A

Seminar Report

On

“ Noise Reduction In vehicles”

Submitted to the

Rajasthan Technical University, Kota

In partial fulfillment of the requirement for the award of the

Degree of

Bachelor of Technology

In

Mechanical Engineering

Guided by: Submitted by:

Mr. M.C.Khatri Urmila Choudhary

Dept. of Mechanical Engg. VIII sem (Mechanical Engg)

Govt. Engineering College, Ajmer 09ME75

Department of Mechanical Engineering

Govt. Engineering College, Ajmer

CERTIFICATE1

This is to certify that a seminar report entitled “Noise Reduction In Vehicle” which is being

submitted to the Rajasthan Technical University by Urmila Choudhary, Final year B.Tech.

(Mechanical) in partial fulfilment of the requirement for the award of degree of Bachelor of

Technology in Mechanical Engg. has been found to be satisfactory and is hereby approved

for submission.

Date:14/02/2013 Mr. M.C Khatri

Place: Ajmer Designation of Guide,

Department of Mech.

Engg.

Govt. Engineering

College, Ajmer

2

ABSTRACT

Active noise control is a technique to cancel unwanted sound using adjustable secondary

sound. In active sound profiling, the target is to obtain a certain sound field or profile and the

power over specific frequencies can be altered in a desired way, even by amplifying it. Active

sound profiling can be used for increasing the sound quality in a passenger car, for example,

by modifying the engine noise inside the car cabin.

Once noise and vibration sources have been identified, the noise and vibration of machinery

can be reduced by the use of vibration isolation, barriers, sound absorbing materials, machine

enclosures or by cabin enclosures used to protect passengers in the case of aircraft or

vehicles. Sound-absorbing materials should always be used in conjunction with barriers and

inside enclosures to improve their effectiveness Sound-absorbing materials have been used

increasingly in the construction of aircraft, spacecraft and ships because of their low weight

and effectiveness when used correctly.

Engine exhaust noise is controlled through the use of silencers and mufflers. It is essential to

the performance of a generator set that the installed exhaust system does not exceed the

engine manufacturer's maximum exhaust backpressure limit.

Pressure drop of exhaust system includes losses due to piping, silencer, and termination. High

backpressure can cause a decrease in engine efficiency or increase in fuel consumption,

overheating, and may result in a complete shut down of the generating system potentially

causing significant damage. Pressure drop is measured in a straight length of pipe 3 to 5

diameters from the last transition change after the turbocharger outlet.

3

CONTENT

Chapter No. Chapter Name Page No.1 Introduction

1.1) Sound theory

1.2) Types Of Noise sources

1.3) Engine Noise sources

1.4) Engine Noise measurement

1.5) Noise Control

1.6 ) Historical Background

5-15

2 Active Noise Control 2.1) Principle Of ANC

2.2 ) Component of ANC

2.3 ) Different Kind of ANC

2.4 ) Basic ANC approach

2.5 ) Applications

2.6 ) Advantages Of ANC

16-21

3 Intake And Exhaust Noise Control

3.1 ) Introduction

3.2 ) Silencers

3.3 ) Silencers Selection Factors

3.4 ) Enhancement of Silencers

3.5 ) Trade off Power and noise Reduction

22-26

4 Sound Absorbing materials 4.1 ) Introduction

4.2 ) Porous Road Pavement

4.3 ) Hybrid Active/passive Sound Materials

4.4 ) Selection Of Sound Materials

27-30

5 Tire Noise Reduction 31-32

4

5.1 ) Winter tires

5.2 ) Reduce ratio of air/rubber ratio

5.3 ) Low roll over resistance

5.4 ) Limit The use of studded tire

5.5 ) Conflicts with other parameters

6 Indian and Global Scenario 33-34

7 Future Trends 7.1 ) New developed Muffler

7.2 ) Intake system with Porous material

7.3 ) Tire with Fiber wheel liners

35-36

8 Conclusions 37

9 References 38

10 Appendixes 38

Chapter1

5

Introduction

Noise control is becoming increasingly important for a wide variety of OEM designers.

Examples of products that take noise control considerations into account during their

design cycles include equipment such as computer hard drives, house appliances, material

handling and transportation equipment etc,. In the transportation market, which includes

aircraft, ground and marine segments, the demand is for low noise level goals. Achieving

these goals is of primary importance for OEM to be continue to be competitive or to keep a

given supremacy in the market. The automotive industry has been a leader in the adsorption

of noise control technologies.

Methods in use for several years for the prediction of interior noise levels include : finite

element method(FEM), statistical energy analysis (SEA),boundary element analysis (BEA)

etc. The internal combustion engine has mechanized the world. Since the early 1900s it has

been our prime source of mechanical power. The vast number of internal combustion engines

in the world today has resulted in air pollution, noise pollution etc.

1.1 DEFINITIONS OF SOUND

Sound can be defined as the perception of vibrations stimulating the ear. If scientifically

taken into account, sound is a periodic disturbance in fluids density or in the elastic strain of a

solid, generated by vibrating objects. These waves or vibrations propagate in two basic ways.

1. Longitudinal waves.

2. Transverse wave

DECIBEL – Sound level is measured in decibel. Sound level in decibels is a logarithmic

rather than a linear measure of change in pressure with respect to a reference pressure level.

A small increase in decibels can represents a large increase in sound energy.

Difference in decibel = 10 log10 (W1/W2)

Technically an increase of 3db represents a doubling of sound energy, and an increase of 10

db represents a ten-fold increase. The measurement for measuring noise is the basic sound

level meter or no: of its derivatives, including noise dosimeters.

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SOUND PRESSURE LEVEL:

We have difference in decibel, 20 log10 n1/2 = 20 log10 (P1/P2). If P2 were given an

absolute value and 20log10 n1/2 were known then P1 would also have an absolute value. In

audio – acoustics, P1 is frequently given the absolute rms value of 2X10-5 N/m which is the

minimum sound pressure fluctuation discernible to human ear. Consequently P1 must also

become an r m s pressure expressed in N/M*2.

20 log10 n1/2 is still in decibels but is now defined precisely as the sound pressure level

(SPL).

SPL = 20 log10 P1 2X10-5 db

In terms of sound pressure level the sensitivity of ear ranges from O db (2X10-

5 N/M*2). Everyday levels very b/w 35 db and 90db.

WEIGHTING CURVES -

The apparent loudness of sound varies with frequency as well as with sound pressure. To

adjust the frequency response of necessary systems to be similar to that of human ear, several

weighting curves proposed.

‘A’ weighted curve was designed to appropriate to human response let sound pressure levels

(<55db) similarly ‘B’ and ‘C’ weighting were intended for use at sound pressure levels of 55

db to 85 db and above 85 db respectively. For almost all practical sound measurement

purposed in industrial as well as automotive applications we follow the dBA weighting curve.

Because dBA curve is very similar to the perception of human ear .Available range of sound

in human beings are 20-20,000 Hz.

1.2 NOISE SOURCEThere has been a direct relationship between the improvement in man’s physical

standard of living and the degree of his development of machines. The industrial

revolution was really a series of social and industrial transformations, beginning in

England with the use of coal in place of charcoal for the smelting of iron, progressing

through the stages of steam engines and electric motors and all the producing and

7

processing made possible by these devices. of the age of gasoline, sea and air for

various types of transportation. For that matter, sweeping mechanical progress

witness automation and the utilization of nuclear energy; but with every new

machine, a little noise is created, with every mechanism employed to do man’s work,

some mechanical or electrical power is converted into acoustical power, so that with

the rise of people’s standard of living there occurs also a rise in the noise level of

people’s confines.

1.2 TYPES OF SOURCES OF NOISE

Sources of noise are numerous but may be classified broadly into two classes as

1. INDUSTRIAL

2. NON INDUSTRIAL

1.2.1 INDUSTRIAL

The industrial may included noises from various industries operating in cities like

transportation, air crafts, rockets, defense equipments, explosions etc. The disturbing

qualities of noise emitted by industrial premises are generally its loudness, its

distinguishing features such as tonal or impulsive components and its intermittency and

duration.

Various sound levels and its effects on Human Being

Sound Source Sound Level In dBA

Subjective Feeling On Human Being

Effects of Human Being

Rockets and missilesheavy explosives

150-160 Unbearable Above 150 dBA may cause severedamage to the whole body such asloss of hearing of both ears, dizziness,nausea, disturbance of speech,confusion or psychosis

8

Jet planes andcannons, explosives

140 Unbearable

Aircraft propeller andmachine guns

130 Unbearable

Diesel, steam engineand ball mills,crackers

120 Unbearable

Electric saws andlooms, heavy trucks

110 Unbearable Above 90 dBA may cause headache,dizziness, tinnitus, insomnia,deafness, heart disease, blood hypertension,gastric ulcers, neurosis,temporary hearing

threshold shift.

Lorries, highwayvehicles and verybusy streets

90-100 Very noisy

Commercial place,air conditioners, loudvoice and busystreets

70-80 Noisy 50-90 dBA may cause variousdegrees of effects in sleeping,studying, working and

talking

Office complex,average loudness ofvoice

60 Noisy Sense of noisy feeling

Ordinary room 50 Quiet Pleasant feeling

Silent night, library 30-40 Very quiet Pleasant feeling

Hospital, church 20-30 Very quiet Serene feeling

Sound proof room,broadcasting studio

10-20 Very quiet

Lower limit of hearing 0 Very quiet Threshold of hearing

1.2.2 NON INDUSTRIAL (TRAFFIC)

In non industrial source , major one is traffic mopeds and scooters with have a

maximum of 75 dBA and 50 dBA respectively, according to new norms from 1st

9

January 2003. the present norms for petrol and diesel driven two wheelers are

50dBA and 82 dBA respectively. Present norms for three wheelers are 82 dBA for

petrol and 85 dBA for diesel will be modified as three wheelers upto 175 cc, 75 dBA

and above 175 cc, 80dBA. Passenger cars can produce maximum noise of 75dBA

present being 82dBA.

DECIBEL RANGES FOR CERTAIN PARAMETERS

Gunshot, jet engine 140dB(immediate danger to hearing)

Fire cracker 125 dB (pain threshold)

Ambulance siren, rock concert 120dB(risk of hearing damage in 7minutes)

Chain saw, snow mobile 110dB (risk of hearing damage in 30minutes)

Movie trailer 93 Db

Ringing telephone 80 dB

Normal conversation 65 dB

Faint sound 30 dB

The elementary as well as complex analysis of noise problems can be simplified by

following a set of guide lines or principles. The principles of noise control can be

summarized as identifications of sources of noise and their relative importance,

listening and evaluation of possible noise control procedures as they applied to

source, path and receiver. Identifications of the relative contributions from both

directed and reflected sound. Difference between absorption and attenuation of

noise. Identification and evaluation of flanking paths and also identification and

evaluation of certain significance of flanking path and structure

INTERNAL COMBUSTION ENGINE NOISE

Several alternative methods can be used to classify internal combustion engine

10

noise. The two most typical classification techniques are discussed below.

1.3 CLASSIFICATION BY NOISE CHARACTERISTICS

One typical engine noise classification technique separates the aerodynamic noise,

combustion noise and mechanical noise.

1. AERODYNAMIC NOISE

2. COMBUSTION NOISE

3. MECHANICAL NOISE

AERODYNAMIC NOISE-aerodynamic noise includes exhaust gas and intake air

noise as well as noise generated by cooling fans, auxillary fans or any other air flow.

COMBUSTION NOISE- combustion noise refers to noise generated by the vibrating

surfaces of the engine structure, engine components and engine accessories after excitation

by combustion forces.

MECHANICAL NOISE-mechanical noise refers to noise generated by the vibrating

surfaces of the engine components and engine accessories after excitation by

reciprocating or rotating engine components.

1.4 CLASSIFICATION BY ENGINE NOISE SOURCES

A second approach to the classification of piston engine noise involves the

Separation of engine noise into the following categories –

1. EXHAUST SYSTEM NOISE

2. INTAKE SYSTEM NOISE

3. COOLING SYSTEM NOISE

4. ENGINE SURFACE RADIATED NOISE

1.4.1 EXHAUST SYSTEM NOISE: Exhaust system noise includes the noise from

exhaust gas pulses leaves the muffler or tail pipe and noise emitted from the

vibrating surfaces of the exhaust system components. Noise emitted from the

surfaces of exhaust system components results from two different types of excitation

forces: those generated by the pulsating exhaust gas flow and those transmitted

from the vibrating engine to exhaust system components. Additional considerations

in the reduction of exhaust system noise include proper selection of piping lengths

and diameters, proper mounting of exhaust system components and proper

positioning of the exhaust outlet.

11

1.4.2 INTAKE SYSTEM NOISE: Intake system noise includes noise generated by

the flow of air through the systems air inlet and noise emitted from the vibrating

surface components. As with exhaust systems surface radiated noise results from

two different types of excitation process: those generated by the pulsating intake air

flow and those transmitted from the vibrating engine to intake system components. In

many instances, an engines air cleaner will provide significant attenuation of intake air noise.

If additional attenuation is required, an intake air silencer can be added to the system. To

minimize intake system surface radiated noise, proper design, selection and mounting of

intake system components are essential.

1.4.3 COOLING SYSTEM NOISE: Water cooled engines are typically cooled by

using a radiator as a heat exchanger – with an axial flow fan is used to draw cooling

air through the radiator. Air-cooled engines generally use a centrifugal fan in

conjunction with shrouding to direct cooling air across the engine. Fan noise consists

of both discrete frequency tones and broadband noise. The broadband components

of fan noise are caused by the shedding of vortices from the rotating fan blades and

by turbulence in the fans air stream.

The discrete frequency components are the result of pressure impulses that occur

each time a fan blade passes an obstacle in the fans pressure field. When fan

blades are spaced at equal angular intervals, the fundamental discrete tone will

occur at the fans blade passing frequency.

F0= fanrotational speed (rpm) xnumber of fan blades

60

1.4.4 ENGINE SURFACE NOISE

Engine surface noise refers to sound emitted from vibrating surfaces of

engine components and accessories and other than items included in the engine

exhaust, in take and cooling systems. Techniques used to reduce engine-surface

radiated noise include a reduction in running clearances and/or machining tolerances

of the engine components , acoustical treatment or re-design of engine components,

use of acoustically treated shields and vibrating isolation and damping of engine

covers an diesel engines than for gasoline engines. Turbo charging of a diesel engine can

result in some reduction of engine surface-radiated noise at high engine loads.

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1.5 ENGINE APPLICATIONS AND NOISE

Application of the internal combustion engine covers a broad spectrum. The internal

combustion engine is now used to power anything from a small hand-held weed

cutter to a large ocean liner. One typical application is as given below.

AUTOMOBILES-The automobile represents the largest single application of the internal

combustion engine in our society; and the automotive industry is primarily responsible for

rapid

advances in internal combustion engine designs in the late 1800s and early1900s.

The automotive industry also became more fervent in implementing measures to

reduce both interior and exterior noise levels. Some methods used to reduce engine related

vehicle noise include improved intake, exhaust, and cooling system designs,

engine compartment treatment, improved engine vibration isolation, and engine

component treatment or redesign.

NOISE EVALUATION DURING ACTUAL RUNNING (TRIAS 20 METHOD)

Measuring layout for acceleration noise (TRIAS 20 Method)

In the case of a motorcycle which has a manual transmission with 5 speeds or

more and with a displacement of 251 cm3 and over, the running test procedure is

that the test motorcycle enters point A in 4th gear, at a speed of 50km/h or 0.75s (s

means engine rpm at maximum horse power) whichever is a lower speed, then the

rider opens the throttle fully at point A and closes it completely acceleration,

maximum sound pressure is measured to the left side of the vehicle at a distance 7.5 m

perpendicular to the running pass.

13

1.6 Noise Control Legislation-Prior to 1970, most surface vehicles noise regulations

where legislated at the state or local level. Recently however, several federal programs have

also been implemented in an effort to minimize a level of environmental noise in our society.

STATE NOISE CONTROL PROGRAMMS

MOTOR VEHICLE NOISE REGULATIONS

Most common form of state-enacted noise legislation applies to motor

vehicles. Historically, trucks have been the first vehicles regulated, with regulations

for automobiles, buses and motor cycles following. Motor vehicle regulations

generally established a quantitative sound limit at a specified distance from the

vehicle.

FEDERAL NOISE CONTROL PROGRAMMES

OCCUPATIONAL SAFETY AND HEALTH ACT (OSHA)

OSHA was enacted in 1970 in an effort to ensure safer conditions for all

workers. The act OSHA specifies the maximum noise level that a worker may be

subjected to during a workday. The OSHA standard is based on a max: allowable

steady-state level of 90dBA for an 8-hr day. When noise level exceed 90dBA, the

permissible duration of noise exposure is reduced.

Figure 1.: Sound Level

14

An OSHA noise does meter is an integrating sound level meter that weighs the level and

duration of time-varying sounds in accordance with OSHA curve. If then displays a value

that represents the time-varying sounds as an equivalent 8hrsteady state level. The noise

dosimeter will also indicate if the time-varying sound

exceeds a level of 115 dB (A) during analysis.

1.7 Historical Background1934 - The first patent for active noise control system was granted to inventor Paul

Lueg U.S. Patent 2,043,416. The patent described how to cancel sinusoidal tones in

ducts by phase-advancing the wave and cancelling arbitrary sounds in the region

around a loudspeaker by inverting the polarity.

1950s - With U.S. Patent 2,866,848, U.S. Patent 2,920,138, U.S. Patent 2,966,549

by Lawrence J. Fogel, systems were created to cancel the noise in helicopter and

airplane cockpits.

1957 - Willard Meeker developed a paper design and working model of active noise

control applied to a circumaural earmuff. This headset had an active attenuation

bandwidth of approximately 50-500 Hz, with a maximum attenuation of

approximately 20 dB..

1986 - Dick Rutan and Jeana Yeager used prototype headsets built by Bose in their

around-the-world flight.

In 1979, Vauxhall offered the Royale for sale in the UK – a 2.8-liter, six cylinder,

executive class (small) car for the on-the-road cost of £8354

(1979 prices). Motor magazine described it as being ‘ in general a refined

car’ (Vauxhall Royale – Star road test, Motor Magazine, 13 January 1979).

By 1989, that car had been replaced by the Vauxhall Senator 2.5i

– a 2.5-liter, six-cylinder , executive class (small ) car for the on the-

road cost of £16529 (19 89 prices ) .

CHAPTER 215

ACTIVE NOISE CONTROL

2.1 Passive noise control

The traditional approach of reducing noise (”sound proofing”) is to use passive methods like

insulation and silencers. A typical example are the ear muff s of headphones. As described in

section2.3, good attenuation is achieved when using materials with special characteristics.

This form of noise reduction works best for higher frequencies, basic ally acting like a low

pass filter. In some cases, the low frequencies are noticed even more .However, when used

for lower frequencies, passive solutions tend to get bulky and heavy as the size and mass of

passive treatments usually depends on the acoustic wavelength, making them bigger and

more massive for lower frequencies.

2.2 Active noise control

Active techniques, known as ”active noise control ” are one of the hot research topics in

acoustics these days. Active noise control (ANC) is using the phenomenon of wave

interference: When two waves with the same amplitude and frequency, but phase-reversed,

traveling the same direction, they will neutralize each other thanks to destructive interference.

The resulting sound is null, the sound energy is transformed into heat. In the simplest form of

ANC, a control system drives a speaker to produce a sound field that is the exact mirror-

image of the off ending sound (the ” disturbance”).

The speaker thus cancels the disturbance by means of destructive interference, and the net

result is no sound at all:

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Figure 2.1: Basic structure of a feed forward ANC system

2.3 Basic ANC components

In control systems jargon, an ANC system consists of the following four major parts:

Plant

— The physical system to be controlled. A typical example is a headphone and the air inside

it.

Sensors

— The vibration sensors, microphones, or other devices that sense the primary disturbance

and monitor how well the control system is performing by measuring the remaining error.

Actuators

— The devices that physically do the work of altering the plant response, usually

electromechanical devices such as speakers or vibration generators.

17

Controller

— A signal processor that controls the actuators. It bases its command son the sensor signals

and on some knowledge of the plant’s response to the actuators.

2.4 Different kinds of ANC

The variety of behavior characteristics of sound waves in different physical surroundings

allow categorization of ANC systems into three different groups.

Global free space cancellation

— The total annihilation of a sound field in three dimensions. Requires the cancellation

source to be placed within close proximity of the acoustic disturbance, as a general guideline

within 0.1 wavelengths of the disturbance source in order to obtain 20 dB global reduction in

sound intensity at any given frequency.

Cavity and duct cancellation

— Deals with noise cancellation in confined spaces, such as a room or a ventilation duct. In a

confined space, reflections from the walls create modal responses, which are generally

present whenever the wavelength of the acoustic wave approaches or decreases below the

dimensions of the cavity. The number of acoustic modes grows rapidly with the increase of

frequency of the sound wave.

Zone-of-silence cancellation

— Provides a localized cancellation of sound field intensity in a very small region of the

overall sound field. A typical cancellation zone will only be about a tenth of a wavelength in

diameter .It should be noted that active noise canceling is best suited for low frequencies

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2.6 Practical experiment

One of the very first ANC experiments consisted of two loudspeakers fed with sinus signals

of the same frequency and amplitude, but phase reversed. By setting these loud speakers up at

the correct distance, global cancellation of the sinus signals could be achieved. This is a

special case because the signals are periodic and always stay the same (a standing sound

wave in the room if you like), and can thus be canceled not only by sending the correct anti -

signal in the same direction as the disturbance (the usual principle of ANC), but also by

sending the anti -signal against the propagation direction of the disturbance.

Figure 2.3.: Two speakers directed against each other at distance d

Two speakers directed against each other at distance d .The nice thing about this experiment

is that the effects of destructive and constructive interference can easily be demonstrated by

changing the distance between the speakers. With the speakers half a wavelength apart,

constructive interference makes the signal to appear much louder than from a single speaker

source.

2. 7 Active noise control applications

Actually, there are many applications of ANC out there already, most of them probably even

unnoticed by the casual user.

2.7.1 Noise reduction in aircrafts

Using ANC to cancel low-frequency noise inside vehicle cabins for passenger comfort is

gaining popularity. Most major aircraft manufacturers are developing such systems, mainly

for noisy propeller -driven airplanes.

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2.7.2 Noise reduction in automobile industry

Automobile manufacturer Honda has an active noise cancellation system designed to reduce

road noise using microphones and speakers placed under the vehicle’ s seats, while Siemens

Automotive manufactures a system which utilizes a speaker mounted inside the air intake

manifold to suppress low frequency engine noise. Another application are active Mufflers for

engine exhaust pipes.

2.7.3. Active headphones

One application that has achieved widespread commercial success are active headphones to

cancel low-frequency noise. Actually, there are two different kinds of active headphones, but

only one uses active noise cancellation. Let’s call the two types active headphones and

amplified Ear muffs.

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Chapter 3Intake And Exhaust Noise Control

3.1 Introduction

Intake noise is generated by the periodic interruption of airflow through the inlet valves in an

engine, thus creating pressure pulsations in the inlet manifold. This noise is transmitted via

the air cleaner and radiates from the intake duct. This form of noise is sensitive to increases in

engine load and can result in noise level increases of 10 to 15 dB from no-load to full load

operation. When a turbocharger is fitted, noise from its compressor is also radiated from the

intake duct. Turbocharger noise is characterized by a pure tone at blade passing frequency

together with higher harmonics. Typical frequencies are from 2 to 4 kHz

3.2 Silencers (MUFFLERS)

Attenuation of noise at engine intakes and exhausts calls for devices which minimize the flow

of sound waves while allowing gases to flow through them relatively unimpeded. Such

devices are effectively acoustic filters. The operational principles of intake and exhaust

silencers (‘mufflers’ as they are called in the USA) can be divided into two types, dissipative

and reactive. In practice, silencers are often a combination of both types.

3.2.1 Dissipative silencers

Dissipative silencers contain absorptive material which physically absorbs acoustic energy

from the gas flow. In construction, this type of silencer is a single chamber device through

which passes a perforated pipe carrying the gas flow. The chamber surrounding the pipe is

filled with sound absorbing material (normally long- fiber mineral wool) which produces

attenuation across a very broad band of frequencies above approximately 500 Hz. The degree

of attenuation is generally dependent on the thickness and grade of the absorbing material,

the length of the silencer and its wall thickness.

21

Figure3.1: Dissipative Silencers

3.2.2 Reactive silencers

Reactive silencers operate on the principle that when the sound in a pipe or duct encounters a

discontinuity in the cross-section, some of the acoustic energy is reflected back towards the

sound source thereby creating destructive interference.

The effectiveness of this technique can be extended by having several expansion chambers

within the same casing connected together by pipes of varying lengths and diameters .

Silencers of this type increase the exhaust back-pressure and result in some power loss.

Figure3.2: Reactive Muffler

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.3.2.3 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.

3.2.4 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.

3.3 SILENCER SELECTION FACTORS

3.3.1 Muffler Acoustic Performance

To assess the success of a new muffler design, there is a need for measures to quantify the

sound reduction obtained. There are at least three such measures in common use:

transmission loss, insertion loss, and noise reduction.

The transmission loss (TL) is defined as the ratio between the sound power incident to the

muffler (Wi) and the transmitted sound power (Wt) for the case that there is a reflection-free

termination on the downstream side

TL = 10log (Wi/Wt) -(1)

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Insertion loss is the most useful. Unlike transmission loss and noise reduction, insertion loss

is dependent on both source and radiation impedances. Insertion loss (IL) is defined as the

difference in sound pressure level at some measurement point in the pipe or outside the

opening when comparing the muffler element under test to a reference system:

IL = 20 log (pm/pr) - (2)

Where pm is the root-mean-square (rms) value of the sound pressure for the muffler under

test, and pr is the rms value of the sound pressure for the reference system.

Sound reduction (SR) is defined as the difference in sound pressure level between one point

upstream of the muffler and one point downstream:

SR = 20 log (pu / pd) - (3)

Where pu is the rms value sound pressure upstream of the muffler and pd is the rms value of

the sound pressure downstream of the muffler. .

3.3.2 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.

.

3.4 Enhancement Of Silencer Performance

Additionally, silencers are positioned in the exhaust system downstream from the catalytic

converter. These are required specifically to smooth exhaust gas pulsations and make them

24

as in audible as possible. The silencers and their pipe work form an acoustically resonant

system which is tuned to avoid exciting bodywork resonances which would aid transmission

of structure borne noise. For this latter reason, it is common for silencers to have a double

skin and insulating layer which also provides thermal insulation. The following are some of

the devices used to overcome specific silencer tuning problems.

(a)The Helmholtz resonator – a through-flow resonator which amplifies sound at its

resonant frequency, but attenuates it outside this range.

(b)Circumferential pipe perforations – create many small sound sources resulting in a

broadband filtering effect due to increased local turbulence.

(c) Venture nozzles – designed to have flow velocities below the speed of sound they are

used to attenuate low frequency sound.

3.5 Trade-off between power increase and noise reduction

When the flow of exhaust gases from the engine to the atmosphere is obstructed to any

degree, back pressure arises and the engine's efficiency, and therefore power, is reduced.

Performance-oriented mufflers and exhaust systems thus strive to minimize back pressure by

employing numerous technologies and methods to attenuate the sound.

Several such exhaust systems that utilize various designs and construction methods:

Vector Muffler –

For larger diesel trucks, uses many concentric cones. Vector™ Performance Booster™ is a

revolutionary diesel exhaust system that increases horsepower and significantly improves fuel

economy. The initial Vector™ system will be available mid 2011 as an aftermarket system

for Class 7 & 8 tractor trailer trucks. The patent-pending Vector™ technology actually breaks

down the sound waves while simultaneously creating a vacuum-like free flowing exhaust

system. Until now, muffler designs haven't changed much over the last 100 years. The old

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idea was to simply pack the muffler pipe with material to muffle the sound, but it also greatly

restricts air flow and creates high backpressure.

Figure 3.3: Vector Muffler

Spiral Baffle Muffler - for regular cars, uses a spiral-shaped baffle system.

Aero Turbine Muffler - creates partial vacuums at carefully spaced out time intervals to

create negative back pressure, effectively "sucking" the exhaust out of the combustion

cylinders.

Corsa Performance Muffler - combines straight-through and resonating technology to

cancel out unwanted harmonics and improve efficiency.

Split, Delay, Merge Muffler - utilizes detouring pipes for virtually zero back pressure and

customizable exhaust sound.

Flowmaster Muffler - uses a less restrictive construction than a typical stock resonator

muffler.

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Chapter 4Sound-Absorbing Materials

4.1 Introduction

Sound-absorbing materials absorb most of the sound energy striking them, making them very

useful for the control of noise.

They are used in variety of locations – close to sources of noise, in various paths, and

sometimes close to receivers.

Although all materials absorb some incident sound, the term “acoustical material” has been

primarily applied to those materials that have been produced for the specific purpose of

providing high values of absorption. The major uses of absorbing materials are almost

invariably found to include the reduction of reverberant sound pressure levels and,

consequently, the reduction of the reverberation time in enclosures, or rooms. A wide range

of sound absorbing materials exist.

In the 1970s, public health concerns helped change the main constituents of sound-absorbing

materials from asbestos based materials to new synthetic fibers. Although, these new fibers

are much safer for human health, more recently, issues related to global warming may

increase the use of natural fibers instead of synthetic ones.

4.2 Porous Road Pavement Surfaces Using Porous Asphalt

To reduce noise is by the use of porous road pavement surfaces. These pavement surfaces can

be classified as granular sound-absorbing materials. Such surfaces have the advantage that

they not only reduce the tire/road noise at the point of its generation, but they also attenuate it

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(and the power plant noise) by absorption of sound as it propagates to nearby residential

areas.

The sound absorption of porous road pavement surfaces is affected by several geometrical

and other parameters of the road pavements:

• Thickness of the porous layer

• Air voids (Va) or road surface porosity

• Air flow resistance per unit length

• Coarseness of the aggregate mix (small or large aggregates etc.)

Figure 4.1 Sound absorption coefficient of a slab of dense graded Super pave mix with a fine open graded fine core of different thicknesses (t) placed on top.

4.3 Hybrid Active/Passive Smart Absorbing Materials

More recently, the use of active noise control has been combined with passive control to

develop hybrid sound absorbers. Active control technologies appear to be the only way to

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attenuate the low-frequency noise components. Therefore, a hybrid passive/ active absorber

can absorb the incident sound over a wide frequency range.

Recent research has been aimed at producing a broadband sound absorber known as smart

foam, which is a hybrid active-passive sound-absorbing material. The absorber is made of

melamine foam (made of melamine resin, a thermo set polymer) with Poly vinylden fluoride

(PVDF) piezoelectric-film-embedded actuators. The composite material produces high sound

absorption at middle and high frequencies due to the melamine foam’s passive properties,

while the low frequency sound absorption is produced by a classical active cancellation

mechanism.

Figure 4.2 Hybrid passive/active absorber cell

4.4 Selection Of sound Absorbing Materials

Sound absorption performance of the porous materials used in automobiles is not so much a

function of type of material (cotton shoddy, PET, or fiberglass), as it is a function of how

well the material construction can be executed to achieve desirable properties for sound

absorption. For open faced materials or materials with a porous scrim, the flow resistivity is

very important. The best material properties are a function of the application such as the

material thickness and boundary conditions. Thinner materials require significantly more

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flow resistivity than thicker materials; therefore, materials that are nearly optimal in one

application may not work well in another application.

4.5 Place where sound absorbing materials used in Vehicle

In the automotive industry, materials used to enclose a noise source (such as the engine) or

the passengers (the cabin enclosure) are usually termed barrier materials. Such barrier

materials are required to reduce airborne sound reaching the cabin from noise sources,

including the engine, fan, exhaust system, tires, and wind. Once airborne and structure-borne

sound has penetrated into the cabin, the sound can be absorbed effectively by the use of

sound-absorbing material.

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Figure 4.3: Sound Barrier and Sound absorbing Materials Application

Chapter 5Tyres Noise Reduction

Figure 5.1: Tire noise causes

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5.1 Adapting winter tyres for all-year use :

The principles used in construction of winter tyres may be partly adapted to summer tyres; in

order that summer tyres may obtain some of the favorable noise characteristics of winter

tyres; yet having handling and wet friction properties acceptable for summer use. This may

include using smaller tread elements, more frequent sipping and softer rubber compounds.

Some compromises like these mentioned above are already seen in the all-weather designs

being so popular in the USA.

5.2 Reducing the air/rubber ratio in the tread pattern:

In the SILENCE project one of the possibilities being explored is the reduction of the

air/rubber ratio in the tread pattern; for example by reducing the width of channels in the

tread pattern. It has been found that a combination of softer rubber and lower air/rubber ratio

may influence tyre/road noise emission on an ISO surface by about 6 dB(A).Typically, winter

tyres may have a Shore hardness of 55-60. It has been well demonstrated that softer rubber

compounds result in lower noise emission, other things being equal. If tyres did not have to

be produced for such high speed categories as today, softer compounds may be used. Softer

tyre rubber compounds are already used in Japan and in USA, but in Europe they are

considered less acceptable due to the high maximum speeds on certain motorways.

Figure 5.2: Influence Of speed On Tyre noise

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5.3 The options for lower rolling resistance:

The examples above have potentially lower rolling resistance in common to the lower noise

emission. However, the rubber compound is of extra importance here and additions such as

silica mean progress to this performance parameter.

5.4 The quiet tyre with no market:

An example of a successful noise reduction design was presented in [Saemann et al, 2001].

Dr Saemann and his colleagues had produced, by means of traditional measures, a truck tyre

that was equally quiet as a slick tyre. However, although the tyre had fully acceptable

properties in other respects than noise, it was found that this tyre was not desired or needed

by the vehicle industry, partly due to its visual appearance, partly due to that there was no

need for any quieter tyre by the vehicle industry. This author thinks that such neglect of quiet

designs will be impossible in the future.

Chapter 6

Indian And Global Scenario Of Noise Reduction

6.1) ANC Scenario

During the last decades, several systems for active engine noise cancellation inside the

passenger cabin have been developed for production vehicles. The systems include:

1. A system developed for a 1.1 liter 4-cylinder car by Lotus Engineering and ISVR in

1988.The system used 4 loudspeakers located in the dashboard and front doors

(integrated into the car audio system) and 8 microphones mounted in the head lining.

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It controlled the engine firing frequency and its harmonics, and reductions of about 10

dB were measured in the front seats above about 3000 RPM. The improvement in the

overall A-weighted sound pressure level was 4–5 dB. Reductions at lower speeds

were measured in the rear due to the suppression of the first longitudinal acoustic

mode, having a nodal line near the front passengers’ head .

2. An active system introduced by Honda in 2003 for a 3l iVTEC V6 engine with

Variable Cylinder Management. In this engine, 3 of the 6 cylinders are temporarily

deactivated. In the active system, active engine mounts are combined with an interior

ANC system, which is integrated with the audio system. It uses 2 interior

microphones but only 1 output signal which is distributed to both front and rear

speakers with a fixed filtering. The ANC system focuses on the 1.5th engine order

below 60 Hz.

3. A 3-microphone 3speaker system by Toyota in its 2008 Crown Hybrid made for

Japanese market only.

4. An ANC system by GM in its 2010 GMC Terrain and the Chevrolet Equinox SUV,

having 2 microphones and 1 loud-speaker. Several experimental systems for engine

noise cancellation inside vehicles have also been constructed. They include a system

with 4 loudspeakers and 4 error sensors in a passenger car, a system using 6

secondary sources and 8 error sensors for a van, and a system in a truck cabin mock-

up with 3 secondary sources and 3 error sensors.

Active systems for controlling the noise radiating from the engine air intake orifice has been

developed and tested by Siemens Automotive. The secondary source was placed inside the air

intake and the error sensor was located near the loud speaker. The feed forward system was

tested in several 6- and 8-cylinder cars, with the reference signal taken from a tachometer in

the engine. The radiated engine noise from the induction system was effectively eliminated

over the control bandwidth, the power draw of the loudspeaker was minimal and the flow

restriction of the actively controlled inlet was significantly reduced compared to the

production air induction system. A similar system was developed by Hyundai Motors and

Seoul National University. An active intake control system for a 4-cylinder engine was

constructed, with two loudspeakers placed on the side of the intake duct. As a result,

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maximum reduction of 30 dB was measured at the dominant 2nd order and 10 dB at the 3rd

and 4th orders under stationary conditions and 20 dB at the 2nd order under sweeping

conditions. Efforts have also been conducted to enhance robustness of the control algorithm

of the active intake system under rapid acceleration.

Conventional silencers involve the use of a muffler system, which contains sound absorbing

materials. It induces flow restriction and increased back pressure, which has a direct effect on

the Performance of the engine. Active exhaust noise control systems can be hybrid, including

a simplified passive muffler and an active muffler, or totally active. Typically the systems

include loudspeakers as the secondary source but also an electrically controlled valve has

been used as the source. Active vibration control has also been applied to vehicles for

narrowband noise reduction. In vehicles with large engines and heavy duty trucks, the

vibration from the engine can cause low-frequency booming inside the passenger cabin. In

order to tackle this problem, active engine mounts adjusting the stiffness of the damping

properties of the mount has been developed. Active engine mounts has been mass-produced

by Toyota and Nissan.

Chapter 7Future Trends

7.1. New Developed Muffler (TCTPPM)

The newly developed muffler consists of two chambers with uniformly perforated tubes

separated by a horizontally placed perforated plate in the middle of muffler. The key feature

of this muffler is the inlet and outlet tubes are provided with end plates. The end plates are

also made perforated to reduce the back pressure produced at the inlet of the muffler. The two

chambers make the exhaust gas to flow out by three pass and attenuate hence, this muffler is

called as Two Chamber Three Pass Perforated Muffler (TCTPPM). The designed muffler

reduces the sound level by 15dB also increased power and lower fuel consumption. When

compared with existing muffler.

7.2. Active Control Of Exhaust Noise

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With this approach, the active system can reduce the sound power output from the exhaust

and may also improve the performance of the car by removing the need for current passive

silencers . Conventional silencers involve the use of a muffler system, which contains sound

absorbing materials. It induces flow restriction and increased back pressure, which has a

direct effect on the performance of the engine.

Active exhaust noise control systems can be hybrid, including a simplified passive muffler

and an active muffler, or totally active. Typically the systems include loudspeakers as the

secondary source but also an electrically controlled valve has been used as the source . Active

vibration control has also been applied to vehicles for narrowband noise reduction. In

vehicles with large engines and heavy duty trucks, the vibration from the engine can cause

low-frequency booming inside the passenger cabin. In order to tackle this problem, active

engine mounts adjusting the stiffness of the damping properties of the mount has been

developed.

7.3. Intake system Noise reduction with Porous Insulator

Transmission Loss Increases as porous material is inserted at high frequency. But at 10000

Hz suddenly decreases because of coincidence effect. Overall TL increases 1.5 dB as

thickness of foam doubles. It plays efficient role at high frequency. TL is high for Polyester

foam because of high density.

7.4. Tire Noise reduction with Fiber wheel Liners

Tire noise has its most pronounced effect at speeds from 50 to 110 kph. One strategy to

reduce tire noise without the expense of redesigning the tire is to provide sound absorption

near the tire. Sound absorption in the exterior space around the tire can be provided with

molded fiber wheel liners in place of hard plastic wheel liners Fiber wheel liners are found on

a wide range of vehicles, from entry level vehicles to luxury vehicles. A fiber acoustical

wheel liner will reduce the tire (source) noise from 1 dB to 8 dB, depending on frequency.

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Fiber wheel liners are lower weight alternatives to plastic wheel liners with weight savings

from 600g to 800g per wheel .

Chapter 8Conclusions

There are two types of noise sources-

1) Noise sources controlled by road speed (Tyre noise , structure borne noise and

transmission noise).

2) Noise sources controlled by engine speed ( exhaust noise, intake noise).

The primary objective of most active noise control systems is the reduction of noise for

personal comfort, reduction of stress and increased concentration. Another major benefit is

low-frequency quieting for applications where passive insulation would be too expensive,

inconvenient or heavy.

For example, the lead-impregnated sheets used to reduce aircraft cabin propeller noise

impose a severe weight penalty, but active control can perform just as well at a much smaller

weight.

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Active noise control also reduces the vibrations induced into mechanical structures, thus

prolonging lifetime and increasing efficiency. The cost for active noise canceling solutions is

of course the additional power consumption by the ANC sensors, controller and actuators, as

well as increased complexity.

Attenuation of noise at engine intakes and exhausts calls for devices which minimize the flow

of sound waves while allowing gases to flow through them relatively unimpeded. Such

devices are effectively acoustic filters.

The operational principles of intake and exhaust silencers (‘mufflers’ as they are called in the

USA) can be divided into two types, dissipative and reactive. In practice, silencers are often a

combination of both types.

Tire noise has its most pronounced effect at speeds from 50 to 110 kph. One strategy to

reduce tire noise without the expense of redesigning the tire is to provide sound absorption

near the tire. Sound absorption in the exterior space around the tire can be provided with

molded fiber wheel liners in place of hard plastic wheel liners Fiber wheel liners are found on

a wide range of vehicles, from entry level vehicles to luxury vehicles

REFERENCES.

1. G. Mylsami, N. Nedunchezhian, “Experimental Study of Diesel Engine Exhaust Noise

Reduction with Perforated Endplate Muffler”, European Journal of Scientific Reseach,2012.

2. M.H.Shojaeefard,R.talebitooti,M.Amirpour Molla and R.Ahmadi, “A study of Intake

System Noise Transmission with Porous insulator Using statical Energy

Analysis”,International Journal of Automotive Engineering, january 2012

3. Jorge P. Arenas ,Malcolm J. Crocker ,”Recent Trends in Sound-Absorbing Materials

Sound and Vibration”, July 2010

4. Andrea Zent, John T. Long, “Automotive Sound Absorbing Material Survey Results” 2007

SAE International.

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