Return-Path: Received: from capitol.mail.pas.earthlink.net ([207.217.120.180] verified) by logan.com (CommuniGate Pro SMTP 4.2b3) with ESMTP id 3221891 for flyrotary@lancaironline.net; Sat, 08 May 2004 14:27:51 -0400 Received: from ip216-26-76-98.dsl.du.teleport.com ([216.26.76.98] helo=michaelm1.teleport.com) by capitol.mail.pas.earthlink.net with esmtp (Exim 3.33 #1) id 1BMWY9-0006xr-00 for flyrotary@lancaironline.net; Sat, 08 May 2004 11:27:49 -0700 Message-Id: <5.2.0.9.0.20040508103952.025efe40@mail.teleport.com> X-Sender: jmpcrftr@mail.teleport.com X-Mailer: QUALCOMM Windows Eudora Version 5.2.0.9 Date: Sat, 08 May 2004 11:27:00 -0700 To: "Rotary motors in aircraft" From: Michael McGee Subject: Fuel injector math was Re: fuel injector prices In-Reply-To: Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="=====================_5796890==.ALT" --=====================_5796890==.ALT Content-Type: text/plain; charset="us-ascii"; format=flowed 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" 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 --=====================_5796890==.ALT Content-Type: text/html; charset="us-ascii" 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 --=====================_5796890==.ALT--