Return-Path: <13brv3@bellsouth.net> Received: from imf19aec.mail.bellsouth.net ([205.152.59.67] verified) by logan.com (CommuniGate Pro SMTP 4.2.8) with ESMTP id 617401 for flyrotary@lancaironline.net; Sat, 22 Jan 2005 11:13:27 -0500 Received-SPF: pass receiver=logan.com; client-ip=205.152.59.67; envelope-from=13brv3@bellsouth.net Received: from rd ([65.6.194.9]) by imf19aec.mail.bellsouth.net (InterMail vM.5.01.06.11 201-253-122-130-111-20040605) with ESMTP id <20050122161257.UHZP2048.imf19aec.mail.bellsouth.net@rd> for ; Sat, 22 Jan 2005 11:12:57 -0500 From: "Russell Duffy" <13brv3@bellsouth.net> To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: Manifold-Reference Fuel Pressure was [FlyRotary]Re: Fuel Injector Sizing Date: Sat, 22 Jan 2005 10:13:17 -0600 Message-ID: <000001c5009d$48aa1a20$6101a8c0@rd> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C5006A.FE0FAA20" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2527 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C5006A.FE0FAA20 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Ain't that what they are supposed to do ? Keep it steady as outside pressure diminishes ? =20 =20 The point is to keep the pressure difference the same between each end = of the injector. Say you have 40 psi of pressure in your injector fuel = rail, and the engine isn't running. When the injector opens, the fuel rushes = from the higher 40 psi end, to the lower 0 psi end. If you only had 10 psi = on your fuel rail, it would still flow, but not nearly as fast, because = there isn't as much pressure difference. This part is pretty easy to see, but what people forget about is that the pressure on the intake side of the injector matters too. =20 =20 Say you have your same 40 psi on the fuel rail, but now the engine is running at idle, with 20 inches of vacuum (-10 psi roughly). Now, = there's a 50 psi difference from one end to the other. Say you run the engine = with a turbo set to 10 psi of boost. Now there's only 30 psi of difference in pressure. This relationship is exactly opposite of what we want, = because we want more fuel at high power, and less at low power. The computer can compensate for this to some extent, but at some point, there are limits = to what you can do with injector timing. =20 =20 The best way to handle this is to use the intake pressure as a = reference, to vary the fuel rail pressure. Now, if the intake pressure rises, or = falls, the fuel rail pressure follows it, so the pressure difference on each = end of the injector stays the same, and fuel sprays the same when you open the injector. Make sense? =20 Cheers, Rusty (stop me before I buy another project) ------=_NextPart_000_0001_01C5006A.FE0FAA20 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Message
Ain't that what they are supposed = to do=20 ?  Keep it steady as outside pressure diminishes ?  
 
The point is to keep the pressure difference = the same=20 between each end of the injector.  Say you have 40 psi of = pressure in your injector fuel rail, and the engine isn't running.  = When the injector opens, the fuel rushes from the higher 40 = psi end,=20 to the lower 0 psi end.  If you only had 10 psi on your fuel rail, = it would=20 still flow, but not nearly as fast, because there isn't as much pressure = difference.  This part is pretty easy to see, but what people = forget about=20 is that the pressure on the intake side of the injector matters = too. =20
 
Say you have your same 40 psi on the fuel rail, = but now the=20 engine is running at idle, with 20 inches of vacuum (-10 psi=20 roughly).  Now, there's a 50 psi difference from one end to = the=20 other.  Say you run the engine with a turbo set to 10 psi of=20 boost.  Now there's only 30 psi of difference in pressure.  = This=20 relationship is exactly opposite of what we want, because we want more = fuel at=20 high power, and less at low=20 power.   The=20 computer can compensate for this to some extent, but at some point, = there are=20 limits to what you can do with injector=20 timing.    
 
The best way to handle this is to use the = intake=20 pressure as a reference, to vary the fuel rail pressure.  = Now,  if the=20 intake pressure rises, or falls, the fuel rail pressure follows it, so = the=20 pressure difference on each end of the injector stays the same, and fuel = sprays=20 the same when you open the injector.  Make=20 sense?
 
Cheers,
Rusty (stop me before I buy another=20 project)
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