Burner

A burner has: a combustion plate part through which air-fuel mixture is ejected; and a flame rod which lies opposite to a portion of the combustion plate part. The combustion plate part is constituted by: a burner frame in a shape of a picture frame; a metal-fiber knit which covers an opening enclosed by the burner frame; and a distribution plate which has formed therein a multiplicity of distribution holes and which sandwiches the metal-fiber knit between the burner frame and the distribution plate so that the air-fuel mixture is ejected from the opening through the distribution holes and the metal-fiber knit. Flame holes for ejecting the air-fuel mixture are formed in a portion of the burner frame, and the flame rod is disposed so as to lie opposite to that portion of the burner frame which has formed therein the flame holes.

TECHNICAL FIELD

The present invention relates to a burner comprising: a combustion plate part through which air-fuel mixture is ejected; and a flame rod which lies opposite to a portion of the combustion plate part.

BACKGROUND ART

In this kind of burner, there is conventionally known one in which a combustion plate part is constituted by: a burner frame in the shape of a picture frame; a metal-fiber knit (i.e., a metal knit formed of a heat resistant metal fiber) which is disposed to cover an opening enclosed by the burner frame; and a distribution plate which has formed therein a multiplicity of distribution holes and which sandwiches the metal-fiber knit between the burner frame and the distribution plate. The air-fuel mixture is thus ejected through the distribution holes and the metal-fiber knit (see, for example, JP-A-2014-9839). The flame rod is disposed in a manner to lie opposite to a portion of the opening to be enclosed by the burner frame, i.e., to lie opposite to a portion of the metal-fiber knit.

When the flame rod is moved closer to the metal-fiber knit, frayed fibers of the metal-fiber knit may come into contact with the flame rod, thereby giving rise to wrong detection of the flame. Therefore, it has been made the practice to dispose the flame rod at a certain degree of distance to the metal-fiber knit. However, this practice has a problem in that, when the flame length has become considerably shorter in weak combustion, the flame ceases to contact the flame rod, thereby giving rise to a misjudgment that a misfiring has occurred.

SUMMARY

Technical Problem

In view of the above-mentioned point, this invention has a problem of providing a burner which is capable of placing the flame rod closer to the combustion plate part such that the flame detection accuracy can be improved.

Solution to Problem

In order to solve the above problem, this invention is a burner comprising: a combustion plate part through which air-fuel mixture is ejected; and a flame rod which lies opposite to a portion of the combustion plate part. The combustion plate part is constituted by: a burner frame in a shape of a picture frame; a metal-fiber knit which covers an opening enclosed by the burner frame; and a distribution plate which has formed therein a multiplicity of distribution holes and which sandwiches the metal-fiber knit between the burner frame and the distribution plate so that the air-fuel mixture is ejected from the opening through the distribution holes and the metal-fiber knit. Flame holes for ejecting the air-fuel mixture are formed in a portion of the burner frame, and the flame rod is disposed so as to lie opposite to that portion of the burner frame which has formed therein the flame holes.

According to this invention, that portion of the combustion plate part which lies opposite to the flame rod corresponds to the burner frame. Therefore, even if the flame rod is made considerably closer to the combustion plate part, frayed fibers of the metal-fiber knit will not be brought into contact with the flame rod. Such being the case, even if the flame length becomes shorter in weak combustion, the flame to be formed on the flame holes will come into contact with the flame rod. The detection accuracy of the flame can thus be improved.

Further, according to this invention, preferably the burner frame has partly formed therein a protruded part which protrudes into the opening, and the flame holes may be formed in the protruded part. In this case, the flame rod will be disposed so as to lie opposite to the protruded part.

The protruded part which protrudes into the opening will rise to a considerably elevated temperature. Therefore, preferably the protruded part is constituted by a separate part which is independent of, but which is attached to, the burner frame. According to this arrangement, instead of forming the entire burner frame of a material higher in heat resistivity, only the separate part that constitutes the protruded part may be formed of a material higher in heat resistivity. This arrangement can therefore contribute to reduction in cost.

Preferably, the flame rod is provided with: a main body portion lying opposite to that portion of the burner frame which has formed therein the flame holes; and an extension portion which extends from the main body portion inward of the opening, and the extension portion is further away from the combustion plate part than is the main body portion. According to this arrangement, even if the flame to be formed above the flame holes in the burner frame at the time of strong combustion is lifted out of contact with the main body portion of the flame rod, the flame to be formed on the metal-fiber knit inside the opening will be in contact with the extension portion of the flame rod. The flame detection accuracy can thus be secured. By the way, since the extension portion of the flame rod is relatively further away from the combustion plate part, i.e., the metal-fiber knit, there will be no possibility of the frayed fibers' coming into contact with the extension portion.

DESCRIPTION OF EMBODIMENTS

The burner according to an embodiment of this invention is provided with a combustion plate part1covering an upper surface of a box-shaped burner body which opens upward (not illustrated) for supplying thereto air-fuel mixture as shown inFIGS. 1 through 3. The combustion plate part1is constituted by: a burner frame2in the shape of a picture frame; a metal-fiber knit4which covers, from the lower side, an opening3enclosed by the burner frame2; and a distribution plate5which has formed therein a multiplicity of slit-shaped distribution holes51and which sandwiches the metal-fiber knit4between the distribution plate5and the burner frame2. Further, a flame rod6is disposed so as to lie opposite to a portion of the combustion plate part1. By the way, the opening3is curved into an arcuate shape in cross section along the front-to-back direction (vertical direction inFIG. 1) and, similarly, the metal-fiber knit4and the distribution plate5are also respectively curved into an arcuate shape in cross section along the front-to-back direction.

The burner frame2has: an opening peripheral part21which is positioned on the same surface level as the opening3; a side plate part22which is bent from the opening peripheral part21downward; and a flange part23which protrudes from a lower end of the side plate part22outward. The burner frame2is then fixed in position at its flange part23to a peripheral part of an upper surface of the burner body. Further, in a state in which the distribution plate5is placed under the metal-fiber knit4, the peripheral parts of the metal-fiber knit4and the distribution plate5are spot welded for fixing to the opening peripheral part21.

In a portion of the opening peripheral part21of the burner frame2, there are formed flame holes24through which the air-fuel mixture is ejected. The flame rod6is disposed so as to lie opposite to that portion of the opening peripheral part21which has formed therein the flame holes24. Further, in that portion of the metal-fiber knit4which overlaps that portion of the opening peripheral part21which has formed therein the flame holes24, there is formed a notched part41. Therefore, the air-fuel mixture is ejected out of the flame holes24without passing through the metal-fiber knit4. Alternatively, by omitting the notched part41, an arrangement may be made such that the air-fuel mixture is ejected out of the flame holes24through the metal-fiber knit4.

In addition, in this embodiment, the flame rod6is provided with: a main body portion61which lies opposite to that portion of the burner frame24which has formed therein the flame holes24; and an extension portion62which is extended from the main body portion61inward of the opening3so as to lie opposite to the metal-fiber knit4. The extension portion62is further away from the combustion plate part1than is the main body portion61(than the main body portion61is away from the combustion plate1).

According to the above-mentioned arrangement, that portion of the combustion plate1which lies opposite to the flame rod6is the burner frame2. Therefore, even if the main body portion61is made considerably closer to the combustion plate part1, the frayed fibers of the metal-fiber knit4will not come into contact with the main body portion61. As a result, even in case the flame length becomes shorter in weak combustion, the flame to be formed on the flame holes24will come into contact with the main body portion61, so that the flame detection accuracy can be improved.

In addition, even if the flame to be formed on the flame holes24is lifted at the time of strong combustion so that the flame ceases to be in contact with the main body portion61of the flame rod6, the flame to be formed on the metal-fiber knit4inside the opening3comes into contact with the extension portion62of the flame rod6. The flame detection accuracy can thus be secured. The extension portion62is relatively largely away from the combustion plate part1, i.e., from the metal-fiber knit4. Therefore, the frayed fibers will not come into contact with the extension portion62.

Description will now be made of a second embodiment with reference toFIGS. 4 and 5. In the above-mentioned first embodiment, the flame holes24are formed in that portion of the opening peripheral part21of the burner frame2which is linearly extended. In the second embodiment, on the other hand, a protruded part25which protrudes into the opening3is provided in a portion of the opening peripheral part21so that the flame holes24are formed in this protruded part25. Then, the flame rod6is disposed so as to lie opposite to the protruded part25that is the portion in which the flame holes24are formed. The flame rod6is provided with: a main body portion61which lies opposite to the protruded part25; and an extension portion62which is upwardly offset from the main body portion61so as to extend inward of the opening3. Similar operation and effect can be obtained in the arrangement according to the second embodiment as in the first embodiment.

By the way, in the second embodiment, the protruded part25is integrally formed in the burner frame2. In a third embodiment as shown inFIG. 6, the protruded part25may be constituted by separate parts26that are separate from the burner frame2but which is attached to the burner frame2. It is to be noted that the protruded part25will reach a considerably elevated temperature because it is protruded into the opening3. In the arrangement of the second embodiment, it is necessary to make the entire burner frame2of a material higher in heat resistivity in order to secure heat resistivity of the protruded part25. This arrangement results in higher costs. On the other hand, in the arrangement according to the third embodiment, only the separate part26that constitutes the protruded part25need be formed of a material higher in heat resistivity. This arrangement can therefore contribute to reduction in cost.

Descriptions have so far been made of embodiments of this invention with reference to the drawings. However, this invention shall not be limited to the above. For example, the flame rod6may be one having no extension portion62of the above-mentioned embodiment. In addition, in the above-mentioned embodiments, the combustion plate1is arranged to look upward so that the air-fuel mixture can be ejected upward. This invention can similarly be applicable to a burner in which the combustion plate is arranged to look downward or look sideways.

REFERENCE SIGNS LIST