NOISE CONTROL

IN

IC ENGINE

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,.

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 waves

BASICS:

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.

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 r.m.s value of 2X10-5 N/M

2which 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).

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.

( Available range of sound in human beings are 20-20,000 Hz )

TYPES OF SOURCES OF

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

 

1. INDUSTRIAL

2. NON INDUSTRIAL

 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.

NON INDUSTRIAL :

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 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.

INTERNAL COMBUSTION ENGINE NOISE :

Several alternative methods can be used to classify internal combustion engine noise. The two most typical classification techniques are discussed below.

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.

 

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

NOISE EVALUATION DURING ACTUAL

RUNNING :

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.

REMEDIAL MEASURES:

Stopping it at the source

1. Improving the engineering in many noisy objects has cut noise nearly by 30 decibels (i.e. snow mobiles)

2. Government has set up regulations to manufacturers such as GM and Mack truck to reduce vibration in heavy gears, axles and transmissions.

3. Reducing sound at the sources by an average of 10 decibel cuts soundness in half.

THANK YOU, ONE & ALL

A.BHARGAV (11007013)