Using the conservation of energy described earlier it is possible to describe
the discharge of water through the orifice. To simplify the determination of
flow from individual sprinklers, the discharge coefficient is lumped with the
constant and the orifice diameter as follows:
Where Q is in gallons per minute, K is the K-factor and P i s in psi. The
K-factor is determined by testing laboratories for each sprinkler model. A
sprinkler is flowed at a large range of pressures from a fairly large reservoir.
The discharge is measured and a value of K is determined at each pressure, the
average of all the K's at different pressures is the K-factor. In the 1970's the
idea of taking into account velocity pressures effect on water flow was
introduced. However, the difference in predicted water flow is small when
compared to the differences occurred when choosing different Hazen-Williams
C-factors. Therefore, in the United States, it is still general practice to let
the design engineer decide if he is going to calculate the effects of velocity
pressure[8]
----- Original Message -----
Sent: Sunday, January 23, 2005 11:22
AM
Subject: [FlyRotary] Re: 12:1 vs 1:1
Pressure Regulation
Ed,
Assuming that most turbo users are limiting boost to 8-10 lbs maximum,
that would be a pretty high fuel pressure.
Assuming 8 lbs of boost @ 12 psi fuel pressure increase per lb of
boost, that would be an increase of 96 lbs (8*12), on top of a static (0) fuel
pressure of 38 lbs, that would be a whopping 134 lbs of fuel pressure if
I understand your message correctly. That seems pretty high, and I
don't know that the injector seal would hold up to that.
I'm
using the Aeromotive regulator, since I had trouble with the Mallory.
It, as you stated is a 1:1 ratio of adjustment. I don't have a panel
mounted fuel pressure gauge, but I do have a sender installed which I can
attach an analog gauge to for testing, and also for the day I put in an
EM-2. With a 38 lb static fuel pressure, the fuel pressure at an idle
was down to about 20 lbs. It did go up with boost, but being on the
ground, it was hard to get an exact reading on the gauge. It responds
kind of slow, and I was also watching where I was going, more so than watching
the gauge. It did look like about 40 something lbs at a 5 lb boost
setting.
I'm
still running rich at low RPM's, but in flight, the mixtures are
good.
Steve Brooks
Here is some food for thought for you turbo
folks. Most of the pressure referenced fuel regulators regulate the
fuel rail pressure on a 1:1 ratio with the manifold pressure change.
In other words if the manifold pressure changes 1psi (2" HG) the fuel
pressure changes 1 psi. This increase does of course increase the rate
at which the fuel will flow through the injector. However, the flow
rate changes on the order of the square root of the pressure
increase (as best I recall). This means if you double your fuel
pressure you Do NOT double your fuel flow.
With higher boost pressures the preferred
regulation ratio is like 12:1 or 12 psi for each psi of manifold
pressure. Not certain that for the lower boost levels being used
in aircraft whether this is really significant - but, just though I
would pass this on in case anyone wants to investigate it further
or comment.
BLOX FMUs
The
Blox fuel management unit is designed to increase the fuel pressure as the
pressure in the intake manifold increases. The Blox FMU is a universally
design product with a 12:1 fixed ratio. The FMU is used on fuel injected
vehicles, either supercharged or turbocharged, using the factory electronic
engine management system. Blox FMU's are available in blue, red, gold and
gun metal
Ed