Most Effective Way Is Joining A Muffler Biology Essay

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The most important issue is to reduce in Noise of engine. The most effective way is joining a muffler in the exhaust pipe. But the muffler require some Specific Design & Construction consideration various noise parameters.The muffler is designed to attenuate both the high and low frequency noises. Reactive portion should be covered with a layer of absorptive material which decreases the noise generated. Material used should with stand with the high temperature range . Resonators are used to attenuate low frequency noises and there tuning can be done to make them flexible to use with different Engines

General Design Principles for an Automotive Muffler - Potente,Daniel

General Principle of muffler design and the advantages of the various Styles of muffler. Muffler application and there functional requirement that should be considered, which include acoustic & non acoustic design .Functional requirement namely adequate Insertion loss, minimum back pressure, space constraint etc. There are many designs available for a particular problem but the design is proven by its performance.

Modeling and Applications of Partially Perforated - H. Luo,'* C. C. Tseb & Y. N. Chen"

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A new approach is presented for modeling concentric partially perforated intruding tube mufflers. For acoustic impedance in the linear regime, a closed form solution of the partially perforated intruding tube muffler transmission loss was first obtained. With this restriction and in the case of zero mean flow, excellent agreement between predicted and experimental results for various mufflers configurations demonstrates the utility and potential of the modeling approach used in the present study.

By tuning the lengths and associated physical parameters to the in-situ case of various straight-through tubular elements, one can achieve rapid and economical modeling of those that are frequently used in many commercial reactive muffler This modeling ability is very useful to a mufflers designer especially in the preliminary design stage.

Abstract

The purpose of our project is to design an exhaust system for Maruti 800 cc engine which can be suited for the minimum power loss and maximum insertion loss the engine will be mounted the rear side of the vehicle. We have to design the complete exhaust system according to the space availability in the engine compartment. The main components that we are using in the exhaust system are primary pipe, muffler and tail pipe.

For designing the exhaust system we must consider Back pressure, Noise, Size & shape, Material.

An exhaust system consists of an exhaust manifold, a front pipe a main muffler or silencer, and a tail pipe with an exhaust tip. Two type of mufflers are currently in use Absorptive type , Reactive type.

In this project we designed the absorptive type muffler and transformed it for the 800 cc Maruti engine.

Absorptive type of mufflers is used where we need the maximum insertion loss and minimum power loss. It is type of free flow where the restrictions are almost negligible. In absorptive type muffler we use perforated pipe and it is enclosed with the help of absorptive material which is glass fibre. Finally it is enclosed with steel casing. The muffler changes the sound energy to the heat with the help of absorbing material.

For the calculation purpose we assumed the pressure at different points on the exhaust and calculated the values for the exhaust velocity, friction loss and head loss. We calculated the pipe length and dimension of the muffler based on the empirical formula and verified our result using the empirical relation.

To study the flow in the exhaust system we made the model in Catia and imported the file on gambit to analyze the flow for better understanding we made the 2d model of system and analyze the flow in the virtual condition and different contours of pressure velocity and turbulence has been plotted and analyzed.

Ch 1 Introduction

Major source of noise pollution is Engine. These engines are used for various purposes such as, in power plants, automobiles, locomotives, and in various manufacturing machineries. Noise pollution created by engines becomes a vital concern when used in residential areas or areas where noise creates hazard.

The main sources of noise in an engine are the exhaust noise and the noise produced due to friction of various parts of the engine. The exhaust noise is the most dominant. To reduce this noise, various kind of mufflers are usually used. The level of exhaust noise reduction depends upon the construction and the working procedure of mufflers.

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To reduce the noise emitted by IC engine muffler are used. There are no of chamber through which the Exhaust gas is passed I e reactive muffler. The reactive type muffler is usually restrictive and prevents even the good engine sounds from coming through, but does a good job of reducing noise .

When the perforated pipe is wrapped with sound deading material i.e. Absorptive muffler, most absorptive type mufflers are less restrictive, but allow too much engine noise to come through. Regardless of the packing material, absorptive type mufflers tend to get noisier with age

1.1 EXHAUST SYSTEM

Automobile exhaust system consist of various devices , which are used for discharging burned gases. Exhaust systems consists of tubing, which are for emitting out exhaust gases. All the burnt gases are exhaled from an engine using one or more exhaust pipes. These gases are expelled out through several devices like, catalytic converter, muffler /silencer, cylinder head, exhaust manifold, turbocharger

Fig 1.1 Exhaust system

Since our project is based on UAV application, hence emission control is not the main concern therefore catalytic converter is not being used in our exhaust system.

1.1.1 Exhaust Pipe

Exhaust Pipes are used to transmit various toxic gases. Temperature of exhaust gases is very hot, so the material must be durable and heat resistant. The exhaust pipes joins exhaust manifold, muffler and catalytic converters together.

1.1.2 Exhaust Manifold Gaskets

Exhaust Manifold Gaskets consists of strong network of pipes that are used for collecting the gases from cylinders, passes them directly to the exhaust. Manifold gaskets are mostly made of cast iron, embossed steel, high temperature fiber material, graphite and other ceramic composites. The main function of gasket is to seal the connection between the manifold and cylinder head. Leakage of gas is prevented by gas manifold.

1.1.3 Exhaust Flange

Exhaust Flange is a type of projecting rim used for attaching, joining or fastening tightly various exhaust pipes with the help of nuts and bolts. Mostly stainless steel Al, Alloy steel, carbon steel ,hardened steel are used for manufacturing of these flanges.

Ch 2 Types of Muffler

The most common element used to silence generator exhausts are reactive mufflers. Reactive mufflers are available in a wide range of cost and performance. The noise is reduced by forcing the exhaust air to pass through a series of tubes and chambers. Each element in the muffler has sound reduction properties that vary greatly with acoustic frequency, and it is the mixing and matching of these elements that constitutes muffler design.

Reactive muffler

Fig 2.1 Reactive Muffler

Reactive silencers generally consist of several pipe segments that interconnect with a number of larger chambers. The noise reduction mechanism of reactive silencer is that the area discontinuity provides an impedance mismatch for the sound wave traveling along the pipe. This impedance mismatch results in a reflection of part of the sound wave back toward the source or back and forth among the chambers. The reflective effect of the silencer chambers and piping (typically referred to as resonators) essentially prevents some sound wave elements from being transmitted past the silencer. The reactive silencers are more effective at lower frequencies than at high frequencies, and are most widely used to attenuate the exhaust noise of internal combustion engines.

2, 3 or 4-chamber designs

All metal construction with no sound absorptive materials

Maximize ratio of body diameter to pipe diameter & volume

Over the years a series of muffler grades have evolved to describe the approximate insertion loss performance for engine exhaust mufflers. The words do not necessarily imply where the mufflers should be used. Note that better quality (e.g. higher insertion loss) mufflers will be physically larger than lower quality units. Although size is not the only factor, you cannot get good acoustical performance without it.

Exhaust Muffler Grades

Industrial/Commercial: IL = 15 to 25 dBA

Body/Pipe = 2 to 2.5 Length/Pipe = 5 to 6.5

Residential Grade: IL = 20 to 30 dBA

Body/Pipe = 2 to 2.5 Length/Pipe = 6 to 10

Critical Grade: IL = 25 to 35 dBA

Body/Pipe = 3 Length/Pipe = 8 to 10

Super Critical Grade: IL = 35 to 45 dBA

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Body/Pipe = 3 Length/Pipe = 10 to 16

Absorptive (secondary) silencers

Absorptive silencers contain fibrous or porous sound-absorbing materials and attenuate noise by converting the sound energy propagating in the passages into heat caused by friction in the voids between the oscillating gas particles and the fibrous or porous sound-absorbing material

Absorptive silencers use fiberglass or other acoustic fill material to absorb noise without any reactive elements (tubes &chambers). Absorptive silencers provide very little noise reduction at low frequencies, so they should never be used as the only silencer in an engine exhaust system. The straight-through design shown here is very useful for absorbing high frequency self-generated noise created by reactive mufflers.

Fig 2.2 Absorptive Muffler

Reactive/Absorptive Silencers

Fig 2.3 Reactive/absorptive muffler

Some manufacturers offer combination reactive/absorptive silencers in a single package unit. Although this sounds like a good idea, you generally will get better overall acoustical performance by using a reactive muffler followed by a separate absorptive silencer. Of course, a combination silencer may be appropriate for installations where there is not enough length in the exhaust system to fit two separate units.

These devices contain fiberglass shielded from the exhaust stream by perforated sheet metal

Provides broad-band noise control

Reactive mufflers work best at 125 Hz and 250 Hz (IL is reduced at high frequencies by self-noise)

Absorptive mufflers work best at 1000Hz and 2000 Hz

Ch. 3 Exhaust system Design

Selection parameters - The use of an exhaust silencer is prompted by the need to reduce the engine exhaust noise. Acoustical, aerodynamic, mechanical, Structure performances, Shape are the basic selection factors for the muffler

Acoustical performance - The acoustical performance criterion specifies the minimum insertion loss (IL) of the silencer, and is usually presented in IL values for each octave band as well as an overall expected noise reduction value. The insertion loss is determined from the free-field sound pressure levels measured at the same relative locations with respect to the outlet of the unsilenced and silenced systems. The IL of a silencer is essentially determined by measuring the noise levels of a piping systems before and after the insertion of a silencer in the exhaust stream. IL data presented by most manufacturers will typically be based upon insertion of the silencer into a standard piping system consisting of specified straight runs of piping before and after the silencer. Exhaust system configurations as well as mechanical design can have a substantial impact on the performance of and exhaust silencer and should be considered at the time of specification. Raw exhaust noise levels should be obtained from the engine manufacturer to determine the necessary noise reduction requirements of the proposed silencer. Specific installation conditions and exhaust noise levels will aid the manufacturer in determining the correct silencer to meet the required noise reduction

Mechanical performance - The Mechanical performance criterion specifies the material properties of the exhaust system to ensure that it is durable and requires little maintenance when incorporated into service. Material selection is especially important in cases involving high temperature or corrosive gases. Traditional carbon steels will typically be sufficient for the majority of applications using Diesel fueled generators. Natural Gas engines will traditionally run at an elevated temperature above their Diesel counterpart, and may require a graded carbon or stainless steel that can maintain an element of structural performance at elevated temperatures.

Aluminized steel is available from many silencer manufacturers and is often preferred for general applications. Aluminized steel is slightly more heat resistant than carbon steel and offers an increased resiliency to corrosion and is often selected as an economical alternative to specifying a stainless steel system. Regular periodic testing of a standby generator will subject the exhaust system to thermal cycles that can contribute to the premature corrosion of carbon steel

Aerodynamic performance- The Aerodynamic performance criterion specifies the

maximum acceptable pressure drop through the silencer (backpressure of the silencer).\ The exhaust flow rate and temperature from the engine manufacturer are required to accurately predict the backpressure of a silencer and piping system. Selection of an exhaust silencer based solely on the diameter of the connecting piping can often lead to improperly selected products that may present installation issues. Traditional head loss calculations utilizing standardized coefficients for sudden contraction and expansion of fluids can be used to approximate the pressure drop through a silencer and combined with the values obtained for the remainder of the piping system. More complex silencer internal structures should be analyzed using Computational Fluid Dynamics (CFD) where traditional empirical calculations or assumptions may lead to inaccurate results. The pressure drop through silencers should be obtained from the manufacturer of the product upon submission of the required flow information.

Structural performance- The Structural performance criterion can specify the geometric restrictions and/or maximum allowable volume/weight of the silencer that can substantially influence the silencer design process. Secondary loading outside of the weight of the silencer can also affect the design and cost of the exhaust system. A standard engine silencer is not traditionally designed to absorb substantial loads due seismic activity, wind or thermal growth of adjacent piping. Silencers that are specifically incorporated as an element of an exhaust "stack" should be designed to accommodate the loads that will be absorbed due to potentially high wind loads as well as seismic activity. A commodity purchased silencer should be isolated from substantial piping runs through the use of flexible expansion joints to reduce or eliminate the transfer of loads and engine vibration. Customized silencers can easily be designed when the force and moment values that can be placed on a connection are indicated at the time of quotation.

Ch.4 Design Parameters

Adequate Insertion Loss - The main function of a muffler is to muffle sound. An effective muffler will reduce the sound pressure of the noise source to the required level. In the case of an automotive muffler the noise in the exhaust system generated by the engine is to be reduced. A mufflers performance or attenuating capability is generally defined in terms of insertion loss or transmission loss. Insertion loss is defined as the difference between the acoustic power radiated with out and with a muffler fitted. The transmission loss Is defined as the between the sound pressure incident at the entry to the muffler to that transmitted by the muffler.

Desired sound Generally, a muffler is used to reduce sound of a combustion engine to a desired level that provides comfort for the driver and passengers of the vehicle as well as minimizing sound pollution to the environment. Muffler designs generally aim to reduce any annoying characteristics of the untreated exhaust noise such as low frequency rumble. There has however been a growing trend in Australia in recent years for young drivers wanting to "hot-up" their vehicles and this includes muffler modification. Muffler modification of a stock vehicle is generally done for two reasons being performance and sound. Vehicles leave the factory floor with mufflers generally designed for noise control not optimal performance. The standard reactive muffler is generally replaced with a straight through absorption silencer for aesthetics and to minimize backpressure and therefore improve vehicle performance.

Backpressure - Backpressure represents the extra static pressure exerted by the muffler on the engine through the restriction in flow of exhaust gasses generally the better a muffler is at attenuating sound the more backpressure is generated. In a reactive muffler where good attenuation is achieved the exhaust gasses are forced to pass through numerous geometry changes and a fair amount of backpressure may be generated, which reduces the power output of the engine. Backpressure should be kept to a minimum to avoid power losses especially for performance vehicles where performance is paramount.

Every time the exhaust gasses are forced to change direction additional backpressure is created. Therefore to limit backpressure geometric changes are to be kept to a minimum, a typical example of this is a "straight through" absorption silencer. Exhaust gasses are allowed to pass virtually unimpeded through the straight perforated pipe.

Size -The available space has a great influence on the size and therefore type of muffler that may be used. A muffler may have its geometry designed for optimum attenuation however if it does not meet the space constraints, it is useless. Generally the larger a muffler is, the more it weighs and the more it costs to manufacture. For a performance vehicle every gram saved is crucial to its performance/acceleration, especially when dealing with light open wheeled race vehicles. Therefore a small lightweight muffler is desirable. Effectively supporting a muffler is always a design issue and the larger a muffler is the more difficult it is to support. A muffler's mounting system not only needs to support the mufflers weight but it also needs to provide vibration isolation so that the vibration of the exhaust system is not transferred to the chassis and then to the passenger cabin. This vibration isolation is usually achieved with the use of hard rubber inserts and brackets that isolate or dampen vibration from the muffler to the chassis.

Durability - The life expectancy of a muffler is another important functional requirement especially when dealing with hot exhaust gasses and absorptive silencers that are found in performance vehicles. Overtime, hot exhaust gasses tend to clog the absorptive material with unburnt carbon particles or burn the absorptive material in the muffler. This causes the insertion loss to deteriorate. There are however, good products such as mineral wool, fiberglass, sintered metal composites and white wool that resist such unwanted effects. Reactive type mufflers with no absorptive material are very durable and their performance does not diminish with time. Generally mufflers are made from corrosion resistive materials such as stainless steel or aluminum. Mild steel or aluminized steel is generally used for temperatures up to 500°C, type 409 stainless steel up to 700 °C and type 321 stainless steel for even higher temperatures. Automotive exhaust gas temperatures are usually around 750 °C.

Shape Automotive mufflers come in all different shapes, styles and sizes depending on the desired application. Generally automotive mufflers consist of an inlet and outlet tube separated by a larger chamber that is oval or round in geometry. The inside detail of this larger chamber may be one of numerous constructions. The end user of the muffler usually does not care what is inside this chamber so long as the muffler produces the desired sound and is aesthetically pleasing. It is therefore the task of the muffler designer to ensure that the muffler is functional as well as marketable.

Ch 5. Determination of primary pipe length

The data used as a basis for pipe length are the length of opening of the exhaust valve in degrees and the gas velocity through the valve port; as the latter can only be calculated as an average figure based on piston speed, a constant is included to bring this nearer the anticipated initial velocity of gas at the moment of exhaust valve opening, when the cylinder pressure is high, as this starts the initial rush of gas down the pipe, after which there is some slowing down.

Length of primary pipe (feet) =ASD2/2000d2

Where A = exhaust valve opening period in degrees of crankshaft rotation.

S = stroke length in inches

D = cylinder bore in inches

d = exhaust valve port diameter in inches

2000 feet/min is the anticipated initial velocity of gas.

This formula should ensure that the pipe, is sufficiently long to give a good wave action, though it should `be borne in mind that this will probably be most evident at higher engine speeds in its effect of torque.

Table 5.1 Primary length

Primary Pipe length

 

 

 

 

 

 

 

 

assumed

calculated

 

EVO in degrees

Stroke length(inches)

cylinder bore(inches)

Exhaust valve dia. In inches

Primary length(feet)

P (cm)

320

2.8

2.56

1.2

2.04

62.19

330

2.8

2.56

1.2

2.10

64.13

340

2.8

2.56

1.2

2.17

66.07

350

2.8

2.56

1.2

2.23

68.02

Pipe Diameter

The diameter of the primary pipes should be based on the dimensions of the valve throughway. However, it is obvious that the flange of the pipe has to match up nicely with the exhaust-port face of the cylinder head, it is usual for the external port to be rather larger in area than the actual valve throat, and it is not always circular in shape but sometimes square or rectangular. Some designers say that the slightly increased area at this point is of benefit in reducing pressure, particularly as there is often a sharp bend in the cast manifold bolted thereto. Three are fairly simple methods of matching up a round pipe section to a square port, which will be detailed later, but is desirable for the pipe proper to start as near to the port as possible.

The valve throat diameter should be measured from the engine, unless it is included in the tabulated data; dimensions such as valve diameter are of little use, as they cannot be related to the former unless several other measurements are also known. To allow for boundary friction in the pipe, its internal diameter should be slightly greater than the valve throat diameter, to the extent of ½ inch minimum. However, all these niceties of dimensioning will have to fit in with what is commercially available in the way of tube sixes. The appendix gives particulars of ordinary cold- drawn seamless steel tubing of 15SWG having a wall thickness of 0.072 inch. Extra high quality, aircraft type tubing can be obtained, but is naturally more expensive. Eighteen gauge is probably the minimum thickness that should be used, if reasonable life is to be obtained.

Tail pipe design

Exhaust tail pipe will have resonances that can amplify engine tones and produce unwanted noise, to avoid amplification of tones we use short tail pipe or size L to 1/4 wavelength (l/4)

Tail Pipe Resonances

fn = nc/(2L)

where:

fn is resonance frequency of pipe

n = 1, 2, 3, …

c is speed of sound

L is length of pipe (ft)

resonance occurs if L = nλ/2

preferred tail pipe length L = λ/4

Ch 6.Design Proposed

inner diameter of 36mm; outer shell diameter of 112 mm;

length of 100mm(approx); Perforated tube running from the inlet to the exit pipe with 120 perforations that are 1.2 mm in diameter. A layer of absorptive material is sandwiched between the perforated tube and the outer casing.

Outer Diameter of pipe is 3.8mm

Inner Diameter 3.6mm

Fig 6.1. Geometry of Exhaust system

Fig 6.2 Model of Reactive muffler

Fig 6.3 Schematic model of Exhaust system

Fig 6.4 line diagram of exhaust system

Calculation

P1 = 1.2bar

hF = FLV2 / 2gd (head loss)

Section A-B. - Taking Pressure constant At point A & point B

 hF = 0.6 * 12 *17.222/ 2*9.8*3.6 = 30.25m

Bend Loss = V2/ 2g = 0.5 * 17.222/ 2*9.8 = 7.56

P1/Æ¿g + v12/Æ¿g = P2/Æ¿g + V22/2g + hf + Bend Loss

(1.2 * 105/1.2 *9.8 )+( 17.222 / 2*9.8 ) = (1.2 * 105/1.2 *9.8 ) + V22/2*9.8 + 30.25 +7.56

V2 = 16.09 m/s

 Section B-C - Pressure is Drop is considered.

hF = 0.6 * 32 *16.092/ 2*9.8*3.6 = 70.44 m

P1/Æ¿g + v12/Æ¿g = P2/Æ¿g + V22/2g + hf

(1.2 * 105/1.2 * 9.8 ) + ( 16.092 / 2*9.8 ) = (1.17 * 105/1.2 *9.8 ) + V22/2*9.8 + 70.44

V2 = 62.45 m/s

Section C-D

hF = 0.6 * 10 *62.452/ 2*9.8*3.6 = 329.51 m

P1/Æ¿g + v12/Æ¿g = P2/Æ¿g + V22/2g + hf

(1.2 * 105/1.2 * 9.8) + (62.252 / 2*9.8) = (1.14 * 105/1.2 *9.8) + V22/2*9.8 + 329.51

 V2 = 81.50 m/s

Using the following relation*

0.5(49.03√°R)/2πf≤L≤2.6(49.03√°R)/2πf

Temp of exhaust = 700 °C or 700 * 0.8 = 560 R

Frequency = 270 Hz

è 0.5(49.03√°560)/2Ï€*270≤L≤2.6(49.03√°560)/2Ï€*270

0.3 ft ≤ L ≤ 1.3Ft

Length of Mufller we have proposed = 42cm

Ch7. Observation & Findings

Piston Speed = stroke length x rpm / 6

Gas speed = ( piston speed x (Cyl. Dia )2 ) / (port dia)2

Table 7.1 Gas speed at various engine speed

Gas Speed at various engine speed

 

 

 

 

 

 

 

 

Calculated

 

assumed

calculated

 

stroke length in inches

RPM

Piston speed(feet/min)

cyl. Dia

port dia.

gas speed (feet/min)

gas speed(m/s)

2.4

1400

560

3.1

1.26

3389.77

17.22

2.4

1500

600

3.1

1.26

3631.90

18.45

2.4

1600

640

3.1

1.26

3874.02

19.68

2.4

1700

680

3.1

1.26

4116.15

20.91

2.4

1800

720

3.1

1.26

4358.28

22.14

2.4

1900

760

3.1

1.26

4600.40

23.37

2.4

2000

800

3.1

1.26

4842.53

24.60

2.4

2100

840

3.1

1.26

5084.66

25.83

2.4

2200

880

3.1

1.26

5326.78

27.06

2.4

2300

920

3.1

1.26

5568.91

28.29

2.4

2400

960

3.1

1.26

5811.04

29.52

2.4

2500

1000

3.1

1.26

6053.16

30.75

2.4

2600

1040

3.1

1.26

6295.29

31.98

2.4

2700

1080

3.1

1.26

6537.41

33.21

2.4

2800

1120

3.1

1.26

6779.54

34.44

2.4

2900

1160

3.1

1.26

7021.67

35.67

2.4

3000

1200

3.1

1.26

7263.79

36.90

2.4

4000

1600

3.1

1.26

9685.06

49.20

2.4

4100

1640

3.1

1.26

9927.19

50.43

2.4

4200

1680

3.1

1.26

10169.31

51.66

2.4

4300

1720

3.1

1.26

10411.44

52.89

2.4

4400

1760

3.1

1.26

10653.57

54.12

2.4

4500

1800

3.1

1.26

10895.69

55.35

2.4

4600

1840

3.1

1.26

11137.82

56.58

2.4

4700

1880

3.1

1.26

11379.94

57.81

2.4

4800

1920

3.1

1.26

11622.07

59.04

2.4

4900

1960

3.1

1.26

11864.20

60.27

2.4

5000

2000

3.1

1.26

12106.32

61.50

2.4

5100

2040

3.1

1.26

12348.45

62.73

2.4

5200

2080

3.1

1.26

12590.58

63.96

2.4

5300

2120

3.1

1.26

12832.70

65.19

2.4

5400

2160

3.1

1.26

13074.83

66.42

2.4

5500

2200

3.1

1.26

13316.96

67.65

2.4

5600

2240

3.1

1.26

13559.08

68.88

2.4

5700

2280

3.1

1.26

13801.21

70.11

2.4

5800

2320

3.1

1.26

14043.34

71.34

 

 

 

 

 

 

 

 

 

 

 

 

 

 

stroke length in inches

RPM

Piston speed(feet/min)

cyl. Dia

port dia.

gas speed (feet/min)

gas speed(m/s)

2.4

1400

560

3.1

1.3

3184.38

16.18

2.4

1500

600

3.1

1.3

3411.83

17.33

2.4

1600

640

3.1

1.3

3639.29

18.49

2.4

1700

680

3.1

1.3

3866.75

19.64

2.4

1800

720

3.1

1.3

4094.20

20.80

2.4

1900

760

3.1

1.3

4321.66

21.95

2.4

2000

800

3.1

1.3

4549.11

23.11

2.4

2100

840

3.1

1.3

4776.57

24.26

2.4

2200

880

3.1

1.3

5004.02

25.42

2.4

2300

920

3.1

1.3

5231.48

26.58

2.4

2400

960

3.1

1.3

5458.93

27.73

2.4

2500

1000

3.1

1.3

5686.39

28.89

2.4

2600

1040

3.1

1.3

5913.85

30.04

2.4

2700

1080

3.1

1.3

6141.30

31.20

2.4

2800

1120

3.1

1.3

6368.76

32.35

2.4

2900

1160

3.1

1.3

6596.21

33.51

2.4

3000

1200

3.1

1.3

6823.67

34.66

2.4

4000

1600

3.1

1.3

9098.22

46.22

2.4

4100

1640

3.1

1.3

9325.68

47.37

2.4

4200

1680

3.1

1.3

9553.14

48.53

2.4

4300

1720

3.1

1.3

9780.59

49.69

2.4

4400

1760

3.1

1.3

10008.05

50.84

2.4

4500

1800

3.1

1.3

10235.50

52.00

2.4

4600

1840

3.1

1.3

10462.96

53.15

2.4

4700

1880

3.1

1.3

10690.41

54.31

2.4

4800

1920

3.1

1.3

10917.87

55.46

2.4

4900

1960

3.1

1.3

11145.33

56.62

2.4

5000

2000

3.1

1.3

11372.78

57.77

2.4

5100

2040

3.1

1.3

11600.24

58.93

2.4

5200

2080

3.1

1.3

11827.69

60.08

2.4

5300

2120

3.1

1.3

12055.15

61.24

2.4

5400

2160

3.1

1.3

12282.60

62.40

2.4

5500

2200

3.1

1.3

12510.06

63.55

2.4

5600

2240

3.1

1.3

12737.51

64.71

2.4

5700

2280

3.1

1.3

12964.97

65.86

2.4

5800

2320

3.1

1.3

13192.43

67.02

Fig7.1 Graph b/w RPM and Exhaust gas velocity

Intake airflow = (Engine size x RPM x 3456) / volumetric efficiency

Exhaust Flow rate = ((Exhaust temperature + 460 ) / 540) x Intake airflow

Table 7.2 Intake Airflow & exhaust air flow

intake airflow

 

 

 

 

 

 

 

 

 

assumed

calculated

 

 

calculated

 

engine size (CID)

RPM

volumetric efficiency

intake airflow (CFM)

intake airflow (m^3/hour)

exhaust temprature(degree F)

exhaust flow rate(CFM)

exhaust flow rate(m^3/hour)

43.2

3000

0.8

30.00

50.87

1740

122.22

206.56

43.2

3100

0.8

31.00

52.56

1740

126.30

213.44

43.2

3200

0.8

32.00

54.26

1740

130.37

220.33

43.2

3300

0.8

33.00

55.95

1740

134.44

227.21

43.2

3400

0.8

34.00

57.65

1740

138.52

234.10

43.2

3500

0.8

35.00

59.35

1740

142.59

240.98

43.2

3600

0.8

36.00

61.04

1740

146.67

247.87

43.2

3700

0.8

37.00

62.74

1740

150.74

254.75

43.2

3800

0.8

38.00

64.43

1740

154.81

261.64

43.2

3900

0.8

39.00

66.13

1740

158.89

268.52

43.2

4000

0.8

40.00

67.82

1740

162.96

275.41

43.2

4100

0.8

41.00

69.52

1740

167.04

282.29

43.2

4200

0.8

42.00

71.22

1740

171.11

289.18

43.2

4300

0.8

43.00

72.91

1740

175.19

296.06

43.2

4400

0.8

44.00

74.61

1740

179.26

302.95

43.2

4500

0.8

45.00

76.30

1740

183.33

309.83

43.2

4600

0.8

46.00

78.00

1740

187.41

316.72

43.2

4700

0.8

47.00

79.69

1740

191.48

323.60

43.2

4800

0.8

48.00

81.39

1740

195.56

330.49

43.2

4900

0.8

49.00

83.08

1740

199.63

337.37

43.2

5000

0.8

50.00

84.78

1740

203.70

344.26

43.2

5100

0.8

51.00

86.48

1740

207.78

351.14

43.2

5200

0.8

52.00

88.17

1740

211.85

358.03

43.2

5300

0.8

53.00

89.87

1740

215.93

364.91

43.2

5400

0.8

54.00

91.56

1740

220.00

371.80

43.2

5500

0.8

55.00

93.26

1740

224.07

378.69

43.2

5600

0.8

56.00

94.95

1740

228.15

385.57

43.2

5700

0.8

57.00

96.65

1740

232.22

392.46

43.2

5800

0.8

58.00

98.34

1740

236.30

399.34

43.2

5900

0.8

59.00

100.04

1740

240.37

406.23

43.2

6000

0.8

60.00

101.74

1740

244.44

413.11

43.2

6100

0.8

61.00

103.43

1740

248.52

420.00

43.2

6200

0.8

62.00

105.13

1740

252.59

426.88

43.2

6300

0.8

63.00

106.82

1740

256.67

433.77

43.2

6400

0.8

64.00

108.52

1740

260.74

440.65

43.2

6500

0.8

65.00

110.21

1740

264.81

447.54

43.2

6600

0.8

66.00

111.91

1740

268.89

454.42

43.2

6700

0.8

67.00

113.61

1740

272.96

461.31

43.2

6800

0.8

68.00

115.30

1740

277.04

468.19

43.2

6900

0.8

69.00

117.00

1740

281.11

475.08

43.2

7000

0.8

70.00

118.69

1740

285.19

481.96

43.2

7100

0.8

71.00

120.39

1740

289.26

488.85

43.2

7200

0.8

72.00

122.08

1740

293.33

495.73

43.2

7300

0.8

73.00

123.78

1740

297.41

502.62

43.2

7400

0.8

74.00

125.47

1740

301.48

509.50

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

engine size (CID)

 

assumed

calculated

 

 

calculated

 

43.3

RPM

volumetric efficiency

intake airflow (CFM)

intake airflow (m^3/hour)

exhaust temprature(degree F)

exhaust flow rate(CFM)

exhaust flow rate(m^3/hour)

43.3

3000

0.83

31.20

52.90

1740

127.10

214.80

43.3

3100

0.83

32.24

54.66

1740

131.34

221.96

43.3

3200

0.83

33.28

56.42

1740

135.57

229.12

43.3

3300

0.83

34.32

58.19

1740

139.81

236.28

43.3

3400

0.83

35.36

59.95

1740

144.05

243.44

43.3

3500

0.83

36.40

61.71

1740

148.28

250.60

43.3

3600

0.83

37.44

63.48

1740

152.52

257.76

43.3

3700

0.83

38.48

65.24

1740

156.76

264.92

43.3

3800

0.83

39.52

67.00

1740

160.99

272.08

43.3

3900

0.83

40.56

68.77

1740

165.23

279.24

43.3

4000

0.83

41.60

70.53

1740

169.47

286.40

43.3

4100

0.83

42.64

72.29

1740

173.70

293.56

43.3

4200

0.83

43.68

74.06

1740

177.94

300.72

43.3

4300

0.83

44.72

75.82

1740

182.18

307.88

43.3

4400

0.83

45.76

77.58

1740

186.41

315.04

43.3

4500

0.83

46.80

79.35

1740

190.65

322.20

43.3

4600

0.83

47.84

81.11

1740

194.89

329.36

43.3

4700

0.83

48.88

82.87

1740

199.12

336.52

43.3

4800

0.83

49.92

84.64

1740

203.36

343.68

43.3

4900

0.83

50.96

86.40

1740

207.60

350.84

43.3

5000

0.83

52.00

88.16

1740

211.83

358.00

43.3

5100

0.83

53.03

89.93

1740

216.07

365.16

43.3

5200

0.83

54.07

91.69

1740

220.31

372.32

43.3

5300

0.83

55.11

93.45

1740

224.54

379.48

43.3

5400

0.83

56.15

95.22

1740

228.78

386.64

43.3

5500

0.83

57.19

96.98

1740

233.01

393.80

43.3

5600

0.83

58.23

98.74

1740

237.25

400.96

43.3

5700

0.83

59.27

100.51

1740

241.49

408.12

43.3

5800

0.83

60.31

102.27

1740

245.72

415.28

43.3

5900

0.83

61.35

104.03

1740

249.96

422.43

43.3

6000

0.83

62.39

105.80

1740

254.20

429.59

43.3

6100

0.83

63.43

107.56

1740

258.43

436.75

43.3

6200

0.83

64.47

109.32

1740

262.67

443.91

43.3

6300

0.83

65.51

111.09

1740

266.91

451.07

43.3

6400

0.83

66.55

112.85

1740

271.14

458.23

43.3

6500

0.83

67.59

114.61

1740

275.38

465.39

43.3

6600

0.83

68.63

116.37

1740

279.62

472.55

43.3

6700

0.83

69.67

118.14

1740

283.85

479.71

43.3

6800

0.83

70.71

119.90

1740

288.09

486.87

43.3

6900

0.83

71.75

121.66

1740

292.33

494.03

43.3

7000

0.83

72.79

123.43

1740

296.56

501.19

43.3

7100

0.83

73.83

125.19

1740

300.80

508.35

43.3

7200

0.83

74.87

126.95

1740

305.04

515.51

43.3

7300

0.83

75.91

128.72

1740

309.27

522.67

 

7400

0.83

76.95

130.48

1740

313.51

529.83

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

engine size (CID)

 

assumed

calculated

 

 

calculated

 

43.3

RPM

volumetric efficiency

intake airflow (CFM)

intake airflow (m^3/hour)

exhaust temprature(degree F)

exhaust flow rate(CFM)

exhaust flow rate(m^3/hour)

43.3

3000

0.85

31.95

54.17

1740

130.16

219.97

43.3

3100

0.85

33.01

55.98

1740

134.50

227.31

43.3

3200

0.85

34.08

57.78

1740

138.84

234.64

43.3

3300

0.85

35.14

59.59

1740

143.18

241.97

43.3

3400

0.85

36.21

61.40

1740

147.52

249.30

43.3

3500

0.85

37.27

63.20

1740

151.86

256.64

43.3

3600

0.85

38.34

65.01

1740

156.19

263.97

43.3

3700

0.85

39.40

66.81

1740

160.53

271.30

43.3

3800

0.85

40.47

68.62

1740

164.87

278.63

43.3

3900

0.85

41.53

70.42

1740

169.21

285.97

43.3

4000

0.85

42.60

72.23

1740

173.55

293.30

43.3

4100

0.85

43.66

74.04

1740

177.89

300.63

43.3

4200

0.85

44.73

75.84

1740

182.23

307.96

43.3

4300

0.85

45.79

77.65

1740

186.57

315.30

43.3

4400

0.85

46.86

79.45

1740

190.90

322.63

43.3

4500

0.85

47.92

81.26

1740

195.24

329.96

43.3

4600

0.85

48.99

83.06

1740

199.58

337.29

43.3

4700

0.85

50.05

84.87

1740

203.92

344.62

43.3

4800

0.85

51.12

86.68

1740

208.26

351.96

43.3

4900

0.85

52.18

88.48

1740

212.60

359.29

43.3

5000

0.85

53.25

90.29

1740

216.94

366.62

43.3

5100

0.85

54.31

92.09

1740

221.27

373.95

43.3

5200

0.85

55.38

93.90

1740

225.61

381.29

43.3

5300

0.85

56.44

95.70

1740

229.95

388.62

43.3

5400

0.85

57.51

97.51

1740

234.29

395.95

43.3

5500

0.85

58.57

99.32

1740

238.63

403.28

43.3

5600

0.85

59.64

101.12

1740

242.97

410.62

43.3

5700

0.85

60.70

102.93

1740

247.31

417.95

43.3

5800

0.85

61.77

104.73

1740

251.65

425.28

43.3

5900

0.85

62.83

106.54

1740

255.98

432.61

43.3

6000

0.85

63.90

108.34

1740

260.32

439.95

43.3

6100

0.85

64.96

110.15

1740

264.66

447.28

43.3

6200

0.85

66.03

111.96

1740

269.00

454.61

43.3

6300

0.85

67.09

113.76

1740

273.34

461.94

43.3

6400

0.85

68.16

115.57

1740

277.68

469.28

43.3

6500

0.85

69.22

117.37

1740

282.02

476.61

43.3

6600

0.85

70.29

119.18

1740

286.36

483.94

43.3

6700

0.85

71.35

120.98

1740

290.69

491.27

43.3

6800

0.85

72.42

122.79

1740

295.03

498.61

43.3

6900

0.85

73.48

124.60

1740

299.37

505.94

43.3

7000

0.85

74.55

126.40

1740

303.71

513.27

43.3

7100

0.85

75.61

128.21

1740

308.05

520.60

43.3

7200

0.85

76.68

130.01

1740

312.39

527.94

43.3

7300

0.85

77.74

131.82

1740

316.73

535.27

7400

0.85

78.81

133.63

1740

321.07

542.60

Ch 8. Approach using CFD & Gambit

Creating geometry in Gambit

For Pipe

Fig 8.1 2D Model in gambit

Open Gambit and select the Working Directory.

Go to Operation Toolbar -Geometry Command Button -Vertex command - Enter all the Vertex individually.

For pipe Structure.

A(0,0,0) ; B(0,0.12,0) ; C(.036,.12,0); D(0.36,0.36,0) ; E(0.32,0.36,0); F(0.32,0,0) ;G(.3907,.1067,0) ;H(.3907,.0707,0)

For Muffler

A(0,0,0),B(0.06,0,0),C(0,0.036,0),D(.06,.036,0),E(.06,0.56,0),F(0.06,-0.56,0),G(0.46,0.56,0),H(0,0.46,0), I(0.46, 0.036,0), J(0.52,0,0),K(0.52,0.036,0)

(*We are doing separately for Pipe separately for Muffler)

Go to Operation Toolbar - Geometry Command Button -Vertex command - Edge Command button- Join all the edges in the desired shape for both pipe & muffler.

Go to Operation Toolbar -Geometry Command Button -Face command -Create Face.

Operation toolbar- Mesh Command button- Edge Command button- Select the edges- give the interval count- click apply

Operation toolbar- Mesh Command button- Face command button- Mesh face- select the face- click apply

Operation toolbar-Zone command button- Specify boundary types command button

For pipe

Pipe left inlet

Velocity inlet

Pipe right outlet

Pressure Outlet

Rest all edges

Wall

File - save

File- export- Check export to 2D mesh

Exit

Set up problem in fluent

Open the Fluent - Select 2ddp - click run

Fig 8.2 fluent startup window

Go to file- read case - Read the .msh file

Fig 8.3 Fluent Grid check

Go to Grid- Check

Grid - Info- Size

Define- material - Solver

Fig 8.4 Solver step

Solver- Pressure Based and space - 2D

Define- Model- uncheck the Energy

Define- model - Viscous- K- epsilon

Fig 8.5 Viscous Model

Click apply

Define boundary condition

Fig 8.6 Operating condition

Define operating condition

Fig 8.7 Boundary Condition

In operating condition

Set the inlet velocity and also check all the boundary condition are same as gambit or not

Solve - Control - Solution- change Momentum, Turbulent Kinetics Energy & Turbulent Dissipation to Second Order Upwind- Click apply

Fig 8.7 Control Solution

Solve - initialize - Initialize

Select in compute the Inlet

Click init then apply then close

Fig 8.8 Initialization step

Solve- Monitor- residual

Check plot

Change the absolute Criteria to 1e-6 for Residual

Click ok

Fig 8.9 Monitor Residual

Solve Iterate

No of iteration 500

Display Vectors

Display Contour

Select Contour of pressure, velocity, turbulence, Wall shear stress

For Pipe

Fig 8.10 Velocity vectors colored by Velocity magnitude

Fig 8.11 Contours of Turbulent Kinetic Energy

Fig 8.12 Contours of Static Pressure

Fig 8.13 Iteration Curve

Fig 8.14 Convergence curve for pipe

Fig 8.15 Contours of velocity magnitude

For muffler

Porous medium

Fig 8.16 Model of muffler section

Open Gambit and select the Working Directory.

Go to Operation Toolbar -Geometry Command Button -Vertex command - Enter all the Vertex individually.

For muffler Structure.

A(0,0,0) ; B(.072,0) ; C(0,.03); D(0.03,0.03) ; E(0.030.0012); F(0.042,0.05) ;G(0.042,0.03) ;H(0.072,0) ; I( 0.072,0.03)

(*We are doing separately for Pipe separately for Muffler)

Go to Operation Toolbar - Geometry Command Button -Vertex command - Edge Command button- Join all the edges in the desired shape for both pipe & muffler.

Go to Operation Toolbar -Geometry Command Button -Face command -Create Faces.

Operation toolbar- Mesh Command button- Edge Command button- Select the edges- give the interval count- click apply

Operation toolbar- Mesh Command button- Face command button- Mesh face- select the face- click apply

Operation toolbar-Zone command button- Specify boundary types command button

For Muffler

left inlet

Velocity inlet

Middle Edge downone

Pressure Outlet

Middle Edge

Pressure inlet

Rest all Edges

Wall

Medium (Face2)

porous (in specify continuum types)

File - save

File- export- Check export to 2D mesh

Exit

In Fluent

Open the Fluent - Select 2ddp - click run

Go to file- read case - Read the .msh file

Go to Grid- Check

Grid - Info- Size

Define- material - Solver

Solver- Pressure Based and space - 2D

Define- Model- uncheck the Energy

Define- model - Viscous- K- epsilon

Click apply

Define boundary condition

Define operating condition

In operating condition

Set the inlet velocity and also check all the boundary condition are same as gambit or not

Specify the inlet velocity, Specify the material properties(density, viscosity)

Solve - Control - Solution- change Momentum, Turbulent Kinetics Energy & Turbulent Dissipation to Second Order Upwind- Click apply

Solve - initialize - Initialize

Select in compute the Inlet

Click init then apply then close

Solve- Monitor- residual

Check plot

Change the absolute Criteria to 1e-6 for Residual

Click ok

Solve Iterate

No of iteration 2000

Display Vectors

Display Contour

Select Contour of pressure, velocity, turbulence

Fig 8.17 Velocity Vectors colored by Velocity Magnitude - muffler

Fig8.18 Contours of Turbulent Kinetic Energy - muffler

Fig 8.19 Contour of Static Pressure - muffler

Fig 8.20 Convergence Curve - muffler

Conclusion

Since the project (Design of muffler) has been intended to fabricate an exhaust system for minimum power loss and maximum insertion loss.

Basically there are two types of muffler available in the market

Reactive Muffler

Absorptive Muffler

Generally reactive mufflers are designed to minimize the attenuation, consist of series of a resonating and expansion chamber that are designed to reduce the sound pressure level at certain frequency.

Absorptive is also known as dissipative muffler, in this type of muffler the sound energy is converted into heat in the absorbing material which is either fibre glass or glass wool. A typically absorptive muffler consist of straight perforated pipe and on this pipe a layer of sound absorptive material and it is enclosed with the help of steel casing

Considering the designing parameter we have take care of

Back pressure

Insertion loss

Size

Durability

Shape

For back pressure we have taken the minimum pressure as 1.05 bars so that we can avoid the back pressure. Since we don't have facilities to measure the sound of the muffled & unmuffled engine therefore we have taken the values from the resources available with us. Considering the engine compartment we calculated the dimensions which are mentioned above. Since the temperature ranges varies from 600-700C that is why we have to consider the material which can withstand with such high temperature. Based on assumption &analysis of pressure & velocity in CFD at different point on the Exhaust system we come to a conclusion that insertion loss will be 10 - 14db, maximum 95 minimum 80.

In dissipating muffle we can add resonator. Basically three types of resonator can be used to it.

Expansion chamber

Side branch Resonator

Helmholtz resonator

In expansion chamber the greater the protrusion in to the muffler greater the insertion loss however the inlet and outlet should be maintain a separation space of at least 1.5 times the diameter of the chamber to ensure the decay of transitory nodes.

Side Branch resonator is used to control pure tones of a constant frequency. It generally takes the form of a short length of pipe whose length is approximately a quarter of the wavelength of the sound frequency to be controlled.

A Helmholtz resonator is similar to a side branch resonator the only difference being that there is a backing volume joined to the connecting orifice