comparative analysis of eg noise suppression systems · according to russian standard gost...

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International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 10, October 2017, pp. 1536–1553, Article ID: IJCIET_08_10_155

Available online at http://http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=8&IType=10

ISSN Print: 0976-6308 and ISSN Online: 0976-6316

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COMPARATIVE ANALYSIS OF EG NOISE

SUPPRESSION SYSTEMS

Nikolay Anatolyevich Khripach, Lev Yurievich Lezhnev, Vsevolod Anatolyevich Neverov,

Denis Alekseevich Ivanov, Boris Arkadyevich Papkin

Moscow Polytechnic University,

Bolshaya Semenovskaya str. 38, Moscow, 107023, Russia

ABSTRACT

This article reviews up-to-date systems of exhaust gas noise suppression and their

influence on operation specification of vehicles. Various alternatives of existing and under

design exhaust systemS are discussed, including resonators and absorbers, as well as

active systems of noise suppression which require for additional power source. Positive

influence of thermoacoustic effect is demonstrated, properties of porous materials are

discussed with regard to intensification of heat exchange. The exhaust systems are

compared in terms of suppression extent, weight and sizes, resistance against flow,

complexity of fabrication and cost. Positive and negative trends are revealed and their

influence on vehicle performances. On the basis of the performed analysis the relevant

findings are obtained and the most efficient and promising trends of further researchers

are determined aimed at improvement of operation performances of vehicles by means of

active exhaust systems.

Key words: Internal Combustion Engine, Exhaust System, Noise Suppression Device, Heat

Exchanger, Acoustics.

Cite this Article: Nikolay Anatolyevich Khripach, Lev Yurievich Lezhnev, Vsevolod Anatolyevich Neverov, Denis Alekseevich Ivanov, Boris Arkadyevich Papkin,

Comparative Analysis of EG Noise Suppression Systems, International Journal of Civil

Engineering and Technology, 8(10), 2017, pp. 1536–1553.

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=10

1. INTRODUCTION

Acoustic pollution of ambient environment is an urgent issue of modern megalopolis. In terms of

impact on human noise occupies the third position after pollution of atmospheric air and drinking

water with chemicals [1]. The highest impact is exerted on cardiovascular system and mental

health. Noise of vehicles has the greatest impact on general level of acoustic pollution (up to 60%).

Comparative Analysis of EG Noise Suppression Systems


Regulatory equivalent sound levels stipulated by sanitary norms in Russia for areas adjacent to

residential districts are 55 dBA at daytime and 45 dBA at nighttime. Herewith, according to

research results at daytime in Moscow central streets the noise level is 70-80 dBA, and in main

radial routes of municipal aims it is 75-82 dBA [2].

According to requirements of UN ECE Regulations No. 51-02, passenger vehicles can generate

noise of maximum level not higher than 74 dBA. However, further reinforcement to 71 dBA is

expected. This requires for serious improvement of vehicle design.

Noise sources can be as follows: internal combustion engine (ICE), exhaust system, ICE inlet

system, transmission, tyres and body (see Fig. 1 [3]). Herewith, contributions of these sources are

different – in addition to noise level there are such performances as sound pressure, intensity,

power and so on. This facilitates determination of the most promising for researches noise sources.

Thus, the level of ICE structural noise is 71 dBA, of exhaust system – 68 dBA, of inlet system –

66.5 dBA, of transmission– 60 dBA, tyre noise (free running) – 68 dBA. However, percentage of

inlet system noise to total external noise level of passenger vehicle is 0.6…6.0%, and that of

exhaust system – 4.8…22.9% [4]. Therefore, the necessity to improve exhaust system is obvious.

Figure 1 Acoustic sources of modern vehicles.

Noise suppression of exhaust system is a contradicting issue – on the one hand it is necessary

to reduce the exhaust gas (EG) volume as much as possible, on the other hand – to provide the

lowest resistance against gas flow. If a vehicle is not equipped with muffler, the volume of engine

Nikolay Anatolyevich Khripach, Lev Yurievich Lezhnev, Vsevolod Anatolyevich Neverov, Denis

Alekseevich Ivanov, Boris Arkadyevich Papkin


operation at 0.25 m from open end of tail pipe can reach 115…130 dBA [5], however, this will

provide maximum resistance for EG discharge. When regular exhaust systems are used which meet

the requirements to sound volume, back pressure at maximum rotation rate can reach 60 kPa and

more.

2. METHODS OF EG NOISE SUPPRESSION

According to Russian standard GOST 12.1.029-80, the means of collective noise suppression are

subdivided into the means reducing noise in the source of its generation and into the means

reducing noise upon its propagation from the source to the protected subject. Acoustic means of

noise suppression, depending on operation principle, are subdivided into sound and vibration

insulating, sound absorbing, damping means and mufflers. Herewith, if a system needs additional

power source for its operation, then such system is considered as active, otherwise, it is passive.

These types of protection should be considered separately.

Passive means of protection

Most of the EG noise suppression systems are based on passive means of protection. High

popularity of such systems is stipulated by their independence, simplicity and reliability. Correctly

selected engineering solutions make it possible to reduce sound volume efficiently, without

deterioration of operation performances.

The main approach to EG noise suppression is the use of mufflers of various designs.

Generally, it is a device comprised of expansion and/or resonator chamber connected by manifolds

or tubes. Conventional muffler is comprised of large expansion chamber separated into three or

four sections by perforated plates installed in peaks (antinodes) of oscillating speed. EG are

transferred through three perforated tubes. These plates and tubes suppress certain oscillations and

absorb a portion of noise of high frequency spectrum. Main disadvantages of this design are high

metal intensity and weight. In addition, at high gas flow rates the plates resonate and become a

source of secondary noise.

Hence, quite often additional chambers are used in exhaust systems which promotes noise

suppression in narrow bands of spectrum. Helmholtz resonator is an example of additional

resonating chamber. Design parameters of resonator, that is, length, throat area, and tank volume,

determine operation frequency providing the highest noise suppression. Figure 2 exemplifies this

device. A quarter-wave resonator is a particular case of Helmholtz resonator. In terms of design

the resonator is a closed at one end tube welded into the main pipeline. Operation is based on noise

suppression at certain frequency by wave in antiphase reflected from the dead end. The length of

such resonator equals to one quarter of sound wave.



Figure 2 Helmholtz resonator (ARK Performance Inc.).

Additional expansion chambers are widely applied not only in exhaust systems but also in inlet

systems. This is stipulated by their simplicity and efficiency. Herewith, the chambers can be both

coaxial and non-coaxial which somewhat simplifies layout issues. Their shapes also have variants:

cylindrical and conical. The differences are illustrated in Fig. 3.

Figure 3 Various configurations of expansion chambers and their properties. L – longitudinal cross

section; λ – wavelength.

Sizes of expansion chambers are often restricted by layout parameters. This leads to necessity

to use fillers of special materials capable to absorb sound. Such mufflers are known as active

(absorbing) or pulse-reaction, depending on design. The most widely used are fillers made of

fibrous sound absorbing materials on the basis if basalt, silicon (thermal resistance up to 750°C)

or glass fibers (to 450°C). Thin and ling fibers are characterized by high sound absorption even at

low thickness of insulating layer. The influence of absorbing materials is illustrated in Fig. 4.




Figure 4 Properties of expansion chambers with and without absorption [6].

The main issues of application of fibrous materials are their resistance against blowing-off and

difficulties of heat removing. The most resistant against blowing-off are materials with long fibers,

stitched or pressed, herewith, increase in length improves reliability. For non-stitched materials it

would be reasonable to use metal heat resistant wire. Such fibrous materials limit maximum

diameter of perforations (not more than 3 mm). While designing exhaust system it is necessary to

take into account that fibrous insulate heat. Hence, with incorrectly selected material or its

thickness pipelines can be deformed as a consequence of high temperature gradient between

external and internal sides.

Since decrease in EG temperature is a possible approach to suppress noise of exhaust system,

the materials with high heat exchange are intensively studied. Application of porous materials as

sound insulating or heat transferring filler becomes more and more popular in various industries.

The research [7] was performed for porous materials at high sound pressure (150 dB) observed

upon operation of aircraft engines. The influence of material porosity, fiber diameter, specimen

thickness and air layer in the material structure on the specimen performances was determined. It

is discovered that the fiber diameter influences greatly on the coefficient of sound absorption:

decrease in the diameter improves insulating properties of material. In addition, with increase in

porosity sound absorption at low frequencies increases (up to 2400 Hz) with simultaneous decrease

at high frequencies (above 2400 Hz). High influence is exerted by specimen thickness. With equal

porosity, diameter and other parameters increase in thickness from 25 mm to 50 mm improves

coefficient of sound absorption nearly in two times at low frequencies. With air layer between

sound source and specimen absorption performances of porous materials in low frequencies can

be significantly improved. These performances are illustrated in Fig. 5.



Figure 5 Influence of design parameters on coefficient of acoustic absorption at sound pressure of 150

dB: (a) fiber diameter, (b) porosity, (c) thickness, (d) air layer.

After consideration of passive methods of EG noise suppression it is possible to highlight some

significant disadvantages of conventional mufflers. Despite good noise suppression in high and

medium frequency bands, in low frequency band below 500 Hz the efficiency of mufflers is very

low. This leads to high fatigability of vehicle drivers and passengers. Moreover, mufflers which

suppress noise above 35 dB creates high resistance against EG flow, thus causing high pump loss

of ICE. Attempts to develop mufflers efficient in wide frequency range result in complicated and

cumbersome designs.

Active means of protection

Active noise suppression, contrary to passive approach, can successfully suppress noise in overall

range of sound spectrum, including low frequency band. A variant of system operation is

illustrated in Fig. 6 and is based on the effect of 1D, 2D or 3D interference which would allow to

reduce sound pressure by means of imposition of compensating sound field generated by additional

sound source. The compensating sound field interferes with initial filed, thus significantly reducing

the noise level.




Figure 6 Operation principle of active noise suppression system

The investigations [8, 9] into the influence of active noise suppression on vehicle performances

demonstrated good results: noise level of passenger vehicle at 2000 rpm decreased by 3.1 dB, at

3000 rpm – by 3.5 dB in comparison with regular system. The assemblies for passenger vehicle

and locomotive are illustrated in Figs. 7 and 8, respectively. Herewith, due to lower resistance of

active muffler the power and economic efficiency improved in average by 2%. Due to peculiar

features of operation of diesel engines the EG noise range is in the low frequency band. Correctly

adjusted active muffler protected against unfavorable conditions made it possible to reduce noise

level by 6.7 dB in overall range of engine operation.

Figure 7 Vehicle loudspeaker Figure 8 Locomotive loudspeaker

Two control algorithms of active noise suppression system were discussed in [10] aiming at

reduction of undesirable noise of exhaust gases. The experimental results demonstrated that

operation performances of filtered-x least mean square algorithm (FXLMS) with algorithm of

feedback neutralization and those of steady controller with programmable variation of feedback

gain are different. It was demonstrated that operation performances of adaptive filter are inferior

to steady controller despite that adaptive filter considers for variable convergence coefficient. This

can be attributed to the fact that the adaptive filter should asymptotically adjust weight coefficient,

and the steady controller operates with factory settings of control system. From another point of

view the adaptive filter is characterized by better adaptiveness to various control conditions (for

instance, temperature and pressure), hence, the adaptive filter is less sensitive to ambient

environment than the steady controller.



Another variant of active system is cooling of EG. It is possible to implement by water injection

directly into gas flow. The influence of this approach on EG temperature and noise level is

discussed in [11]. Thus, at 2000 rpm and the load of 90 Nm the temperature decreased from 430°C

to 110°C. However, the influence of noise after water injection was such that the noise level was

higher than during operation of single engine which is illustrated in Fig. 9. This effect can be

decreased by insulation of nozzles and modification of injection direction (not perpendicularly but

along the flow).

Figure 9 Influence of water injection on sound pressure level

A method of ICE exhaust noise suppression by forced EG cooling in special heat exchanger is

proposed in [12]. This is performed using engine cooling fluid. The influence of EG cooling on

noise level (the so called thermoacoustic effect) was determined experimentally. Thus, with

temperature decrease by 100°C in one and the same exhaust system the level decreases by 2 dBA,

and with cooler EG the decrease is more pronounced.

Similar to the above considered, the work [13] is devoted to determination of interrelation

between EG cooling and the level of noise suppression. The obtained results demonstrate that

cooling of muffler can be considered as a method of noise suppression. In addition, it was

established that specific fuel consumption decreased by about 10%. Maximum noise suppression

achieved 1.2% as illustrated in Fig. 10.




Figure 10 Influence of heat exchanger on EG noise level

Vetus Company (the Netherlands) is a major developer and manufacture of equipment for

watercrafts. One of recent developments of the company is a device for cooling of engine EG

aiming at decrease in noise level illustrated in Fig. 11 [14]. Herewith, high extent of EG cooling

enables application of non-metallic engineering materials in exhaust system, thus decreasing the

weight of exhaust system and providing high resistance against corrosion. Three-body design (Fig.

12) provides good noise suppression, however, large sizes (length over 500 mm) imposes

significant constraints upon operation.

Figure 11 Noise suppression device with water cooling



Figure 12 Three-body exhaust noise suppression device with water cooling

Halyard Company (Great Britain) for many years carries out researches in the field of noise

suppression of exhaust systems of marine vessels. The recent developments make it possible to

increase significantly the operation quality of exhaust system – water separators during idle engine

run decrease EG noise from 85 dBA to 62 dBA [15]. Single and two-chamber mufflers with water

cooling also have good performances. The applied materials of mufflers on the basis of special

resins can continue operation at 300°C. In addition, their application improves acoustic

performances due to ability to absorb oscillations unlike metallic mufflers.

In addition to noise suppression EG cooling is an inexpensive approach to increase reliability

and lifetime of catalytic converter. The work [16] was devoted to discussion of assembly for heat

exchange intensification between EG and cooling fluid. The most rational configuration of internal

ribbing was determined by general criteria (illustrated in Fig. 13). The generated heat flow achieves

more than 4.8 KW at maximum load.

Figure 13 Schematic view and optimum shape of heat exchanger




Sango company (Japan), specializing in the field of heat accumulators, Rankine cycle

machines, thermoacoustics and thermoelectricity, developed heat exchanger for recovery

illustrated in Fig. 14 [17]. The design is intended for installation in hybrid vehicles of small size.

Figure 14 Heat exchanger for recovery of EG thermal energy

Futaba Industrial Co., Ltd. (Japan) optimized [18] the assembly for EG heat recovery of

previous generation which boosts engine heating transferring EG heat via heat exchanger to engine

cooling fluid. This variant was applied for Mazda3 Hybrid. The thermal capacity of the assembly

illustrated in Fig. 15 is by 30% higher, and the volume and weight of the heat exchanger decreased

by about 50%.

Figure 15 EG heat recovery system

Delphi Company (USA) developed EG heat exchanger illustrated in Fig. 16, where residual

heat of engine exhaust gases is recovered [19]. The system is capable to recover from 5 kW to 7

kW on vehicle moving at 35-45 miles per hour.



Figure 16 Heat exchanger of exhaust gases

The above considered devices make it possible to decrease EG temperature, at the same time

solving minor issues of maintenance of engine and overall vehicle. The obtained heat is used for

rapid heating of engine and passenger compartment in cold environment, thus reducing fuel

consumption and operation time of electric heating. However, it is necessary to take into account

that heat is redistributed without its generation. Herewith, the issue of intensification of excessive

heat recovery can appear.

It is known that active noise suppression system operates with additional energy source. The

most widely applied variants are utilization of electricity of vehicle circuit or electricity generation

of EG energy. While converting heat into electricity it is possible to obtain more efficient complex

which can be required at any time. If thermoelectric modules are used for this aim, it is possible to

supply power to active noise suppression system without load on vehicle circuit and excessive

power can be either accumulated or used for other vehicle needs.

Thus, Tenneco (USA) proposes in-vehicle system of recovery of EG thermal energy [20] using

thermoelectric converters (TEC modules), its main component is illustrated in Fig. 17. Modern

TEC are based on the Seebeck effect: generation of electromotive force in closed circuit comprised

of different conductors connected in-series, the junctions between them have different

temperatures. The main advantage of such devices is that they do not have moving parts, thus

enabling development of systems with high lifetime and independent operation. Cylindrical TEC

modules at external side contact with hot EG, and at internal side with cooling fluid from engine

cooling system. The assembly can generate maximum power of 0.9 kW. The on-going studies are

devoted to increase in this performance with simultaneous increase in reliability and decrease in

expenses.

Figure 17 On-board system of thermal energy recovery




Sufficient success in optimization of acoustic properties of muffler-heat exchanger with TEC

modules was achieved in [21]. Two heat exchangers were designed, fabricated and tested (see Fig.

18). The tests were performed on four-cylinder engine test bench. In addition to sufficient

efficiency of heat recovery by TEC module the EG noise was suppressed (Fig. 19).

Figure 18 Models of the first (a) and the second (b) types

However, in low frequency band further optimization of noise suppression is required.

Simulated and experimental results should be distinguished. It is proposed to improve

experimental conditions by identification of engine noise and improvement of processing accuracy

of heat exchanger aiming at reduction of external and internal noises, respectively.

Figure 19 Test results of noise of EG heat exchangers

While summarizing the overview of active noise suppression systems it should be mentioned

that systems of complex design are often material intensive upon fabrication, expensive and with

low operation life upon maintenance.

3. RESULTS

It is convenient to compare EG exhaust systems with reactive mufflers as the most popular. The

complexity of comparison is that most promising technologies are presented by prototypes without

commercial embodiment. Table 1 of EG noise suppression systems can highlight efficiency of a

certain method. It should be mentioned that comparison of suppression properties was performed

on the basis of test reports with maximum available value.



Table 1 Comparison of specifications of noise suppression system

Description Suppression

properties Weight and sizes

EG flow

resistance

Complexity of

fabrication Cost

Passive systems

Reactive muffler

High

performances at

high frequencies;

Poor suppression

at low frequencies

High weight is sizes High resistance

Simple design,

regular production

technology

Low cost

Additional

resonator/expansion

chambers

Good

performances at

preset

frequencies;

No significant

influence at other

frequencies

Increase in weight

and sizes of main

system

Low resistance

Simple device;

Complicates main

system

Can increase the

system cost by 1.5

times

Absorption mufflers Expansion of

operation range

Lower sizes in

comparison with

reactive mufflers

but higher weight

Low resistance

Highly absorbing

materials with

contradicting

properties are

required

Can increase the

system cost by 1.5-4

times

Active systems

Wave interference

Noise decrease by

3.5 dB in

comparison with

initial system

High sizes, high

weight of applied

acoustic devices

Does not

influence

Requires for

complicated control

system, high

quality insulating

materials

High cost

(€300…€1,200)

[22]

Injection of cooling fluid

Noise level is

equalized, further

researches are

required

Low sizes of active

part, tank with

cooling fluid is

required

Low resistance

by nozzles

Complex design of

nozzles, tubes and

control system

Commercially

unavailable

Water heat exchanger

(including TEC units

and for watercraft)

Decrease by 2 dB

per each decrease

in EG temperature

by 100°C

High sizes and

weight of overall

facility with storage

tank of cooling

fluid, significant

decrease in sizes

upon application of

ICE cooling fluid

Can be high in

the case of

multiple steps,

depends on

design of heat

exchanger

Free-machining

materials, simple

design for

watercraft; design

of medium

complexity for land

vehicles with

various materials;

complicated supply

and discharge of

cooling fluid

For watercraft:

system cost

increases at least by

8 times.

For land vehicles:

high cost due to

TEC units and

additional cooling

circuit




Efficiency of a certain system can be most conveniently expressed in terms of maximum level

sound pressure generated by EG. It is seen in Fig. 20 that the highest effect is achieved by decrease

in EG temperature. According to scientific reports sound level of systems upon maximum engine

load does not exceed 90 dB. At the same time active noise suppression system on the basis of wave

interference cannot provide such performances. Maximum noise suppression with regular system

equals to about 3-3.5 dB, herewith, the facility sizes are high. As shown in [21], combination of

resonator chambers and thermoacoustic effect makes it possible to achieve advanced performances

of EG exhaust systems.

Figure 20 Comparison of noise suppression systems

Not least important specification for vehicles is weight. Comparison of systems in terms of this

property is complicated by several factors:

• There is a wide scatter in the weight of reactive and absorption mufflers of various manufacturers;

• Weight of pilot facilities can be estimated only visually on the basis of applied commercially

available units;

• Heat exchangers with heat carrier can hardly be separated into active and passive constituents.

Therefore, determination of system weight is a complicated task requiring for individual

consideration. Approximate specifications are illustrated in Fig. 21where weights of active parts

of the considered systems are compared.



Figure 21 Comparison of weights of various systems

4. DISCUSSION

On the basis of comparison it is possible to state that the most promising for application on road

vehicles are combinations of various systems comprised of absorption mufflers (based on porous

materials, for instance) and heat exchangers. Porous materials not only promotes noise suppression

increasing its efficiency. These combinations can take into account advantages (simplicity and

regular production of the first systems and adjustment for wide frequency range of the second

systems) and to compensate disadvantages of constituents. Thus, combined exhaust systems (that

is, comprised of both passive and active means of noise suppression) can be considered as the most

promising facilities for further researches.

5. CONCLUSIONS

It is possible to conclude that despite detailed knowledge of passive noise suppression and its

nearly maximum efficiency such systems are widely applied. Moreover, after development of

more perfect, sustaining and inexpensive materials (porous, for instance) the share of active

(absorbing) and reactive mufflers increases. This is obviously stipulated by high independence of

their operation. However, potential of such systems decreases due to narrow frequency range of

these facilities. As a consequence, there is an increasing number of developments in the field of

active noise suppression. Obvious advantages, such as wide operation range, low EG flow

resistance, low sizes, are compensated by such disadvantages as high cost, insufficient reliability,

and low level of knowledge.

ACKNOWLEDGMENTS

This work was supported by the Ministry of Education and Science of the Russian Federation

within the subsidiary grant agreement No. 14.574.21.0144 dated September 26, 2017. Unique

identifier: RFMEFI57417X0144.




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