JPH0138201B2 - - Google Patents

Description

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

Conventional structure and its problems Conventionally, this type of hot air heater has been used to connect an air heater to the outside through 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 A rectifying pipe 5 consisting of a
Furthermore, it passes through the exhaust chamber 6 and is discharged outdoors again through the exhaust pipe 7. Solid arrows indicate the flow.
On the other hand, the warm air supplied into the room undergoes heat exchange with the combustion tube 3, the bender 4, and the exhaust chamber 6, in addition to the rectifier tube 5 where the air sucked in by the indoor circulation fan 8 functions as a heat exchanger. The rectifier pipe 5, combustion tube 3, bender 4, and exhaust chamber 6 will be referred to as a heat exchanger block hereinafter.

In such a configuration, especially during ignition at low temperatures, the temperature difference between the various parts of the heat exchanger block is large, resulting in a temperature boundary layer with a uniform cross section, which changes the acoustic impedance and causes pressure waves. brings reflection to. In addition, as time passes, the temperature boundary layer shifts to the lower temperature side, and the repetition period of reflection changes accordingly, resulting in a variable frequency of the pressure wave, which matches the resonance of the system such as the combustion tube. In this case, there was a problem in that combustion oscillations, which are a type of self-excited oscillations, occurred, although for a short time.

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 that becomes the reflective edge, suppresses the repetition of reflection of pressure waves, and reduces the sharpness of resonance. The purpose is to soften the flame and 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 a combustion cylinder, which also serves as a combustion chamber, by a control plate having a communication hole that communicates the burner side and the bender side.

With this configuration, from the state before ignition to several seconds after ignition, that is, during the time when combustion vibration is most likely to occur, part of the pressure waves excited during ignition are reflected by the control board, and the pressure waves are reflected from the burner side. Reflection occurs between the temperature boundary layer, which has a uniform cross section, and which shifts to the lower temperature side with time. 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 that pass through the communication holes provided in the control board propagate through each part of the heat exchanger block, but are reflected at the boundary between the bender and the rectifier tube, where the cross-sectional change is particularly large, and become reflected waves for control. Propagates to the plate side. Moreover, the temperature boundary layer is
Because the high-temperature exhaust gas flow is deflected and flows through the communication hole provided in the control plate, the temperature distribution on the downstream side of the control plate is disturbed and uneven, and the pressure waves reflected from the rectifier tube are caused by irregular reflection edges. The sharpness of the resonance is eliminated, and the conditions that cause combustion oscillations can be removed.

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. The high-temperature exhaust gas after combustion is forcibly guided downward by the communication hole 10 of the control plate 9 provided in the passageway of the combustion tube 3, passes through the bender 4, the rectifier pipe 5, and the exhaust chamber 6 to the exhaust pipe ( (not shown) is discharged outdoors.

In the above configuration, especially when starting at low temperatures,
The pressure waves generated by ignition propagate through the passages of each part of the heat exchanger block, but are partially reflected by the control plate 9 and propagate toward the burner. Further, the pressure wave passing through the communication hole 10 is also reflected by the rectifier tube 5 whose cross-sectional area is suddenly reduced, and then propagates toward the control plate 9 side. However, since the control plate 9 is provided near the burner surface, the reflected waves toward the burner have a high frequency due to reflection, and the result is significantly different from the resonance of the system that causes combustion vibration.

On the other hand, although heat propagation due to combustion is slower than pressure waves, it progresses in the direction of the rectifier tube 5. At that 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 by 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 a state in which the flow for indoor circulation shown by a dashed line in FIG. It shows that the flow is located on the side where it collides with the outer wall of the combustion tube 3. In addition, the resonance state that occurs in the pipe when the control plate 9 and the burner surface are at both ends is caused by the interference of two or more pressure waves, creating a pressure field where the areas of high pressure and areas of low pressure do not change over time. In standing wave resonance, if the distance between both ends is l and the speed of sound is C, then the resonant frequency is expressed as =C/2l. However, since the control plate 9 is provided obliquely, the wavelength of the pressure wave with the control plate 9 as one end gradually changes according to the inclination angle of the control plate 9. In addition to this effect, it is also possible to suppress the occurrence of standing wave resonance due to its shape, which has a great effect on suppressing self-excited vibrations caused by pressure fluctuations during initial ignition.

In addition, as shown in FIG. 4, the control board 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 flows through the communication hole. Forced to 10. the result,
Indoor circulating air is one that undergoes efficient heat exchange.

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

(1) By installing a control plate in the combustion cylinder that has a communication hole that partitions the passage and makes the temperature distribution uneven on the downstream side, 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, it is possible to prevent standing waves from occurring in the combustion tube and bender, and by combining the effects of (1) above, combustion vibration can be further suppressed. Can be done.

(3) By providing the communication hole of the control plate provided in the combustion cylinder on the side where the indoor circulating air flow collides with the outer wall surface of the combustion cylinder, efficient heat exchange becomes possible.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway sectional view of a conventional forced air supply and exhaust hot air heater, and 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.
FIG. 3 is a partially cutaway front view of a heat exchanger block showing another embodiment of the present invention, and FIG. 4 is a Y--
It is a sectional view taken along the Y line. 1... Burner block, 2... Air supply pipe, 3...
Combustion tube, 4... Bender, 5... Rectifier tube, 6...
Exhaust chamber, 7... Exhaust pipe, 9... Control board, 10...
Communication hole.

Claims (1)

[Scope of Claims] 1. A burner block consisting of a combustion fan and a burner has an air supply pipe on the upstream side, a combustion cylinder, a bender, a rectifier pipe, an exhaust chamber, and an exhaust pipe on the downstream side, and in the combustion cylinder A combustion vibration prevention device that is equipped with a control plate that has a communication hole that partitions the passage and makes the temperature distribution on the downstream side uneven. 2. The combustion vibration prevention device according to claim 1, wherein the control plate is provided obliquely to the burner surface. 3. The combustion vibration prevention device according to claim 2, wherein the communication hole of the control plate provided in the combustion cylinder is provided on the side where the indoor circulating air flow collides with the outer wall surface of the combustion cylinder.