JPH0421088B2 - - Google Patents

Description

[Detailed description of the invention] Industrial applications The present invention relates to a pulse combustor.

Conventional Structure and Problems When a pulse combustor is started, combustion air is supplied to the combustion chamber using fuel gas and a blower fan, and combustion is forced by operating a spark plug. Once the system stabilizes and forms a combustion cycle, combustion air is automatically sucked in and self-ignition continues pulsed combustion at a constant frequency of tens to hundreds of hertz even when the spark plugs and blower fan are stopped.

Such a pulse combustor burns under high load, has good heat transfer characteristics, automatically performs ignition and air supply/exhaust except during startup, and has the advantages of a simple structure.

However, a problem with the pulse combustor is that it produces a lot of noise during combustion. For this purpose, a muffler is installed, but since the acoustic impedance changes when a muffler is installed, the fundamental frequency of the combustion cycle may change. For this reason, the muffler that you have taken the pains to install is often not as effective as expected. Therefore, the air pulse device is surrounded by an air cushion chamber, and the acoustic impedance of the air cushion chamber is made large enough so as not to affect the fundamental frequency of pulse combustion.
Even when a muffler is attached, a predetermined frequency can be maintained, making the muffler effective at muffling noise. However, in the case of pulse combustion, since the combustion noise is very loud, there are problems such as vibration of the wall surface of the air cushion chamber and leakage of sound from the wall surface, especially sound leakage in the low frequency range. For this reason, even if a muffler is installed to reduce the noise emitted from the supply and exhaust ports, there have been cases in which the noise leaking from the main body becomes louder.

OBJECTS OF THE INVENTION The present invention has been made in view of these problems, and it is an object of the present invention to provide a pulse combustor with a simple structure and low noise.

Structure of the Invention In order to achieve the above object, the present invention provides a perforated plate in the air supply path with a gap between the inner wall surface and the air supply path.
This void is filled with sound absorbing material.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described with reference to FIG.
As shown in Fig. 1, the pulse combustor of this embodiment has the following features:
Combustion chamber 1, tail pipe 2, spark plug 3, air chamber 4, air supply path 5, air valve device 6, perforated plate 7, air cushion chamber 8, fuel supply path 9,
It is composed of a fuel valve device 10 and a sound absorbing material 11.

The combustion sound of the pulse combustor has harmonic components consisting of a fundamental frequency _{of 0} determined by the shapes of the combustion chamber 1 and the tail pipe 2 and sounds at integral multiples of the fundamental frequency. Since this fundamental frequency ₀ is a low frequency sound ranging from tens to hundreds of hertz, this sound vibrates the wall surface of the air cushion chamber 8, causing sound leakage from the wall surface, especially low frequency component sound. It's making the leak bigger.

Therefore, in this embodiment, in order to reduce the sound that passes through the air valve device 6 and enters the air cushion chamber 8, a gap is created in the air supply path 5 and the inner wall surface of the air supply path 5. A perforated plate 7 is provided, and a sound absorbing material 11 is provided in the gap between the air supply path 5 and the perforated plate 7.
is filled with. The perforated plate 7 may be a metal plate with many small holes, or a material with many small holes such as sintered metal or foamed ceramic. As shown in FIG. 2, the combustion sound 12 that has passed through the air chamber 4 is absorbed by a large number of small holes 13 formed on the surface of the perforated plate 7, and the sound is absorbed by the air supply path 5 and the perforated plate 7.
Enter the void between. Since the void is filled with sound absorbing material 11, the sound that enters the void is transmitted to the air supply path 5.
While the sound is absorbed by the sound-absorbing material 11, the combustion sound 12 is repeatedly collided and dispersed between the inner wall surface and the surface of the perforated plate 7, and the combustion sound 12 is muffled by mutual interference. Silencing due to this mutual interference is effective over a wide range from low frequency ranges to high frequency ranges. Further, since the sound absorbing material 11 has the property of blocking fluid and allowing sound pressure to pass through, even if the present invention is implemented, the flow state of the air supply path 5 will not change and combustion will not be affected. Furthermore, the present invention does not use a method of simultaneously attenuating sound pressure and flow pressure by providing an expansion chamber or the like in the air supply system as a method for reducing combustion noise. Combustion noise can be muffled without attenuating the operating pressure of 14. As a result, the air valve 14 can be opened and closed smoothly, and combustion noise can be reduced while maintaining a good combustion state.

As described above, the combustion noise generated in the combustion chamber 1 is muffled when passing through the air supply path 5 and is radiated to the air cushion chamber 8. Therefore, the low-frequency sound component that causes the wall surface of the air cushion chamber 8 to vibrate is attenuated, the wall surface of the air cushion chamber 8 hardly vibrates, and the leakage of sound from the wall surface is significantly reduced. Therefore, noise can be reduced compared to conventional pulse combustors.

Effects of the Invention According to the present invention, the vibration of the wall surface of the air cushion chamber and the leakage of sound from the wall surface are significantly reduced, which is effective in reducing the noise of the pulse combustor.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a pulse combustor according to an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of an air supply path of the pulse combustor. DESCRIPTION OF SYMBOLS 1... Combustion chamber, 2... Tail pipe, 5... Air supply path, 6... Air valve device, 7... Perforated plate, 8... Air cushion chamber, 11... Sound absorbing material.

Claims (1)

[Claims] 1. A tail pipe connected to one end of the combustion chamber, a fuel supply passage and an air supply passage connected to the other end of the combustion chamber, a fuel valve device connected to the fuel supply passage, and an air supply passage connected to the air supply passage. a valve device; an air cushion chamber housing the air valve device therein and connected to the air supply path;
A pulse combustor in which a perforated plate is provided with a gap between the inner wall surface of the air supply path and a sound absorbing material is filled in the gap.