JPS6023718A - Device for preventing occurrence of combustion vibration - Google Patents

Abstract

PURPOSE:To prevent the occurrence of combustion vibration during ignition at a low temperature time, by a method wherein the inside space of a combustion cylinder combined with a combustion chamber is partitioned by a control plate having a communicating hole which intercommunicates the burner side and the bender side. CONSTITUTION:A burner block 1 is located so that a burner is positioned in a direction extending orthogonal to the direction of axis of a combustion cylinder 3, and high temperature exhaust gas after combustion is forcibly guided downward by means of a communicating hole 10 in a control plate 9 located within a passage in a combustion cylinder 3, and is exhausted to the outside from an exhaust pipe through a bender 4, a flow uniformizing pipe 5, and an exhaust chamber 6. Location of the control plate causes disturbance of a temperature boundary layer formed in the passage, and causes non-uniformization of a reflecting state at the boundary layer of a pressure wave during ignition in which combustion vibration is caused, and this removes the cause of the occurrence of combustion vibration. The control plate 9, positioned in a slanted manner, has a communicating hole 10, formed by a plurality of pores, on the side where the air for circulation in the chamber collides with the outer wall of a combustion chamber 3. This constitution removes the source of the production of a steady wave generated in a combustion cylinder and a communicating passage, which are most related to acoustic resonance of a system holding combustion vibration, and enables to perform efficient heat exchange.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a device for preventing combustion vibrations occurring in a forced air exhaust hot air heater, particularly during startup.

Conventional Structure and Problems Conventionally, this type of hot air heater has been used to connect outdoor air heaters from an air supply pipe 2 communicating with the upstream side of a burner block 1 consisting of a combustion fan and a burner, as shown in Fig. 1. The combustion air of It passes through a rectifier pipe 5 consisting of a rectifier pipe 5, an exhaust chamber 6, and then is discharged outdoors via an exhaust pipe 7. Solid arrows indicate the flow.

On the other hand, the warm air supplied into the room is air sucked in by the indoor circulation fan 8 and heat exchanged with the heat exchanger block constituted by the combustion tube 3, the rectifier tube 5, and the like.

In such a configuration, the temperature difference between each element of the heat exchanger block is large, especially during ignition at low temperatures, resulting in a temperature boundary layer with a uniform cross section, which changes the acoustic impedance and is reflected in the pressure wave. bring about.

Also, as time passes, the temperature boundary layer shifts to the lower temperature side,
Along with this, the repetition period of reflection changes and the frequency of the pressure wave changes, and if that frequency matches the resonance of the system such as the combustion tube, a type of self-excited vibration occurs, albeit for a short time. The problem was that combustion oscillations occurred.

Purpose of the Invention The present invention makes the temperature distribution on the downstream side of the control plate that partitions the combustion cylinder passage non-uniform, disturbs the temperature boundary layer which becomes the reflection edge, suppresses the repetition of reflection of pressure waves, and reduces the sharpness of resonance. Soften,
The purpose is to prevent combustion vibrations that occur during ignition at low temperatures.

Structure of the Invention In order to achieve this object, the present invention partitions the inside of the combustion cylinder, which also serves as a combustion chamber, by a control plate having a communication hole that communicates the burner side and the pengo side.

With this configuration, when ignition lags a few seconds after ignition from the state before ignition, that is, at the time when combustion oscillations are most likely to occur, part of the pressure wave excited during ignition is reflected by the control board, and over time the pressure wave is reflected from the burner side to the lower temperature side. Reflection occurs between the cross-sectionally uniform temperature boundary layer and the transition to . However, since the control plate is provided near the burner surface in the same combustion cylinder, the time taken to pass through the control plate is fast, and the frequency of reflection becomes high, making it difficult to match the resonance of the system. On the other hand, the pressure waves passing through the communication holes provided in the control board propagate through each heat exchanger element, but are reflected at the boundary between the bender and the rectifier tube, where the cross-sectional change is particularly large.
It becomes a reflected wave and propagates toward the control board. In addition, in the temperature boundary layer, the high-temperature exhaust gas flow is deflected and flows through the communication hole provided in the control plate, so the temperature distribution is disturbed and uneven on the downstream side of the control plate, and the pressure waves reflected from the rectifier tube are uneven. Due to the regular reflection edges, the sharpness of the resonance is eliminated, and the conditions that cause combustion oscillations can be eliminated.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. Note that the same members as in FIG. 1 are given the same numbers.

In FIG. 2, a burner (not shown) is attached to the burner block 1 in a direction perpendicular to the axial direction of the combustion tube 3, and a flame is formed at the end of the combustion tube 3 on the burner side. Ru. The high-temperature exhaust gas after combustion is forcibly guided downward by the communication hole 10 of the control plate 9 provided in the passage of the combustion tube 3, passes through the bender 4, the rectifier pipe 5, and the exhaust chamber 6, and then flows into the exhaust pipe (Fig. (not shown) is discharged outdoors.

In the above configuration, especially during startup at low temperatures, the pressure waves generated by ignition propagate through the passages of each element, but are partially reflected by the control plate 9 and propagate toward the burner. Also, communication hole 1
The pressure wave that has passed through 0 is also reflected by the rectifier tube 5 whose cross-sectional area has suddenly become smaller, and then propagates toward the control plate 9 side. However, since the control plate 9 is placed close to the burner surface, the frequency of the reflected waves toward the burner becomes high, resulting in a result that is significantly different from the resonance of the system that causes combustion vibration. Although heat propagation due to combustion is slower than pressure waves, it progresses in the direction of the rectifier tube 5. At this time, a temperature boundary layer with a uniform cross section is formed up to the control plate 9 provided in the combustion tube 3 passage, but if the exhaust gas passage is forcibly changed due to the communication hole 10 provided below the control plate 9. On the downstream side of the control plate 9, the temperature distribution becomes non-uniform in the upper and lower parts of the passage, causing disturbances in the temperature boundary layer. As a result, the pressure waves reflected by the rectifier tube 5 are reflected by the temperature boundary layer, but the reflection state is uneven compared to a boundary layer with a uniform cross section, and the frequency component is not one, resulting in sharp resonance. can be prevented. As a result, it is possible to suppress the generation of self-excited vibrations that occur due to the repetition frequency of this reflection and coincident with the acoustic resonance of the system.

Next, another embodiment of the present invention will be described with reference to FIGS. 3 and 4.

In FIG. 3, the control plate 9 in FIG. 2 is provided obliquely with respect to the burner surface, and the communication hole 10 is composed of a plurality of small holes. Further, FIG. 4 shows the relationship between the indoor circulation air flow and the communication hole 10, which is indicated by a dashed line in the cross section in FIG. 3.

According to the above configuration, since the control plate 9 is provided obliquely, the wavelength of the pressure wave having one end of the control plate 9 gradually changes according to the inclination angle of the control plate 9. In addition to the effects described above, the generation of standing wave resonance can also be suppressed due to the shape, and a great effect is obtained in suppressing automatic vibrations caused by pressure fluctuations during initial ignition.

In addition, as shown in FIG. 4, the control plate 9 has a communication hole 10 consisting of a plurality of small holes on the side where the indoor circulation air collides with the outer wall of the combustion tube 3, so that high temperature exhaust gas is removed. It is forcibly guided to the communication hole 10. As a result, indoor circulating air undergoes heat exchange efficiently.

Effects of the Invention As described above, the vibration combustion prevention device of the present invention provides the following effects.

(1) By providing a control plate with a communication hole in the combustion cylinder that partitions the passage and makes the temperature distribution on the downstream side uneven, it disturbs the temperature boundary layer formed in the passage and causes combustion oscillations. It makes the reflection state of the pressure wave at the boundary layer uneven during ignition and eliminates the cause of its occurrence.

(2) By installing a control plate diagonally in the combustion tube passage, the cause of the standing waves that occur in the combustion tube and the communication passage, which are most related to the acoustic resonance of the system that sustains combustion vibration, is removed,
Combustion vibration can be further suppressed by combining the effect of (1) above.

(3) By providing the communication holes in the control board on the side that collides with the indoor circulating air flow, efficient heat exchange becomes possible.

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway sectional view of a conventional forced air supply/exhaust hot air heater, Fig. 2 is a partially cutaway front view of a heat exchanger block showing an embodiment of the combustion vibration prevention device of the present invention, and Fig. 3 4 is a partially cutaway front view of a heat exchanger block showing another embodiment of the present invention, and FIG. 4 is a sectional view taken along the Y-Y line in FIG. 3. 1...Burner block, 2...Air supply pipe, 3.
Combustion tube, 4... Communication path, 5... Rectifier pipe, 6...
Exhaust chamber, 7... Exhaust pipe, 9... Control board, 10
・Communication hole. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3

Claims (3)

[Claims] (1) A burner block consisting of a combustion fan and a burner has an air supply pipe on the upstream side, a heat exchanger block consisting of a combustion tube, a bender, a rectifying pipe, and an exhaust chamber on the downstream side, and an exhaust pipe, and the above-mentioned A combustion vibration prevention device that is equipped with a control plate that has a communication hole in the combustion cylinder that partitions a passage and makes the temperature distribution on the downstream side non-uniform. (2) The combustion vibration prevention device according to claim 1, wherein the control plate is provided diagonally with respect to the burner surface. (3) The combustion vibration prevention device according to claim 2, wherein the communication hole provided in the control plate is arranged on the side that collides with the indoor circulation air flow.