|
|
At 06:46 2004-05-08, you wrote:
- ----- Original Message -----
- From: Bulent Aliev
- Sent: Friday, May 07, 2004 7:54 AM
- To: Rotary motors in aircraft
- Subject: [FlyRotary] Re: fuel injector prices
-
- On 5/6/04 11:31 PM, "John Slade"
<sladerj@bellsouth.net> wrote:
- >> 550 cc/min = 0.1453 Gallons. So 0.1453
Gallons * 60 (minutes) = 8.718
- >> Gallons/ hour x 6 (lbs/gallon) = 52 lbs/ hr. Or a 550
cc/min
- >> injector would
- >> flow approx 52 lbs of fuel if it flowed wide open for one
hour or
- >> 52 lbs/hr.
- >>
- >> for the NA engines the stock injector is the 460 cc/min
(sometimes they
- >> varied a bit around that figure)
- >> 460 cc/min = 0.1215191gallons so performing the
same
- >> calculations = 7.29114
- >> gallons/hr x 6 = 43.75 lbs/hour
- >
- > Ed.
- > Thanks. I follow that So with 4 of these 550cc suckers going
full belt I'd
- > be capable of expelling 52/6 * 4 = 34.67 gals/hr. Seems a
bit excessive!
- > Also - does fuel pressure factor into the equasion?
- > John
- John, I believe it does. If the EC2 controls only the pulse length,
Higher
- pressure will expel larger quantity of fuel than lower pressure for
the same
- injector opening. I don't think the EC2 takes into account the
capacity of
- the injector?
- Bulent
- Yes, pressure will definitely affect flow rate. There is a
standard pressure that is used (40 psi I think) to spec injectors
at. Mazda regulators put out between 35 - 40 psi depending on
manifold pressure.
- An EFI system that didn't take into account the injector flow rate
would be doomed to failure. Mode 3 on the EC2 is there to
compensate for differences in flow rate. There is always a limit to
how much can be compensated for, of course.
- Tracy
Yes, as a general rule, flow through an orifice is a function of the
square root of the differential pressure across the orifice. There
are limitations for this but over a given range it is accurate for our
purposes.
Fluid
Flow: Q
Valve Flow
characteristic: Cv
Differential
Pressure: dP
Fluid Specific Gravity:
G (Gasoline =
0.72)
Q
= Cv (dP/G)^1/2
(Flow = Cv times the square root of (dP divided by G))
using injectors rated 40 lb/hr @ 40 psi (Cv = 5.37):
Fuel
Pressure Approx.
Fuel flow
20
psi 28.3
pph
30 34.7
40 40.0
50 44.7
60 49.0
70 52.9
80 56.6
Okay, it's still raining outside so here is:
Enough rope to hang yourself with:
We know that higher pressures will atomize the fuel better providing
better efficiency and at low engine speeds perhaps better idle. So
would it be good to go with smaller injectors and higher fuel
pressure?
Which injectors rated at 40 psi would work for 80 psi and the same flow
rate?
Looking for 38 pph on a 80 psi system and solving for Cv:
Cv =
Q/[(dP/G)^1/2]
= 38/[(80/.72)^1/2]
= 3.61
If this were a 40 psi injector it would flow:
Q = 3.61 *
(40/.72)^1/2
=
26.9 pph
? -> It might idle better but is it going to work at 8000
rpm?
ONLY YOUR DYNO KNOWS FOR SURE !!
Try it BEFORE you fly it.
Okay, Diana says it stopped raining, I'm outahere.
MGM
Mike McGee, RV-4 N996RV, O320-E2G, Hillsboro, OR
13B in gestation mode, RD-1C, EC-2
|
|