X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 13 Dec 2007 14:59:54 -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 2579526 for lml@lancaironline.net; Thu, 13 Dec 2007 10:46:30 -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: Ao8CAA/iYEdAMf4VZGdsb2JhbACCcox5mm4 X-IronPort-AV: E=Sophos;i="4.24,162,1196661600"; d="scan'208,217";a="39543236" Received: from rs5.liveoakhosting.com (HELO secure5.liveoakhosting.com) ([64.49.254.21]) by ironport5.liveoakmail.com with ESMTP; 13 Dec 2007 09:45:48 -0600 Received: (qmail 19194 invoked from network); 13 Dec 2007 09:45:48 -0600 Received: from ip68-108-233-192.br.br.cox.net (HELO ?10.0.1.4?) (68.108.233.192) by rs5.liveoakhosting.com with (AES128-SHA encrypted) SMTP; 13 Dec 2007 09:45:48 -0600 Mime-Version: 1.0 (Apple Message framework v752.3) In-Reply-To: References: Content-Type: multipart/alternative; boundary=Apple-Mail-1-210209494 X-Original-Message-Id: From: Walter Atkinson Subject: Re: [LML] Re: GAMI Injectors - question for Walter X-Original-Date: Thu, 13 Dec 2007 09:45:41 -0600 X-Original-To: "Lancair Mailing List" X-Mailer: Apple Mail (2.752.3) --Apple-Mail-1-210209494 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=WINDOWS-1252; delsp=yes; format=flowed Scott: I have no disagreement with anything in your last post, but we should =20= keep in mind that the high fuel pressures being used in auto engines =20 to aid in fuel atomization do present some safety challenges in =20 aircraft. Walter On Dec 13, 2007, at 9:14 AM, Sky2high@aol.com wrote: In a message dated 12/12/2007 9:05:59 A.M. Central Standard Time, =20 fredmoreno@optusnet.com.au writes: 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. Fred, this is the only time it actually matters to me. At anything =20 other than WOT, the pressure in the manifold is, by definition and =20 observation, lower than that at WOT. The amount of flight (or taxi) =20 time spent at low power is inconsequential. At any time the throttle =20= (air valve controller) reduces the MAP below the pressure of the air =20 used to feed the injector bleed hole (whether ram or upper cowl =20 cooling air), everything is fine as the assist air is being sucked in. This issue is important in a turbocharged engine because a great deal =20= of engine operational time is spent with the MAP at a higher pressure =20= than normally available air to be supplied to each injector - =20 especially at higher altitudes. Thus, "deck pressurized" air is =20 tapped and fed to the injectors to at least keep the bleed hole air =20 at the same pressure as the induction system. But, that is not the only issue. I will again get to that later. 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. It is time to talk to more modern engine experts (I am not one, but I =20= stayed at a Holiday Inn Express once). There are probably no single =20 outlet injectors in any of the efficient water cooled automobile =20 engines extant today. Electronic injectors do not need air to =20 atomize the fuel. Even my 1800cc Honda motorcycle uses 50 psi fuel =20 delivery to electronic injectors with 12 holes in each to better =20 atomize the fuel in the induction system (also utilizes 2 intake =20 valves, 2 spark plugs and is water cooled). Auto/motorcycle engines =20 don't fly (much). 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. Yes, designs for kerosene powered turbines. 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. Again, so little tach time is spent at very low power, it is not an =20 issue. But the sucking (vacuum) produced by reducing the throttle =20 and the draw of the cylinder supplies adequate air for atomization. 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. Yes, fine. 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. Not with a good ram air system. Conclusion (Sorry Scott, if I am right) =96 The extra effort to gain =20= a 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. Maybe. The air available to each injector is EQUAL in pressure. =20 There is an observed effect. After installation a different cylinder =20= is the first to reach peak when leaned. Other users have reported a =20 tighter CHT temperature spread. I have seen a tighter fuel flow =20 spread at peak EGTs. I do not have sophisticated equipment to =20 measure the difference in a meaningful way. I don't care. My =20 indications are that I have a better balanced system than I did =20 before and without running with different sized injectors. That is, =20 I may have accomplished some fine tuning at little cost. I hope that =20 no one else makes use of this technique - there are some untested =20 areas, such as what happens by blocking all of the injector air. 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! Yes, I am relying on my observations and the implementations that all =20= turbocharged engines use - I. E. the deck pressure (MAP) shall not =20 exceed the air pressure available at each injector. 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 >>>>>>>>>>>>>>>> Scott Krueger MotorMouth, Charlatan, Bon Vivant, Escapee, Etcetera... See AOL's top rated recipes and easy ways to stay in shape for =20 winter.-- For archives and unsub http://mail.lancaironline.net:81/lists/lml/=20 List.html --Apple-Mail-1-210209494 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=WINDOWS-1252 Scott:

I have no disagreement = with anything in your last post, but we should keep in mind that the = high fuel pressures being used in auto engines to aid in fuel = atomization do present some safety challenges in aircraft.

Walter


On Dec 13, = 2007, at 9:14 AM, Sky2high@aol.com= wrote:

=
In a message dated 12/12/2007 9:05:59 A.M. Central Standard Time, = fredmoreno@optusnet.com.au = writes:

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

=93Very nice set-up. Did you use a turbo-type = injector to hook to the ram air? [Yes]=94

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 helps 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 =

Fred, this = is the only time it actually matters to me.=A0 At anything other than = WOT, the pressure in the manifold is, by definition and observation, = lower than that at WOT.=A0 The amount of flight (or taxi) time = spent at low power is inconsequential.=A0 At any time the throttle (air = valve controller) reduces the MAP below the pressure of the air used to = feed the injector bleed hole (whether ram or upper cowl cooling air), = everything is fine as the assist air is being sucked in.=A0=A0
=A0
This = issue is important in a=A0turbocharged engine because a great deal of = engine operational time is spent with the MAP=A0at a higher = pressure=A0than normally available air to be supplied to each injector - = especially at higher altitudes.=A0 Thus, "deck pressurized" air is = tapped and fed to the injectors to at least keep the bleed hole air at = the same pressure as the induction system.=A0
=A0
But, that is not the = only issue.=A0 I will again get to that later.

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 helps 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.

It is time to = talk to more modern engine experts (I am not one, but I stayed at a = Holiday Inn Express once).=A0 There are probably no single outlet = injectors in any of the efficient water cooled automobile engines extant = today.=A0 Electronic injectors do not need air to atomize the fuel.=A0 = Even my 1800cc Honda motorcycle uses 50 psi fuel delivery to=A0electronic = injectors with 12 holes in each=A0to better atomize the fuel in the = induction system (also utilizes 2 intake valves, 2 spark plugs = and is water cooled).=A0 Auto/motorcycle engines don't fly (much).
=
=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 Gas Turbine Combustion which 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.
=A0
Yes, designs for = kerosene powered turbines.

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.

Again,= so little tach time is spent at very low power, it is not an issue.=A0=A0= But the sucking (vacuum) produced by reducing the throttle and the draw = of the cylinder supplies adequate air for atomization.
=

=A0So 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.

Yes,= fine.

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

=
Not with a good ram air system.
=

=A0Conclusion (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=A0More importantly for Scott, the speed contribution may be = zip.=A0

Maybe.=A0 The air available to each injector is EQUAL in = pressure.=A0 There is an observed effect.=A0 After installation a = different cylinder is the first to reach peak when leaned.=A0 Other = users have reported a tighter CHT temperature spread.=A0 I have seen a = tighter fuel flow spread at peak EGTs.=A0 I do not have = sophisticated=A0equipment to measure the difference in a meaningful = way.=A0 I don't care.=A0 My indications are that I have a better = balanced system than I did before and without running with different = sized injectors.=A0 That is, I may have accomplished some fine tuning at = little cost.=A0I hope that no one else=A0makes use of this technique - = there are some untested areas, such as what happens by=A0blocking all of = the injector air.=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!

Yes, = I am relying on my observations and the implementations that all = turbocharged engines use - I. E. the deck pressure (MAP)=A0shall not = exceed the air pressure available at each injector.

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
Scott Krueger
MotorMouth, = Charlatan, Bon Vivant, Escapee, = Etcetera...
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