Exhaust System

Parts including exhaust system
1. Turbo charger
2. Waste gate
3. Piping
4.Silencer
5. Exhaust manifold

1.1 Turbocharger
Turbocharger are employed to achieve higher specific engine power output by converting some of the energy in the exhaust gas steam in the form of pressure energy this raised inlet pressure force more air in to engine cylinders allowing more fuel to be burned and thus resulting higher power output.
Hot exhaust gases exit cylinder and enter the turbine side turbocharger the turbine blade and compressors blade shared commonshaft.The exhaust gases drive the which in turn drive the compressor blades on air intake side the turbine blade. The high speed rotation the intake air to provide more oxygen for combustion.


Fig1.1 Turbocharger
Waste gate
Turbocharger equipped with a waste gate can efficiently operate in a much border range of altitude and ambient condition
it operated to vent the exhaust flow away from the turbocharger .the reduced exhaust flow slows the turbocharger avoid over speed and exhaust speed and excessive boost pressure.
On some natural gases waste gate may be manually adjusted .for sight conditions to optimize the throttle t position for efficiency and improved response.
Piping
The function of the exhaust piping is to convey the exhaust gases from the engine exhaust outlet to the silencer and other exhaust system components, terminating at the system outlet.

Silencer

Silencer is device which is used for reducing noise .it is also called as mufflers which noise depend up on the parameter such like gas velocity, Backpressure of exhaust gases and temperature of exhaust gases. Different type of material are used for silencer such like steel according to the there are two basic types :- (1) Absorptive type (2) Reactive type

Exhaust noise is one of the principal noise sources of any engine installation. The purpose of the silencer is to reduce the noise of the exhaust before it is released to the atmosphere. Exhaust noise arises from the intermittent release of high pressure exhaust gas from the engine cylinders, causing strong gas pressure fluctuations in the exhaust system. This leads not only to discharge noise at the exhaust outlet, but also to noise radiation from exhaust pipe and silencer surfaces. A well designed and matched exhaust system will significantly reduce noise from these sources. The silencer makes a major contribution to exhaust noise reduction. Excessive noise is objectionable in most applications. The required degree of silencing depends on factors such as the application type, whether it is stationary or mobile and whether there are any legal regulations regarding noise emission. For example, excessive noise is objectionable in a hospital or residential area but may well be acceptable in isolating station.

1.4.1 Silencer Rating
Silencers are typically rated according to their degree ofSilencing.

-Industrial silencer (sound reduction up to 12-18 dB)
-Residential silencer (sound reduction up to 18-25 dB)
- Critical silencer (sound reduction up to 25-35 dB)
- Hospital silencer (sound reduction up to 32-42 dB)

' Level 1
Silencer System 'Residential' ' Suitable for industrial areas where background noise level is relatively high or for remote areas where partly muffled noise is permissible.

' Level 2
Silencer System 'Critical' ' Reduces exhaust noise to an acceptable level in localities where moderately effective silencing is required 'such as semi residential areas where moderate background noise is always present.

' Level 3
Silencer System 'Supercritical' ' Provides maximum silencing for
residential, hospital, school, hotel, store, apartment building and other areas where
background noise level is low and generator set noise must be
kept to a minimum.


Fig 1.2.Exhaust manifold
1.5 Exhaust manifold
Exhaust manifold collect the exhaust gases from each cylinder channel to exhaust outlet. it is designed for giving minimum back pressure and turbulence.
Cat product used
-Dry water cooled
-Air shielded water cooled
1.5.1Characteristic of dry manifold
-Most preferable manifold
-cost effective
-maximum possible exhaust
-radiate more heat and high surface temp
Characteristic of water cooled manifold
-surface temp is lower.
-it has high capacity of cooling system.
-it reduces the exhaust energy deliver to turbocharger.
Air shielded water cooled manifold
In air shielded water cooled manifold make use of insulating air cavity is used between exhaust manifold so it is mostly used in turbocharger type vehicle where large amount of exhaust energy is delivered.
1.5.4Heat shielding
Heat shielding may be used as a shielding of hot surfaces and protecting the component or operator from excessive heat.It depends on the factors such like
-installation type
-environment
-legislative environment
So for the guards are also provided
1.5.5Blankets(soft manifold shield)
-blankets are made of insulating layer of thermal cloth of outer layer.
-most blankets placed with steel springs or wire which will be laced over blankets.
1.5.6Hard wrap(hard manifold shield)
-It is used on engine itself for example in a vee between cylinder blanks the hard wrap it consist of three layer
-Thermal sheet
-Blankets of fibre glass
-Sheet of banded metal
1.5.7Guards and shield
Guards and shield are made using perforated shield metal they are shield. they are installed with air gap between the shield and hot surface

CHAPTER-2MUFFLER DESIGN
Muffler is a device which is provide for silencing noise and also reduces the problem of back pressure. The sole purpose of muffler is to reduce engine noise emission. If you have ever heard a car running without a muffler you will have an appreciation for the significant difference in a noise level a muffler can make. If vehicle did not have a muffler there would be an un bearable amount of an engine exhaust noise in environment .noise is defined as an unwanted sound.
Sound is a pressure wave formed from pulse of alternating high and low pressure air. In an automotive engine, pressure waves are generated exhaust valves repeatedly opens and lets high pressure gas in to exhaust system. These pressure pulse are sound we hear. As the engine rpm increases so do the pressure fluctuations and therefore the sound emitted is of higher frequency.
All noise emitted by automobile does not come the exhaust system .other contributors to vehicle noise emission include intake noise ,mechanical noise and vibration induced noise from the engine body and transmission.
There are two types of muffler design.
-Absorptive muffler
-Reactive muffler
Generally automotive muffler will have both reactive and absorptive properties. the reactive and reflective muffler use the phenomena of destructive interference to reduce the noise. This means that they are designed so that sound waves produce by an engine partially cancel them out in the muffler. for complete interference to occur a reflected pressure wave of equal amplitude and 180 degrees out of phase needs to collide with the transmitted pressure waves. Reflection occur when there is a change of geometry or an area discontinuity.
A reactive muffler, generally consist of a series of resonating and expansion chambers that are design to reduce the sound pressure level at certain frequencies. The inlet and outlet tubes are generally offset and have perforation that allow the sound waves to scatter out in numerous directions inside a chamber resulting in destructive interference.
Reactive muffler can be used in car exhaust system where the exhaust gas flow and noise emission varies with the time they have ability to reduce noise at various frequencies due to numerous chambers and changes in geometry that the exhaust gases are forced to pass through.
The down side the reactive muffler is that large back pressure are created however for passengers cars where noise emission and passengers comfort is primary requirement at that time it is useful of that on roads.
An absorptive muffler uses absorption to reduce the noise. Sound waves are reduced their energy is converted in to heat in the absorptive material. A typical absorptive muffler consists of a straight, circular and perforated pipe that is encased in a larger steel housing. Between the perforated pipe and the casing is a layer of sound absorbing material that absorb some of the pressure pulses.
Absorptive mufflers create less backpressure then reactive mufflers; however they do not reduce noise as well.
Generally reactive mufflers use resonating chamber that target specific frequency to control noise where as an absorptive silencer reduce noise considerably over the entire spectrum and more so at higher frequency
It is good to practise to design a muffler to work best in the frequency range where entire has the highest sound energy .in practises the sound spectrum of an engine exhaust is continuously changing as it is depend on the engine speed that is continuously varying when the car is being driven. It is impossible to design a muffler system that is completely destructive interference, however some were always occur.
Noise spectrum variation makes muffler design quite difficult and testing is the only sure way to determine whether the muffler performs well at all engine speeds. However as a general rule of thumb,exhaust noise is generally limited to fundamental frequency and first few harmonics ,which can be calculated so these frequency should be used as a starting point for preliminary muffler design.
A practical way of determining the frequency range to be controlled is to be measure the unmuffle noise this measure spectrum can then be used to identify the frequencies at which higher level noise occur. The high noise level frequencies should be treated with appropriate noise control to achieve on overall reduction.

Fig 2.1.Typical reactive automotive muffler

Fig 2.2. Absorptive automotive muffler

Functional requirement of exhaust muffler
Insertion loss
Backpressure
Size
Durability
Desired sound
Cost
Shape
Style

Insertion loss
The main function of muffler is to attenuate the sound An effective muffler will reduce the sound pressure of the noise source to require levelInsertion loss is defined as the difference between the acoustic power radiated without and with a muffler fitted.It is defined as the difference between the sound power incidents at the entry to the muffler that to that transmitted by the muffler.
As a general principal while developing an automotive muffler a reactive muffler with many area discontinuities will achieve a greater attenuation than one with the fewer area discontinuities will achieve greater attenuation than one with fewer area discontinuities. The addition of sound absorptive material will always increase attenuation capacity of muffler but should be located at appropriate place.
2.2.2 Back pressure
Back pressure represent the extra static pressure exerted by the muffler on the engine through the restriction in flow of exhaust gases.
Generally the better a muffler is at attenuating around the more backpressure is generated. In reactive muffler where good attenuation is achieved the exhaust gases are forced to pass through the numerous geometry changes and a fair amount of backpressure may be generated which reduce the power output of engine backpressure should be kept minimum to avoid power losses especially for performance vehicles where performances are paramount.

Every time exhaust gases are forced to change in direction additional back pressure crated therefore to limit the backpressure geometric changes are to be kept to a minimum a typical example of this is a straight through absorption silencer exhaust gases are allowed to pass virtually unimpeded through the straight perforated pipe.

Perforated pipe :

it is the pipe in which number of holes are provided at equal distance which is also equal sized and which is provided for spreading of exhaust gases without back pressure which reduce the power

Durability

The life expectancy of muffler is another important functional requirement especially when dealing with hot exhaust gases and absorptive silencer that are found in performance vehicles.
Overtime exhaust gases tend to clog the absorptive material with in burnt carbon particles or burn the absorptive material in the muffler this cause the insertion losses to Detroiter. There are however, good products such as mineral wool, fibreglass, sintered metal composites and white wool that resists such unwanted effects.
Generally in muffler the material are used such like
500 c ' mild stainless steel
700 c -409 stainless steel
centigrade more-321 type stainless steel

2.2.5 Shape and style

Automotive mufflers come in all different shapes ,styles and sizes depending up 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 one of numerous constructions. The end user of the muffler usually does not care what is inside in this chamber the end user of the muffler does not care what is inside in 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.

2.2.6 Possible muffler design

Automotive mufflers usually have a circular or elliptical cross-section, circular shaped cross section is the best sited in a vehicle as it delays the onsets of higher order modes.

Most formulas that used to predict the transmission loss of a muffler assume plane wave propagation the properties of the following designs are only valid up to cut-off frequencies where higher order mode occurs generally for all mufflers maximum transmission loss occurs at odd multiple of quarter length.
The most basic type of silencing element that may be used for intake and exhaust muffler is expansion chamber the inlet and outlet tube may be coaxial known as concentric expansion chamber or offset known as offset expansion chamber.
The sudden expansion or contraction type of chamber cause sound waves to reflect back and interfere with each other.

Expansion chambers are efficient in attenuating low frequency sound which makes them ideal for automotive application so the do no attenuate high frequency sound so as well as it 'beams' straight through the muffler


Fig 2.3 Illustration of Incident, reflected and transmitted sound waves

Fig 2.4.Simple expansion chamber

It has been proved that larger the expansion ratio higher the transmission loss
And always the length of the chamber should be atleast 1.5 times to its diameter.

Similar a slandered expansion chamber is the extended inlet and outlet expansion chamber in which the tubes are extended in the expansion chamber.
Benefit of such design is that part of the chamber between the extended pipe and side wall act as a side branch resonator therefore improving transmission loss.

The grater the protrusion in to the muffler the greater the transmission loss
However the inlet and outlet tubes should maintain the separation space of at least 1.5 times the diameter of the chamber to ensure the decay of evanescent modes.

Noise can be further attenuated by the addition of porous material inside the expansion chamber whilst maintaining the same muffler dimension sound waves loose energy when they travel through porous medium


Fig2.5.Straight absorptive muffler

The absorptive material cause the fluctuating gas particles to convert acoustic energy in to heat.

The main benefit of straight through absorptive silencer is that insignificance backpressure is generated therefore improving vehicle performance .the perforated tube is used to guide the exhaust flow and avoid the creation of turbulence as is found in an expansion chamber.

The main material used to guide the exhaust flow ,yet allow sound waves to escape is usually perforated steel with an open area of approximately 20%
An absorptive silencer cause produce more consistent transmission loss the expansion chamber tl is typically domed shape as can be the absorptive material not only iro but this humps but also increase transmission loss dramatically especially for better higher frequencies.


Fig 2.6.muffler with and without absorptive material
A side branch resonator is a muffling device used to control pure tones of constant frequency .it generally takes the form of short length of pipe whose length is the quarter of the wavelength of the sound frequency to be controlled.

A Helmholtz resonator is similar to side branch resonator the only difference being that there is backing volume joined to the connecting orifice. If it is found that the unmuffled exhaust noise spectrum has noticeable peaks found than muffler ,resonator side Brach resonator may be used to target the specific resonant frequencies. The resonating chamber style of muffler is extremely efficient in providing noise control for specific frequency band however the attenuation band is narrow. This characteristic is not use full in automotive silencer because attenuation is needed over all frequencies.


Fig 2.7.Side branched resonator


Fig 2.8.Helmholtz Resonator

If broader and improved attenuation spectrum is require than multiple resonator should be used. Each chamber is designed to reduce a specific frequency being odd multiple of quarter wavelength apart as chamber increases the attenuation is also increases.


Fig 2.9.Muffled vs.Unmuffled exhausts noise

The insertion loss of the absorptive muffler fitted to formula sae vehicle has been measured to assess this style of muffler and it's attenuation characteristics. This performance vehicle uses straight through absorptive muffler as it provide the require attenuation of 18 DBA as well as being lightweight and produce minimum backpressure for increase engine
performance.
The measurement shows that this absorptive muffler is a good broadband attenuator and control noise extremely well at low frequency and high frequencies. the absorptive material provide all the high frequency attenuation as expected of such muffler and the resonating effect of central chamber is controlling the mid to low frequencies.

CHAPTER-3 BASIC TYPES OF SILENCER
3.1 Reactive silencer.

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 travelling 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. A generic reactive engine silencer comprised of two proportionally sized chambers with a pair of interconnecting tubes is shown below.


Fig 3.1.Reactive silencer

3.2 Absorptivesilencer

Absorptive silencers usually have relatively wideband noise reduction
Characteristics at middle and higher frequencies. Absorptive silencers are often used to attenuate the engine intake noise or supplement the performance of reactive silencers for the engine exhaust noise control. The sound absorbing materials are generally held in position by the use ofa perforated metal liner. Knowledge of the structural content of an exhaust system is important when considering the inclusion of a catalytic element or Selective Catalytic Reduction (SCR) system in conjunction with the silencer. Particulate migration of the insulation into the exhaust stream over a period of time can cause the catalytic element to become fouled and substantially impact or impede its performance.

3.3 Combination silencer.

Some silencers combine both reactive and absorptive elements to extend the noise attenuation performance over a broader noise spectrum. Combination silencers are also widely used to reduce engine exhaust noise.


Fig 3.2.Comparison of Reactive, Absorptive and combine silencer
3.4 Spark arresting silencer.

Federal, state, local and municipal bylaws often dictating exhaust installations have provisions for arresting sparks from internal combustion engines. If an engine is to be used in an area where there is potentially dry vegetation of other combustible materials that are likely to be ignited by any hot carbon passing through the exhaust, one must incorporate spark-arresting capabilities into the silencer. Most approved spark arresting systems will employ diffusers or
Modified interconnecting tubes that create a centrifugal flow action in the exhaust to direct carbon particulate into a collection chamber. The particulate trap should be periodically inspected and cleaned to ensure proper functionality of the spark arresting capabilities of the silencer.

3.5 Catalytic silencer.

To enhance exhaust gas emission control one may incorporate a catalytic converter element into a silencer to reduce the Oxides of Nitrogen (NOx), Carbon Monoxide (CO), and Non-Methane Hydrocarbons (NMHC) discharged in the exhaust stream. A catalytic converter is comprised of a NOx catalyst and an oxidation catalyst. The NOx beds reduce the NOx into benign N2 and H2O, while the oxidation catalyst reacts with CO and HC to form water vapour and carbon dioxide. Inclusion of the catalytic element into the body of an exhaust silencer can reduce the cost of a combination system by eliminating the need for a separate acoustic silencer as well as specialized catalyst housing and tracking system.

3.6 Heat recovery silencer.

Most of the energy available in the fuel used in reciprocating and gas turbine engines is rejected in the form of heat. A reciprocating engine running at full load converts about one-third of the available energy into useful work, while the remaining two thirds of the available energy is lost in the form of heat rejection. In a prime power installation where the rejected heat can be used to provide energy to auxiliary applications a heat recovery silencer can yield attractive savings. Typical applications of heat recovery silencers for internal combustion engines include hot water heating, steam generation, heat transfer fluid heating, etc.

3.7 Tuned silencer.

When the low frequency noise within a narrow band is extremely high, a tuned silencer can be designed to combat the specific offending frequencies. Tuned silencers consist of pipe segments and cavities that are used to produce a low frequency resonance at a required frequency. The accurate prediction of the tuned (resonance) frequency is extremely important to facilitate a match of the peak frequency for reducing the narrow band noise to a desirable level. A small deviation of the silencer resonance frequency from the peak frequency of the noise will greatly degrade the silencing ability

3.8 Active silencer.

Active silencing, or sound cancellation systems, employ detectors used in sensing the noise in an exhaust pipe and a loudspeaker that is used to reintroduce an inverted signal have been developed to reduce low frequency noise. The theoretical effect of reintroducing an inverted signal will result in complete elimination of sound from the exhaust silencer. Although the idea of sound cancellation is very simple and attractive, there are a variety of complications and problems arising

from erratic fluctuations in the sound source. Active silencing is relatively expensive at the present
time, and its acoustic attenuation performance at high frequencies is also limited. Widespread use will be dependent upon continued development of lower cost systems with improved performance realized through the use of better analytical algorithms, transducers and processors.

3.9 Silencer selection factors

The use of an exhaust silencer is prompted by the need to reduce the engine exhaust noise. In most applications the final selection of an exhaust silencer is based on a compromise between the predicted acoustical, aerodynamic, mechanical and structural performance in conjunction with the cost of the resulting system.

3.9.1 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. he 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

3.9.2 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.

3.9.3Structural 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.

3.10 Types of Multi-chamber silencers

3.10.1 EN Series Silencers

For the majority of engines and operating conditions, multi-chamber type silencers provide maximum noise attenuation within acceptable back pressure limits. Most naturally aspirated and supercharged engines need this type of silencer. Many turbocharged engines are best silenced with this design also. Factors which influence the choice of silencer design are explained on the


Fig 3.3. EN series silencer
3.10.2 ET Series Silencers Straight-Through Silencers

Some engines require very low exhaust system back pressures for maximum performance. Many turbocharged engines and some naturally aspirated engines fall into this category. For these engines, straight-through, reactive silencers are available
to provide adequate silencing while imposing negligible restriction on exhaust gas flow.

Fig 3.4. ET series silencer
3.10.3ES Series Silencers Spark Arresting Silencers

Operating locations exist where fire hazards and safety codes require removal of sparks from exhaust gases. Universal's spark arrestor silencers are engineered to perform the dual function of spark arrestment and silencing for all internal combustion engines.


Fig 3.5.ES series silencer

3.11 Measurement setup

Fig 3.6. Measurement setup

CHAPTER-4 DESIGN AND METHODOLOGY
Before design there are five criteria require to consider.
The acoustic criteria which specify the minimum noise reduction required from the muffler as function of frequency. The operating conditions must be known because large steady flow velocities or large alternating velocities may alter its acoustic performance.
The aerodynamic criteria which specifies the maximum acceptable average pressure drop through the muffler at given temperature and mass flow.
The geometric criteria, which specifies the maximum allowable volume and restrictions on shape.
The mechanical criteria, which may specify the material from which it is durable and require little maintenance.
The economical criteria are a vital in marketplace.
Step 1.
The first step in any design and development is to set a target by doing benchmarking exercise of same kind of models. The same will applicable for the silencer here, to set a target in terms of transmission loss of same engine power models of competitor benchmarking vehicles. Based on provided engine input data and benchmark study target for backpressure and noise are range decided.

Step 2.
After benchmarking exercise, one need to calculate the target frequencies to give concentration of higher transmission loss for calculating the target frequencies engine maximum power rpm is required and calculation follows.

Formulate:



Fig 3.7.Approach paper design methodology for muffler

STEP 3.

Muffler volume calculation

Volume of muffler

(V_m) =V_f??[??/4(d^2??l)]??(No.. of cylinder./2)
STEP 4.
Internal conFiguration and concept design
Based on transmission loss and target frequencies designer draws few concept of internal conFiguration that meet the packaging dimension within the volume mention above.
Each concept and internal conFiguration is formulated to best possible conFiguration so as to achieve best acoustic performance and best back pressure.
Perforation: perorated pipe is the important acoustic element of muffler which is tuned in line with problematic frequency indentified in 2nd step
The diameter of hole to be drilled/punched is calculated by thumb rule.
d_1=1.29/'N
So probability porosity is given by ??= (??/4'??d_1'^2)/C^2
The designer needs to keep in mind that lesser the porosity more in restriction and more will be the backpressure
Open area ratio AOP is given

Lesser the Aop better the transmission loss and better the acoustic performance.
At this stage the diameter of the hole to be drilled, pitch, number of the holes per raw, number of raws for each pattern of hole is frozen. Thus, the design of perforated tube for individual hole pattern is finalized based on this best concepts are designed and carry forward virtual simulation.

STEP 5:

Virtual simulation

Based on above mentioned approach, different concepts will be arrived with optimum combinations of different elements inside volume of the silencer. Finalised concepts will be verified virtually using CAE simulation
software's towards the achievement of transmission loss and back pressure.

Cfd analysis

When steady air flow passes through mufflers, there will have steady pressure drop which is related to flow and geometry of air passages. Pressure drop in an exhaust muffler plays an important role for the design and development of mufflers.

Predication of pressure drop will be very useful for the design and development of muffler. To predict the pressure drop associated with the steady flow through the muffler CFD has developed over the last two decades. So the flow prediction can be made reliable.

TRANSMISSION LOSS ANALYSIS
Prediction of transmission loss virtually is an important analysis required for the development of muffler at an
initial design stage. There are different software packages available in market for predicting the transmission loss. We have used virtual lab for Transmission loss measurements.

It is also to be noted the limitations of the CAE tools, as the co-relation at higher frequencies is difficult since the plane wave theory holds good only up to 3000Hz beyond which the wave is no more 2 dimensional but 3dimensional for which the computations are far complex to match the practical results. Hence need of research to blend both strengths of CAE & Practical resulting in a Practical approach/methodology. After completion of simulation the best three concepts will (with less back pressure and higher transmission loss) be taken forward for the prototype manufacturing to check for the transmission loss and back pressure physically.

STEP 6: PROTOTYPE MANUFACTURING
All the above stages combined with the packaging of the engine evolve the design of the prototype muffler and those; can be taken up for manufacturing.
Following are some of the important Manufacturing considerations summarized based on experience:

-there should not be any leakage of gas from one chamber to another.
-Full welding is better than stitch welding.
- Acoustic performance of extruded tubes with perforations is better than the tubes that are made out ofperforated and welded sheets.
- CEW or ERW tubes are the common materials used.
- Either of Crimping or full welding of jacket can be used.
- Either of flanged or flared tubes can be used as end connections of the muffler. However, with leakage point of view, flanged connections are better. But at the same However, with leakage point of view, flanged connections are better. But at the same time, this adds to the
Weight and cost of the exhaust system. Bearing all above in mind, a physical prototype is made in such a way that there will not be any tooling investment for the prototype.

STEP 7: EXPERIMENTAL TESTING AND DESIGN FINALIZATION

The experimental determination of backpressure on engine and transmission loss on two source method for different concepts of verified. The prototypes of all concepts that are made at the above step are tested for the transmission loss to verify the target value.
Transmission loss
The TL is the difference in sound power level between the incident wave entering and transmitted waveExciting muffler when the muffler termination is anechoic, TL is a property of the muffler only. In this work anAttempt has been made to experimentally measure transmission loss by actually using the experimental set-up.Two source techniques gives good results for the measurement of transmission loss at the different sound.

Assumption and boundary conditions

Flow is considered to be steady
Air is considered as the fluid for computations
Flow considered as Turbulent ( K-??Model)
Inlet considered as Mass flow boundary condition in 320 Kg/hr
Inlet Temperature of fluid in 520 ??C
Outlet considered as pressure outlet opened to atmosphere


Fig 3.8.Sectional view of silencer
'

CHAPTER-5.DESIGN OF INDUSTRIAL REACTIVE SILENCER
5.1 Where industrial silencer use??
Gas turbine
Coal fired power plant
Petrochemical process
Industrial ventilation system
Tunnel and mine ventilation system
Steam/gas vent system
Gas turbine/jet engine test shells

5.2Working criteria:
To reduce the noise by increasing transmission loss
To improve the efficiency by reducing back pressure

5.2.1Method for noise reduction in silencer
Que. 1-Why we choose silencer?
Attenuation characteristic of silencer
Inner diameter:57mm
Outer shell diameter:112mm
Length:457mm
1.6mm perforated tube
Total no of perforation:1160
Diameter of perforation:3.2 mm
Exhaust noise measurement were maid at distance:0.5 meter and 45deg with exhaust outlet
Instrument use for noise measurement:B&K precision sound level analyzer


Fig5.1 muffled vs. unmuffled vehicle

5.2.1.2Que 2-Transmission loss occur in reactive and non reactive silencer
We have analyze the data if we use any absorptive material in the silencer than there is more transmission loss occurs compare to nonabsorptive material.
The TL is the difference in sound power level between the incident wave entering and transmitted waveExciting muffler when the muffler termination is anechoic; TL is a property of the muffler only.
Two source techniques gives good results for the measurement of transmission loss at the different sound.


Fig5.2 transmission loss in muffler

5.2.1.3 Measurement of Transmission loss
Single expansion chamber
The simplest form of reactive silencer is the single expansion chamber by considering the reflection and expansion of sound wave as they propagate through the discontinues at A and B

Fig 5.3 single expansion chamber

Tl=10 log[1+1/4 '(m-1/m)'^2 'sin'^2 kl]
M=silencer cross section area/inlet and exit duct cross-section area=s_2/s_1
K=wave number=2??/??
L=chamber length
kL=n??/2(n=1,3,5,7'')
And Zero transmission occur at
KL=n?? (n=1,2,3,4''..)
Now for design purpose
K=2??/??
L=n??/4 putting (n=1,3,5,7'.)

Proving result:

Fig5.4transmission loss vs. noise

Conclusion:
-As transmission loss increase the noise reduction is increase so if we want to reduce the noise than it is require to increase the transmission loss.

5.2.2 Method for improving efficiency of engine by reducing backpressure in silencer
Actual industrial silencer design
Modify the design
Comparison result

Fig5.5baffles provide in silencer

Fig5.6baffles in both side of silencer

5.2.2.1Geometrical details of Silencer as Actual use in industry
Width: 24'
Height: 24'
Silencer length: 60'
Open area: 36.7%
Inlet boundary: at 60' upstream of the silencer, i.e., 2.5 times of the model width
Outlet boundary: at 120' downstream of the silencer, i.e., 5 times of the model width

Cavity Model in Solid works

Fig5.7solid works model of silencer

Silencer Geometry in ANSYS Workbench

Fig5.8 model in analysis

Meshing of Silencer

Fig5.9 meshing of silencer


Fig5.10 bricks meshing in buffle
No. of Nodes:-27200
No. of Elements:-21756
Meshing Type:- 3D
Type of Element: - Brick

Fig5.11 hot air analysis
Define Type of Analysis

Fig5.12 define type of analysis

Define Air Domain for Silencer.
Domain Type: - Fluid
Domain Fluid: - Air
Domain motion: - Stationary

Fig 5.13 define air domain of silencer
Define Heat Transfer and Turbulence model.

Fig5.14 heat transfer model

Heat Transfer Model: - Total Energy
Turbulence Model: - K- epsilon
Where k is the turbulence kinetic energy and is defined as the variance of the fluctuations in velocity. It has dimensions of (L2 T-2); for example, m2/s2.
?? is the turbulence eddy dissipation (the rate at which the velocity fluctuations dissipate), as well as dimensions of k per unit time (L2 T-3) (e.g., m2/s3).
The k-?? model introduces two new variables into the system of equations. The continuity
Equation is then:
'??/'t+ ''(??U)=0
and the momentum equation becomes
'??U/'t+ ''(??U'U)-''(??eff'U)='P^'+ ''(??eff'U)T+B
Define Solid Domain for Silencer Baffles.
Domain Type: - Solid
Domain Material: - Steel
Domain motion: - Stationary

Fig5.15 solid domain of silencer baffles

Define Heat Transfer and Turbulence model.

Fig5.16 turbulence model
Heat Transfer Model: - Thermal Energy
Define inlet for Silencer
Define inlet Velocity: - 12.1 m/s
Static Temperature: - 300 K

Fig5.17 define inlet of silencer

Define Outlet for Silencer.
Define Average Static Pressure
Relative Pressure :- 0 Pa

Fig5.18 define outlet of silencer
Define Domain Interface for Silencer Fluid Domain and Baffles.

Fig5.19 domain interface for silencer

Define Solver Control Criteria.

Number of Outer loop iteration: - 100
Convergence Criteria:-
Residual Target :- 1e-4
Run the Analysis
Get the Result................


'

4. DESCRIPTION

Description should have following parts:

a. Field of Application : AUTOMOBILE ENGINEERING
b. Prior Art/Background of the Invention: SILENCER MODIFICATION
c. Summary of the Invention:First we have seen that actually silencer is used for silencing purpose but if this use in industry there is no majar problem of noise but in industry use the silencer for silencing purpose if reactive silencer is used than there is problem arising of efficiency due to backpressure.

d. Objects of Invention:
1) Effect of transmission loss on noise reduction
2) Reducing the backpressure in silencer.

e. Drawing


f. Description of Invention:
-first we measure the data of noise for different frequency through the measurement setup
than we measure transmission losses vs different frequency from this two chart we compare it than we get relation between transmissionlossvs noise and we get result that as transmission loss increases than noise reduction increases.
-first we take one section of silencer than we analysis of this silencer design in ansys and we get chart of pressure distribution and velocity distribution and find backpressure
After that we modify design and do analysis and get result of decreasing backpressure.

g. Examples: Industrial silencer use in gas turbine

h. Claims (Not required for Provisional Application)

7. ABSTRACT OF THE INVENTION

' Flow analysis
Flow field in a silencer is analyzed for velocity and pressure distribution along the flow system. The comparison of pressure drop from different methods and characteristics of these methods discussed.
' Consideration of silencer's impacts to the flow system
A silencer is designed to attenuate noise but is naturally a part of the flow system and it can impose adverse effects on other components in the system such as fans, gas turbines, valves, elbows and ducts, etc. Statically, a silencer and other components of the flow system affect flow distribution and pressure drop on each other. Dynamically, the installation of a silencer can affect the stability of the flow system or stable operation of other components, especially to flow sensitive equipment such as gas turbines.
' Consideration for flow characteristics in the design of a silencer
In actual applications, the flow distribution upstream of a silencer is far from uniform, for example, at downstream of a butterfly valve. The methods of making silencer inlet flow uniform and protecting acoustic absorption material are discussed.

Note:
*Repeat boxes in case of more than one entry
*To be signed by the applicant(s)or the authorized registered patent agent
*Name of the applicant should be given in full, family name in the beginning
*Complete address of the applicant should be given stating with postal index no. / code, state and country
*Strike out the column which is/are not applicable

'

CHAPTER-7 CONCLUSION

Optimization Table
Sr No. Diffuser Slope Condition Outlet Generated Pressure(Pa) Pressure Drop(Pa)
1 0(Original) 292.1 213
2 30 236.3 201.2
3 45 204.6 180.54
4 60 178.1 150.41

Optimization chart:


Fig 5.41 pressure drop at different angle

REFERENCES
[1] G. W. Stewart 1922 Physics Review 20, 528-551 Acoustic waves filters.
[2] D. D. Divis, Jr. G.M. Stokes, D. Morse, and G.L.Stevens, JR 1954 NACA 1192 'Theoretical and
Experimental Investigation of Muffler with Comments on Engine- Exhaust Muffler Design'
[3] J. Igarashi and M.Toyama 1958 Aeronautical Research Institute, University of Tokyo, Report no.339, 223-
241 Fundamental of acoustical silencers (I)
[4] J. Igarashi and M.Toyama 1960 Aeronautical Research Institute, University of Tokyo, Report no.351, 17-31
Fundamental of acoustical silencers (III)
[5] M. L. Munjal, A.V. Sreenath and M. V. Narasimhan 1970 Journal of sound and Vibration 26, 173-191,
Velocity ratio in the analysis of linear dynamical system
[6] ASTM E 477 ' 96, Standard Test Method for Measuring Acoustical and Airflow Performance and Duct LinerMaterials and Prefabricated Silencers.
[7] L. L. Beranek, and I. L. Ver, Noise and Vibration Control Engineering ' Principles and Applications, May 1992.
[8] D. A. Bies and C. H. Hansen, Engineering Noise Control ' Theory and Practice, Second Edition 1996.
[9] Intertek, Report No.3057361-002, June 2004.
[10] I. E. Idelchik, Handbook of Hydraulic Resistance, Second Edition, Revised and Augmented, 1986.

Source: ChinaStones - http://china-stones.info/free-essays/engineering/exhaust-system.php



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