLITTER 300, DVB 300, 300 with partition, LIN and STD type with the suffixes SPLITTER, DVB, SETTI, LIN and STD, we can affirm that
ηej_SPLITTER>ηej_DVB>ηej
ηb_SPLITTER>ηb_DVB>ηb_SETTI>ηb_LIN>ηb_STD
The entire power range of the STD or LIN gas cookers making up a common cooking top, which is typically of 600÷800 W for the auxiliary; 1500÷2500 W for the semi-rapid; 2500÷3500 W for the rapid; 3500÷5000 W for the optional multiple crown, requires specific burners and corresponding equipment.
An advantageous opportunity of the invention, at least applicable to any variant described herein, provides, instead, the possibility of making burners 300 of the various powers required by resorting for most part to a few modular basic elements.
Such variant provides (see in particular
It is clear that, in order to use a single unchanging modular element 336 for all the powers Wb provided, said Wmin the maximum power provided for the auxiliary burner of a generic cooking top 400 of a particular model, Wmax the maximum power provided for the rapid burner or for the existing multiple crown burners, Z the maximum number of ejectors that a DVB burner 300 can receive, the sizing of the modular functional element 336 is preferred to be made for a power Wb equal to at least half of that provided for the auxiliary (Wb>=Wmin/2) and at least 1/Z times the maximum provided (Wb>=Wmax/Z).
Of course, the unchanging modular elements 336 may be shaped so as to be directly joined to each other without the need for interlayer elements 337 when Z takes the maximum value provided and/or constructively possible (which, generally can be 6).
This variant offers enormous advantages from the logistical and productive point of view: with very few components made for example of pressed sheet welded to each other or die-cast components that can be assembled together, it is possible to obtain all the codes of the list.
Although not shown in the figure, even such burner 300 with a single ejector 310 may be provided, in addition, with the suction of complementary air AIR13c from an axial socket 329 equivalent to the already described axial channel 329; at the outlet of the mixture into the diffusion chamber 328. However, the figure shows an alternative to such solution consisting of a narrow section zone 327.a substantially at the end or within the second stretch 323 of the diffuser 315 where the section narrowing is sufficient to bring the pressure of the mixture below the atmospheric pressure. Such narrow section 327.a is caused by a distributing body 347 which obstructs part of the channel for the flow of the mixture. Such distributing body 347 has passages 348 communicating with the outside through which complementary air AIR13c can reach the mixture leaning it up to a titre certainly ≧STC.
Such complementary air intake means AIR13c is not, according to the invention, specific of burners 300 with a single ejector 310 as in
As for the power modulation, a burner 300 may be regulated via a single adjusting valve that supplies all the Z injectors 310 in parallel, connected to a single manifold conduit (not shown in the figures). This type of regulation is herein referred to as “modulating parallel”.
However it is also possible to connect each ejector 310 or different groups of ejectors 310 separately to a single special valve that enables them sequentially modulating the power delivered by a first group of ejectors 310 from minimum to maximum before moving on to modulate a subsequent group, and so on. This type of regulation is herein referred to as “modulating progressive”.
This extreme power modulability, even if easily possible, may however be overabundant compared to the practical needs, as it is sufficient, as also in the electric cookers, a discreet adjustment with a sufficient number of steps.
The architecture of the burner 300 according to the invention, compared to the known burners, offers advantageously and easily such a completely new possibility of discrete power adjustment with a modulation ratio that can depend only on the number Z of ejectors 310 available. Choking does not take place by reducing the gas pressure to the injectors 310 in a continuous manner, but each of them may be solely supplied ON/OFF at maximum power (for which, then, may be optimized as to ηej) or not supplied at all.
Considering, for example a burner 300 (DVB or DVB-Splitter) with Z=6 ejectors 310 the discrete adjustment levels available are OFF, 33% (two ejectors out of 6), 50% (three out of 6), 66% (four out of six) and 100% (six out of six) by simply enabling the ejectors in a suitable sequence.
The modulation ratio Y thus obtained is 100/33≈3 as well as already for the LIN burners. However, thanks to this unique feature of modulating the power through the ON/OFF activation of the single ejectors 310, the DVB burners 300 ensure efficiencies ηb and optimal and constant combustion ratios [CO]/[CO2] throughout the regulation of the burner; this by employing simple shut-off valves, far more simple, economical, reliable and compact than the special valves and common adjusting valves. This type of regulation is herein referred to as “discrete progressive”
It has been experimentally noted that the burners 300 of the first basic DVB or DVB-Splitter version 300 maintain acceptable functional features also disabling one or more ejectors 310, provided that the consequent operation configurations of the horizontal vortex are balanced (axial-symmetrical or substantially axial-symmetrical). In other words, the active ejectors 310 must be in an axial-symmetrical or substantially axial-symmetrical position, or there would be a considerable decay of the efficiency ηej due to the eccentricity of the consequent horizontal vortex.
On the other hand such need for a substantial axial-symmetry does not exist for “partition” burners 300 according to the second basic version, with broad freedom of modulation that may provide, then, also the activation of a single ejector 310 at a time.
It is clear that the three different regulation modes described, “modulating parallel”, “modulating progressive” and “discrete progressive” may, in turn, be combined together in multiple variants or be simultaneously present in the same cooking top 400 but on different burners 300.
However, the fact that the titre of the mixture obtained in the burners 400 according to the invention may be ≧STC, would accentuate the problems of instability of the flames already described when talking about the LIN burner if flame spreading caps 318 according to the technologies known from the same LIN burners were used.
However, it is possible (see
Therefore a slot 317 of increasing section ensures flame stability if
In fact, if the flame tends to stall due to excessive speed of the mixture or type of mixture, it moves towards an outermost part of the slot 117 where the speed of the mixture reduces; vice versa, in the event of a tendency to backfire, this moves towards the innermost part of the slot where the speed of the mixture exceeds the flame speed Vf.
If the chosen modulation ratio Y is very high, it may be necessary to provide slots 117 and thus flame spreading caps 318 specific for various gas families but this may be the only adaptation required by a burner 300 according to the invention.
With such diverging slots 317, the flame F is often nested within them which causes high heating of the flame spreading cap 318. Consequently, it must be of material resistant to combustion temperatures, for example steel alloy so called refractory such as AISI 321 or 309 or 910 alloys or, preferably, ceramic.
It is not necessary to dwell on such flame spreading caps with diverging slots because per se known and used, for example, in certain types of gas heaters or radiant panels.
With one or more of the devices provided for by the described variants relating to the regulation, a DVB burner 300 may, in principle, be modulated at least from the power Wmin currently provided for the auxiliary burners to the maximum power Wmax of the current multiple crown burners.
As to the adjustment of a DVB burner 300 to different types of gas, while a LIN burner, as already said, must be completely replaced, including the flame spreading cap 218, a DVB burner 300 allows the use of a single type of ejector 310 and corresponding Venturi 312 for both methane and LPG and, above all, in general, the use of the same flame spreading cap 318 having the same slots 317, thanks to the possibility to exclude/include the ejectors 310 as desired. For example, a DVB or DVB/Splitter burner 300 with a number of ejectors 310 Z=4 would use all of them when supplied with methane while, to configure the LPG supply it would suffice to permanently exclude 2 opposite ejectors 310 and, optionally, to act on the preload of the one-way valve 330 of the axial channel 329.
Once the various features on which the burner 300 with multiple ejectors 310 is based have been clarified it is clear that many variants, also exemplary, are possible without departing from the scope of the invention.
Finally, it is clear that a burner 300 according to the invention achieves all the stated objects in addition to ensuring further multiple advantages.
| Number | Date | Country | Kind |
|---|---|---|---|
| AN2014A000130 | Aug 2014 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2015/001466 | 8/21/2015 | WO | 00 |
