how noise shield could be optimized in order to more noise attenuation, but no concern about heat transfer, etc?
is there any source that classified these materials for engines?
Which part of engine?
Piston usually is made of alluminium alloy because of lower density than steel, good tensile strength. Cylinder usually is made of cast iron. Advantage is good abrasive and wear resistance and better absorb shock and vibrations and reduce noise. Depend of carbon content, spherodize graphite may be used when higher hardness needed. Parts of bearings, depends of tension and temperature are made of differ materials, eg. for Diesel (self combustion) engine SnSb11Cu6 is used.
What else?
Taking into consideration 'noise absorber' you have to remember about combustion system - how the fuel explode? Usually some additional systems such as Exhaust Gas Recirculation exist in newer cars- recirculation of exhaust gas into the combustion. It kills engine but decreases emmissions and noise. More exhaust gas = less oxygen. Less oxygen = weaker explosion. Weaker explosion = low power. In fact, 'Worldwide Fuel Charter - ACEA' recommend no more oxygen in fuel composition than 2,7%. So, it limits the use of biofuels. Another topic is fuel additives, such as anti-knock agents which decreases noise.
use mufflers in Exhaust and Add zig zag design in frequency changers....
Thank all of you for your answers. but I mean materials, which have been used as "noise shield" or "acoustic cover" in order to isolate the whole engine and reduce noises which emitted from engine surface(muffler has been used for exhaust system noise reduction).
more info @ attached link.
so choosing material based on engine application is a challenging issue. I am looking for a comprehensive source for this topic.
http://papers.sae.org/2003-01-1719/
Perhaps porous materials could be utilized, as it can be used in acoustics, and dampener perhaps.
@Tzhaquib Fadhlullah Thafarallah. Of course it could be a good idea, if it doesn't harm other design aspects of engine, for example, permissible temperature. so I think may be I could find a source which classified materials for this usage with their advantages and disadvantages.
Excuse me for misunderstanding :) Try rock wool, polystyrene foam, polyethylene foam, always as layered composites.
@janusz Rebis. Both of your comments are really help full for me. THANKS a lot.
What you need is material that is thermally conductive yet a sound insulator (sound absorber). In most materials, these properties go hand in hand, ie a good thermal conductor is usually a good sound conductor rather than opposite. I have seen some metal "foam" material that results in millions of small air cavities that would work for this. However, the material was developed for lightening purposes for military and aerospace applications so the price is likely prohibitive except for extreme applications where price does not matter.
Personally, a much better approach is to look at the root causes of engine noise (ne by one) and improve on each of these starting with the biggest contributors first (I know this is outside the scope of your question)
Thank you Simon Saba for your precise answer.
In case of metals, heaviness could be bothering alongside by cost. maybe I should find some polymers having that properties you have said.
and of course I should have a tradeoff between sound attenuation and heat transfer.
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