The design of the new exhaust muffler of the hotte

2022-10-12
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Development of a new exhaust muffler for Dongfanghong LR6105 diesel engine

Abstract This paper studies five new exhaust silencers with different structures for Dongfanghong LR6105 diesel engine, among which the new No. 2 muffler with the best silencing effect can reduce the engine bench exhaust noise by 12.8db (a) and the vehicle noise by 1.2dB (a) compared with the original muffler

key words: diesel engine; Noise; Exhaust; Muffler

1 preface

Dongfanghong LR6105 diesel engine is the supporting engine of Dongfanghong lt1101 truck. One of the reasons for the high noise of lt1101 vehicle is that the original muffler of LR6105 diesel engine is not ideal, which can not meet the needs of vehicle muffler. In order to reduce the noise of lt1101 vehicle, five new mufflers with different structures were designed, and the engine bench test and vehicle noise measurement were carried out on various mufflers. The results show that the new No.2 muffler has the best silencing effect. Compared with the original muffler, the new No.2 muffler has a noise reduction of 12.8db (a) for engine bench exhaust noise and 1.2dB (a) for vehicle noise reduction

2 structure and performance analysis of the original muffler and design of the new muffler

2.1 structure and performance analysis of the original muffler

Figure 1 (a) is the structural diagram of the original muffler of Dongfanghong LR6105 diesel engine. The insertion loss of muffler measured under the calibrated working condition is 19.0db (a), see Table 1. The insertion loss of truck exhaust muffler is generally required to be more than 25dB (a). Therefore, the silencing amount of the original muffler is too small to meet the requirements of the engine exhaust muffler for trucks. The main reasons for the small silencing amount of the original muffler are: (1) the structure is single, which is only composed of three-stage expansion chamber. (2) Small volume. (3) There is a lack of perforated acoustic elements with good silencing effect inside

(a) original muffler

(b) new No. 1 muffler

(c) new No. 2 muffler sound-absorbing material: glass fiber

(d) new No. 3 muffler sound-absorbing material: rock wool

(E) new No. 4 muffler

(f) new No. 5 muffler

Figure 1 muffler structure diagram

2.2 NEW muffler design

for further lowering Shanghai Great World Guinness headquarters learned this news.Low exhaust noise of the rear engine, Five new mufflers with different structures are designed, and their structural diagrams are shown in Figure 1 (b), (c), (d), (E) and (f). The determination of the main technical parameters of the muffler is described below

2.2.1 determination of muffler volume ratio

when designing a muffler, first determine the volume ratio of the muffler, that is, the ratio of the total volume of the muffler V to the engine displacement VH (v/vh)

in the diesel engineering hand book, lley, a British company, recommends that for a four stroke engine with a cylinder displacement of VH, a number of cylinders of N, and a speed of N, the total volume of the muffler can be estimated as follows v [1]

where k is a constant, k=35000, which is applicable to trucks

according to formula (1), calculate the total volume of the exhaust muffler of LR6105 diesel engine for lt1101 truck. Take k=35000, n=2800r/min, n=6, and you can get:

that is, the volume ratio of the original muffler of LR6105 diesel engine is calculated to be 3.9, which is lower than the calculation value of formula (2). The small volume ratio of the original muffler is one of the reasons for the poor silencing effect. Based on the theoretical calculation results of formula (2) and the overall layout of the muffler on the vehicle, the volume ratio of the five selected new silencers is 5.5, slightly larger than the theoretical calculation value

2.2.2 determination of the number of silencer cavities

single cavity silencers are difficult to meet the requirements of engine exhaust noise attenuation. Most practical engine exhaust silencers are composed of 2 ~ 4 cavities. The research shows that the silencing amount of the muffler does not increase proportionally with the increase of the number of cavities. On the contrary, the more the number of cavities, the greater the exhaust back pressure; The greater the power loss of the muffler; Moreover, the structure, weight and process performance of the muffler are poor, so more than four cavities will be more than worth the loss. The principle of selecting the number of cavities of the muffler is to select the muffler with a small number of cavities as far as possible on the premise of meeting the requirements of noise reduction

lr6105 diesel engine's original muffler is a three chamber structure, and the five new mufflers designed to increase the amount of noise elimination all adopt a four chamber structure

2.2.3 determination of perforation rate and aperture of perforated pipe and perforated plate

the new muffler adds acoustic elements of perforated pipe and perforated plate. Perforated acoustic elements mainly use the blocking effect of small holes on air flow to achieve the purpose of silencing. The noise reduction of perforated acoustic elements is mainly related to the perforation rate and the aperture of small holes. The smaller the perforation rate, the smaller the aperture of the small hole, the greater the amount of noise elimination. However, if the perforation rate is too small and the aperture of the small hole is too small, the flow resistance loss of the air flow will be greater, resulting in the loss of engine power and poor economic performance. Generally, the hole diameter of perforated acoustic elements is taken as φ 3mm~ φ 8mm, the perforation rate can be 7% ~ 15% [2]

the perforation rate of the perforated pipe of the new No. 1 muffler designed is 10.1%, and the aperture is φ 6mm; The perforation rate of perforated plate is 11.0%, and the aperture is φ 6mm。 The perforation rate of perforated pipes of new type 2, 3, 4 and 5 silencers is 9.5%, and the aperture is φ 6mm, perforation rate of perforated plate is 11.3%, aperture φ 4mm。

the new No. 5 muffler has no perforated plate, and the perforated plate is replaced by an internal intubation

2.2.4 selection of sound-absorbing materials

porous sound-absorbing materials are arranged in the first and fourth cavities of the new No. 2 and No. 3 silencers. When sound waves reach the surface of porous sound-absorbing materials, most of them will be absorbed, so as to achieve the purpose of noise elimination. Whether the exhaust of internal combustion engine is nonlinear and what is the degree of nonlinearity? The sound-absorbing material selected for the muffler should not only have a high sound absorption coefficient, but also have the characteristics of high temperature resistance and corrosion resistance. Considering the highest noise in the high frequency range (250Hz ~ 4000Hz) of diesel engine exhaust noise, see Figure 2. Therefore, ultra-fine glass fiber and rock wool are selected as new sound-absorbing materials for No. 2 and No. 3 silencers respectively. The sound absorption coefficients of these two kinds of sound absorption materials are very high, especially in the medium and high frequencies, the average sound absorption coefficients are more than 0.8 [3]. Ultra fine glass fiber has high temperature resistance of 700 ℃ and rock wool has high temperature resistance of 650 ℃, and these two materials have good corrosion resistance, so they can fully meet the service conditions of internal combustion engines

Figure 2 muffler exhaust noise spectrum

a-original muffler b-new No.2 muffler

3 muffler test

3.1 engine bench test

the insertion loss and power loss of the muffler were measured on the engine bench according to GB "internal combustion engine exhaust muffler measurement method". The test results are shown in Table 1. The insertion loss of the new No. 2 muffler is the highest, up to 31.8db (a), which is 12.8db (a) higher than the 19.0db (a) of the original muffler. The other new types have been derived from the original single screw. The twin screw, multi screw 3, 4 and 5 silencers are 10.8db (a), 9.9db (a) and 7.1db (a) higher than the original silencer respectively. Compared with the original silencer, the power loss and fuel consumption of the new 2, 3 and 4 silencers have little change. Compared with the original muffler, the power loss and fuel consumption of the new No. 1 and No. 5 muffler are slightly increased

Figure 2 shows the exhaust noise spectrum of the original muffler and the new No. 2 muffler. It can be seen from the figure that compared with the original muffler, the exhaust noise of the new No. 2 muffler has a large amount of noise reduction in the whole frequency range, especially in the medium and high frequency range with high exhaust noise

3.2 vehicle noise measurement

in order to examine the noise reduction effect of the muffler on the vehicle, the test was carried out according to GB "motor vehicle noise measurement method", and the new type 1, 2, 4 and the original muffler were selected to inspect whether the lt1101 truck sample has cracks, and the vehicle external speed noise was measured. The results are shown in Table 2. It can be seen from table 2 that the noise reduction effect of the new No. 2 muffler is the best. Compared with the original muffler, the acceleration noise outside the vehicle is reduced by 1.2dB (a). The noise reduction of the new No. 1 muffler is 0.3dB (a), and the noise reduction of the new No. 4 muffler is 0.5dB (a). Equipped with the new No. 2 muffler, the external noise of lt1101 truck has been reduced to 85.5db (a), lower than the limit of 86.0db (a) specified in GB

4 conclusion

(1) the original muffler has a single structure, small volume and poor silencing effect, which can not meet the needs of automobile silencing

(2) among the five newly designed silencers, the new No. 2 muffler has the best silencing effect. The engine bench exhaust noise reduction is 12.8db (a), and the vehicle noise reduction is 1.2dB (a). After using the new No. 2 muffler for lt1101 vehicle, the noise outside the vehicle has been lower than the limit of 86.0db (a) specified in GB

(3) the power loss and fuel consumption of the engine equipped with the new No. 2 muffler have little change with the original muffler, indicating that the new No. 2 muffler has not affected the dynamic performance and economic performance of the engine while increasing the amount of noise elimination, which indicates that the design of the new No. 2 muffler is feasible. In order to reduce the noise of lt1101 vehicle, the new No. 2 muffler can be considered as a substitute for the original muffler

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