JPH02211316A - Muffler and muffling method - Google Patents

Abstract

PURPOSE:To reduce the sound of exhaust at a high sound absorption rate without bringing in deterioration with time, as an exhaust resistance is being made to be small by making a constitution in which a pitch type carbon fiber is used as a sound absorbing material. CONSTITUTION:A muffler 5 is connected communicatingly with an engine 1 through an exhaust manifold 3 and the 1st exhaust pipe 4, and at the same time, the 2nd exhaust pipe 6 discharging exhaust gas into atmosphere, is communicatingly connected to the muffler 5. At the muffler 5, the respective one ends of the 1st, the 2nd exhaust pipes 4, 6 are inserted into a casing 7 in a state in which they are on different levels, and a curl shaped pitch type carbon fibre 9 is inserted, as a sound absorbing, material, into the inside of the casing 7 forming a flow route for a high temperature exhaust gas in a pressurization state, and thus, a constitution is made. As a result, the energy of sound is excellently damped by means of this pitch type carbon fiber 9.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is applicable to various internal combustion engines and pulse combustion engines such as vehicle engines such as automobiles, industrial engines such as engines that drive pumps and various equipment, and marine engines. This invention relates to a silencer and a method of silencing the sound used in appliances, etc.

<Conventional technology> Conventional expansion-type silencers mainly use rock wool or glass fiber as sound-absorbing materials, and resonance-type silencers also absorb sound wave energy in a wide frequency band. In order to more effectively reduce noise, materials similar to those described above are used as sound absorbing materials.

<Problem to be solved by the invention> However, in the above-mentioned silencer using glass fiber or the like as a sound absorbing material, sound absorption and attenuation of acoustic energy by the sound absorbing material are affected by the viscosity, thermal conduction, and molecular absorption of the sound absorbing material. However, the muffling effect is still not sufficient, and mufflers for internal combustion engines are not suitable for exhaust gas. Further reduction in sound is desired.

In addition, in conventional mufflers, it is known that increasing the amount of sound-absorbing material inserted increases the silencing effect, but increasing the amount of sound-absorbing material inserted increases exhaust resistance and reduces the output of the internal combustion engine. At the same time, fuel efficiency decreases and becomes uneconomical, and when trying to satisfy the contradictory demands of having as little exhaust resistance as possible and making the exhaust noise as low as possible,
The reality is that the above-mentioned silencer using glass fiber or the like as a sound absorbing material cannot be improved beyond the current situation.

Further, conventional sound absorbing materials such as glass fibers have the disadvantage that their performance deteriorates over time due to hydrolysis due to moisture in exhaust gas and high temperatures.

Therefore, a sound absorbing material with excellent high temperature properties, no deterioration (and high sound absorption coefficient) is desired.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a muffler that can reduce exhaust noise with a high sound absorption coefficient without causing deterioration over time while reducing exhaust resistance. shall be.

Means for Solving the Problems> In order to achieve the above objects, a first muffler according to the present invention is constructed using pitch-based carbon fiber as a sound absorbing material.

As the pitch-based carbon fiber, coal-based pitch, petroleum-based pitch, isotropic pitch, optically anisotropic mesophase pitch, and the like can be used as raw materials. Preferably, an isotropic pitch is used.

In order to achieve the above-mentioned object, the second muffler according to the present invention is constructed by providing pitch-based carbon fiber as a sound absorbing material in a fluid flow path.

For example, pitch-based carbon fibers are inserted inside a casing that passes high-temperature exhaust gas discharged from an engine.

In order to achieve the above-mentioned object, the noise reduction method of the third invention is carried out by covering the noise source with pitch-based carbon fiber.

The exterior of the casing, engine housing, etc. through which the high-temperature exhaust gas passes is coated with pitch-based carbon fiber.

The above-mentioned pitch-based carbon fiber is manufactured, for example, as follows.

Isotropic pitch with a softening point of 230 to 320°C, prepared from coal-based pitch, is spun at 270 to 360°C by the vortex method, and after spinning, it is infusible in air at 300 to 350°C, and the infusible fiber is produced. By carbonizing and firing at 650-1300℃, the fiber diameter is 10-188m, the bulk density is 0.01-0.06 g/d, and the length is 3-13cm.
111 tensile strength is 50 to 100 kg/am'', tensile modulus is 2.7 to 5 ton/vs'', and elongation is 1.7 to 2.
4% slightly curled pitch-based carbon fibers are obtained. The obtained pitch-based carbon fiber can be used as a sound absorbing material as it is or after being compressed or loosened.

Pitch-based carbon fiber obtained by winding up the pitch discharged from a nozzle or pulling it with an air sucker to thin it can also be used.

The carbonization firing treatment is preferably carried out at a temperature of 850 to 970°C, more preferably 870 to 950°C, from the viewpoint of heat resistance and high sound absorption characteristics. Further, uncurled straight pitch-based carbon fibers can also be used, but the use of curled fibers spun by the vortex method as described above has a greater sound absorption effect.

Spinning methods for obtaining curled pitch-based carbon fibers include a vortex method, a rotary spinner method, a jet method, and the like. Note that the spinning method does not matter.

In this way, by specifying the raw material pitch, the properties of the spinning pitch, the spinning method, and the carbonization firing temperature, the viscosity, heat conduction, and sound absorption coefficient due to molecular absorption can be further improved.

The muffler of the present invention is not limited to one formed in a tubular shape, but also includes a muffler chamber formed in a box shape.

The pitch-based carbon fiber used in the present invention can be used as a sound absorbing material even at room temperature, but is more effective at temperatures above 100''C.

The upper limit of the usage temperature varies depending on the atmosphere of the environment in which it is used, and when used in a non-oxidizing atmosphere, it can be used up to 1300°C. When used in an oxidizing atmosphere, it can be used up to 650°C. Approximately 500 when the allowable oxidation loss is small
It is best to use up to ``C.''

The muffler or the muffler method of the present invention provides an automobile engine,
Can be used for various noise sources such as industrial engines, marine engines, pulse combustion equipment, and crushers.

<Effect> After various considerations, it is clear from the comparative experiment results described below that by using pitch-based carbon fiber as a sound absorbing material, especially when used at high temperatures, it is possible to achieve results that cannot be obtained with conventional sound absorbing materials. It has been found that heat resistance and high sound absorption coefficient can be obtained. Focusing on this, pitch-based carbon fibers are used as sound-absorbing materials to effectively attenuate acoustic energy by providing them in the fluid flow path in a silencer or covering noise sources. be able to.

<Example> Next, an example of the present invention will be described in detail based on the drawings.

Softening point of 290℃ (280~2
The isotropic pitch of approximately 340°C (333~
After spinning, the fibers are infusible at about 320°C (305-335°C) in air, and the infusible fibers are heated at about 910°C (880-950°C).
℃), the fiber diameter is approximately 14 μI.
m (13 to 15 μm), bulk density 0.05 g/cd,
The average length is approximately 7cm (4~locm), the tensile strength is approximately 80kg/ms", and the tensile modulus is approximately 3.5ton/+w
A slightly curled pitch-based carbon fiber with an elongation of about 2% was obtained.

450 g of curled pitch-based carbon fiber obtained in this way,
It was inserted into an expansion type muffler connected to a 1500 cc, 4-stroke gasoline engine for automobiles.

The configuration of the above-mentioned silencer and the configuration of the silencing performance measuring device will be explained using the schematic configuration diagram of FIG. 1. In FIG. ing.

Further, a muffler 5 is connected to the engine 1 through an exhaust manifold 3 and a first exhaust pipe 4, and a second muffler 5 is connected to the muffler 5 to release exhaust gas into the atmosphere.
Exhaust pipes 6 are connected in communication.

The muffler 5 has one end side of each of the first and second exhaust pipes 4 and 6 inserted into the casing 7 in a stepped manner, and the casing 7 forms a flow path for pressurized high-temperature gas. The above-mentioned curled pitch-based carbon fiber 9 is inserted as a sound absorbing material inside.

In each example, the pitch-based carbon fiber 9 was fixed with punching metal. In order to reduce scattering of the pitch-based carbon fibers 11I9, it is preferable to cover the pitch-based carbon fibers 9 with a heat-resistant woven fabric.

A sound insulation box lO is attached to the pipe end of the second exhaust pipe 6, and a predetermined location within the sound insulation box 10 (at an angle of 45° to the longitudinal direction of the second exhaust pipe 6, 500 m from the pipe end) A microphone 11 that measures the sound pressure of the exhaust sound is installed at a distance of .

As the silencer 5, the inner diameter (diameter) of the casing 7 is
is 200M, longitudinal length is 300mo+, exhaust pipe diameter is 42.7u, engine output is 2ops, rotation speed is 400Orpm, engine exhaust gas temperature is 474~5.
The sound pressure of the exhaust sound was measured under operating conditions of 0.4°C (temperature at the inlet of the muffler), and the results shown in the bar graph in FIG. 2 were obtained.

Straight pitch-based carbon fibers were produced under the same production conditions as in Example 1, except that the pitch discharged from the nozzle was pulled and thinned using an air sunker and spun without using the vortex method.

450 g of the straight pitch-based carbon fiber was inserted into the casing 7 as a sound absorbing material.

450 g of straight pitch-based carbon fibers produced using petroleum-based pitch as a raw material were inserted into the casing 7 as a sound absorbing material.

450 g of conventionally used glass fiber was inserted into the casing 7 as a sound absorbing material.

Curled pitch-based carbon fiber 450 manufactured under the same conditions as in Example 1 except that the carbonization firing temperature was 970°C.
g was inserted into the casing 7 as a sound absorbing material.

Example 1" I- Curled pitch-based carbon fiber 45 manufactured under the same conditions as in Example 1 except that the carbonization firing temperature was 1300 ° C.
0g was inserted into the casing 7 as a sound absorbing material.

Using the silencers of Examples 2 to 5 and Comparative Example 1 described above, the sound pressure of the exhaust sound was measured under the same conditions as described in Example 1, and the results shown in the bar graph in FIG. 2 were obtained. Ta.

In addition, using the silencers of Examples 1 to 5 and Comparative Example 1, engine output was 30 ρS and rotation speed was 250 Orp.
The time required to consume 5 cc of fuel under operating conditions of 15 cc, that is, the fuel consumption (min 15 cc), was determined, and the results shown in the bar graph in FIG. 3 were obtained.

Furthermore, for the amount of attenuation of exhaust sound at each of a large number of predetermined frequencies, from the viewpoint of raw materials, a coal-based pitch was used (Example 1)
A comparison was made between the pitch and the petroleum pitch (Example 3), and the results shown in the bar graph in FIG. 4(a) were obtained. AP shown in FIG. 4(a) is the measured value of the total noise [this is also the same in FIG. 4(b) and (C), which will be described later].

The displayed value is a decibel value, and the audible sound reduction effect was large.

In addition, from the viewpoint of carbonization firing temperature, those carbonized and fired at 930°C (corresponding to Example 1), those carbonized and fired at 970°C (Example 4), and those carbonized and fired at 1300°C (Example 5). ) When comparing each, we found that (b) in Figure 4
) obtained the results shown in the bar graph.

Ta.

In addition, from the viewpoint of spinning properties, curly ones (Example 1)
When comparing the straight hair type (Example 2), it was found that the fourth
The results shown in the bar graph in (C) of the figure were obtained.

As a result of the above, the straight pitch-based carbon fiber of Example 2 and the curled pitch-based carbon fiber of Example 5 with a carbonization firing temperature of 1300°C were inferior to those of Comparative Example 1 in terms of fuel efficiency. However, in terms of exhaust noise, the output is 20 ps and the rotation speed is 400 or so, which is the practical speed range for automobiles.
pm was reduced better in all Examples than in Comparative Example 1.

Moreover, according to the muffler of the above-described embodiment, exhaust noise can be reduced in all frequency ranges, and noise on the sense of hearing (frequency band of the audible range) can be reduced satisfactorily. Listening by multiple panelists revealed that the sound quality was soft and the silencing effect was large.

When curled pitch-based carbon fibers obtained at a carbonization firing temperature of 870 to 970°C are used, (1) petroleum-based spinning pitch is used, and (2) pitch-based carbon fibers made from coal-based pitch are used. Both exhaust noise and fuel consumption were further reduced compared to when the firing temperature was 1300° C. and (2) when the fiber shape was straight hair.

Therefore, when the silencer of Example 1 is used, the noise level can be lowered to an average of 63.8 dB even though it is an expansion type as described above, and when applied to an automobile silencer, it is possible to reduce the noise level to an average of 63.8 dB. This has the advantage of being able to provide a good muffling effect without having to be constructed into a complicated resonance type, and of providing a muffler with a simple structure and low cost.

11 As shown in the longitudinal cross-sectional view of FIG. 5, the exhaust pipe 12 is inserted and penetrated into the casing 7.
A large number of exhaust holes 13 are formed in the inner cylinder of the casing 7, and partition plates 1 are provided in the casing 7 and the exhaust pipe 12 at predetermined intervals in the longitudinal direction.
4... are provided to constitute a resonance type muffler 5. Then, on the inner peripheral surface of the casing 7, which forms a flow path for exhaust gas as a high-temperature, high-pressure fluid, as a sound absorbing material,
A curled pitch-based carbon fiber 9 is inserted and held by a punching metal 15.

As the curled pitch-based carbon fiber, 55 g of slightly curled pitch-based carbon fiber obtained in the same manner as in Example 1 was used. This curled pitch-based carbon fiber has a fiber diameter of approximately 14 μm (13 to 15 μm) and a bulk density of 0.5 μm.
058 /aj, average length 7cm (4-10CII)
Met.

110 g of glass fiber having a bulk density of 0.08 g/c4 was used as a sound absorbing material in place of the pitch-based carbon fiber of Example 6. An experiment was conducted in which 55g of glass fiber was inserted in the same manner as in Example 6, but the silencing effect was extremely low, so 110g of glass fiber was inserted.
Glass fibers are inserted.

The silencer 5 of Example 6 and Comparative Example 2 was 75
Connects to 0cc, 4-stroke industrial gasoline engine,
The sound pressure of the exhaust sound was measured in the same manner as in Example 1 above under the operating conditions of engine output 17 ps, rotation speed 360 Orpm, and engine exhaust gas temperature 610°C (however, the muffler inlet temperature). I got the graph shown.

As a result, in Example 6 (indicated by the solid line), despite using half the amount compared to Comparative Example 2 (indicated by the broken line), the total noise level was 2.7 dB or more, especially for frequencies 1 to 4 K.
At +1 z, the noise level could be reduced by an average of 2 to 6 dB or more. In addition, in the hearing test conducted by a plurality of panelists, Example 6
The sound was quite soft. Furthermore, when the amount used increases, the exhaust resistance increases, but the silencing rate also increases.

Upper side 1 Obtained under the same manufacturing conditions as Example 1, with a thickness of l0CI11,
Bulk density is 0.05g/ct, basis weight is 500g/n?
(7) Layer two sheets of curled pitch-based carbon fiber 9 and
As shown in the partially cutaway side view of the figure, the oil pan 16 provided at the bottom of the engine l is coated and the thickness is 0.
．． Reference numeral 18 in Figure 0 indicates a dynamometer, which is held by a steel holding plate 17 of 6a+a.

An engine 1 in which the oil pan 16, which is a part of the noise source, is coated with pitch-based carbon fiber 9 in this way (shown by a solid line) and an engine 1 in which it is not coated with anything (shown by a broken line)
While gradually changing the rotation speed of engine 1 using
The noise generated thereby was measured using a sound level meter installed one layer away from the engine 1, and the results shown in the graph of FIG. 8 were obtained. As a result, noise could be reduced by approximately 1.0 to 1.3 dB (on average) at any rotation speed.

In addition, one layer of the pitch-based carbon fiber of Example 7 was pasted with packing tape to the oil pan of engine 1 installed in an actual 1500cc passenger car C, and the front wheels were driven at a rotational speed of 400 rpm with the front wheels jacked up. As shown in the plan view of FIG. 9, sound level meters were installed on each of the side P1 and front P2 of the vehicle body to measure the noise level, and the results shown in Table 1 below were obtained.

(The following is a blank space) Table 1 As is clear from these results, by silencing the oil pan, which is a part of the noise source, the noise around the vehicle body can be reduced by 1.5 to 2.5 dB (average value ) and was able to reduce it extremely effectively.

Further, from the above results, it can be inferred that noise can be further reduced when not only the oil pan but also the engine housing, which is a source of noise, is coated with pitch-based carbon fiber.

Although the pitch-based carbon fiber of the present invention reaches a maximum engine exhaust temperature of about 650° C., no weight loss is observed because the exhaust gas contains little oxygen, and it is also excellent in durability.

Note that if the firing temperature is 870°C or lower, the high temperature resistance will decrease, so it is more desirable to set the carbonization temperature to 870 to 970°C.

<Embodiment 8> This embodiment 8 is applied to a pulse combustion burner, and first, the configuration of the pulse combustion burner will be described.

As shown in the partially cutaway side view of FIG. 10, a combustion chamber 20 is provided in the liquid tank 19, and a burner head 21 inserted into the combustion chamber 20 includes an air flap valve 22 and an intake silencer 23. , orifice 24, intake day coupling chamber 2
Combustion air is taken in through the strainer 27 and the safety shutoff valves 2B and 2.
8, fuel gas is taken in through a governor 29, a gas cushion tank 30, an orifice 31, and a gas flapper valve 32.

An exhaust day coupling chamber 34 is connected to the combustion chamber 20 through an immersion pipe 33 having an appropriate length to maintain the combustion cycle.
An exhaust muffler 35 is connected in communication with the exhaust muffler 35 .

The combustion chamber 20 has a combustion chamber load of 1.3 to 2°0X.
It is designed to be IO'kcal/s+'h.

The intake day coupling chamber 25 and the gas cushion tank 30 are for preventing the pulsating flow of combustion air and fuel gas from affecting the upstream side.

Said air flapper valve 22 and gas flapper valve 32
is for intermittent supply of air and gas.

The exhaust decoupling chamber 34 functions as a stabilizer and a primary muffler for stably maintaining the combustion cycle.

The intake fan 26 is activated only at the start of combustion and at the time of post purge.

As shown in the sectional view of FIG. 11, each of the intake silencer 23 and the exhaust silencer 35 includes first and second exhaust pipes 4a within the casing 7a.

One end side of each of the casings 6a is inserted in a stepped manner, and the above-mentioned curled pitch-based carbon fiber 9a is inserted as a sound absorbing material into the inside of the casing 7a which forms a flow path for pressurized high-temperature exhaust gas. Then, a cylindrical gold plate 1i with a line spacing of lOm is placed on the inner peripheral surface side of the pitch-based carbon fiber 9a.
136 and is configured to be fixedly held.

The pitch-based carbon fiber in Example 8 was DonaCarbo S-2, which has basic physical properties as shown in Table 2 below.
No. 10, S-310, and 5G-210 (all manufactured by Adore Co., Ltd.) are used.

(Hereinafter, blank space) Table 2 Next, the noise measurement results and durability tests conducted using the intake silencer 23 and the exhaust silencer 35 of Example 8 will be described.

The length in the longitudinal direction (indicated by A) is 165 mm, and the outer diameter is 10 mm.
A first exhaust pipe 4a with an inner diameter of 28 mm is inserted into the casing 7a of 6-mm diameter so that the insertion length (indicated by B) is 40 m5, and a second exhaust pipe with an inner diameter of 28 mm is inserted into the casing 7a. The insertion length (indicated by C) of the tube 6a is 8011II11.
The intake muffler 23 and the exhaust muffler 35 were each constructed by inserting pitch-based carbon fibers 9a having a bulk density of 50 kg/po to a thickness of 10a+a+.

On the other hand, a comparative example was prepared in which the pitch-based carbon fiber 9a was not filled. Using these, the sound pressure of the exhaust sound for each frequency was measured at a position 20 On+m away from the second exhaust pipe 6a in a direction of 45 degrees, and the results shown in the graph of FIG. 12 were obtained.

Note that the exhaust gas temperature at the outlet of the exhaust silencer 35 was about 200°C.

As a result, as described above, by optimally setting the longitudinal length of the casing 7a and the insertion amounts of the first and second exhaust pipes 4a and 6a, the ALL PASS of the silencer can be improved.
The noise level at (A P ) is 86 dB when no sound absorbing material is used, and it can be reduced to 83 dB in the example filled with pitch-based carbon fiber 9a as the sound absorbing material, and moreover, the sound silencing effect is It appears from around 400 Hz and becomes noticeable on the high frequency side around 200011z, making it clear that the embodiments of the present invention can significantly reduce the noise level.

In addition, an 80 dB equal noise level line was determined for a conventional silencer filled with glass fiber as a sound absorbing material, and a 75 dB equal noise level line was determined for the example of the present invention, and the results are shown in FIG. I got it.

As a result, in the example of the present invention, although the noise level is 5 dB lower, it is closer to the intake silencer 23 and the exhaust silencer 35 than the comparative example, and the noise level is 5 dB lower. It was clear that the levels could be significantly reduced.

(2) Pitch-based carbon fibers 9a are filled in the upper casing 7a to a thickness of 20 carp, and are used as a heating boiler at the Metsuki factory. Applied to a pulse combustion burner with a combustion load of 50,000 Kcal/h, after 100 hours and 500
The sound pressure of the exhaust sound for each frequency after the passage of time is 50011II in a direction of 45 degrees from the second exhaust pipe 6a.
When measurements were taken at the 11# position, the graph shown in FIG. 14 was obtained.

From this result, there was no change in the silencing effect even after 500 hours (equivalent to about half a year in actual operating conditions).
It is clear that it is extremely durable. Also,
After 500 hours had elapsed, the state of the filled pitch-based carbon fibers was observed, and neither oxidation by exhaust gas at about 300°C nor blowing off by exhaust flow was observed. Furthermore, fibers such as pitch-based carbon fibers, glass fibers, and rock wool were immersed in condensed water of exhaust gas, sealed in glass ampoules, and an elution test of fiber components was conducted at 200 to 300"C. In contrast, elution of components such as silicon Si and calcium Ca was observed in glass fiber and rock wool.
No change was observed in pitch-based carbon fibers, and it was clear that the durability could be further improved.

<Effects of the Invention> In the present invention, pitch-based carbon fiber is used as a sound absorbing material, and high sound absorption efficiency can be obtained.

Even when compared to the case of using a known sound absorbing material that is widely used as a sound absorbing material, (1) the use of pitch-based carbon fiber, which weighs about 1/2 of glass fiber, has a sound absorbing effect greater than that of glass fiber. The sound absorbed using pitch-based carbon fiber has a large amount of absorption when measured with a sound level meter, but according to the auditory senses of panelists, the sound is softer, which is a great effect.

■ Since it has a sound absorbing effect when used in small amounts, pressure loss is reduced when pinch type carbon fiber is installed in the fluid flow path. Therefore, when installed in the exhaust gas pipe of an engine, etc.,
Improves fuel efficiency compared to conventional sound absorbing materials.

■ Pinch carbon fiber has excellent heat resistance, so
It can be used in higher temperature environments than conventional sound absorbing materials such as glass fiber. It can be used up to 650'C in an oxidizing atmosphere and 1300'C in a non-oxidizing atmosphere.

■ Pitch-based carbon fiber has excellent chemical resistance, and its physical properties do not change over time, so there is little deterioration.

When glass fiber is used to absorb sound from engine exhaust gas, it is hydrolyzed by moisture in the exhaust gas, but this does not occur with the sound absorbing material of the present invention.

■ Although the reason is not yet clear, pinch type carbon fiber has a more pronounced effect when used at high temperatures than at room temperature.

[Brief explanation of the drawing]

The drawings show an embodiment of the muffler and sound muffling method of the present invention, and FIG. 1 is a schematic configuration diagram of an expansion type muffler, and FIG.
Fig. 3 is a bar graph showing the measurement results of the sound pressure of exhaust sound, Fig. 3 is a bar graph showing the measurement results of fuel efficiency, Fig. 4 is a bar graph showing the measurement results of the amount of exhaust sound attenuation for each frequency, and Fig. 5 is a bar graph showing the measurement results of exhaust sound attenuation for each frequency. , a schematic configuration diagram of a resonance type silencer, FIG. 6 is a graph showing the measurement results of the sound pressure of exhaust sound, FIG. 7 is a partially cutaway side view of Example 7, and FIG. 8 is a graph showing the sound pressure of the exhaust sound. A graph showing the measurement results, FIG. 9 is a plan view showing the noise measurement position, FIG. 10 is a partially cutaway side view showing the schematic configuration of the pulse combustion burner, and FIG. 11 is a diagram showing the silencer of Example 8. Vertical cross-sectional view, Figure 12 is a graph showing the measurement results of the sound pressure of exhaust sound for each frequency, Figure 13 is a diagram showing the equal noise level line, and Figure 14 is for each frequency related to the durability test. 3 is a graph showing the measurement results of the sound pressure of the exhaust sound. 5.23.35...Silencer

Claims (7)

[Claims] (1) A silencer characterized by using pitch-based carbon fiber as a sound absorbing material. (2) A silencer characterized in that pitch-based carbon fiber is provided as a sound absorbing material in a fluid flow path. (3) The temperature of the environment in which the pitch-based carbon fiber is placed is 100 to 1300°C.
The silencer described in section 2). (4) The muffler according to any one of claims (1) to (3), wherein the pitch-based carbon fiber is obtained by spinning, infusible, and carbonizing coal-based isotropic pitch. (5) A noise reduction method characterized by covering a noise source with pitch-based carbon fiber. (6) The noise reduction method according to item (5), wherein the temperature of the environment in which the pitch-based carbon fibers are placed is 100 to 1300°C. (7) The noise reduction method according to claim 5 or 6, wherein the pitch-based carbon fiber is obtained by spinning, infusible, and carbonizing coal-based isotropic pitch.