Combustion apparatus

The present application is based on and claims the priority benefit of Japanese Patent Application 2008-053633 filed on Mar. 4, 2008, the contents of which are incorporated herein by reference in its entirety.

1. Field of the Invention

The present invention relates to a combustion apparatus provided with an all primary combustion burner for supplying hot water or the like.

2. Description of the Related Art

Conventionally, there has been known a combustion apparatus for supplying hot water which is composed of an all primary combustion burner and a combustion cabinet. On the top of the combustion cabinet, there is disposed a heat exchanger; and the all primary combustion burner having a combustion plate with a plurality of burner ports is disposed inside the combustion cabinet. This kind of the combustion apparatus having the all primary combustion burner has an advantage in making the apparatus compact sized; on the contrary, however, it has a problem that heat loss is easy to occur when the combustion cabinet becomes hot.

In regard to this problem, there has been known a combustion apparatus as disclosed in, for example, Japanese Patent Laid-open No. 2007-292342, in which a ventilation gap between an outer side surface of the burner and an inner side surface of the combustion cabinet in the conventional art is maintained, and the ventilation gap is supplied with air from a fan as cooling air to form a cooling air curtain circulating on the top of the burner along the inner side surface of the combustion cabinet while the fan blows air to the burner as primary air.

According to the combustion apparatus described in the above, the combustion cabinet is cooled by the air curtain; resultantly, the heat loss of the combustion cabinet is prevented. On the other hand, however, a part of the cooling air in the ventilation gap flows into and circulates above i peripheral area of the combustion plate, and they are mixed into a mixture gas erupted from the burner ports in the peripheral area before the mixture gas is completely combusted. As a result, the air excess rate in the mixture gas becomes extremely high, which lifts up the flames from the combustion ports in the peripheral area of the combustion plate, leading to a deteriorated combustion performance.

The present invention has been accomplished in view of the aforementioned problems, and it is therefore an object of the present invention to provide a combustion apparatus capable of preventing a heat loss from a combustion cabinet without deteriorating a combustion performance thereof.

To attain an object described above, the combustion apparatus according to the present invention is provided with an all primary combustion burner, which has a combustion plate with a plurality of burner ports disposed on the top thereof, in a combustion cabinet, wherein a part of an inner side surface of the combustion cabinet which encloses a combustion chamber where a mixture gas erupted from the combustion plate is combusted is covered with a cover made of an insulation material; and the cover is provided with a concave portion at an outer side surface thereof having contact with the inner side surface of the combustion cabinet, and an insulation air layer is defined by the concave portion.

According to the present invention, the heat from the combustion flames of the mixture gas can be prevented from being transferred to the combustion cabinet by the cover. Therefore, it is not necessary to circulate cooling air between the outer side surface of the burner and the inner side surface of the combustion cabinet, and resultantly, the combustion performance will not be deteriorated by the circulation of the cooling air in the peripheral area of the combustion plate. However, if the cover is solid, the cover will become very hot as the combustion continues. The heat will be transferred from the cover to the combustion cabinet, making the combustion cabinet excessively hot. In regard to this problem, the present invention defines the insulation air layer with the concave portion in the outer side surface of the cover to inhibit the heat transferred from the cover to the combustion cabinet so as to effectively prevent the heat loss from the combustion cabinet.

It is preferable that the insulation air layer according to the present invention is configured to have a thickness in a range of 28% to 44% with respect to a total thickness of the cover from an inner side surface of the combustion cabinet to the inner side surface of the cover. If the thickness of the insulation air layer is smaller than 28% of the total thickness of the cover, the insulation effect of the insulation air layer cannot be obtained effectively; on the other hand, however, if the thickness of the insulation air layer is greater than 44% of the total thickness of the cover, the part of the cover opposing to the insulation air layer becomes too thin to prevent the heat amount from entering the insulation air layer, causing the temperature of the insulation air layer to rise, which makes the combustion cabinet excessively hot.

Moreover, according to the present invention, it is desirable that an upper edge of the inner side surface of the cover is formed with a beveled portion. By forming the beveled portion at the upper edge of the inner side surface of the cover, it is difficult for the cover to absorb heat than the case where the upper edge of the inner side surface thereof is angular, thereby, to improve the insulation performance.

FIG. 1 is a perspective view of a combustion apparatus according to an embodiment of the present invention.

FIG. 2 is a side view of the combustion apparatus illustrated in FIG. 1 cut away along II-II line.

FIG. 3 is a front view of the combustion apparatus illustrated in FIG. 2 cut away along III-III line.

FIG. 4 is a graph illustrating a relationship between a thickness of an insulation air layer and a temperature of a combustion cabinet in the combustion apparatus of an embodiment.

As illustrated in FIG. 1 , reference numeral 1 denotes a combustion cabinet. On the top thereof, there is disposed an object to be heated (not shown) such as a heat exchanger for supplying hot water or the like. Inside the combustion cabinet 1 , there is disposed an all primary combustion burner 2 .

The combustion cabinet is constituted of a bottom plate 11 , a rear plate 12 and two side plates 13 and 13 formed by bending a single piece of plate, and a front plate 14 fixed at an upper position between front ends of the two side plates 13 and 13 . The front plate 14 is provided with an ignition plug 14 a and a flame detection element 14 b such as a flame rod and so forth. As illustrated in FIG. 2 and FIG. 3 , the combustion cabinet 1 is disposed with an air supply chamber 4 which is located at a lower position than the burner 2 . The air supply chamber 4 is demarcated by a partition plate 3 . In the bottom plate 11 , there is opened a connection port 11 a . An air supply duct of a fan 5 is plugged into the connection port 11 a and supplies the air supply chamber 4 with air from the fan 5 . The partition plate 3 is constituted of an under plate portion 31 for supporting the burner 2 and a front plate portion 32 which is fixed at a lower position of a front surface of the burner 2 and is also served as a damper for defining a primary air chamber 4 a leveled up in the front portion of the air supply chamber 4 . The upper end of the front plate portion 32 is formed with a protection portion 32 a which is bent frontward and acts as a top surface of the primary air chamber 4 a and a flange portion 32 b which is bent from the front end of the protection portion 32 a upward and is joined to a lower portion of a back surface of the front plate 14 .

As illustrated in FIG. 2 and FIG. 3 , the burner 2 is a plate-type burner comprising a burner main body 21 and a combustion plate 22 mounted at the top of the burner main body 21 . The burner main body 21 is of a box shape, provided with a support leg portion 21 a and a spacer portion 21 b , both of which are protruding out of the burner main body 21 . The support leg portion 21 a is disposed at a lower surface of the burner 2 and is seated on the under plate portion 31 of the partition plate 3 . The spacer portion 21 b is disposed at a rear surface of the burner 2 and is adjoined to the rear plate 12 of the combustion cabinet 1 . The combustion plate 22 is made of ceramics and is configured to have a plurality of burner ports at a top surface of the burner main body 21 . The combustion plate 22 is prevented from loosing from the burner main body 21 by a tension frame 23 which presses the combustion plate 22 downward at a circumferential edge of an upper surface thereof. A flange portion 21 c which is a protruded portion spread circumferentially is disposed on an outer side surface of the burner main body 21 at a lower position than the combustion plate 22 , and the tension frame 23 is fixed at the flange portion 21 c.

An inflow port 24 is opened at a lower portion of the front surface of the burner main body 21 . The inflow port 24 communicates with the primary air chamber 4 a through an opening 32 c formed in the front plate portion 32 of the partition plate 3 which is fixed at the lower portion of the front surface of the burner main body 21 . Inside the burner main body 21 , there are provided a mixing chamber 25 which is located at a lower position and extends rearward from the inflow port 24 , and a distribution chamber 26 which is located at a higher position than the mixing chamber 25 and communicates with the mixing chamber 25 through an opening 25 b formed at a rear portion of an upper surface plate 25 a of the mixing chamber 25 . A distribution plate 26 a is provided in the distribution chamber 26 to demarcate the distribution chamber 26 into an upper chamber section and a lower chamber section. The distribution plate 26 a is formed with a plurality of distribution ports 26 b so as to keep uniform the pressure in the distribution chamber 26 between the combustion plate 22 and the distribution plate 26 a . The combustion plate 22 is divided into 3 parts in the lateral direction. Similarly, the inflow port 24 , the mixing chamber 25 and the distribution chamber 26 are divided into 3 parts in the lateral direction as well. Therefore, the burner 2 of the present invention is essentially a combination of 3 burners.

A front surface of the primary air chamber 4 a is occluded by a gas manifold 6 . The gas manifold 6 is provided with a gas nozzle 6 a , facing the inflow port 24 . Thereby, fuel gas from the gas nozzle 6 a and the primary air from the primary air chamber 4 a are flown into the mixing chamber 25 of the burner 2 and are mixed therein to produce a mixture gas having a fuel gas concentration lower than a theoretical air-fuel ratio. The mixture gas is erupted from the burner ports in the combustion plate 22 through the distribution chamber 26 and is subjected to an all primary combustion. Note that the gas manifold 6 is omitted and not shown in FIG. 1 .

A part of an inner side surface of the combustion cabinet 1 which encloses a space for the mixture gas erupted from the combustion plate 22 to combust therein is provided with a cover 7 . The cover 7 is molded from an insulation material of superior thermal insulation properties, such as glass wool and so forth, to have a cross sectional shape similar to a laid capital letter “U” (the capital letter “U” is placed horizontally after being rotated for 90 degrees). A concave portion 7 a is formed at an outer side surface, which has contact with the inner side surface of the combustion cabinet 1 , of the cover 7 to define an insulation air layer 7 b.

According thereto, the heat from the combustion flames of the mixture gas can be prevented from being transferred to the combustion cabinet 1 by the cover 7 . Therefore, it is not necessary to circulate cooling air between the outer side surface of the burner 2 and the inner side surface of the combustion cabinet 1 , and resultantly, the combustion performance will not be affected by the circulation of the cooling air in the peripheral area of the combustion plate 22 . However, if the cover 7 is solid, the cover 7 itself will become very hot as the combustion continues. The heat will be transferred from the cover 7 to the combustion cabinet 1 , making the combustion cabinet 1 excessively hot. In regard to this problem, the present invention defines the insulation air layer 7 b at the inner side surface of the cover 7 to inhibit the heat from being transferred from the cover 7 to the combustion cabinet 1 so as to effectively prevent the heat loss from the combustion cabinet 1 .

If the thickness of the insulation air layer 7 b is too thin, the insulation effect of the insulation air layer cannot be obtained effectively.

On the other hand, however, if the thickness of the insulation air layer 7 b is too thick, the part of the cover 7 opposing to the insulation air layer 7 b becomes too thin to prevent the heat produced by the combustion flames from entering the insulation air layer 7 b , causing the temperature of the insulation air layer 7 b to rise, which makes the combustion cabinet 1 excessively hot.

Therefore, a test was carried out to find a preferable thickness of the insulation air layer 7 b . The cover 7 tested has an entire thickness t 1 of 9 mm which is counted from the inner side surface of the combustion cabinet 1 to the inner side surface of the cover 7 . The entire thickness t 1 is substantially equal to a gap between the outer side surface of the upper portion of the burner main body 21 and the inner side surface of the cabinet 1 . A plurality of covers 7 with insulation air layer 7 b of different thickness t 2 were tested. A vertical dimension h of the cover 7 is set at 20 mm and a vertical dimension of the insulation air layer 7 b is set at 14 mm. Moreover, an upper edge of the inner side surface of the cover 7 is formed with a beveled portion 7 c by cutting away the corner for 2 mm.

In the test, an input power of the burner 2 is set at 48.8 kW and the air excess rate is set at 1.15, a temperature at a portion (point A in FIG. 3 ) where the upper end of the cover 7 has contact with the combustion cabinet 1 , which will become the hottest part of the combustion cabinet 1 , was determined. The determination result is shown in FIG. 4 . It is clear from FIG. 4 that the temperature at the point A went up to only 173° C. when the thickness t 2 of the insulation air layer 7 b was 3 mm. However, when t 2 is smaller than 3 mm, the temperature at the point A rises at an accelerated rate in accordance to the decrement of t 2 ; on the other hand, when t 2 is greater than 3 mm, the temperature at the point A rises in proportion to the increment of t 2 . If t 2 is set in a range of 2.5 mm to 4.0 mm, the temperature at the point A remains below 185° C., and the heat loss from the combustion cabinet 1 can be prevented accordingly. Note that if the entire thickness t 1 of the cover 7 is altered, it is preferable that the thickness t 2 of the insulation air layer 7 b be altered in proportion to t 1 . The entire thickness t 1 of the cover 7 used in the test is 9 mm, when t 2 is at 2.5 mm, the rate of t 2 with respect to t 1 is roughly 28% which is obtained by 2.5/9; and when t 2 is at 4.0 mm, the rate of t 2 with respect to t 1 is roughly 44% which is obtained by 4/9. Therefore, the heat loss from the combustion cabinet 1 can be prevented effectively by setting the thickness t 2 of the insulation air layer 7 b in a range of 28% to 44% with respect to the entire thickness t 1 of the cover 7 .

Moreover, it is easy for the cover 7 to absorb heat when the upper edge of the inner side surface thereof is angular. In regard to the problem, as mentioned in the above, by forming the beveled portion 7 c at the upper edge of the inner side surface of the cover 7 , it is difficult for the cover 7 to absorb heat, thereby, to improve the insulation performance.