Intake runner sizing..

[orlin steven jared]

> ~ Anyways, here is the equation:
> ~ 
> ~    _c_ {_(ab+a+1)+-(((ab+a+1)^2 - 4ab))^.5_}
> ~ f= 2pi {         2ab(L/A)sub 1 * V sub 1   }
> ~ 
> ~ where:  a=(L sub 2 A sub 1)/(L sub 1 A sub 2)
> ~ 	b=(V sub 2)/(V sub 1) 
> ~ 	V sub 1= Vswept/2*((CR + 1)/(CR - 1))
> ~ 	c=speed of sound
> ~ 
> ~ CR:  Volumetric Compression Ratio
> ~ L sub 1:  Inlet pipe length
> ~ A sub 1:  Inlet pipe area (cross sectional)
> ~ L sub 2:  Air duct length
> ~ A sub 2:  Air duct area (cross sectional)

The entire part of the above equation in brackets should actually
have a square root sign around it. Also, c is not equal to
the speed of sound exactly, but the sonic speed of the inlet
gases.  I have the value back home, but it is still an
approximation.

I think I could make a few more clarifications in the above
definitions, but I don't have the paper handy right now..

> I have been lurking for this for some time (I have a WWW page
> just licking its chops for this info).....

So have I, for a few weeks just deleting mail because I haven't
had time to keep up :(.  I only started reading the last couple
of posts in this thread, because this equation caught my eye.
I just used it in a recent homework assignment for my
"fundamentals of internal combustion engines" class.

> A few questions:
> The equation appears to be a solution for a quadratic. Is the sign
> of the numerator term (ab+a+1), (the term before the +-), really
> positive?

YEs.

> The denominator term of 2ab(L/A)sub 1, I do not see the definition
> of this (to reference the "sub 1").  Or is this just 2ab(L/A)?
> 
> Is Vswept the volume swept by the piston?

I don't believe so.  It's actually "Veffective", for which there
is yet another formula.   I'll post this stuff maybe tommorrow,
from the ASME paper.

> Are the units self-consistant (i.e. use feet in speed of
> sound and cubic feet for Vswept, and feet for lengths and
> cross-sections.

When I worked it out I got the inverse of units of length %-(
So I'm not too sure what's up with that.  I'm going to ask
my professor about it.

Better than that, I could ask prof Engleman who is in the
department. :-)

> Very nice info - Bruce

Probably of limited use in real world engine/intake building
though.  The equation above only definies the natural frequencies
of the inlet system.  And it is still very 'iffy', because it
really only works for tubular intakes, and designs where you
can accurately measure all lengths and volumes.

There is another equation in the paper which comes closer for
engine builders to be able to 'take to the work bench'.  It
is an RPM for a tuning peak.




Steve