1. Field of the Invention
The present invention relates to a combustion apparatus, and more particularly relates to a combustion apparatus adapted for use with a hot-water supply system, a boiler or the like.
2. Related Art
The xe2x80x9cthick and thin fuel combustionxe2x80x9d method known in the art is designed to burn a fuel gas in its thin state. At least one main flame formed by burning a thin gas and at least one auxiliary flame formed by burning a thick gas will be jetted in juxtaposition to each other in this prior art system. In detail, such a thin gas for forming the main flame is composed a volume of the gas premixed with an amount of air whose volume is about 1.6 times as much as the theoretical amount of air for said gas. A thick gas for forming the auxiliary flame contains a lesser amount of air.
In the thick and thin fuel combustion method, the fuel gas is burned with such an excess of air so that flame temperature is kept relatively lower to produce a less amount of nitrogen oxides. Thus, some types of current house-held water heater are constructed using such burners of the thick and thin fuel combustion system.
Examples of thick and thin fuel combustion apparatuses widely used heretofore are disclosed in the Japanese Patent Laying-Open Gazettes No. 10-238719 and No. 10-47614.
In the apparatus shown in the Gazette No. 10-238719, two fuel-air mixtures of different concentrations are prepared outside a burner body and fed thereto through respective burner ports. This system requires an external gas concentration regulator, which will render the apparatus more complicated in structure. One of the gas-air mixtures will be jetted at a very low rate through one of the burner ports whose opening area is so small that it is difficult to manufacture the apparatus and to precisely regulate the rate of jetted fuel-air mixtures.
In another thick and thin fuel combustion apparatus shown in the Gazette No. 10-47614, air is mixed internally thereof with a fuel gas fed through a fuel nozzle. This apparatus that does not need any external regulator for controlling the concentration of fuel-air mixture will be made simpler in structure.
However, these prior art combustion apparatuses have their principal parts manufactured each by combining metal plates one with another, which have been pressed or otherwise processed to have corrugations or the like. The pressing of metal plates can not ensure a satisfactory preciseness in dimension of said parts, often failing to provide an airtight mutual consolidation of their lateral sides. Consequently, a considerable quantity of gas mixture flowing in between two metal plates is likely to leak sideways through crevices present between the metal plates forming a fuel feed passage. In such an event, concentration and jet rate of fuel gas would suffer from fluctuation, resulting in an unstable combustion thereof.
An object of the present invention is therefore to provide an improved combustion apparatus that will stabilize combustion of a fuel gas.
In order to achieve this object, the present invention has made the following improvements.
From a first aspect, the present invention provides a combustion apparatus that comprises at least one main burner port for jetting and burning a thin fuel gas mixture, and at least one auxiliary burner port for jetting and burning a thick fuel gas mixture. This apparatus further comprises an air intake for introduction of air or the thin gas mixture, and a fuel intake for introduction of air and the thick gas mixture, in addition to a thin gas passage and a thick gas passage. The air intake communicates with the thin gas passage for supplying the main burner port with the gas, and the fuel intake communicates with the thick gas passage for supplying the auxiliary burner port with the gas. Characteristically in the apparatus of the invention, the thick gas passage surrounds in part a portion of the thin gas passage, and the portion of this passage has at least one supplementary gas openings formed therein. A controlled amount of the thick gas mixture flowing through the thick gas passage will enter the thin gas passage through the said supplementary gas ope nings.
The main burner port cooperates with the auxiliary burner port that jets high-concentration gas rather than the gas jetted from the main burner port. Thus, there will be established a condition for thick and thin fuel combustion such that a flame formed out of the main flame is stabilized by another flame formed out of the auxiliary burner port.
As noted above, the thick gas passage in the present invention surrounds a portion of the thin gas passage, and the portion of this passage has the supplementary gas opening formed therein. By virtue of this structure, a controlled amount of the thick gas mixture will enter the thin gas passage through which a highly thin gas mixture, or almost the air itself, is flowing. The fraction of fuel gas mixture will be stirred within the thin gas mixture or air so as to spread uniformly through-out it, spontaneously, smoothly and instantly when it flows into the thin gas passage. Thus, the gas mixture being jetted out from the main burner port will be homogenized in concentration of gas, thereby stabilizing the main flame. Incomplete combustion can now be almost avoided when starting operation of this apparatus, thus diminishing the amount of ecologically harmful exhaust gas.
From a further aspect, and also in order to achieve the object mentioned above, the present invention provides a combustion apparatus that comprises at least one main burner port for jetting and burning a thin fuel gas mixture, and at least one auxiliary burner port for jetting and burning a thick fuel gas mixture. This apparatus further comprises an air intake for introduction of air or the thin gas mixture, and a fuel intake for introduction of air and the thick gas mixture, in addition to a thin gas passage and a thick gas passage. The thin gas passage for supplying the main burner port with the gas communicates the air intake with the main burner port, and the thick gas passage for supplying the auxiliary burner port with the gas communicates the fuel intake with the auxiliary burner port. Characteristically in the apparatus of the invention, it comprises a blending station for intermixing the air with the thick gas mixture delivered from the fuel intake. Further, the thick gas passage has an enlarged or expanded section and a constricted section, with the former section directly continuing to the auxiliary burner port so as to supply it with the thick gas mixture. The constricted section of the thick gas passage intervenes between the blending station and the enlarged or expanded section. Thus, a part of the gaseous fuel flows from the blending station into the thin gas passage in order to form the thin gas mixture blown out through the main burner port. The remainder of the gaseous fuel will pass through the blending station and advance through the constricted section so as to remain as the thick gas mixture until blown out of auxiliary burner port.
Also in this apparatus provided herein from the further aspect, the main burner port cooperates with the auxiliary burner port that jets the fuel-air mixture richer in the fuel than the gas jetted from the main burner port. Thus, here is also established a condition for thick and thin fuel combustion such that a flame formed out of the main flame is stabilized by another flame formed out of the auxiliary burner port.
The thin and thick gas passages formed in the apparatus will feed respective gas mixtures to the respective burner ports. The gaseous fuel having entered the apparatus through the fuel intake is then mixed with the air within the blending station, before diverged into the thin and thick gas passages.
The remainder of air-fuel mixture will be agitated well when it passes through the constricted section of a reduced cross-sectional area, before advancing into the enlarged section of the thick gas passage. The gas mixture being blown from the auxiliary burner port will thus be of a homogenized concentration of gas and consequently generate a stable flame so long as the apparatus operates.
From a still further aspect, the present invention provides a combustion apparatus that comprises at least one main burner port for jetting and burning a thin fuel gas mixture, and at least one auxiliary burner port for jetting and burning a thick fuel gas mixture. This apparatus further comprises an air intake for introduction of air or the thin gas mixture, and a fuel intake for introduction of air and the thick gas mixture, in addition to a thin gas passage and a thick gas passage. The thin gas passage for supplying the main burner port with the gas communicates the air intake with the main burner port, and the thick gas passage for supplying the auxiliary burner port with the gas communicates the fuel intake with the auxiliary burner port. Characteristically, this apparatus comprises a blending station such that its cross-sectional flow area gradually decreases towards a downstream end of said station in order to intermix the air with the thick gas mixture delivered from the fuel intake. Further, the apparatus comprises a branching station constructed such that a part of the thick gas mixture will flow from this station through at least one supplementary gas opening and then into the thin gas passage in order to form the thin gas mixture to be blown out through the main burner port. The remainder of the gaseous fuel will pass through the blending station and advance through the constricted section so as to remain as the thick gas mixture until blown out of auxiliary burner port.
It is to be noted here that in some of the prior art apparatuses air will be blended with a gaseous fuel that is introduced into the apparatus through a fuel inlet or nozzle. The stream of such a fuel gas will cause a spontaneous but insufficient mixing thereof with air. There is a possibility that an uneven mixing of fuel with air will result from any error or disorder in location and/or angle of the fuel inlet.
The blending station in the present invention gradually decreases its cross-sectional area from the fuel intake until reaching the downstream end of the blending section. By virtue of this structure of said blending section, the flow speed of the mixture of a fresh air and a gaseous fuel will gradually increase to thereby bring about a uniform blending of them, so that the mixture flowing out of the downstream end continuously produces a stable flame.
Even if the fuel nozzle or inlet would be somewhat offset relative to the fuel intake, whether in four directions or in an angular direction, the fresh air will surely be intermixed homogeneously with the gaseous fuel within the apparatus of the invention. The thick gas mixture composed of the gaseous fuel and the fresh air well intermixed therewith is diverged into the thick and thin gas passages, so that the ratio in gas concentration of the thick gas mixture to the thin one is kept stable. Thus, the main and auxiliary flames will never fluctuate nor vary in the course of time as to their combustion state.
It may be possible to incorporate into the blending station a proper means for accelerating the mixing of fuel and air. The accelerating means may be of any desired shape insofar as it can stir the fuel in the air while the mixture thereof is flowing to the downstream end. Either a portion of the constituent part of the blending station, or a discrete member, may be employed as such an accelerating means.
In typical examples of the apparatuses summarized above, a central row of the main burner ports is sandwiched between two side rows of the auxiliary burner ports so that main flames will be kept stable. However, since the amount of the gas jetted from two side rows of auxiliary burner ports become uneven, there is a possibility that two side rows of auxiliary flames become somewhat unbalanced.
The branching station included in the apparatus just summarized above may be intended to play a very important role to avoid such an unbalance. The branching station disposed at a middle region of the constricted section will serve to divide the fuel gas mixture, in a well-balanced manner, into two branches of thick gas passage. One of these branches extends along one side of the thin gas passage, with the other branch extending along the other side of said thin gas passage. Thus, a part of the fuel gas mixture leaving the blending station will flow into the thin gas passage so as to form a thin gas mixture to be jetted from the main burner ports. On the other hand, the remainder of said fuel gas mixture also leaving the blending section will rush into the constricted section, before being diverged into two streams respectively flowing through two branches of thick gas passage, wherein these branches are disposed each beside the central thin gas passage. Thus, the two streams of thick gas mixture will be jetted in harmony from the respective rows of auxiliary burner ports.
In more detail, metal plates may be pressed each to be of a predetermined shape before overlaid one on another to form the passages and the like mentioned above. The predetermined shape will include grooves and ribs, and dimensional accuracy thereof being much higher at their middle regions than at their end regions. Thus, the constricted section formed intermediate between opposite ends of each gas passage will be made most precise in dimension.
By virtue of this feature, the branching station disposed at a middle region of the constricted section can divide the gas mixture flow into two branch streams almost of the same flow rate, whereby a good balance will be ensured between the auxiliary flames.
Each combustion apparatus summarized above may be constructed using four generally parallel walls, that is two central or inner walls and two outer walls sandwiching them. In this case, the two inner walls will define between them the thin gas passage leading to the main burner ports. On the other hand, one of the inner walls and one of the outer walls will define one of branches of the thick gas passage leading to the auxiliary burner ports. Similarly, the other inner wall facing the other outer wall will define between them the other branch also leading to the other auxiliary burner ports.
Such a structural principle will not only simplify the structure and manufacture of combustion apparatus, but also render it smaller in size.
Characteristically, the blending station may be formed by reducing the cross-sectional area of thick gas passage, gradually towards its downstream end from the fuel intake.
In other words, the blending station in the present invention may be tapered off towards its downstream end. Thus, the flow speed of the mixture of a fresh air and a gaseous fuel will gradually increase to facilitate the blending of them, so that a uniform mixture flowing out of the downstream end maintains a constant concentration.
Even if the fuel nozzle or inlet would be somewhat offset relative to the fuel intake, whether in four directions or in an angular direction, the fresh air will surely be intermixed homogeneously with the gaseous fuel within the apparatus of the invention. The thick gas mixture composed of the gaseous fuel and the fresh air well intermixed therewith is diverged into the thick and thin gas passages. Ratio in gas concentration of the thick gas mixture to the thin one is now kept stable, so that the main and auxiliary flames will never fluctuate nor vary in the course of time as to their combustion state.
A plurality of the described combustion apparatuses may be combined one with another to form a cluster or group of them. Also in this case, any error in positional and/or angular arrangement of each fuel gas feed nozzle will not cause any instability in concentration of the thick and thin gas mixtures. Any uneven combustion will not take place in the group of said apparatuses as a whole.
It may be possible to add to the blending station a proper means for accelerating the mixing of fuel and air. The accelerating means may be of any desired shape insofar as it can stir the fuel in the air while the mixture thereof is flowing to the downstream end. Either a portion of the constituent part of the blending station, or a discrete member, may be employed as such an accelerating means.
Alternatively, the blending station may characteristically be formed by at first reducing the cross-sectional area of thick gas passage gradually a given distance from the fuel intake, and by increasing again said cross-sectional area downstreamly of the given distance and towards the distal end of said gas passage.
Due to such a tapered-off-and-clavate shape of the blending station, the mixture of fuel gas taken in together with fresh air through the fuel intake will be accelerated in the taper-off region to be blended uniformly while lowering its pressure. This mixture will then be decelerated in the clavate region to restore its pressure before diverged into the thick and thin gas passages.
Also characteristically, the branching station for directing the part of thick gas mixture to the thin gas passage may be disposed downstreamly of a neck where the blending station has a minimum cross-sectional area.
Due to such a position of the branching station in and relative to the blending station, a well-mixed and homogeneous gas mixture will be delivered from the latter station to the former station.
This feature will stabilize the concentration ratio of the gas mixture flowing through the thick gas passage to the other gas mixture flowing through the thin gas passage, thus avoiding any unstable combustion of the main and auxiliary flames.
It may be possible to incorporate into such a tapered-off blending station a proper means for accelerating the mixing of fuel and air, for the sake of facilitating the mixing of the gaseous fuel with the fresh air, both being sucked in through the fuel intake.
Well-mixed gas mixtures thus produced owing to such a mixing-acceleration means will be supplied to both the thick and thin gas passages, thereby avoiding uneven combustion that would otherwise be caused by any uneven and insufficient mixing of the fuel gas with the fresh air.
The accelerating means may be of any desired shape insofar as it can stir the fuel in the air while the mixture thereof is flowing to the downstream end. Either portions of some constituent parts of the blending station, or discrete members, may be employed as such an accelerating means.
For example, either bent or curved zones or constricted sections may be formed in the thick and/or thin gas passages in order to assist the components of each gas mixture to intermix with each other quicker and thoroughly. However, air or gaseous fuel will produce noise or a whistling sound when they run past those bent zones or constricted sections.
The present inventors have tested a variety of countermeasures for preventing such a noise or sound, and found that certain convex or concave portions formed in the wall of each gas passage would be highly effective. In addition, such convex or concave portions have proved useful to make more uniform in pressure and more homogeneous in composition each successive mass of the gas mixture flowing by them.
Therefore, the combustion apparatus provided herein may be designed such that the inner wall surface of each thin and/or thick gas passages has partially or wholly certain convex or concave portions.
Preferably, these convex or concave portions are formed in the passage wall disposed adjacent to a deflecting or bent area. The air and fuel gas will flow smoothly along such a wall while generating minute or small vortices, but diminishing large vortices that would cause the noise or whistling sound. Each flow of the thick or thin gas mixture will not suffer from any uneven mixing but be rendered uniform in pressure, while forming a substantially laminar flow directed to the respective downstream regions.
According to experiments which the present inventors have conducted, the most effective anti-noise shapes of those convex or concave portions are round columns, hemispheres, triangular columns, cones, triangular pyramids, burred portions or the like that are easy to form.
Characteristically, the thick gas passage may comprise an enlarged or expanded section communicating with the auxiliary burner ports, as well as a constricted section opened towards the enlarged section so as to feed thereto the thick gas mixture.
The thick gas mixture will be agitated well when it passes through the constricted section of a reduced cross-sectional area, before advancing into the enlarged section of the thick gas passage. The gas mixture being blown from the auxiliary burner ports will thus be of a homogenized concentration of gas and consequently generate stable flames so long as the apparatus operates.
In detail, the enlarged or expanded section may be spread in a plane and have an end opened outwards, so as to comprise an elongated region having a cross section extending in parallel with another plane that includes the open ends of burner ports, as well as a constricted section. An opening of the constricted section communicates with the interior of the enlarged section, and is offset from the center of an imaginary line along which the enlarged section extends. However, the opening of said constricted section, and/or the direction of jetting the thick gas mixture therefrom, may face the center of said imaginary line.
Although the constricted section""s opening is positioned offset relative to the center of the enlarged section, the thick gas mixture jetted from such an opening will not be delivered superfluously to any limited region of said enlarged section. Because the direction of said opening and/or the jetting direction face the center of enlarged section, the gas mixture will rush in this direction to spread uniform throughout the enlarged section. All portions of each auxiliary burner port will thus receive portions or tributaries of the gas mixture flow at the same rate and with a reduced time lag between them, before respectively jetting and burning it. All the gas flow tributaries will be ignited readily in unison to form stable unit flames so as to provide an auxiliary flame all over the full length of each auxiliary burner port, thereby improving inflammability of fuel gas mixture as a whole to be simultaneously burnt at the auxiliary burner ports and stability of main flames assisted with auxiliary flames. The quantity of raw gas not burnt but wasted when igniting this combustion apparatus to start its operation will now be reduced to a noticeable degree.
Ignition can be done at any region of the elongated auxiliary burner port. If the gas mixture tributary effluent from the innermost region most remote from the air intake is ignited at first, then a unit flame thus produced is not likely to be fanned by the fresh air stream flowing in from the air intake. In this case, ignition of, flame propagation within and extinguishing of this combustion apparatus will be effected smoothly, thereby reducing waste of raw gas. The so-called pulsating combustion will also be avoided when a user operates the apparatus to change its fire condition.
A deflector or the like member may be disposed in the enlarged or expanded section so as to face the outlet opening of the constricted section, at a location xe2x80x98extrapolatedxe2x80x99 therefrom.
The gas mixture blown from the constricted section at any given angle into the enlarged section will, in this case, collide with the deflector and be directed towards the center of elongated enlarged section of the thick gas passage. Such a deflector or the like member will facilitate distribution of the gas mixture within the enlarged section.
Also in this case, all the portions constituting each auxiliary burner port will thus receive portions or tributaries of the gas mixture flow at the same rate and with a reduced time lag between them, before respectively jetting and burning it. All the gas flow tributaries will be ignited readily in unison to form stable unit flames so as to provide an auxiliary flame all over the full length of each auxiliary burner port, thereby improving inflammability of fuel gas mixture as a whole to be simultaneously burnt at the auxiliary burner ports and stability of main flames assisted with auxiliary flames. The quantity of raw gas not burnt but wasted when igniting this combustion apparatus to start its operation will now be reduced to a noticeable degree. Further, uniform jet of the gas mixture from the full length of elongated and enlarged section will lower the level of operation noise of this apparatus.
The deflecting means may be of any proper shape, such as a flat plate, a bent plate, a tubular piece, a perforated plate and so on to be chosen in view of the deflected direction. The deflecting means may not necessarily be a single member but be a pair or group of two or more members.
In a case wherein shape and/or position of the constricted section can not be designed freely, but causing a problem in the structure of combustion apparatus, employment of the deflecting means will resolve such a problem. Even if the structure of said apparatus would undesirably delimit the direction of outlet opening of the constricted section jetting the fuel gas, the deflecting means will be useful to avoid any disadvantage resulting from such a structural condition.
It may also possible to construct a plurality of dams within the enlarged or expanded section communicating with the outlet opening of the constricted section. xe2x80x98Inter-damxe2x80x99 canals each formed between and extending over the dams may preferably not be in alignment with the extrapolation of constricted section.
Such a misalignment of the inter-dam canals will inhibit the jet stream of gas mixture from directly entering any one or some of the canals from the constricted section. The jet stream will instead impinge at first on the nearest or proximal dam to be decelerated and deflected to flow along it while being distributed longitudinally of the elongated section. As a result, the gas mixture stream is divided into tributaries flowing through respective inter-dam canals so as to be blown out of auxiliary burner ports.
All the inter-dam canals receive, at a reduced time lag between them, the gas mixture tributaries at the same rate to be uniformly jetted out from the elongated auxiliary burner ports.
Each inter-dam canal may be of a smaller cross-sectional area as compared with the thick gas passage and each auxiliary burner port. Agitation of each tributary within such a canal will contribute to a better mixing of the mixture components.
Another apparatus similar to but somewhat different from that which has just been discussed above may be employed.
Thus, from a yet still further aspect, the present invention provides a combustion apparatus that comprises at least one main burner port for jetting and burning a thin fuel gas mixture, and at least one auxiliary burner port elongated or expanded for jetting and burning a thick fuel gas mixture. This apparatus further comprises a thick gas passage that is composed of an enlarged or expanded section of a larger cross-sectional area, and a constricted section of a smaller cross-sectional area and opened into the enlarged section so as to supply it with the gas mixture. Characteristically, this apparatus comprises a plurality of dams such that inter-dam canals formed each between the adjacent two dams are of different cross-sectional areas.
The inter-dam canals of larger cross-sectional areas and less resistant to the gas mixture flows are more receptive thereof than the other ones of smaller areas. Therefore, the one inter-dam canal standing as a target for the jet from the constricted section may preferably be of the smallest cross-sectional area. In this way, all the canals will receive the gas mixture tributaries substantially at the same rate and at a least possible difference in time lag between all the portions of each auxiliary burner port. All the gas flow tributaries will be ignited readily in unison to form stable unit flames so as to provide an auxiliary flame all over the full length of each auxiliary burner port. The quantity of raw gas not burnt but wasted when igniting this combustion apparatus to start its operation will now be reduced to a noticeable degree. Uniform jetting of the gas mixture from said auxiliary burner port does also reduce operation noise generated by this apparatus.
In a characteristic example of the combustion apparatus just discussed above, two or more plates are overlaid one on another such that convex or concave portions of these plates will form cavities. Other portions of the plates will be pressed together to provide airtight seals such that the cavities continue from and communicate with each other to form passages for air and fuel gas. Some plate portions that are of convex or concave shapes in the same direction will be pressed together to undergo plastic deformation so as to form interference fit engagements serving as some of the seals.
This technique is employed herein, because any simple doubling of convex or concave portions is difficult to provide an airtight seal between them. It is to be noted in this connection that such preliminarily pressed or bent convex or concave portions are not of strictly precise curvatures or radii thereof, inevitably leaving an interstice between them.
It is difficult to interpose forcibly any sealant or the stuffing material between them. If any sealant or the stuffing material is forcibly interposed between such preliminarily pressed convex or concave portions, then irregular deformation will be produced around them to change cross-sectional areas of the gas passages to an impermissible extent.
The interference fit engagements formed herein by the plastic deformation technique noted above resolve this problem, since they do not have any interstice or clearance between the plate portions convex or concave in the same direction and closely contacting one another. Gaps present between the plate portions are now airtightly divided into regions that respectively constitute the gas passages each sealed at any desired points.
Fuel gas mixtures flowing through such properly sealed passages will neither leak therefrom nor undesirably mingle with each other. Concentration and jet quantity of the fuel gas mixture are now kept uniform over the full length of each burner port, thereby affording a stabilized state of combustion.
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