While we can read and hear everywhere about the energy losses of a thermic engine through heat dispersion and mechanical frictions, I never heard a word about sound.
Isn't the sound produced by the engine an energy loss too? Or is it exclusively inherent to the other forms of losses which causes the sound (frictions and gaz expensions...), and doesn't count as an energy by itself? I understand it might be negligible, but do you think it is quantifyable, by measuring DB levels, wavelenght etc?
Sorry if this is a dumb question, as I'm definitly not one of the technical heads here.
xpensive wrote:Well...er...ah, imagine running in space, where it's very cold, cooling won't be much of a problem.
Have to bring an oxygen flask though.
Sound is indeed a result of other losses. If the engine was thermally ideal it would produce no noise at all as all energy is converted from chemical to work. Obviously this isn't the case in the real world so the expansion of gasses produces pressure waves (i.e. sound).
Also you have frictional losses as you said that contribute.
But what can be said is that compared to mechanical and thermal losses, sound energy is low and not really worth analysing. It's in an order of magnitude much below the other two.
xpensive wrote:Well...er...ah, imagine running in space, where it's very cold, cooling won't be much of a problem.
Have to bring an oxygen flask though.
Cooling IS a problem in space.
Yeah, you only have radiation to get rid of it, not the greatest method indeed.
Efficient engines tend to be quiet engines as you can see with the Audi R10 LeMans cars. I guess that taking out more energy by turbochargers and using soot filters both would add to this. F1 will continue for a while with the petrol V8 but HERS and using turbos in the exhaust could improve the efficiency and dampen the sound.
Formula One's fundamental ethos is about success coming to those with the most ingenious engineering and best ..............................organization, not to those with the biggest budget. (Dave Richards)
If you were to run the engine in space you would still have sound traveling through the exhaust gas as its expelled, and back through the intake manifold as well.
Grip is a four letter word. All opinions are my own and not those of current or previous employers.
WhiteBlue wrote:Efficient engines tend to be quiet engines as you can see with the Audi R10 LeMans cars. I guess that taking out more energy by turbochargers and using soot filters both would add to this. F1 will continue for a while with the petrol V8 but HERS and using turbos in the exhaust could improve the efficiency and dampen the sound.
The higher pressure your exhaust gasses are, the louder it will be. Turbo diesels do not rev very high and they have the insulating effect that the turbochargers have so they are inherently quiet. High-revving engines (of any size) will be louder than a lower revving version.
I read in a Popular Mechanics magazine a few months (year?) ago about a stove that was developed for third world countries. It burned wood/dung/whatever and produced heat, ice, and electricity.
Thermoacoustics refers to the generation of sound waves through the non-uniform heating of gas — illustrated by the “singing” of hot glass vessels, which can be heard during the glass blowing process. This phenomena has been known for centuries, but could offer new possibilities in the energy conversion process.
The concept of the proposed device is based on proven thermoacoustic engines and refrigerators developed for applications such as combustion-fired natural gas liquefaction and radioisotope-fuelled electric power generation. Los Alamos Laboratories, in collaboration with several industrial partners, has played a lead role in the development of thermoacoustic technology.
Using thermoacoustic technology is a more efficient way of using wood as a fuel than using an open fire to cook. It produces fewer pollutants. The device will also have few moving parts making it more reliable.
This moving part, the linear alternator, would be developed at The University of Nottingham in conjunction with GP Acoustics, a company which produces loudspeaker equipment.
The electricity was made from a speaker type thing in the burning chamber, and it said that the electricity was generated from the noise of the fuel burning instead of some kind of Peltier device(what I would have expected).
So, along these lines, if these transducers? were added to the exhaust system, not only could they be used to absorb the soundwaves, and convert it into electricity, but I'm guessing could be electrically manupulated to change the "tuning" of the exhaust?
Well, maybe it is insignificant. However, how insignificant? If there is someone interested in this house, here you have my long answer.
Sound is another form of energy. I'll try to explain how to measure it, from what I remember of my physics. I did not get an A+ in physics, so I expect corrections.
First, xpensive question: sure, in space many forms of energy cannot be transmited easily, because you don't have an atmosphere to transmit them.
Sound is one of the hard to transmit ones, but as pointed by cba_, thermic energy also is hard to transmit in space (you have to rely on radiation, because convection does not work). However, the fact that some energy cannot be radiated easily doesn't mean is not being produced.
The energy in sound is easy to calculate. Actually, for those that remember what a dB is, it is actually a measure of energy density, called the energy density level, because it is measured against a reference.
If you transform the energy level from a relative scale to an absolute one, you get the energy density, normally called w
Now, if you transform the energy density using the speed of sound in the media, you get the energy intensity, that is, you transform the energy from volume to area.
Finally, if you know the area through the sound is being radiated (that is, you know the surface of the sphere where you're measuring the sound, at some distance from its source) you can transform the energy intensity to energy.
The equations (if I'm not mistaken) are:
Le (sound energy level in dB) = 10 log10 (w1/w0)
In english, the energy level of sound in dB is ten times the logarithm of the energy density of the sound you are measuring, divided by an energy density of reference. That energy of reference, chosen by all the sound engineers of the world (actually, proposed by Mr. Bell in person, if I am not mistaken), is called w0.
FYI, the energy density of reference is equal to 10^-12 J/m3, or, in english, 0.000000000001 Joules per cubic meter.
So, again in english, if you manage to create 0.1 Joules per cubic meter of sound energy, you get 100 dB, because the energy density you have created is 10.000.000.000 times the energy of reference. The logarithm of 10.000.000.000 in base 10 is equal to 10 (simply, count the number of zeroes to get the base 10 logarithm). Now, 10 multiplied by 10, as stated in the previous formula, gives you 100 dB.
Finally, if you know the energy density level and you want to transform it to energy pressure, you use the speed of sound in the media, like this:
w (energy density in J/m3) = I/c (I is energy intensity of sound in W/m2, c is the speed of sound in m/s)
So, if you have 100 dB at, I don't know, 1 meter from the source, in air, at atmospheric pressure, you have (as I said before) 0.1 J/m3 of energy density. Now, roughly speaking c is 340 m/s, so, you have an energy intensity of:
I = 0.1 J/m3 * 340 m/s = 34 Watts/m2
We're getting closer. Now, a sphere with 1 meter radius has a surface of 4*Pi m2, which is roughly 12 m2. The energy radiated into the sphere is:
E = 34 Watts/m2 * 12 m2 = 410 Watts
Not much, that's not even one HP (more like half Hp). That's assuming that the engine sounds give you a reading of 100 db at 1 meter, something I'm not even sure.
Remember that 110 dB means a lot more energy (we're talking about a logarithmic scale) and that if the sound energy density level (dB) is measured at 2 meters of distance from the source then you have 4 times the energy because the sphere has four times the area. Besides, we're talking peak values of energy: sound is a wave, but I won't go into RMS measurementes for this first, back of the envelope, approach. I don't want to bore everybody to death.
The fact is that you get the same amount of energy from an incredibly loud source as the one you need to power a light bulb. This gives you an idea of how sensitive our ears are.
Finally, the real energy of the sound of an engine is in its note and pitch and in the subtle ways it has to energize a human mind: the sound of an italian engine is notable in that respect. I have lost my faith in the ability of the forum to dig that, but, sorry, I had to say it.
I like the pitch and whine of Italian engines in particular. Especially a red line shift to the next gear. Or the sigh on the down note of a playful blip of the throttle.
The Italian sound that really energizes me is the voice of an attractive Italian woman, especially if she is looking into my eyes as she speaks, after that - an Alfa Romeo inline 4 or it's racing V8 or V12/ flat 12 brothers, the Maserati V8's are a good note, so are the the V12 from the 60's, Ferrari V8/V6 and all the 12 cylinder engines - very good. I like the voice of almost all Italian engines. Including Ducati, MV, Benelli and a host of others. I like some Italian wines and certainly home cooked Italian food too. Just sitting in a woman's kitchen is pleasure. Many countries offer gifts to the world. Italy offers a bounty. How fortunate to have shared a few of the treasures.
