Published on Jan 10, 2016
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.
There 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 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.
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 includes exhaust gas and intake air noise as well as noise generated by cooling fans, auxillary fans or any other air flow.
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 refers to noise generated by the vibrating surfaces of the engine components and engine accessories after excitation by reciprocating or rotating engine components.
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.
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.
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.
A variety of design parameter affect at the sound-emission levels of axial-flow fans, but fan blade tip speed is the dominant factor. To minimize fan tip speed, while still providing sufficient engine cooling, the cooling system’s efficiency must be as high as possible. To maxmise cooling system efficiency in water-cooled engines, the following consideration should be made-
1. use water pump and radiator that have adequate capacities, furthermore, be sure that the radiator core has sufficient surface and air flow areas.
2. use a fan with proper aerodynamic blade design.
3. use a shroud to prevent recalculation of air from the high pressure side of the fan in the low pressure side. Clearance between the tips of the fan blades and the shrouding should be minimal.
4. reduce air flow resistance and turbulence in the system. This can be achieved through proper shroud design, proper spacing between the radiator, proper radiator core design.
Improving the engineering in many noisy objects has cut noise nearly by 30 decibels (i.e. snow mobiles)
Government has set up regulations to manufacturers such as GM and Mack truck to reduce vibration in heavy gears, axles and transmissions.
Reducing sound at the sources by an average of 10 decibel cuts soundness in half.
Without doubt, plugging up your ears is the cheapest and easiest method of noise control.
If you have to be around loud noise protecting yourself with earplugs is better than doing.
Excessive exposure to loud noise and or exposure to a quick sound noise could cause serious damage to your ears.
1) Noise cancellation systems by Jeffery .N Denenberg.
2) A study of noise reduction method on motorcycle- SAE 1999-01-3257 JSAE 9938012
3) Design strategies for low noise engine concepts by F.K Brandl, P.Wunsche
4) Noise control in IC engines – BAXA
5) Diesel engine reference book- Bernard Challen