cfm-gps

[Patrick G. Moore]

Hi All:

Since noone has answered part of this original
question, I got out an old fluids book.

To translate volume flow into mass flow we basically
just need the density of the air.
Rho = 2.51E-3 slugs/f3 at 32F and 1 ATM
    = 2.12E-3 slugs/f3 at 122F and 1 ATM

So a 255 cfm flow at 122F would make
255 /60s * 2.12E-3 = 9.01E-3 slugs/s

1 slug = 14.594 kg -> 131.49 g/s

Of course we have the normal p = Rho*R*T relation
working on the air.  So when under boost, Rho goes up
(unless the MAF is a draw-thru like Dave).

I found R = 1715 f2/(s2 degR) for air where degR is degrees Rankin
degR = degF + 491.69

For those who don't know what a slug is, it is a unit of mass
like a gram.  In the english system, to get pounds, multiply
slugs by 32.2 f/s2. ie.. 1 lb = 32.2 slug f/s2.

Does this look in the ballpark?  Lets see...
A 36 lb/hr injector would be
(36 * 32.2 / 3600) * 14.594 / 1000 = .004699 g/s
Try 8 of these -> .03759 g/s

That's nothing near 14.7:1.

Maybe the MAF measures mass flow directly, I haven't looked at
flow past a hot wire for years.  Then 255 g/m -> 4.25 g/s.
That gives 113:1 ratio.. Huh?

Oh maybe the injectors are rated in lb/s instead. Then 8, at 100%
duty cycle could put out 135.324 g/s.

Then to get a 14.7:1 mix we need 131.49 g/s air / 14.7 = 8.944 g/s fuel.
Therefore the duty cycle of the 8 36lb injectors would be 8.944/135.324
* 100 = 6.6%.  Still doesn't seem right.

If MAF measured directly in g/s then 255 g/s air needs 12.82% duty cycle.
Closer!

Help!  What is the right combo of assumptions. What does a MAF measure.
What are injectors specified at.

Sorry in advance for confusing everyone.

PS: I havn't looked at the excel spreadsheet yet, because I am on unix.

Pat