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Re: [T3] too much mind time (advanced intro to applied mechanics :-)

Hey Toby-

> Lemme see if I have this right.  Since I'm a male and considered an
> I'll use a semi-visual :)

I swear, there WAS a visual in my explanation!  So what if it was in my mind
only!  :-)

>               Pressure Wave and Direction
> Time Period         Valve   Plenum
>      1                  H -->
>      2                  L <--
>      3                  L -->
>      4                  H <--
> Is this correct?

Yup!  Each of those time periods is what we were calling a quarter-wave.

> Why does the wave suddenly change direction in the plenum?

Moving air has inertia, that's the whole basis of this thing.  It's a crude
explanation, but here goes: What happens is that the positive wave exits the
runner into the plenum and the air in the runner is still moving, causing a
vacuum pulse to be generated.  This pulse travels back to the valve as air
behind it "fills in the gap."  Then, at the valve, there is no air reservoir
to exchange with, so the wave simply reflects back toward the plenum.

> Why not continue it's travel to the OTHER valve?  And what effect is there
> if this wave does continue to the other valve?

The plenum damps out most of the wave effects.  You can imagine that with
all other things equal, the larger the plenum, the larger the dampening.
The reason you want even intake pulses generated at the plenum (i.e. you
don't want a two-cylinder plenum with the cylinders firing 180 degrees from
one another) is so that the average pressure seen by each cylinder is
absolutely identical.  If you measure plenum pressure, then you'll see that
every time an intake valve opens, the plenum pressure decreases.  If all
cylinders see the same pattern, all is fine.

> What
> about the other pulses that are happening in the intake system, how do
> affect the others?

If you want to get really accurate, then I know of two other ways.  One is
to write out a whole slew of differential equations with various conditions
and solve them.  The other is to buy a good engine simulation program that
did that work for you :-)

> I have to go to the bathroom, are we there yet? :)

We'll stop at the ice cream shop.  I still need my ice cream!

> Lastly, for us wanna-be mechanical engineers, can you recommend any books
> for us beginners, like Mechanical Engineering for Dummies?  :)  I have two
> books on fastener technology (how screws, rivets and such work, where to
> place them, figuring out torque, and other completely geeky stuff) but I
> need more about material science and fluid, wave mechanics,
> etc. as well.

You mean a general overview of stuff?  I don't know of any offhand, sorry...

Want to know something funny?  At school, I can sit in a lecture hall and
write out equations and solve problems on paper all day long.  So can
everyone else.  But, whereas a good number of them don't really embrace the
concepts (i.e. they are learned, not understood), I do.  And, as dorky as it
sounds, I have to attribute all of that to my infatuation with these silly,
old hunks of German metal and, to a lesser degree, my involvement with
developing a Solvent Recovery System.  A VW education... sheesh... there's
something wrong with me... :-)

Take care,

Too much? Digest! mailto:type3-d-request@vwtype3.org Subj=subscribe

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