Combustion Apparatus

Abstract

A combustion apparatus 1 includes an intermediate member 6 constituted by a premixer 2 and a burner port assembly 3 and an air passage member 5, the intermediate member 6 being interposed between two air passage members 5. Fuel gas flows into an opening row part 10. The opening row part 10 has a number of openings 8 arranged linearly, so that the fuel gas introduced into the row part 10 is uniformly discharged through each of the openings 8. The fuel gas discharged through the openings 8 of the row part 10 bumps into air at mixing spaces 39. Fuel gas discharged through slots is homogenous and uniform in flow rate. Fuel gas produces a primary flame in a first combustion part 46 to perform a primary combustion. Unburned combustible components are discharged outside through openings of the first combustion part 46 and produce a secondary flame with air supplied through the distal end portion of the air passage member 5.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to combustion apparatuses, and more particularly to a combustion apparatus recommended to be used in a water heater or a bath heater.

2. Description of the Related Art

A combustion apparatus is a main component in a water heater or a bath heater and in widespread use at home as well as at factories.

Recently, environmental destruction resulting from acid rain has become a grave social issue, and thus, there is a pressing need to reduce a total amount of emission of NOx (nitrogen oxides).

There is a combustion apparatus employing a combustion system called the “thick and thin fuel combustion” method adapted to be used in a small device such as a water heater and to reduce NOx emissions.

The “thick and thin fuel combustion” method is designed to produce a main flame from a lean gas mixture composed of fuel gas premixed with air of about 1.6 times the amount of the theoretical amount of air and to arrange around the main flame an auxiliary flame produced from a rich gas mixture with a small amount of mixed air and a high gas concentration.

A combustion apparatus based on the thick and thin combustion is known for such a configuration as disclosed in the patent documents 1 and 2, for example.

A combustion method with a less amount of NOx emissions also includes a combustion system called the “two-staged combustion” method.

The “two-staged combustion” method is adapted to inject a fuel gas in an oxygen-deficient condition to produce a primary flame by igniting the gas, so as to produce a secondary flame by supplying a secondary air to unburned gas.

The patent document 3 discloses a combustion apparatus employing the two-staged combustion method.

Patent Document 1: JP 5-118516A

Patent Document 2: JP 6-126788A

Patent Document 3: JP 52-143524A

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

A combustion apparatus employing the thick and thin fuel combustion method generates a less amount of NOx emissions, being well-reputed in the market, but is disadvantageous in low Turn Down Ratio (T. D. R). Especially, the combustion apparatus employing the thick and thin fuel combustion method is disadvantageous in difficulty to burn in an area having a low heating value.

Specifically, in the thick and thin fuel combustion method, a main flame is produced from a lean gas mixture composed of fuel gas premixed with air of about 1.6 times the amount of the theoretical amount of air, as described above. The gas mixture has a low burning rate because of its leanness.

The combustion apparatus employing the thick and thin fuel combustion method is provided with a fan for facilitating generation of a lean gas mixture, but the fan would become deteriorated due to years of use thereof, resulting in gradually reducing its blowing volume. Clog of a filter of the fan might reduce its air blowing volume. Such a reduced air blowing volume caused by aging is liable to reduce an amount of air in the gas mixture producing a main flame, rendering the amount of mixed air approaching the theoretical amount of air. As a result, a combustion speed of the main flame is liable to become more rapid due to aging. Therefore, the proximal end of flame is liable to gradually approach burner ports due to aging. Thus, combustion in an area having a low heating value would render the proximal end of flame approaching to burner ports, resulting in damaging the burner ports. Consequently, a combustion apparatus employing the thick and thin fuel combustion method is forced to restrict combustion in an area having a low heating value on an anticipated aging.

In addition, the thick and thin fuel combustion method causes such a complaint as a narrow range of usable gas. Specifically, fuel gas supplied by a gas maker may be constituted by a single component, but in many cases, by a plurality of components. That causes different combustion speed depending on makers of fuel gas even if their amounts of heat generation (amounts of heat per unit volume) are the same among them.

Since the thick and thin fuel combustion method produces a main flame in an air excess condition, fuel gas having a slow combustion speed might cause blow off, resulting in an unstable combustion.

In contrast, the two-staged combustion method can have a higher Turn Down Ratio than the thick and thin fuel combustion method. Further, a wide variety of fuel gas is available. However, the two-staged combustion method burns fuel gas in an oxygen-deficient condition, resulting in an unstable combustion. Provably for this reason, we found none of practical devices such as water heaters that are offered commercially and employ the two-staged combustion method.

In order to put to practical use as a combustion apparatus, it is necessary to produce such flame as to uniformly spread over a certain area. This can be achieved by producing a primary flame and a secondary flame in a balanced manner and uniformly throughout the entire area of a combustion site.

However, it is difficult to produce the primary and the secondary flames in a balanced manner and to uniformly distribute the flames throughout the entire area of the combustion site. For example, the primary flame might be partly extinguished, resulting in an excessive secondary flame at downstream thereof, or all fuel might burn out at a site to produce the primary air, resulting in extinguishment of the secondary flame at downstream thereof. Therefore, we found no combustion apparatus employing the two-staged combustion method, among devices such as water heaters having put to practical use.

An object of the present invention made in view of the problems and drawbacks in the art described above is therefore to improve a combustion apparatus performing two-staged combustion and to develop such a combustion apparatus as producing a primary flame and a secondary flame in a balanced manner and spreading the flames uniformly throughout the entire area of a combustion site.

Means to Solve the Problem

In order to solve the problems and drawbacks described above, an aspect of the present invention provided herein is a combustion apparatus, including at least one premixer adapted to premix therein fuel gas and air and having an opening row part with openings arranged in a row, at least one air passage member of a wall shape having at least one distal air emission opening at its distal end, and at least one burner port assembly arranged between two of the air passage members or between the air passage member and another wall, having a burner port-upstream passage formed between the opening row part and the burner port assembly and a first combustion part formed by a space enclosed by the burner port assembly and the air passage member, so that the air is supplied to the air passage member, the burner port-upstream passage, and the premixer, and so that the fuel gas is supplied to the premixer to be premixed with the air within the premixer, and whereupon the resulting air-fuel gas mixture is supplied through the openings of the opening row part into the burner port-upstream passage to be further mixed with air and to be discharged through the burner port assembly into the first combustion part in an oxygen-deficient condition, so as to burn and to further burn upon air supply through the distal air emission opening of the air passage member.

The present aspect has the premixer, in which fuel gas and air are premixed. The premixer has the opening row part with the openings arranged in a row, through which the fuel gas is distributed to the burner port-upstream passage. The fuel gas is mixed with air also in the burner port-upstream passage. Therefore, according to the configuration of the present aspect, the resulting air-fuel gas mixture flowing in the burner port-upstream passage is well mixed and homogenous. Consequently, the homogenized fuel gas is discharged through all areas of walls of the burner port assembly. That produces a primary flame and a secondary flame in a balanced manner and spreads the flames uniformly throughout the entire area of a combustion site.

It is preferable to have a certain space adjacent to the opening row part and within the burner port-upstream passage. This space becomes a mixing space in which fuel gas and air are mixed. The openings of the opening row part are preferably open toward the mixing space.

Further, it is preferable that the mixing space extends substantially over full width of the opening row part.

The mixing space extending in this way promotes homogenization of pressure.

It is preferable that the openings of the opening row part are open in a direction cross to a flowing direction of the air flowing in the burner port-upstream passage.

Fuel gas is discharged in a direction cross to the air flow direction through the openings of the opening row part, having frequent bumping into the air. That promotes mixture of the fuel gas and the air.

A variety of configurations can be considered as the burner port assembly. An employed configuration, for example, may be such that the burner port assembly includes a burner port-forming part and two side walls and has an opening between the two side walls and on the site opposite to the burner port-forming part, wherein the opening row part of the premixer is surrounded by the side walls, and wherein the air is supplied through the opening between the walls.

Further, it is recommended to have such a configuration that the air passage member has a combustion part-facing air emission opening for emitting air therefrom toward the first combustion part. At this time, it is preferable that the burner port assembly has a plurality of burner port groups, the combustion part-facing air emission opening being arranged at a site corresponding to between the burner port groups of the burner port assembly.

The first combustion part is a site where the primary flame is produced, whereas the secondary flame is produced outside of the first combustion part by air supplied through the distal air emission opening. The combustion part-facing air emission opening is arranged so as to discharge air from the side toward between the burner port groups of the burner port assembly, so that the air is blown from surroundings of the burner port groups, thereby ensuring stabilizing the primary flame. Further, the air is supplied from under the primary flame, so as to produce the secondary flame at an early stage and perform a complete combustion of fuel gas adjacent to the primary flame. That allows compact combustion space, thereby shortening the total length of the primary and the secondary flames. The proximal end of the secondary flame is also stabilized.

It is recommended that the air passage member has an inclined surface, on which the combustion part-facing air emission opening is formed.

According to this arrangement, air is jetted in an oblique direction, without obstructing the flow of a main part of the primary flame or the flow of fuel gas.

Further, according to this arrangement, the air is introduced along the flow of the main part of the primary flame or the flow of fuel gas, without accumulating in the vicinity of the wall of the air passage member.

Specifically, fuel gas flows substantially parallel to the wall within the first combustion part. Thus, in the case of introducing air in a direction perpendicular to the first combustion part from the air passage member, the air bumps into the primary flame or the fuel gas, resulting in possible accumulation. If air accumulates in the vicinity of the wall of the air passage member, the accumulated air may cause combustion of surrounding unburned gas and produce flame in the vicinity of the wall of the air passage member. The wall may be excessively heated and glow.

In response, the air jetted in an oblique direction is introduced along the flow of the primary flame or the flow of fuel gas, so as to produce the secondary flame at a site distant from the air passage member. That avoids glowing of the wall of the air passage member.

Further, it is also recommended that the air passage member has an upstream air emission opening for emitting air and at upstream of a part of the member defining the first combustion part, the air emitted through the upstream air emission opening flowing toward a side of the burner port assembly.

According to the above-mentioned arrangement, air discharged through the upstream air emission opening flows toward the side of the burner port assembly, so that oxygen is supplied to the side of the burner port assembly. That produces stable flame at the side of the burner port assembly, holding the proximal end of the primary flame. As a consequence, the primary flame is stabilized.

Still further, it is also recommended that the burner port assembly has a central opening and a side opening, so that the fuel gas is discharged through the side opening slower than the fuel gas discharged through the central opening, and the air flows in the vicinity of the side opening of the burner port assembly.

This arrangement makes a clear distinction between the burner port for producing a main part of the primary flame and the burner port for producing an auxiliary flame.

Specifically, according to the above-mentioned arrangement, the flow rate of fuel gas discharged through the side opening is slower than that of fuel gas discharged through the central opening, and whereby flame produced at the side opening is hardly blown off. Further, air is supplied to the vicinity of the side opening, so that fuel gas discharged through the side opening performs a relatively stable combustion and holds the proximal end of the primary flame. As a consequence, the primary flame is stabilized.

The side opening may be constituted in such a manner that the burner port assembly is constituted by a main body and a decompression wall disposed at a side of the main body, the main body and the decompression wall defining therebetween a gap that has a side opening, and the main body having an opening, through which a part of the fuel gas flowing in the main body flows into the gap.

According to the above-mentioned arrangement, fuel gas is introduced through the opening formed on the main body into the gap formed between the side wall and the decompression wall, but an amount of the fuel gas (more properly, the fuel gas premixed with air) is restricted by the opening, so that the flow rate of the fuel gas discharged through the side opening becomes slower than that of fuel gas discharged through other sites.

The openings of the opening row part each may be of a slot-like shape.

Further, the opening row part may have an inclined surface, on which the openings are formed. At this time, the opening row part has preferably an inner angle at 180 degrees or less.

Fuel gas is discharged in an oblique direction by forming the openings on the inclined surface. That allows the fuel gas more frequent contact with air flow, promoting mixture of fuel gas and air.

Further it is recommended that the distal end of the air passage member is of an acute-angled ridge-like shape.

The air emission opening is formed on the distal end of the air passage member, so as to supply secondary air. According to the above-mentioned arrangement, the distal end of the air passage member is of an acute-angled ridge-like shape, thereby ensuring less air flowing around within the member. That stabilizes a discharging direction of air.

ADVANTAGEOUS EFFECT OF THE INVENTION

The combustion apparatus of the present invention produces the primary and the secondary flames in a balanced manner and uniformly distributed throughout the entire area of the combustion site, being practical.

Further, the combustion apparatus of the present invention achieves a less amount of NOx emissions and a higher Turn Down Ratio. Still further, the combustion apparatus of the present invention is widely adapted to fuel gas having any combustion speed, so as to be used for all types of gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional perspective view conceptually illustrating a configuration of a combustion apparatus of the present invention;

FIG. 2 is a perspective view of a combustion apparatus in a practical embodiment of the present invention;

FIG. 3 is a plan view of the combustion apparatus in FIG. 2 accommodated in a casing;

FIG. 4 is a sectional view taken along the lines A-A of FIG. 3;

FIG. 5 is a sectional view of the combustion apparatus in FIG. 2;

FIG. 6 is a perspective view showing an internal structure of the combustion apparatus broken in a stepwise fashion;

FIG. 7 is an exploded perspective view of the combustion apparatus in FIG. 2;

FIG. 8 is an exploded sectional view of the combustion apparatus in FIG. 2;

FIG. 9 is a perspective view of a premixer of the combustion apparatus in FIG. 2;

FIG. 10 is a sectional view taken along the lines A-A of FIG. 9;

FIG. 11 is a sectional view taken along the lines B-B of FIG. 9;

FIG. 12 is a perspective view of an air passage member of the combustion apparatus in FIG. 2;

FIG. 13 is an enlarged view of a concaved part of the air passage member in FIG. 12;

FIG. 14 is a perspective view of a burner port assembly of the combustion apparatus in FIG. 2;

FIG. 15 is an enlarged front view of a trough for engagement of the burner port assembly in FIG. 14;

FIG. 16 is a side view showing the burner port assembly joined to the premixer;

FIG. 17 is an enlarged view showing the vicinity of the proximal end of the burner port assembly in FIG. 16;

FIG. 18 is an illustration diagram showing a positional relationship between openings of the premixer and ribs of the air passage member;

FIG. 19 is an illustration diagram showing a positional relationship between openings of a premixer and ribs of an air passage member of another embodiment;

FIG. 20 is an illustration diagram showing air flow within the air passage member of the present embodiment;

FIG. 21 is an illustration diagram showing air flow within the air passage member of another embodiment;

FIG. 22 is an exploded perspective view of a combustion apparatus of another embodiment;

FIG. 23 is an exploded perspective view of a combustion apparatus of still another embodiment; and

FIG. 24 is a partly enlarged plan view showing a positional relationship between burner port groups of the burner port assembly and combustion part-facing air emission openings of the air passage member.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Now, an embodiment of the present invention will be described below in detail, making reference to the accompanying drawings. First, an outline configuration and basic functions of the present invention will be described, referring to a schematic view of FIG. 1. An embodiment in FIG. 1 conceptually illustrates the present invention.

In the following descriptions, the vertical positional relationship is based on a combustion apparatus 1 positioned upright and producing flame at an upper part thereof. Terms “upstream” and “downstream” are based on an air or fuel gas flow. A “width direction” denotes a lateral direction (a direction of an arrow “W” in the figure) with a part having the maximal area of the combustion apparatus facing the front.

The combustion apparatus 1 of the present embodiment is used by accommodating more than one apparatus in a casing or alone. The combustion apparatus 1 includes a premixer 2, a burner port assembly 3, and two air passage members 5. In the combustion apparatus 1, the premixer 2 and the burner port assembly 3 are engaged with each other to constitute an intermediate member 6, which is interposed between the two air passage members 5. However, in the actual use, a plurality of the air passage members 5 and a plurality of the intermediate members 6 are alternately arranged to form a planar shape in an order such as the air passage member 5, the intermediate member 6, the air passage member 5, the intermediate member 6, the air passage member 5, and so on.

The premixer 2, a component of the combustion apparatus 1, serves to premix fuel gas and air therewithin. The premixer 2 includes a mixing part 7 having a curved passage and an opening row part 10 having openings 8 arranged in a row. The opening row part 10 has a cavity of a substantially square shape in a cross section extending lengthwise and linearly.

The air passage member 5 generally has a thin wall shape. The air passage member 5 is constituted by a first face 11 and a second face 12, each made of a thin plate, in such a manner that the first and the second faces 11 and 12 are connected with forming a narrow gap therebetween, the three sides except the bottom being joined, thereby defining a cavity to be an air passage 13 inside.

Specifically, the first and the second faces 11 and 12 are made by folding a unitary plate. Its distal end has an acute-angled bent portion 14, the bent portion 14 making up a top portion 9, which extends in ridge-like lines.

The proximal end of the air passage member 5 is open between plates of the first and the second faces 11 and 12, forming an air inlet 15.

In the air passage member 5, openings for emitting air are formed at three areas. Since the air passage members 5 and the intermediate members 6 are alternately arranged to form a planar shape, as described above, the same numbers of openings are formed at the same portions of the first and the second faces 11 and 12 of the air passage members 5.

The openings for emitting air are formed at the distal end, a position facing to a first combustion part 46, and a position facing to the intermediate member 6, roughly describing.

Specifically, the plates of the first and the second faces 11 and 12 of the air passage member 5 are arranged in parallel in their most parts, but are angularly folded only at their distal ends, forming inclined surfaces 16 and 17 at the first and the second faces, respectively. The inclined surfaces 16 and 17 each have distal openings 20. Further, distal openings 21 are formed at a tip (ridge line). The distal openings 20 and 21 are formed for supplying a secondary air to a secondary flame.

The first and the second surfaces 11 and 12 of the air passage member 5, as shown in FIG. 1, has the air passage 13 formed in such a manner as being narrower at its distal end than at its proximal end and having steps at positions corresponding to the proximal end of the first combustion part 46, which steps also constitute inclined surfaces 22. Combustion part-facing air emission openings 23 are formed at each of the steps. The air emission openings 23 are designed to supply the secondary air therethrough to the primary flame in the first combustion part 46, so as to bum part of the primary flame to produce the secondary flame within a part of the first combustion part 46.

Further, air emission openings (upstream air emission openings) 48 are formed at a position facing to the intermediate member 6. The air emission openings (upstream air emission openings) 48 serve to stabilize an auxiliary flame by supplying air therethrough to each side of the burner port assembly 3.

The burner port assembly 3 is mainly constituted by a main body 25 and decompression walls 26. The main body 25 of the burner port assembly 3 is made by bending a piece of metal plate, having a top face 30 functioning as burner ports and two side walls 31 and 32 bent at a substantially 90 degree angle at the both edges of the top face 30. Right and left sides of the burner port assembly 3 are closed with only its bottom in the figure opened. The top face 30 of the burner port assembly 3 has an elongated shape with an A-line shape cross section. The top face 30 has slots regularly arranged, which constitute burner ports 33. The burner ports 33 formed at the main body 25 function as “central openings.”

The side walls 31 and 32 each have a protruding part 34 protruding outwards (in a thickness direction) at its intermediate portion. The protruding part 34 is formed across the full width of the burner port assembly 3.

Open ends of the side walls 31 and 32 are bent at a substantially 90 degree angle twice as shown in the figure, each forming outside a trough (or a gutter) 38 for engagement. The troughs 38 have bottom walls 36 vertical to and outer walls 37 parallel to the respective side walls 31 and 32.

The decompression walls 26 are attached to the main body 25, as described above. The decompression walls 26 are fixed to the respective side walls 31 and 32 of the main body 25, forming gaps 29 between the respective side walls 31 and 32 of the main body 25. The gaps 29 each have an opening at a top of the figure. The opening functions as a side opening 27.

Openings 35 are formed at the side walls 31 and 32 and at positions facing to the decompression walls 26. The gaps 29 are communicated with an inner space of the main body 25 via the openings 35.

Next, a relationship between components will be described below.

In the present embodiment, as described above, the premixer 2 and the burner port assembly 3 are engaged, thereby constituting the intermediate member 6. More specifically, the opening row part 10 of the premixer 2 is placed between the side walls 31 and 32 of the burner port assembly 3. In the actual producing process, the premixer 2 is inserted from the opening (bottom in the figure) between the side walls 31 and 32 of the burner port assembly 3 to join the both members.

The side walls 31 and 32 and the opening row part 10 have partly contact with each other by their concave and convex shapes not shown, thus being unified. As described above, the side walls 31 and 32 and the opening row part 10 have partly contact with each other by their concave and convex shapes, and in other words, they partly keep away from each other. The cross section in FIG. 1 shows a cross section at a site where the side walls 31 and 32 and the opening row part 10 keep away from each other.

Sites corresponding to the protruding parts 34 of the side walls 31 and 32 are away from the accommodated opening row part 10. The protruding parts 34 each correspond to a row of openings 8 of the opening row part 10. Thus, outsides of the openings 8 of the opening row part 10 keep away from the side walls 31 and 32, so as to form spaces (mixing spaces) 39 wider than the other portions. The spaces 39 extend over full width corresponding to all the openings 8.

A relatively large space 47 is formed between the side walls 31 and 32 and between the top of the opening row part 10 and the top face 30 of the burner port assembly 3. In the present embodiment, the mixing spaces 39 and the space 47 downstream of the opening row part 10 form a burner port-upstream passage 49.

The air passage members 5 are attached to the both sides of the intermediate member 6. Each of the air passage members 5 is joined with the intermediate member 6 by engaging the air inlet 15 of the proximal end of the member 5 with the trough 38 of the burner port assembly 3. Specifically, the outer wall 37 of the trough 38 is inserted into the air inlet 15 and the tip of the air passage member 5 is inserted into the trough 38, and whereby the air passage member 5 is brought into contact with the bottom wall 36 of the trough 38.

The air passage member 5 and the intermediate member 6 (the burner port assembly 3) have partly contact with each other by the concave and convex shape, and thus the both members are unified. The both members have partly contact with each other as just described, and in other words, keep partly away from each other. The cross section of FIG. 1 shows a site where the air passage member 5 and the intermediate member 6 (burner port member 3) keep away from each other so as to facilitate understanding their functions. However, at an end (the bottom edge in the figure) upstream of the combustion apparatus 1, a space 40 between the air passage member 5 and the intermediate member 6 are closed by the bottom wall 36 of the trough 38. Thus, the space 40 between the air passage member 5 and the intermediate member 6 is not directly communicated with outside at the proximal end.

The burner port assembly 3 is interposed between the two air passage members 5 as described above, the top face 30 of the assembly 3 lying below (in the figure) the top level of the air passage members 5 and, so to say, buried between the air passage members 5. Therefore, a space ahead of the top face 30 of the assembly 3 is partitioned by walls of the two air passage members 5. In the present embodiment, a space enclosed by the top face 30 of the assembly 3 and the two air passage member 5 functions as the first combustion part 46.

Next, a function of the combustion apparatus 1 will be described in detail below.

A number of the combustion apparatus 1 are opposed within a casing not shown, with air being sent by means of a fan 41 from the bottom in the figure. Fuel gas is introduced into the apparatus 1 through a gas inlet 43 of the premixer 2 by means of a nozzle 42.

First, air flow will be described. The air flow is shown by thin lines in FIG. 1.

Air blow generated by the fan 41 is straightened through openings 45 of a straightening vane 44 so as to be introduced into the combustion apparatus 1 through the proximal end (bottom in the figure) of the apparatus 1.

There are three routes for air introduced into the apparatus 1. The first route passes through inside the air passage member 5, the air flowing through the air inlet 15 formed at the proximal end of the air passage member 5 into the air passage member 5 and going up to the distal end through the air passage 13 within the air passage member 5. Most of the air is discharged outside through the distal openings 20 and 21.

Part of the air flowing in the air passage member 5 is discharged also through the combustion part-facing air emission openings 23 and the air emission openings (upstream air emission openings) 48.

The air having been discharged through the air emission openings 23 is discharged in a direction diagonally to the front of an axis line of the apparatus 1 from the inclined surfaces 22 of the steps.

Further, the air having been discharged through the air emission openings 48 flows in the space 40 between the air passage member 5 and the intermediate member 6 to the side of the burner port assembly 3.

The second route passes through inside the intermediate member 6. The intermediate member 6 is constituted by the opening row part 10 of the premixer 2 interposed between the side walls 31 and 32 of the burner port assembly 3. Gaps (openings) exist between the opening row part 10 and the burner port assembly 3 and a part of the gaps (openings) is open at the bottom of the intermediate member 6.

Therefore, the air is introduced through the openings 28 into between the premixer 2 and the side walls 31 and 32 of the burner port assembly 3.

This air flows through the gaps between the side walls 31 and 32 and the opening row part 10, entering the mixing spaces 39, and then flowing into the space 47 between the opening row part 10 and the top face 30 of the burner port assembly 3. That is, the air described above flows in the burner port-upstream passage 49. Finally, the air is discharged through the slots, i.e., the burner ports 33, into the first combustion part 46. Part of the air having entered the space 47 enters the gaps 29 between the main body 25 and the side walls 31 and 32 through the openings 35 formed on the side walls 31 and 32 of the main body 25 and is discharged into the first combustion part 46 through the side openings 27.

Next, the third route for air will be described in detail below. The third route is a route for the primary air, which is introduced with fuel gas through the gas inlet 43 of the premixer 2. The third route is the same route as that of fuel gas flow, being illustrated in the following description as that of the fuel gas flow. The fuel gas flow is indicated by arrows in solid line in FIG. 1.

Fuel gas is introduced into the third route with the primary air through the gas inlet 43 of the premixer 2 to be mixed with air in a part such as the mixing part 7, the resulting mixture flowing into the opening row part 10. The opening row part 10 has a number of openings 8 arranged linearly, so that the fuel gas having been introduced thereinto is evenly discharged through each of the openings 8. The fuel gas having been discharged through the openings 8 of the row part 10 enters the mixing spaces 39 formed between the side walls 31 and 32 of the burner port assembly 3 and the openings 8 of the row part 10 to be mixed with air flowing in the burner port-upstream passage 49 (including the mixing spaces 39).

The air flowing in the burner port-upstream passage 49 (including the mixing spaces 39) flows vertically (from bottom to top), whereas the fuel gas having been discharged through the openings 8 of the row part 10 flows in a direction perpendicular to the air flow. Thus, the fuel gas hits hard the air also at the mixing spaces 39, and whereby mixing of the fuel gas with the air 5 is facilitated. Further, the mixing spaces 39 each extend throughout in a longitudinal direction of the opening row part 10, thereby smoothing pressure.

After having passed through the mixing spaces 39, the fuel gas flows into the space 47, during which the mixing of the fuel gas with the air is enhanced. After that, the fuel gas flows in the same way as the flow in the burner port-upstream passage 49, entering the space 47 between the opening row part 10 and the top face 30 of the burner port assembly 3, and being mostly discharged through the slots (the burner ports) 33 into the first combustion part 46. Part of the air having entered the space 47 enters the gaps 29 between the decompression walls 26 and the sidewalls 31 and 32 of the main body 25 through the openings 35 formed on the side walls 31 and 32, being discharged through the side openings 27 into the first combustion part 46.

The fuel gas having been discharged through the burner ports 33 is mixed with air within the premixer 2 and further mixed with air within the mixing spaces 39, and thus, being uniformed and being discharged through the burner ports 33 at a uniform rate.

However, though the fuel gas discharged through the burner ports 33 is mixed with air, an amount of the air is below a theoretical amount of air. That is why the fuel gas discharged through the burner ports 33 is in an oxygen-deficient condition, failing in achieving a complete combustion only with this fuel gas.

Ignited, the fuel gas produces the primary flame in the first combustion part 46, so as to perform a primary combustion. However, the fuel gas is not completely burned because of insufficient oxygen as described above, resulting in generating a great deal of unburned combustible component.

The unburned combustible component is discharged outside through opening of the first combustion part 46. Herein, air is supplied to outside of the first combustion part 46 through the distal end of the air passage member 5. Therefore, the unburned combustible component performs a secondary combustion upon oxygen supply. In other words, an area outside of the first combustion part 46 functions as a secondary combustion part and produces the secondary flame.

Further, in the present embodiment, air is supplied to the proximal end of the primary flame, so as to produce an auxiliary flame in the proximal end of the primary flame.

In the present embodiment, fuel gas is discharged not only through the burner ports 33, i.e., the “central openings,” but also through the side openings 27. However, the flow rate of fuel gas discharged through the side openings 27 is slower than that of fuel gas discharged through the burner ports 33. Specifically, the fuel gas enters the gaps 29 between the decompression walls 26 and the side walls 31 and 32 of the main body through the openings 35 formed on the side walls 31 and 32, being discharged through the side openings 27 into the first combustion part 46. That restricts an amount of fuel gas entering the gaps 29, resulting in a small amount of fuel gas discharged through the side openings 27. Conversely, the side openings 27 each have a large opening space. Thus, the fuel gas discharged through the side openings 27 has a low flow rate.

Further, as described above, part of air passing though the air passage member 5 is discharged through the air emission openings (upstream air emission openings) 48 into the space 40 between the air passage member 5 and the intermediate member 6, reaching the side faces of the burner port assembly 3 through the space 40. Therefore, the side faces of the assembly 53 is richer in oxygen than other parts, ensuring that the fuel gas discharged through the side openings 27 performs a relatively stable combustion with reception of air supply.

Coupled with a low flow rate of the fuel gas as described above, a stable auxiliary flame is produced in the vicinity of the side openings 27. The proximal end of the primary flame is held by small flames produced in the vicinity of the side openings 27.

Still further, in the present embodiment, the air having been discharged through the combustion part-facing air emission openings 23 stabilizes the secondary flame. Specifically, in the present embodiment, the inclined surfaces 22 are located at the first and the second faces 11 and 12 of the air passage member 5 and at sites corresponding to the proximal ends of the first combustion part 46. The air emission openings 23 are formed on the inclined surfaces 22, thereby supplying air diagonally to an air flow direction from the proximal end of the first combustion part 46. Thus, the supplied air is supplied into the first combustion part 46 without obstructing the primary flame or the flow of unburned gas. As a consequence, part of unburned gas within the first combustion part 46 starts combustion and partly produces a secondary flame, which merges with the external secondary flame, thereby stabilizing the secondary flame produced outside.

Yet further, in the present embodiment, the combustion part-facing air emission openings 23 are diagonally open, without obstructing the primary flame or the flow of unburned gas, as described above. Consequently, the secondary flame is produced at a distance from the air passage member 5 and does not excessively heat the air passage member 5.

The combustion apparatus of the present embodiment therefore stabilizes both the primary and the secondary flames, thus being practical.

Now, a more practical configuration example of the present invention will be described in referring to the following figures after FIG. 2. The embodiment described below is practically designed for embodying the present invention and has the most recommended configuration.

A combustion apparatus shown in the figures following after FIG. 2 has the same basic configuration and basic function as those in the above-mentioned embodiment, but is practically designed to detail. The same numerals are assigned to components that carry out the same functions as those in the foregoing embodiment, and descriptions of the duplicated functions are simplified.

A plurality of combustion apparatuses 1 shown in FIG. 2 are accommodated in parallel in a casing 54 as shown in FIGS. 3 and 4. The combustion apparatus 1 of the present embodiment also includes a premixer 2, a burner port assembly 3, and air passage members 5. The premixer 2 and the burner port assembly 3 are engaged to constitute an intermediate member 6, which is interposed between the two air passage members 5.

A shape of the premixer 2 is shown in FIGS. 9, 10, and 11. The premixer 2 is formed by a unitary sheet steel pressed and molded into an unfolded form having a concave and convex shape on its surface, which is bent and connected at its periphery by means of a spot welding. The spot welding is done at flanges 51 of the periphery.

The premixer 2 after assembly has such a shape that a front plate 52 as shown in FIGS. 8 and 9 is coupled with a rear plate 53 symmetric to the front plate 52. The premixer 2 has a rounded shape with a flat top part 50 and is sealed at its periphery so as to prevent gas from being leaked.

The premixer 2 forms therein a unitary gas passage between the front and the rear plates 52 and 53. Specifically, the sheet steel forms a space at a portion where the concave and convex shapes of the front and the rear plates 52 and 53 correspond to each other, thereby forming the gas passage by the space.

In the premixer 2 employed in the present embodiment, as shown in FIG. 9, the gas passage is roughly divided into upper and lower parts. More specifically, the gas passage mainly consists of a mixing passage 19 and an opening row part 10.

Referring to FIG. 9, the mixing passage 19 is formed at the lower part of the premixer 2, from an entrance of the gas passage to the opening row part 10. Starting with the entrance of the passage, a gas inlet 43 is open at the corner of the lower part of the combustion apparatus 1. The gas inlet 43 has therein a squeezed portion 55 where its cross-sectional area is locally squeezed and at downstream thereof a diameter expansion portion 56 where the cross-sectional area is gradually expanded. A uniform cross-section portion 57 having a uniform cross-sectional area continues at further downstream. The passage from the gas inlet 43 through the squeezed portion 55 and the diameter expansion portion 56 to the uniform cross-section portion 57 is straight.

The end of the uniform cross-section portion 57 is connected to the opening row part 10 with the passage bent at a right angle.

Herein, in the present embodiment, a portion just before the opening row part 10 is not squeezed.

Referring to FIG. 9, the opening row part 10 is located at the upper part of the premixer 2 and extends throughout in a longitudinal direction. A cross-sectional area of the row part 10, in other words, the space between the front and the rear plates 52 and 53 at the row part 10 is wide, as shown in FIGS. 10 and 11.

Referring to FIGS. 10 and 11, the row part 10 has a cross section of two-tiered configuration with a small area portion 58 having a slightly small cross-sectional area near the top part 50.

Specifically, the row part 10 has such a cross section that the top part 50 is flat with upper part vertical walls 81 vertically extending from its both sides. Bottom edges of the upper part vertical walls 81 each are connected to inclined walls, extending slightly outward. Further, bottom edges of the inclined walls are contiguous to lower part vertical walls 82.

The small area portion 58, which is an outer surface of the row part 10, has a number of openings 8 at both of the front and the rear plates 52 and 53. The openings 8 are formed linearly in a row at predetermined intervals.

In the present embodiment, the openings 8 are formed only at the front and the rear sides of the row part 10, and not at the top part 50.

Next, the air passage member 5 will be described in detail below, in referring to FIGS. 8, 12, and 20. The air passage member 5 is also formed by a unitary sheet steel pressed and molded into an unfolded form having a concave and convex shape on its surface, which is bent and connected at its periphery by means of a spot welding. The air passage member 5, as shown in FIG. 8, is constituted by a first face plate 11 and a second face plate 12 joined at their periphery with a small gap, which forms a cavity to be an air passage 13.

The distal end of the air passage member 5 has an acute-angled bent portion, which constitutes a top portion 9 extending in ridge-like lines.

The air passage member 5, as shown in FIG. 12, has flanges 83 at both sides adjoining the bent portion, the flanges 83 being secured each other at the both sides by means of a spot welding.

The proximal end of the air passage member 5 is open between the first and the second face plates 11 and 12, which form an air inlet 15.

Referring to FIG. 12, the air passage member 5 is of a thin wall shape and roughly divided into three areas in a height direction in its upright position.

Specifically, the areas consists of an introduction portion 60 from the proximal end to about one third of the total height, an intermediate portion 61 from the introduction portion 60 to about two thirds thereof, and a first combustion part-forming portion 62 of another one third near the distal end.

The air passage member 5 constitutes a passage headed toward the distal end from the air inlet 15, a cross-sectional area of the passage becoming narrower toward the distal end.

Specifically, the portion from the air inlet 15 to about one third of the total height (the introduction portion 60), as shown in FIG. 8, has a substantially uniform cross-sectional area. In other words, in the introduction portion 60, the first and the second face plates 11 and 12 are parallel without changing intervals therebetween as shown in the cross section in FIG. 8.

The intermediate portion 61 has a roughly tapered shape.

Specifically, as shown in the figures, the intermediate portion 61 is extended in a tapered shape with its lower part being wider and narrowing as going upward. However, a protruding portion 84 is formed between the distal end of the tapered portion and the first combustion part-forming portion 62. Both sides of outer walls defining the protruding portion 84 are parallel.

The first combustion part-forming portion 62 has a substantially uniform cross-sectional area (except the top portion 9), but its cross-sectional area per unit length is about one third compared with that of the introduction portion 60. Steps composed of inclined surfaces 22 are formed between the portion 62 and the portion 61.

The air passage member 5 has openings for emitting air at three areas. The areas consist of the distal end portion, a position facing to a first combustion part 46, and a position facing to the intermediate member 6, roughly describing.

Specifically, the first and the second face plates 11 and 12 of the air passage member 5 are angularly folded at their distal ends, forming inclined surfaces 16 and 17 at the first and the second face plates, respectively. The inclined surfaces 16 and 17 each, as shown in FIG. 12, have circular distal openings 20. Circular distal openings 21 are also formed at the tip portion (ridge line portion).

Further, in the present embodiment, the top portion 9 and the inclined surfaces 16 and 17 have distal openings 63 and 64 of short and long slot-like shapes. The shorter distal openings 63 each extend over entire heights of the inclined surfaces 16 and 17 and the top portion 9. The longer distal openings 64 each extend from portions where the first and the second face plates 11 and 12 are in parallel to the top portion 9.

The longer slots (distal openings) 64 are larger in number than the shorter slots (distal openings) 63; two or three of the longer slots 64 being arranged in a row, thereafter the shorter slot 63 being arranged, then two or three of the longer slots 64 being arranged in a row, and so on. Such a sequence of arrangement is made over all area in a longitudinal direction of the air passage member 5.

The above-mentioned circular distal openings 20 and 21 are formed between two of the slots (distal openings) 63 or 64.

The distal openings 20 and 21 are, as well as in the foregoing embodiment, formed for supplying a secondary air to a secondary flame.

Further, combustion-part-facing air emission openings 23 are formed on the inclined surface 22 between the first combustion-part forming portion 62 and the intermediate portion 61. The air emission openings 23 are to supply a secondary air to a primary flame taking place in the first combustion part 46, so as to burn a part of the primary flame and produce a secondary flame.

Still further, air emission openings (upstream air emission openings) 48 are formed adjacent to the boundary between the introduction portion 60 and the intermediate portion 61. The air emission openings (upstream air emission openings) 48 serves to supply air to a side of the burner port assembly, so as to stabilize an auxiliary flame.

The first and the second face plates 11 and 12 of the air passage member 5 each have concave and convex shapes at each portion for forming a gap between the both plates or between each plate and another member.

Describing successively, near the distal end, a plurality of troughs 70 and 71 extending heightwise are formed on walls defining the first combustion part-forming portion 62. The troughs 70 and 71 each have a concave or hollow shape in surface view and extend heightwise in parallel. The trough 70 is shorter than the trough 71. The troughs 70 and 71 are formed mainly for strengthening the plates.

In the present embodiment, the troughs 70 and 71 are arranged over full width of the air passage member 5 in such a sequence of arrangement as a plurality of the short troughs 70, thereafter a plurality of the long troughs 71, then a plurality of the short troughs 70, and so on.

Further, the distance between the long troughs 71 are wider than that between the other troughs.

Concaved parts 72 each as shown in FIGS. 12 and 13 are formed every between the long troughs 71 and adjacent to the proximal end of the long troughs 71. The concaved parts 72 each have also a streamline shape and a concave shape in surface view. More specifically, the concaved parts 72 each are formed by a large circle and a small circle with their centers displaced from each other and a common tangent connecting the circles, the large circle being located at upstream of the air passage and the small circle being located at downstream of the air passage. A line connecting the centers of the two circles is in parallel to an air flowing direction. The common tangent connecting two circles have an inclination angle of 30 degrees or less relative to the line connecting the centers of the circles.

Six ribs 73 are formed, as shown in FIG. 12, on the intermediate portion 61 of the air passage member 5. The ribs 73 each are arranged in parallel to an air flowing direction. The ribs 73 each have contact with an outer surface of the intermediate member 6 so as to form a gap therebetween, as described below, and have a tip (ridge), whose location (distance from the center line of the air passage member 5) is thoroughly at the same level at any site. Specifically, as described above, the intermediate portion 61 has a tapered cross section of the passage, but the height of the ribs 73 (size of protuberances) increases in an inverse tapered manner as going upward, the location of the tips being at the same level.

A number of troughs 75 are also formed in parallel on the introduction portion 60. The troughs 75 each extend from the proximal end of the air passage member 5 toward the distal end and have a concave shape in surface view.

A trough 77 extends in a transverse direction (in a direction perpendicular to an air flow) adjacent to the introduction portion 60.

The trough 77 is formed mainly for positioning.

A protuberance 80 of a substantially triangular shape is formed on the central portion at each side of the air passage member 5.

Now, the burner port assembly 3 will be described below. Referring to FIGS. 8 and 14, the burner port assembly 3 is constituted by a main body 25 with a decompression wall 26 welded at its each side.

The main body 25 of the assembly 3 is also formed by a unitary sheet steel pressed and molded into an unfolded form having a concave and convex shape on its surface, which is bent and connected at its periphery by means of a spot welding. The main body 25, as shown in FIG. 14, has flanges 85 at both sides adjoining a top face 30, being joined by the flanges 85, and a face opposite to the top face 30 is open.

The main body 25 of the assembly 3, as shown in FIGS. 8 and 14, has the top face 30 functioning as burner ports and two side walls 31 and 32 bent at a substantially 90 degree angle at the both edges of the top face 30. The top face 30 of the assembly 3 has an elongated shape with an A-line shape cross section. The top face 30 is of a roof-like shape, with a ridge portion 86 at the center being the highest and its both sides being gradual inclined walls 87.

As described above, the burner port assembly 3 is made by bending a piece of metal plate, which is tucked down at the ridge portion 86 of the top face 30. Thus, as shown in the figure, the tucked portion protrudes downward as a vertical wall 88 within a cavity of the assembly 3.

The top face 30 of the main body 25 has slot-like openings, which constitute burner ports (central openings) 33. Each of the slots (burner ports 33) extends in a width direction of the top face 30. A plurality of the slot-like openings are formed in parallel over all area in a longitudinal direction of the top face 30. As shown in FIG. 14, a plurality of slot-like openings make up a burner port group 89, a plurality of the burner port groups 89 being arranged at regular intervals on the top face 30.

As to a cross section of the main body 25, as shown in FIG. 8, the main body 25 has two squeezed portions 78 and 79. Conversely, there are two protruding portions, i.e., a distal protruding portion 90 and an intermediate protruding portion 91, except a proximal end portion.

Specifically, the main body 25 has the distal protruding portion 90 including the top face 30 described above and the intermediate protruding portion 91 formed at the middle portion. The distal squeezed portion 78 is formed between the intermediate protruding portion 91 and the distal protruding portion 90. The proximal squeezed portion 79 is formed adjacent to the proximal end of the intermediate protruding portion 91.

Among the protruding portions 90 and 91 and the squeezed portions 78 and 79 described above, the distal protruding portion 90 and the intermediate protruding portion 91 are formed over full width of the burner port assembly 3.

Small openings 35 are formed, as shown in FIG. 14, in a row on the side of the distal protruding portion 90.

The proximal squeezed portion 79 has a plurality of ribs 92, as shown in FIG. 14. The ribs 92 each protrude outside in surface view; in other words, form a trough 93 within the cavity, as shown in FIG. 6. The ribs 92 each extend in a height direction of the assembly 3 and are arranged in parallel in a width direction of the assembly 3.

Open ends of the side walls 31 and 32 are, as shown in FIGS. 6, 8, 16, and 17, bent at a substantially 90 degree angle twice, each forming outside a trough (or a gutter) 38 for engagement. The troughs 38 have bottom walls 36 vertical to and outer walls 37 parallel to the respective side walls 31 and 32.

The outer wall 37 constituting the trough 38 has a front view of a substantially trapezoidal shape. Specifically, the both sides of the outer wall 37 are inclined as shown in an enlarged view in FIG. 15 in a tapered shape. Further, as shown in FIGS. 16 and 17, the side walls 31 and 32 within the troughs 38 each have protuberances 95. The protuberances 95 are positioned at both ends of the trough 38, respectively; one protuberance 95 for each end.

The decompression walls 26 are fixed to the upper ends of the respective side walls 31 and 32 of the main body 25. The decompression walls 26 each are, as shown in FIG. 14, an elongated plate, covering the entire area of the distal protruding portion 90 of the main body 25. Gaps 29 are formed between the decompression walls 26 and the respective side walls 31 and 32 of the main body 25. The gaps 29 each have an opening at a top of the figure. The opening functions as a side opening 27. Herein, the decompression wall 26 has, as shown in FIG. 8, a small protuberance 97 on its inner surface, the protuberance 97 contacting with the main body 25 to maintain the distance of the side opening 27.

As described above, the openings 35 (FIG. 14) are formed in a row on the distal protruding portion 90. The gaps 29 are communicated with an inner space of the main body 25 via the openings 35.

In the both ends of the main body 25, the side walls 31 and 32 are joined by a spot welding to constitute flanges 85 and have gaps 98 therebetween from the proximal end to the vicinity of the intermediate protruding portion 91.

Next, relationship between components will be described below, making reference to FIGS. 5 and 6.

In the present embodiment, the premixer 2 and the burner port assembly 3 are engaged to constitute the intermediate member 6, as well.

The burner port assembly 3 (intermediate member 6) is, as described above, interposed between the two air passage members 5, the top face 30 of the assembly 3 lying below (in the figure) the top level of the air passage member 5 in the figure and, so to say, buried between the air passage members 5. Therefore, a space ahead of the top face 30 of the assembly 3 is partitioned by walls of the two air passage members 5. In the present embodiment, a space enclosed by the top face 30 of the assembly 3 and the two air passage member 5 functions as the first combustion part 46.

The intermediate member 6 is constituted by the burner port assembly 3 and the premixer 2 engaged therewith in such a manner as inserting the premixer 2 with the top part 50 ahead into a cavity of the assembly 3. At this time, the flanges 51 formed at the both sides of the premixer 2 are engaged with the gaps 98 formed at the both ends of the assembly 3. Then, the tips of the premixer 2 come into contact with the innermosts of the gaps 98, respectively, and whereby positioning in an inserting direction is done.

The vertical walls 82 formed at the lower part of the opening row part 10 of the premixer 2 come into contact with the inner wall of the proximal squeezed portions 79 of the assembly 3, respectively, and whereby positioning in a thickness direction is done.

The small area portion 58 of the opening row part 10 of the premixer 2 comes to the position of the intermediate protruding portion 91 of the assembly 3.

As for gaps between the opening row part 10 of the premixer 2 and the assembly 3, as described above, the small area portion 58 is situated in the intermediate protruding portion 91 of the side walls 31 and 32 of the assembly 3. Specifically, the intermediate protruding portion 91 corresponds to the position of the row parts of the openings 8 of the opening row part 10. Consequently, outer sides of the openings 8 of the row part 10 is away from the side walls 31 and 32, thereby forming spaces (mixing spaces) 39 wider than the other portions. The mixing spaces 39 extend over full width corresponding to all the openings 8.

As described above, the lower part of the row part 10 of the premixer 2 has contact with the inner walls of the proximal squeezed portion 79 of the assembly 3. Thus, the outer walls of the row part 10 have contact with the inner walls of the assembly 3 with no space at most sites in a width direction. However, the proximal squeezed portion 79 has, as described above, a plurality of ribs 92, the inner surfaces of which are the troughs 93 (FIG. 6). Consequently, the outer walls of the row part 10 are kept away from the inner walls of the assembly 3 at the sites of the ribs 92. Further, the ribs 92 each extend in a height direction of the assembly 3, thereby ensuring that the mixing spaces 39 are communicated with the proximal end of the assembly 3.

Herein, as to a positional relationship between the ribs 92 and the openings 8 formed on the row part 10 of the premixer 2, as shown in FIG. 18, the openings 8 are situated above the ribs 92. In other words, the openings 8 are on extensions of the ribs 92. In the present embodiment, as shown in FIG. 18, the ribs 92 correspond one-to-one with the openings 8, but may not correspond, as shown in FIG. 19, in such a manner that the openings 8 are more than the ribs 92 or vice versa.

There are gaps between the proximal end of the assembly 3 and the premixer 2. Thus, the mixing spaces 39 are communicated with outside via the ribs 92 (troughs 93) and the above-mentioned gaps.

On the other hand, above the mixing spaces 39, there is a relatively large space 47 between the side walls 31 and 32 and between the top part 50 of the row part 10 and the top face 30 of the assembly 3. In the present embodiment, the above-mentioned mixing spaces 39 and the space 47 at downstream of the row part 10 constitute a burner port-upstream passage 49.

Referring to FIGS. 5 and 6, the air passage members 5 are joined with the both sides of the intermediate member 6. Each of the air passage members 5 is secured to the intermediate member 6 by engaging the air inlet 15 at the proximal end of the member 5 with the trough 38 of the burner port assembly 3. Specifically, the outer wall 37 of the trough 38 is inserted into the air inlet 15 and the tip of the air passage member 5 is inserted into the trough 38, and whereby the air passage member 5 is brought into contact with the bottom wall 36 of the trough 38.

Herein, the outer wall 37 of the trough 38 is, as described above, of a trapezoid shape in surface view and has the both sides in a tapered shape, so that the inner wall of the air inlet 15 follows the tapered shape of the outer wall 37 of the trough 38 in joining the air passage member 5, and whereby positioning in a width direction is done.

When the air passage member 5 fits in a regular place in the burner port assembly 3, as shown in FIG. 17, the protuberances 95 formed in the trough 38 engage with the outer edges of the trough 77 formed adjacent to the opening of the air passage member 5, with a feeling of click stop.

Further, when the air passage member 5 fits in the regular place, as shown in FIG. 24, the burner port-facing air emission openings 23 are situated between the burner port groups 89 of the assembly 3 in a width direction.

At the upstream end (the bottom in the figure) of the combustion apparatus 1, the space 40 between the air passage member 5 and the intermediate member 6 is closed by the bottom wall 36 of the trough 38. Thus, the space 40 between the air passage member 5 and the intermediate member 6 is not directly communicated with outside at the proximal end.

As shown in FIGS. 5 and 6, the distal squeezed portion 78 comes to the side of the upstream air emission openings 48 of the air passage member 5. The distal squeezed portion 78 is a concaved portion of the surface of the assembly 3, so that there is a gap between the air passage member 5 and the assembly 3 adjacent to the upstream air emission openings 48.

Further, the gap is communicated with the first combustion part 46. Specifically, the air passage of the air passage member 5 is tapered toward the distal end beyond the openings 48, so that the outer wall of the air passage member 5 becomes situated to the inward side of the air passage toward downstream, forming wider space between the member 5 and the assembly 3. Herein, the outer wall of the air passage member 5 and the burner port assembly 3 partly contact with each other via the ribs 73 formed on the member 5.

Now, a function of the combustion apparatus 1 will be described below.

A number of combustion apparatuses 1 are accommodated in the casing 54 as shown in FIG. 3 and air is sent by the fan 41 from the bottom in the figure as shown in FIG. 4. Further, fuel gas is introduced through the gas inlet 43 of the premixer 2 by means of a nozzle.

Air flows in the substantially same way as the above-mentioned embodiment, that is; air blow generated by the fan 41 is straightened through openings of a straightening vane 44 (FIG. 4) so as to be introduced into the combustion apparatus 1 through the proximal end (bottom in the figure) of the apparatus 1.

There are three routes for air introduced into the apparatus 1, as well as in the foregoing embodiment. Specifically, the first route passes through the air passage member 5, as shown in FIG. 6, the air blow being introduced through the air inlet 15 formed at the proximal end of the air passage member 5 into the air passage member 5 and going up to the distal end through the air passage 13 within the member 5. Most of the air is discharged outside through the distal openings 20 and 21.

Herein, in the present embodiment, as shown in FIG. 20, the distal end of the air passage member 5 is acute-angled and the distal openings 63 and 64 among all the distal openings are slots extending over entire heights of the inclined surfaces 16 and 17 and the top portion 9, thereby preventing air from staying in the distal end portion or causing turbulent flow.

As shown in FIG. 21, for example, in the case that the distal end portion of the air passage member is of a round shape, air having introduced through the air inlet 15 bumps into a circular surface of a ceiling to flow around the distal end portion along the circular surface. The air flowing therearound bumps into air flow newly supplied as indicated by arrows, resulting in disturbing emission of newly supplied air and distorting an emission direction. In this way, a rounded shape of the distal end portion of the air passage member 5 generates turbulent flow or air eddy, resulting in an unstable direction of air flow. That causes flicker of the secondary flame. Further, according to the experiments by the inventors, it is noisy.

On the other hand, the present embodiment has the acute-angled distal end portion as shown in FIG. 20, thereby ensuring less portion into which supplied air bumps and less air flowing around the distal end portion. Further, the slot-like openings are formed on the inclined surfaces, so that most of air bumping into the inclined surfaces is discharged outside through the slot-like openings. That stabilizes an emission direction of air, causes less flicker of the secondary flame, and reduces the noise. However, in the present invention, a shape of the distal end of the air passage member is not limited, and may be round as shown in FIG. 21.

In the combustion apparatus 1 of the present embodiment, part of air flowing in the air passage member 5 is discharged also through the combustion part-facing air emission openings 23 and the air emission openings (upstream air emission openings) 48.

The air having been discharged through the combustion part-facing air emission openings 23 is discharged in a direction diagonally to the front of an axis line of the apparatus 1 from the inclined surfaces 22 toward between the burner port groups 89 and 89 of the burner port assembly 3.

The air having been discharged through the openings (upstream air emission openings) 48 flows in the space 40 between the air passage member 5 and the intermediate member 6, and then reaches the side of the burner port assembly 3. More specifically, the air having been discharged through the openings 48 is discharged into a gap formed by the proximal squeezed portion 78 of the burner port assembly 3, and then flows in the space formed by the tapered wall of the air passage member 5 to be discharged to the side of the burner port assembly 3.

The second route passes through inside the intermediate member 6, into which air is introduced through the openings 28 into between the premixer 2 and the side walls 31 and 32 of the burner port assembly 3.

This air flows through the troughs 93 (the reverse side of the ribs 92) formed on the inner surface of the burner port assembly 3, entering the mixing spaces 39, and then flowing into the space 47 between the opening row part 10 and the top face 30 of the burner port assembly 3. That is, the air described above flows in the burner port-upstream passage 49. Finally, the air is discharged through the slots, i.e., the burner ports (central openings) 33, into the first combustion part 46. Part of the air having entered the space 47 enters the gaps 29 between the main body 25 and the side walls 31 and 32 through the openings 35 formed on the side walls 31 and 32 of the main body 25 and is discharged into the first combustion part 46 through the side openings 27.

Now, the third route for air will be described in detail. The third route is a route for the primary air, which is introduced with fuel gas through the gas inlet 43 of the premixer 2. The third route is the same route as that of fuel gas flow, being illustrated in the following description as that of the fuel gas flow. The fuel gas flow is indicated by arrows in solid line.

Fuel gas is introduced into the third route with the primary air through the gas inlet 43 of the premixer 2 to be mixed with air in a part such as the mixing part 7, the resulting mixture flowing into the opening row part 10. Herein, in the present embodiment, there is no squeezed portion between the uniform cross-section portion 57 and the opening row part 10. Thus, the fuel gas enters the opening row part 10 without variation in flow rate in particular.

The fuel gas having entered the row part 10 is uniformly discharged through each opening 8. Specifically, the row part 10 is not too small inside, thereby dissipating fine eddy generated in a part such as an indirect passage in the premixer 2. Further, as described above, there is no squeezed portion just before the row part 10, so that the fuel gas introduced into the row part 10 has small variation in flow rate over the cross section of the passage. Therefore, the row part 10 has small variation in pressure inside, so that the fuel gas is uniformly discharged through each opening 8. Opening diameters of the openings 8 may be narrowed down so as to equalize jetted gas volume.

The fuel gas having been discharged through the openings 8 of the row part 10 enters the mixing spaces 39 constituted by the intermediate protruding portion 91 of the burner port assembly 3, so as to be mixed with air flowing in the burner port-upstream passage 49 (including the mixing spaces 39).

The air flowing in the mixing spaces 39 flows from bottom to top in the figure and is straightened.

Specifically, the air flowing into the mixing spaces 39, which is introduced thereinto through the openings 28 between the premixer 2 and the side walls 31 and 32 of the burner port assembly 3, passes through the troughs 93 (the reverse side of the ribs 92) formed on the inner surface of the burner port assembly 3, thus being laminar airflow.

More specifically, in the present embodiment, most portion of the proximal squeezed portion 79 of the burner port assembly 3 has contact with the outer walls of the premixer 2, but the proximal squeezed portion 79 has a number of troughs 93 formed on its inner surface, thus having gaps at sites of the troughs 93. Each trough 93 is communicated with the mixing spaces 39. Therefore, air having introduced through the openings 28 between the premixer 2 and the side walls 31 and 32 passes through a number of troughs 93, then reaching the mixing spaces 39. The troughs 93 are elongated passages arranged in parallel at regular intervals, so that the introduced air is straightened by flowing in a plurality of troughs 93.

The air flowing in the burner port-upstream passage 49 (including the mixing spaces 39) flows in a height direction of the apparatus 1, whereas the fuel gas having been discharged through the openings 8 of the row part 10 flows into the mixing spaces 39 in a direction perpendicular to the air flow. Thus, the fuel gas having been discharged through the openings 8 of the row part 10 bumps into the air also at the mixing spaces 39, so as to be promoted to be mixed with the air.

Additionally, in the present embodiment, the openings 8 of the row part 10 are on extensions of the troughs 93 (the reverse side of the ribs 92), respectively, so that the air having passed through the troughs 93 bumps into the fuel gas having been discharged through the openings 8 more certainly.

Further, the mixing spaces 39 extend over full width of the row part 10, thereby smoothing its pressure.

The fuel gas, which passes through the mixing spaces 39, flows upward, and flows into a space formed by the distal protruding portion 90, is promoted to be mixed with the air during flowing there. Then, most of the fuel gas is discharged into the first combustion part 46 through the slots, i.e., the burner ports 33.

The fuel gas having been discharged through the slots is homogenous and uniform in flow rate when being discharged through the slots because the gas is mixed with the air within the premixer 2 and further within the mixing spaces 39.

Part of the air having entered the space 47 enters the gaps 29 between the main body 25 and the side walls 31 and 32 through the openings 35 formed on the side walls of the main body 25, then being discharged through the side openings 27 into the first combustion part 46.

Being ignited, fuel gas produces the primary flame in the first combustion part 46 to perform the primary combustion. Unburned combustible components are discharged outside through the openings of the first combustion part 46 to perform the secondary combustion with air supplied through the distal end portion of the air passage member 5.

Further, in the present embodiment, air is supplied into the proximal end of the primary flame to produce an auxiliary flame at the proximal end of the primary flame.

In short, in the present embodiment, part of fuel gas is discharged through the side openings 27 into the first combustion part 46. However, the flow rate of the fuel gas discharged through the side openings 27 is slower than that of the fuel gas discharged through the slots. Specifically, the fuel gas enters the gaps 29 between the main body 25 and the side walls 31 and 32 through the openings 35 formed on the side walls of the main body 25, then being discharged through the side openings 27 into the first combustion part 46. Therefore, the fuel gas entering the gaps 29 is restricted in volume, and whereby gas volume discharged through the side openings 27 is small. However, the side openings 27 each have a large opening space, so that the fuel gas discharged through the side openings 27 flows slowly.

Further, as described above, part of the air passing through the air passage member 5 is supplied to the fuel gas discharged through the side openings 27, thereby ensuring a complete combustion.

Specifically, the air having been discharged through the air emission openings (upstream air emission openings) 48 flows through the gaps formed by the side walls of the air passage member 5 and the distal squeezed portion 78 of the burner port assembly 3 along the gaps formed by the tapered walls of the air passage member 5, then reaching the sides of the burner port assembly 3.

A stable auxiliary flame is produced adjacent to the side openings 27, coupled with a low flow rate of fuel gas as described above. Thus, the proximal end of the primary flame is held by small flames produced adjacent to the side openings 27.

Also in the present embodiment, air is diagonally supplied through the combustion part-facing air emission openings 23 formed on the inclined surfaces 22, thereby starting combustion of part of unburned gas in the first combustion part 46 and producing partly a secondary flame. This secondary flame becomes continuous with the secondary flame outside.

Further, in the present embodiment, air is discharged to between the burner port groups 89 of the burner port assembly 3, so that the air is sufficiently supplied to the vicinity of the burner port groups 89, thereby stabilizing the primary flame certainly.

Also in the present embodiment, the air having been supplied through the combustion part-facing air emission openings 23 does not obstruct the primary flame or a flow of unburned gas, thereby producing the secondary flame at a point distant from the air passage member 5 so as not to heat the member 5 excessively.

Consequently, the combustion apparatus of the present embodiment stabilizes the first and the second flames, being practical.

The above-mentioned embodiment illustrates the premixer having openings for discharging fuel gas at its side by an example. This configuration discharges fuel gas in a direction perpendicular to an air flow, thereby having frequent bumping of fuel gas and air, which promotes mixture thereof.

For exerting the similar effect, such a configuration as diagonally discharging fuel gas can be considered. As shown in FIG. 22, for example, inclined surfaces 66 and 67 of a roof-like shape are formed on the top of a premixer 2, with slot-like openings 68. In the present embodiment, fuel gas is discharged diagonally in front through the slot-like openings 68. As a consequence, the fuel gas bumps into air, so as to be promoted to be mixed with the air. Further, the present embodiment hardly causes eddy of fuel gas or air, thereby stabilizing fuel gas concentration.

A combustion apparatus shown in FIG. 23 has slot-like openings 69 formed on the top of a premixer.

It is recommended to discharge fuel gas in a direction cross to an air flow, but the present invention does not except such a configuration as discharging fuel gas along an air flow as shown in FIG. 23.

In the embodiments shown in the figures following after FIG. 2, each member has a number of concave and convex shapes on its surface. The concave and convex shapes each exert not only a function of constituting passages but also a function of improving rigidity of each plate. The concave and convex shape not constituting the passages only exerts the function of improving rigidity of each plate.

In each embodiment described above, gaps between metallic plates constitute a unitary passage. Specifically, a concave portion is formed on one or both plates, thereby forming a gap between the one and the other plates. Herein, it is one of design variations to form a concaved portion or the like on either plate in forming a passage, and the present invention is not limited to the above-mentioned embodiments. In the above-mentioned embodiments, for example, the second route includes a passage passing between the inner surface of the burner port assembly 3 and the outer peripheral surface of the premixer 2 so as to secure the passage by forming the troughs 93 on the inner surface of the burner port assembly 3. However, by contraries, a passage may be constituted by forming a concaved portion or the like on the premixer 2.

Claims

1. A combustion apparatus, comprising: at least one premixer adapted to premix therein fuel gas and air and having an opening row part with openings arranged in a row;at least one air passage member of a wall shape having at least one distal air emission opening at its distal end; andat least one burner port assembly arranged between two of the air passage members or between the air passage member and another wall,having a burner port-upstream passage formed between the opening row part and the burner port assembly and a first combustion part formed by a space enclosed by the burner port assembly and the air passage member,so that the air is supplied to the air passage member, the burner port-upstream passage, and the premixer, andso that the fuel gas is supplied to the premixer to be premixed with the air within the premixer, and whereupon the resulting air-fuel gas mixture is supplied through the openings of the opening row part into the burner port-upstream passage to be further mixed with air and to be discharged through the burner port assembly into the first combustion part in an oxygen-deficient condition, so as to burn and to further burn upon air supply through the distal air emission opening of the air passage member.

2. The combustion apparatus as defined in claim 1, having a mixing space adjacent to the opening row part within the burner port-upstream passage,the openings of the opening row part being open toward the mixing space.

3. The combustion apparatus as defined in claim 1, wherein the mixing space extends substantially over full width of the opening row part.

4. The combustion apparatus as defined in claim 1, wherein the air flows in the burner port-upstream passage in a flowing direction and the openings of the opening row part are open in a direction cross to the flowing direction.

5. The combustion apparatus as defined in claim 1, wherein the burner port assembly comprises a burner port-forming part and two side walls and has an opening between the two side walls and on the site opposite to the burner port-forming part,wherein the opening row part of the premixer is surrounded by the side walls, andwherein the air is supplied through the opening between the walls.

6. The combustion apparatus as defined in claim 1, wherein the air passage member has a combustion part-facing air emission opening for emitting air therefrom toward the first combustion part.

7. The combustion apparatus as defined in claim 6, wherein the air passage member has an inclined surface, on which the combustion part-facing air emission opening is formed.

8. The combustion apparatus as defined in claim 6, wherein the burner port assembly has a plurality of burner port groups,the combustion part-facing air emission opening being arranged at a site corresponding to between the burner port groups of the burner port assembly.

9. The combustion apparatus as defined in claim 1, wherein the air passage member has an upstream air emission opening for emitting air and at upstream of a part of the member defining the first combustion part,the air emitted through the upstream air emission opening flowing toward a side of the burner port assembly.

10. The combustion apparatus as defined in claim 1, wherein the burner port assembly has a central opening and a side opening, so that the fuel gas is discharged through the side opening slower than the fuel gas discharged through the central opening, and the air flows in the vicinity of the side opening of the burner port assembly.

11. The combustion apparatus as defined in claim 1, wherein the burner port assembly is constituted by a main body and a decompression wall disposed at a side of the main body,the main body and the decompression wall defining therebetween a gap that has a side opening, andthe main body having an opening, through which a part of the fuel gas flowing in the main body flows into the gap.

12. The combustion apparatus as defined in claim 1, the openings of the opening row part each being of a slot-like shape.

13. The combustion apparatus as defined in claim 1, the opening row part having an inclined surface, on which the openings are formed.

14. The combustion apparatus as defined in claim 1, the opening row part having an inner angle at 180 degrees or less.

15. The combustion apparatus as defined in claim 1, the distal end of the air passage member being of an acute-angled ridge-like shape.