X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 13 Dec 2007 10:14:41 -0500 Message-ID: X-Original-Return-Path: Received: from ironport5.liveoakmail.com ([216.110.12.21] verified) by logan.com (CommuniGate Pro SMTP 5.2c1) with ESMTP id 2578354 for lml@lancaironline.net; Wed, 12 Dec 2007 15:59:27 -0500 Received-SPF: none receiver=logan.com; client-ip=216.110.12.21; envelope-from=walter@advancedpilot.com X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: Ao8CACfaX0dAMf4VZGdsb2JhbACCcoxt X-IronPort-AV: E=Sophos;i="4.24,158,1196661600"; d="scan'208,217";a="39463141" Received: from rs5.liveoakhosting.com (HELO secure5.liveoakhosting.com) ([64.49.254.21]) by ironport5.liveoakmail.com with ESMTP; 12 Dec 2007 14:58:47 -0600 Received: (qmail 32180 invoked from network); 12 Dec 2007 14:58:46 -0600 Received: from 216-107-97-170.static.networktel.net (HELO ?10.0.1.4?) (216.107.97.170) by rs5.liveoakhosting.com with (AES128-SHA encrypted) SMTP; 12 Dec 2007 14:58:46 -0600 Mime-Version: 1.0 (Apple Message framework v752.3) In-Reply-To: References: Content-Type: multipart/alternative; boundary=Apple-Mail-2-142592251 X-Original-Message-Id: From: Walter Atkinson Subject: Re: [LML] GAMI Injectors - question for Walter X-Original-Date: Wed, 12 Dec 2007 14:58:44 -0600 X-Original-To: "Lancair Mailing List" X-Mailer: Apple Mail (2.752.3) --Apple-Mail-2-142592251 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=WINDOWS-1252; delsp=yes; format=flowed Fred: =46rom my perspective: 1) The turbo injectors do not have screens like the NA injectors =20 do. They have air inlets from an upper deck reference line. Scott =20 is using those. 2) The delta air pressure is most important at WOT. 3) Atomized fuel is liquid droplets. Liquid fuel does not burn. The =20= purpose of the atomization is to make the droplets as small as =20 possible so they VAPORIZE quickly upon hitting the warm metal in the =20 induction port. Vaporized fuel in the presence of oxygen burns. 4) The temperature of the metal does not affect atomization (the =20 design of the nozzle and the upper deck preference air pressure does =20 that), it affects vaporization. 5) A delta P of 3" Hg is adequate to result in excellent fuel =20 atomization to aid in vaporization. More pressure does not =20 necessarily make things better. 6) This is most notable at WOT and high power cruise, not the other =20 way around! Based on our research, Scott's set-up is a significant =20 improvement over the NA nozzles. Whether or not it's worth the =20 effort is for each to decide. If *I* went back to a NA set-up, I'd =20 darn sure consider doing it. It works. 7) GAMI does have the hard data on this. I'm sure they'd consider =20 some of it proprietary, but it's fairly well appreciated by the OEMs =20 of nozzels and engines. Walter On Dec 12, 2007, at 9:05 AM, Fred Moreno wrote: Referring to Scott=92s set up using a pitot tube in the cowl inlet to =20= pressurize the fuel injector air inlets, Walter wrote: =93Very nice set-up. Did you use a turbo-type injector to hook to the =20= ram air? [Yes]=94 This topic raises some questions in my mind that just won=92t go away. =20= Pesky things. The fuel injectors have holes in them so that air can flow from a =20 high pressure region into the injector to the lower pressure region =20 in the intake port. Along the way the flow of air helps to atomize =20 the fuel assisting combustion. There are the bits of =93data=94 (I use the term loosely) rumbling = around =20 in my mind that suggest the injector air flow is not important at =20 wide open throttle and thus irrelevant to high power cruise performance. The question is: True or False? Data bit #1: I recall the following when talking to an auto engine =20 =93expert.=94 Modern electronic fuel injection systems control fuel = flow =20 by varying pulse length, but the fuel pressure remains constant. A =20 jet of fuel is pointed at the back of the intake valve. The intake =20 valve which runs moderately hot helps to vaporize the fuel. Further =20 vaporization occurs as the intake air is drawn by the intake valve =20 into the cylinder. The space between valve and valve seat creates an =20= annular venturi of sorts, and as we know, venturis are highly =20 effective at atomizing liquid fuel. So in auto engines higher fuel =20 pressure squirting on the intake valve plus a bit of heat plus the =20 high shear stresses that occur when the flow passes the valve and =20 seat all combine to provide good atomization over a wide range of =20 power conditions. Data bit #2: I spent some years working in gas turbine combustion to =20 reduce NOx emissions. This led me to Arthur Lefebvre=92s book Gas =20 Turbine Combustion which reports on the huge amounts of work done on =20 fuel atomization in jet engines. The problem is that between cold =20 day sea level take off power and flight idle at the start of descent =20 at 36,000 feet, there is a huge difference in fuel flow. This =20 creates major problems for atomization over the entire range of =20 operation, and has resulted in a lot of fancy fuel injector designs. Our simple constant flow fuel injection systems are more like turbine =20= injectors than modern electronic auto injectors. Data point #3: Aircraft fuel injectors tend to squirt at the wall of =20 the intake port (also warm) and not at the back of the intake =20 valve. So cold, low power (idle) atomization maybe particularly =20 poor. And low power which calls for low air flow in the intake port =20 also leads to poor atomization. Help needed. So methinks the following: In our constant flow fuel injectors, at idle and low power settings, =20 the fuel flow is so low that the injector by itself does not squirt, =20 but dribbles fuel out in a low pressure stream. Poor atomization =3D =20= lousy combustion. So to improve atomization, we add air assist =20 atomization. Fortunately, low power also means low manifold =20 pressure, and so ambient pressure (or upper deck pressure) will force =20= air through the fuel injector where it can atomize the fuel dribble =20 and =96 magic! =96 good (or at least improved) combustion. One can =20 expect at least 5 or 10 inches of mercury delta P between intake port =20= and ambient, good enough to spray gasoline. At high power and in cruise (in particular, wide open throttle at =20 altitude) the manifold pressure virtually equals the ambient =20 pressure. No delta P means no atomization air through the injector. =20= But not to worry =96 the cylinder head is hot so the fuel is hitting a =20= hot surface inside the intake port, and moreover, the MASS FLOW RATE =20 of air through the intake port is high so that the fuel is well =20 sheared and mixed when air and fuel pass through the venturi between =20 intake valve and valve seat. Conclusion (Sorry Scott, if I am right) =96 The extra effort to gain a =20= few inches of WATER pressure using the pitot ram tube set up to =20 pressurize the injector air is not worthwhile at higher power =20 settings. At lower power settings, the delta P IS large enough to =20 provide atomization. So for higher power settings or wide open throttle, there is little =20 to be gained by fancy air distribution systems for air injection =20 flow. More importantly for Scott, the speed contribution may be zip. There are two things that can modify this argument. The first is that the pressure in the intake port is not constant at =20 the =93manifold pressure=94 but surging up and down as the cylinder goes = =20 gulp-gulp-gulp, and so there may well be some delta P during the =20 intake stroke when the cylinder is sucking on the intake port. If =20 this pressure fluctuation is not too fast for the flow in the =20 injector, it may assist in atomization. But the effect is due to =20 periodic low pressure in the intake port due to induction, not a tiny =20= bit of additional pressure from the pitot ram air set up. The second thing that can modify the argument is DATA! One sound =20 data point is worth 1000 speculations. Has a good before and after =20 test under carefully controlled conditions shown performance =20 improvements in terms of power, mixture distribution, or beneficial =20 effect on the harmonic convergence? If so, Publish or Perish! What say you, Walter? Teach us some more about fuel atomization at =20 higher power settings and wide open throttle. What does the data =20 show? If no data, you are invited to speculate as well. One Walter =20 speculation =3D 1000 Fred speculations. Always Curious Fred --Apple-Mail-2-142592251 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=WINDOWS-1252 Fred:

=46rom my = perspective:

1) =A0The turbo injectors = do not have screens like the NA injectors do. =A0They have air inlets = from an upper deck reference line. =A0Scott is using = those.

2) = The delta air pressure is most important at WOT.

3) Atomized fuel = is liquid droplets. =A0Liquid fuel does not burn. =A0The purpose of the = atomization is to make the droplets as small as possible so they = VAPORIZE quickly upon hitting the warm metal in the induction port. = =A0Vaporized fuel in the presence of oxygen burns.

4) The temperature of the = metal does not affect atomization (the design of the nozzle and the = upper deck preference air pressure does that), it affects = vaporization.

5) =A0A delta P of 3" Hg = is adequate to result in excellent fuel atomization to aid in = vaporization. =A0More pressure does not necessarily make things = better.

6) = This is most notable at WOT and high power cruise, not the other way = around! =A0Based on our research, Scott's set-up is a significant = improvement over the NA nozzles. =A0Whether or not it's worth the effort = is for each to decide. =A0If *I* went back to a NA set-up, I'd darn sure = consider doing it. =A0It works.

7) GAMI does have the hard = data on this. =A0I'm sure they'd consider some of it proprietary, but = it's fairly well appreciated by the OEMs of nozzels and = engines.

Walter




On Dec 12, 2007, at 9:05 = AM, Fred Moreno wrote:

Referring = to Scott=92s set up using a pitot tube in the cowl inlet to pressurize = the fuel injector air inlets, Walter wrote:

=A0=A0

This topic raises some questions in my mind that just = won=92t go away. =A0Pesky things.

The fuel = injectors have holes in them so that air can flow from a high pressure = region into the injector to the lower pressure region in the intake = port.=A0 Along the way the flow of air=A0helps to atomize the fuel = assisting combustion.

There are = the bits of =93data=94 (I use the term loosely) rumbling around in my = mind that suggest the injector air flow is not important at wide open = throttle and thus irrelevant to high power cruise = performance.=A0

The = question is: True or False?

Data bit = #1: I recall the following when talking to an auto engine =93expert.=94 = =A0Modern electronic fuel injection systems control fuel flow by varying = pulse length, but the fuel pressure remains constant.=A0 A jet of fuel = is pointed at the back of the intake valve.=A0 The intake valve which = runs moderately hot=A0helps to vaporize the fuel.=A0 = Further vaporization occurs as the intake air is drawn by the intake = valve into the cylinder.=A0 The space between valve and valve seat = creates an annular venturi of sorts, and as we know, venturis are highly = effective at atomizing liquid fuel.=A0 So in auto engines higher fuel = pressure squirting on the intake valve plus a bit of heat plus the high = shear stresses that occur when the flow passes the valve and seat all = combine to provide good atomization over a wide range of power = conditions.

=A0

Data bit = #2: I spent some years working in gas turbine combustion to reduce NOx = emissions.=A0 This led me to Arthur Lefebvre=92s book=A0Gas Turbine = Combustion=A0which = reports on the huge amounts of work done on fuel atomization in jet = engines. =A0=A0The problem is that between cold day sea level take off = power and flight idle at the start of descent at 36,000 feet, there is a = huge difference in fuel flow.=A0 This creates major problems for = atomization over the entire range of operation, and has resulted in a = lot of fancy fuel injector designs.

Our = simple constant flow fuel injection systems are more like turbine = injectors than modern electronic auto injectors.

Data = point #3: Aircraft fuel injectors tend to squirt at the wall of the = intake port (also warm) and not at the back of the intake valve.=A0=A0 = So cold, low power (idle) atomization maybe particularly poor. =A0And = low power which calls for low air flow in the intake port also leads to = poor atomization.=A0 Help needed.

So = methinks the following:

In our = constant flow fuel injectors, at idle and low power settings, the fuel = flow is so low that the injector by itself does not squirt, but dribbles = fuel out in a low pressure stream. =A0Poor atomization =3D lousy = combustion.=A0 So to improve atomization, we add air assist = atomization.=A0 Fortunately, low power also means low manifold pressure, = and so ambient pressure (or upper deck pressure) will force air through = the fuel injector where it can atomize the fuel dribble and =96 magic! =96= good (or at least improved) combustion.=A0 One can expect at least 5 or = 10 inches of mercury delta P between intake port and ambient, good = enough to spray gasoline.

At high = power and in cruise (in particular, wide open throttle at altitude) the = manifold pressure virtually equals the ambient pressure.=A0 No delta P = means no atomization air through the injector.=A0 But not to worry =96 = the cylinder head is hot so the fuel is hitting a hot surface inside the = intake port, and moreover, the MASS FLOW RATE of air through the intake = port is high so that the fuel is well sheared and mixed when air and = fuel pass through the venturi between intake valve and valve = seat.=A0

=A0

Conclusion = (Sorry Scott, if I am right) =96 The extra effort to gain a few inches = of WATER pressure using the pitot ram tube set up to pressurize the = injector air is not worthwhile at higher power settings.=A0 At lower = power settings, the delta P IS large enough to provide = atomization.=A0

So for = higher power settings or wide open throttle, there is little to be = gained by fancy air distribution systems for air injection flow. =A0=A0Mor= e importantly for Scott, the speed contribution may be = zip.=A0

=A0

There are = two things that can modify this argument.=A0

The first = is that the pressure in the intake port is not constant at the =93manifold= pressure=94 but surging up and down as the cylinder goes = gulp-gulp-gulp, and so there may well be some delta P during the intake = stroke when the cylinder is sucking on the intake port.=A0 If this = pressure fluctuation is not too fast for the flow in the injector, it = may assist in atomization.=A0 But the effect is due to periodic low = pressure in the intake port due to induction, not a tiny bit of = additional pressure from the pitot ram air set up.

The = second thing that can modify the argument is DATA!=A0 One sound data = point is worth 1000 speculations.=A0 Has a good before and after test = under carefully controlled conditions shown performance improvements in = terms of power, mixture distribution, or beneficial effect on the = harmonic convergence?=A0 If so, Publish or Perish!

What say = you, Walter?=A0 Teach us some more about fuel atomization at higher = power settings and wide open throttle.=A0 What does the data show?=A0 If = no data, you are invited to speculate as well.=A0 One Walter speculation = =3D 1000 Fred speculations.

Always = Curious Fred

=A0