COMBUSTION APPARATUS

Abstract

The present invention provides a combustion apparatus capable of obtaining a smaller heating value than usual and capable of reducing the amount of a mixed gas without causing a change in the mixture ratio of air and a fuel gas. A shutter member 4 is provided, which narrows the flow passage of a gate section 25 of a duct 23 when a mixed gas, which is produced by mixing air and a fuel gas, is forcibly sent from the duct 23 to a distribution chamber 12 by a fan 2.

Claims

1. A combustion apparatus comprising: a gas burner; and a premixing device which forcibly sends a mixed gas generated by mixing a fuel gas with air to the gas burner, wherein the gas burner includes a plurality of flame holes and a distribution chamber in which a mixed gas directed toward the flame holes is evenly distributed, and the premixing device includes; a fan; an air intake passage which takes in air drawn in by the fan; a fuel gas supply passage through which a fuel gas at an atmospheric pressure is supplied to the air intake passage; a mixed gas flow passage through which a mixed gas produced by mixing air and the fuel gas and sent out by the fan to a downstream, is introduced into the distribution chamber; and a flow passage reducing device which changes a flow passage area of the mixed gas flow passage in a reducing direction.

2. The combustion apparatus according to claim 1, wherein the flow passage reducing device includes a gate section shaped like a rectangular opening, through which the mixed gas in the mixed gas flow passage passes; and a shutter member shaped like a rectangular plate, which narrows the gate section in a direction across the mixed gas flow passage thereby to reduce the mixed gas flow passage.

3. The combustion apparatus according to claim 1, wherein the distribution chamber includes a partition member that partitions a combustion range of the gas burner into two cells, and the flow passage reducing device is configured to guide the mixed gas in the mixed gas flow passage into one of the two cells of the distribution chamber in a case where the flow passage area of the mixed gas flow passage is reduced to a predetermined area.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 is an explanatory perspective view illustrating a combustion apparatus according to an embodiment of the present invention;

[0022] FIG. 2 is an explanatory side view of a fan;

[0023] FIG. 3 is an interior plan view illustrating the fan and a duct partially cut away; and

[0024] FIG. 4 is a diagram illustrating the relationship between the number of revolutions of the fan and the heating value of a gas burner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] An embodiment of the present invention will be described with reference to the accompanying drawings. A combustion apparatus according to the present embodiment is incorporated in a water heater (not illustrated).

[0026] Referring to FIG. 1, the combustion apparatus has a gas burner 1, a fan 2, and a fuel gas supply pipe 3, which is a fuel gas supply passage. The fan 2 and the fuel gas supply pipe 3 constitute a premixing device according to the present invention.

[0027] The gas burner 1 is provided such that a plurality of flame holes (not illustrated) opens downward thereby to form flames on the bottom surface of the gas burner 1.

[0028] A heat exchanger 11 is connected to the bottom part of the gas burner 1. The heat exchanger 11 has therein a meandering water pipe and a fin (not illustrated). The gas burner 1 heats water passing through a water pipe of the heat exchanger 11.

[0029] A distribution chamber 12 is connected to the top part of the gas burner 1. The downstream end of a duct 23, which will be discussed hereinafter, is connected to one side of the distribution chamber 12. The distribution chamber 12 forms a space in communication with the flame holes of the gas burner 1. Further, the interior of the distribution chamber 12 is divided into two cells by a plate-like partition member 13, which rises to the top surface of the gas burner 1. In the present embodiment, the partition member 13 is provided at a position where the volumes of the two cells become equal.

[0030] The duct 23 corresponds to the mixed gas flow passage in the present invention, and is connected to the downstream side of the fan 2. The mixed gas forcibly sent from the fan 2 passes through the duct 23 to be supplied into the distribution chamber 12. As illustrated in FIG. 2, the duct 23 has a flow passage having a rectangular shape in a sectional view.

[0031] The fan 2 has a motor 21 and an air intake pipe 22, which is an air intake passage, as illustrated in FIG. 2. The air intake pipe 22 is connected to the upstream side of the fan 2, and the lower end thereof is opened as an intake port. Connected to the air intake pipe 22 is the downstream end of the fuel gas supply pipe 3.

[0032] The fan 2 is a so-called turbine type, and provided with a rotatable turbine 24, as illustrated in FIG. 3. The turbine 24 is rotatively driven by the motor 21 (refer to FIG. 1 or FIG. 2).

[0033] The fuel gas supply pipe 3 is provided with a pressure regulation device 31 referred to as Zero Governor. The pressure regulation device 31 decreases the pressure of a fuel gas, which is supplied at a predetermined positive pressure, to the atmospheric pressure. In other words, the fuel gas flowing in the fuel gas supply pipe 3 passes through the pressure regulation device 31 so as to be supplied to the air intake pipe 22 at the atmospheric pressure.

[0034] When the turbine 24 is rotated by the motor 21 in the fan 2, a negative pressure is generated in the air intake pipe 22. This causes external air to be drawn toward the fan 2 through the air intake pipe 22. Further, since the downstream end of the fuel gas supply pipe 3 is connected to the air intake pipe 22, the fuel gas, the pressure of which has been decreased to the atmospheric pressure by the pressure regulation device 31, is drawn into the air intake pipe 22.

[0035] Thus, in the state in which the fan 2 is at a halt and no negative pressure has been generated in the air intake pipe 22, no fuel gas flows into the air intake pipe 22 from the fuel gas supply pipe 3. Once the fan 2 is actuated and a negative pressure is produced in the air intake pipe 22, the fuel gas at a flow rate which is proportional to the magnitude of the negative pressure will be drawn into the air intake pipe 22 from the fuel gas supply pipe 3.

[0036] Then, the fuel gas drawn into the air intake pipe 22 is mixed, in the fan 2, with air drawn in through the lower end of the air intake pipe 22, and supplied through the duct 23 to the gas burner 1.

[0037] The number of revolutions of the fan 2 corresponds with the number of revolutions of the motor 21. The magnitude of the negative pressure in the air intake pipe 22 increases or decreases according to the level of the number of revolutions of the fan 2. At this time, even if the magnitude of the negative pressure in the air intake pipe 22 increases or decreases, causing the amount of air drawn into the air intake pipe 22 to increase or decrease, the amount of the fuel gas drawn into the air intake pipe 22 from the fuel gas supply pipe 3 also increases or decreases accordingly at the same degree, so that the mixture ratio of the mixed gas supplied to the gas burner 1 will remain constant.

[0038] Further, in the present embodiment, the downstream end of the duct 23 is provided with a gate section 25 shaped like a rectangular opening, as illustrated in FIG. 3. Further, a shutter member 4, which is swingably supported, is provided inside the duct 23. The shutter member 4 is provided such that the rectangular plate part thereof closes half the gate section 25. The gate section 25 and the shutter member 4 constitute the flow passage reducing device in the present invention.

[0039] If the shutter member 4 fully opens the gate section 25, then the mixed gas from the duct 23 flows in the directions indicated by arrows A and B into both of the two cells partitioned by the partition member 13 in the distribution chamber 12. Meanwhile, if the shutter member 4 is swung to close half the gate section 25, then the mixed gas will flow only in the direction indicated by arrow B and flow into one of the two cells partitioned by the partition member 13.

[0040] If the shutter member 4 is fully opened, then flames will be formed in an area a corresponding to the entire surface of the gas burner 1. If the half of the gate section 25 is closed by the shutter member 4, then the flames formed will be concentrated mainly in an area b. Thus, even if the supply amount of the mixed gas decreases when the shutter member 4 closes half the gate section 25, an adequate amount of the mixed gas will be supplied to the flame holes, enabling the gas burner 1 to maintain satisfactory combustion.

[0041] Further, the flow resistance of the mixed gas flowing from the duct 23 toward the distribution chamber 12 is low when the shutter member 4 is fully opened, whereas the flow resistance of the mixed gas flowing from the duct 23 toward the distribution chamber 12 increases when the shutter member 4 closes half the gate section 25.

[0042] As the flow resistance of the mixed gas flowing from the duct 23 toward the distribution chamber 12 increases when half the gate section 25 is closed, the flow rate of the mixed gas will decrease even if the number of revolutions of the fan 2 remains the same, as compared with the case where the gate section 25 is fully opened.

[0043] As described above, the amount of the mixed gas is regulated by changing the opening degree of the gate section 25 by the shutter member 4, so that even if the flow rate of the mixed gas passing through the gate section 25 decreases, the mixture ratio of air and the fuel gas in the mixed gas will not be influenced, thus maintaining a constant mixture ratio.

[0044] Further, the gas burner 1 can be stably operated with a heating value which is smaller than a normal heating value corresponding to the number of revolutions of the fan 2 which is below a lower limit value, without causing the actual number of revolutions of the fan 2 to become smaller than the lower limit value.

[0045] The relationship between the number of revolutions of the fan 2 and the heating value of the gas burner 1 according to the present embodiment will now be described with reference to FIG. 4.

[0046] In FIG. 4, a straight line L1 indicates the relationship between the number of revolutions of the fan 2 and the heating value (input) of the gas burner 1 when the gate section 25 is fully opened. The number of revolutions of the fan 2 is proportional to the supply amount of the mixed gas. Hence, the heating value of the gas burner 1 is proportional to the supply amount of the mixed gas.

[0047] To decrease the heating value in the gas burner 1, the number of revolutions of the fan 2 is decreased. However, a lower limit value RL is set for the number of revolutions of the fan 2, so that the fan 2 cannot be rotated at a speed that is lower than the lower limit value RL. For this reason, if the gate section 25 is fully opened, then the lower limit value of the heating value will be CL1, and no heating value below CL1 can be obtained.

[0048] To further decrease the heating value, therefore, the gate section 25 is half closed by the shutter member 4. This causes the number of revolutions of the fan 2 and the heating value to have a correlation denoted by a straight line L2. Thus, decreasing the number of revolutions of the fan 2 to the lower limit value RL enables the heating value to decrease to CL2.

[0049] It is to be understood that the present invention is not limited to the disclosed embodiments, and various changes and modifications can be made within the concept and scope of the present invention.