Density of the medium through which sound propagates makes a great

 > influence on the speed of the sound wave (It goes faster in water
 > than air and faster in a solid than water) and if I am not wrong the
 > density of the charge coming from a turbo is significantly more than
 > that of the charge in a normally aspirated engine. To this, of
 > course, increased temp. has to be factored in too.
 >
 > Corrections are well received.
 >
 > Alfonso Lebron-Berges
 >

This is true in liquids and solids, but in gases temperature rules.  All
three phase have terms in the equation for both density and temperature
(independent of the influence of one onto the other).  But in gas, the
density component falls out to nearly zero.  Conceptually this is true
because in solids, the molecules are more or less in constant contact with
each other where in gas each molecule more or less flies around on its own
and only "occasionally" bumps into another.  Sound waves are therefore
carried by the average speed of the molecules as they cross albeit very small
pieces of empty space.  Temperature is actually defined as the
root-mean-square of the velocity of the molecules and as such is essentially
the sole determinant of the speed of sound in a gas.

An illustration of this is the thermosphere.  In general, the speed of sound
falls as you go higher with the falling temperature and density.  But the
thermosphere is an area of the atmosphere above the stratosphere where the
temperature actually rises as you go higher.  As I recall, it eventually
reaches temperatures on the order of 200deg C!  And indeed, the speed of
sound up there is higher than it is here on the surface despite the density
being very very low.  Of course,  sound as we know it would be impossible
because the 'air' molecules (mostly hydrogen by that point) are so few and
far between.

The AirCraft Rotary Engine NewsLetter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org