Return-Path: Received: from mailout1.pacific.net.au ([61.8.0.84] verified) by logan.com (CommuniGate Pro SMTP 4.3c2) with ESMTP id 755250 for flyrotary@lancaironline.net; Tue, 22 Feb 2005 20:12:21 -0500 Received-SPF: none receiver=logan.com; client-ip=61.8.0.84; envelope-from=peon@pacific.net.au Received: from mailproxy2.pacific.net.au (mailproxy2.pacific.net.au [61.8.0.87]) by mailout1.pacific.net.au (8.12.3/8.12.3/Debian-7.1) with ESMTP id j1N1BXA6029262 for ; Wed, 23 Feb 2005 12:11:33 +1100 Received: from ar1 (ppp2D6D.dyn.pacific.net.au [61.8.45.109]) by mailproxy2.pacific.net.au (8.12.3/8.12.3/Debian-7.1) with SMTP id j1N1BSMp005574 for ; Wed, 23 Feb 2005 12:11:29 +1100 Message-ID: <00cc01c51944$0d50d940$6d2d083d@ar1> From: "Leon" To: "Rotary motors in aircraft" References: Subject: For Todd "Vena Contracta" Take 2 was Re: Returnless Fuel System - Fuel Cooler Date: Wed, 23 Feb 2005 12:07:30 +1100 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_00C7_01C519A0.3FF61200" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1409 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1409 This is a multi-part message in MIME format. ------=_NextPart_000_00C7_01C519A0.3FF61200 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable RE: [FlyRotary] Returnless Fuel System - Fuel CoolerHey Todd, I think you may have missed the point or lost the plot good buddy. = Firstly, where did the 1/8" line come into it?? Secondly, there = 'ain't no "impellors" in an EFI pump. They use rollers!! TOTALLY = different animals to centrifugal pumps!. =20 I AM also aware that the flow through any orifice is controlled by the = differnetial pressure. What I still don't get is the bit about = "pressure recovery", as my issue is the flow in the open flow return = line as it exits rthe regulator !!! The regulator is providing that = back pressure in the fuel rail, and as the "back pressure" increases, = the pressure drop through the pump outlet orifice decreases. At any = rate, there is NO chance of cavitation unless there is no fuel head on = the pump inlet! =20 Anyway, let me rephrase the questions again: SITUATION #1 I have an EFI pump that has a good head of fuel on it. It is connected = to a fuel rail in the normal way, via a pressure regulator set at 45 = PSI. This means that there is 45 PSI back pressure on the pump. I = observe a given fuel flow out the return line. When the engine is = started, the regulator brings the rail pressure back to about 32-33 = PSI. I have about 25" MAP (Manifold Absolute Pressure) at idle. I notice = the fuel flow out the return line INCREASES as the rail pressure drops = when the engine starts. The regulator is connected to an open flow 1/4" ID line which returns to = the surge tank in the normal way, and the surge tank is vented to = atmosphere. The pump is pumping through a restrictor, say 3/16". The = question is: QUESTION #1 "What limits the flow of the fuel IN THE RETURN LINE??. The 3/16" = restriction, or the 1/4" ID of dump line itself. " By observation, I know that as load (MAP) is increased on the engine = and the RPM rises, and as more & more fuel goes to the injectors, the = fuel pressure in the rail rises in concert with the increased manifold = pressure, (therefore even more back pressure on the pump up to 45 PSI @ = WOT), and the amount of bypass fuel from the regulator diminishes. So = the only time I'm liable to have flow issues in the return line is at = idle, (which would be indicated by the regulator not being able to = control the pressure in the rail). By observation, fitting a high capacity Bosch Motorsport or SX pump, I = actually have this problem, which is why I use a 5/16" return line in = these instances. The problem then goes away. Again by observation, at the limit, IF the EFI pump is incapable of = supplying the necessary fuel to the engine at WOT and high RPM, the = fuel flowing from the return line ceases completely. Soon after this, = as the engine RPM continue to rise, the pressure in the fuel rail = begins to drop, as the pump cannot pump any more fuel, and the engine = begins to run out of fuel. I have watched this on the dyno MNAY times. SITUATION #2 I have the same EFI pump, this time on the bench. It has a good head = of fuel on it. QUESTION #2 "For any given restrictor, say our 3/16" one again, does the rate of = flow from the pump into an open container (vented to armospheric - no = other restrictions - open flow)" a. increase, =20 b. stay the same, or c. decrease=20 if I attach a length of fuel line of 1/14" ID to the pump outlet. =20 QUESTION #3 "What happens if I drill the outlet out to 1/4" and do the same as in = Question #2. QUESTION # 4 "What happens if I drill the restriction out to 9/32" " Cheers buddy, Leon (waiting with my little velvet bag to catch the pearls). ----- Original Message -----=20 From: Bartrim, Todd=20 To: Rotary motors in aircraft=20 Sent: Tuesday, February 22, 2005 8:34 AM Subject: [FlyRotary] Re: For Todd "Vena Contracta" was Re: Returnless = Fuel System - Fuel Cooler Hi Leon; I'm a little late responding as I spent the weekend rebuilding my = dirt bike with one of them ole fashioned piston engines what go up & = down to make something go round 'n round? What a goofy idea! Anyways, back to the subject at hand. Pressure recovery ?... so = what? Well without pressure differential there is no flow. None. I = realize that jets are used to meter flow and that a restriction is an = impediment to flow, however my point was that if the EFI pump has an = outlet of say 1/8" into a 3/8" line (or in Bob's case, his 1/4" return = line) it does not have the equivalent flow of a 1/8" line. While it will = not have full flow of an unrestricted line due to permanent pressure = loss, it will recover much of its pressure resulting in a much greater = flow than would be provided by a 1/8" tube. To calculate this the Beta = ratio of the "orifice" is required, however it really isn't that = important. Besides, I can't find right now the required formula. I = should get back to studying this as I return to school for 4th year in 2 = months and I can be assured that there will be at least one twisted = question concerning this on the incoming exam. Someone had mentioned drilling out the pump outlet to reduce this = restriction, but that would be a really bad idea. The pump outlet is = usually sized smaller than the pipe that it is sized for in order to = provide adequate back pressure to the pump to prevent cavitation. If you = drill out this outlet, then bubbles can/will form in the impellor and = the resulting cavitation will result in less flow and quite possibly the = vapour lock that we are trying to avoid. This restriction does not = diminish the requirement for a proper sized tube to be plumbed to it in = order to achieve rated flow. Just my 2 bits worth Cheers Todd So I just can't see what the size of an attached pipe has to do with = the flow rate through a "vena contracta" ("vena constricta"??). You = also say "but much of this pressure is recovered downstream" Hmmmmmm, = ... I say "so what"??. We aren't interested in pressure drops or = pressure recovery, ... it's flow rates that are the SOLE issue, and the = capacity of an open flow 1/4 inch line to get rid of the fuel dumped by = the regulator. =20 Leon ------=_NextPart_000_00C7_01C519A0.3FF61200 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable RE: [FlyRotary] Returnless Fuel System - Fuel = Cooler
Hey Todd,
 
I think you may have missed the = point or lost=20 the plot good buddy.  Firstly,  where did the 1/8" line come = into=20 it??  Secondly,  there 'ain't no "impellors" in an EFI = pump. =20 They use rollers!!  TOTALLY different animals to centrifugal=20 pumps!.  
 
I AM also aware that the = flow through any=20 orifice is controlled by the differnetial pressure.  What = I still=20 don't get is the bit about "pressure recovery", as my issue is = the=20 flow in the open flow return line as it exits rthe=20 regulator !!!  The regulator is providing that back=20 pressure in the fuel rail,  and as the  "back pressure"=20 increases,  the pressure drop through the pump outlet orifice=20 decreases.  At any rate,  there is NO chance of = cavitation unless=20 there is no fuel head on the pump inlet!  
 
Anyway,  let me rephrase the = questions=20 again:
 
SITUATION #1
 
I have an EFI pump that has a good = head of=20 fuel on it.  It is connected to a fuel rail in the normal = way,  via a=20 pressure regulator set at 45 PSI.  This means that there=20 is 45  PSI back pressure on the pump.  I observe a given = fuel=20 flow out the return line. When the engine is started,  the = regulator=20 brings the rail pressure back to about 32-33 PSI. I have about = 25" MAP=20 (Manifold Absolute Pressure) at idle. I notice the fuel flow = out the=20 return line INCREASES as the rail pressure drops when the engine=20 starts.
 
The regulator is connected to an open=20 flow 1/4" ID line which returns to the surge tank in the = normal=20 way,  and the surge tank is vented to atmosphere.  The = pump is=20 pumping through a restrictor,  say 3/16".  The question=20 is:
 
QUESTION   #1
 
"What limits the flow of the fuel IN = THE RETURN=20 LINE??.  The 3/16" restriction,  or the 1/4" ID of dump line=20 itself. "
 
By observation,  I know that = as load=20 (MAP) is increased on the engine and the RPM rises,  and as = more &=20 more fuel goes to the injectors,  the fuel pressure in the rail = rises in=20 concert with the increased manifold pressure,  (therefore even more = back=20 pressure on the pump up to 45 PSI @ WOT),  and the amount of bypass = fuel=20 from the regulator diminishes.  So the only time I'm liable to have = flow=20 issues in the return line is at idle,  (which would be indicated by = the=20 regulator not being able to control the pressure in the = rail).
 
By observation,  fitting a high = capacity Bosch=20 Motorsport or SX pump,  I actually have this problem,  = which is=20 why I use a 5/16" return line in these instances.  The problem then = goes=20 away.
 
Again by observation,  at the=20 limit,  IF the EFI pump is incapable of supplying the = necessary fuel=20 to the engine at WOT and high RPM,  the fuel flowing from the = return line=20 ceases completely.  Soon after this, as the engine RPM = continue to=20 rise,  the pressure in the fuel rail begins to drop,  as = the pump=20 cannot pump any more fuel,  and the engine begins to run out of = fuel. =20 I have watched this on the dyno MNAY times.
 
SITUATION #2
 
I have the same EFI pump,  this = time on the=20 bench.  It has a good head of fuel on it.
 
QUESTION #2
 
"For any given restrictor,  say = our 3/16" one=20 again,  does the rate of flow from the pump into an open container = (vented=20 to armospheric - no other restrictions - open flow)"
 
a.   increase,  =
b.   stay the same,  = or
c.   decrease =
 
if I attach a length of fuel line of = 1/14" ID to=20 the pump outlet. 
 
QUESTION #3
 
"What happens if I drill the outlet out = to=20 1/4"  and do the same as in Question #2.
 
QUESTION # 4
 
"What happens if I drill the = restriction out to=20 9/32" "
 
Cheers buddy,
 
Leon
(waiting with my little velvet bag to = catch the=20 pearls).
 
----- Original Message -----
From:=20 Bartrim, Todd
Sent: Tuesday, February 22, = 2005 8:34=20 AM
Subject: [FlyRotary] Re: For = Todd "Vena=20 Contracta" was Re: Returnless Fuel System - Fuel Cooler

Hi Leon;
   =20 I'm a little late = responding as I spent=20 the weekend rebuilding my dirt bike with one of them ole fashioned = piston=20 engines what go up & down to make something go round 'n round? = What a=20 goofy idea!
   =20 Anyways, back to the = subject at hand.=20 Pressure recovery ?... so what? Well without pressure = differential there=20 is no flow. None. I realize that jets are used to meter flow and that = a=20 restriction is an impediment to flow, however my point was that if the = EFI=20 pump has an outlet of say 1/8" into a 3/8" line (or in Bob's case, his = 1/4"=20 return line) it does not have the equivalent flow of a 1/8" line. = While=20 it will not have full flow of an unrestricted line due to = permanent=20 pressure loss, it will recover much of its pressure resulting in = a much=20 greater flow than would be provided by a 1/8" tube. To calculate this = the Beta=20 ratio of the "orifice" is required, however it really isn't that = important.=20 Besides, I can't find right now the required formula. I should get = back to=20 studying this as I return to school for 4th year in 2 months and I can = be=20 assured that there will be at least one twisted question concerning = this on=20 the incoming exam.
   =20 Someone had mentioned = drilling out the=20 pump outlet to reduce this restriction, but that would be a really bad = idea.=20 The pump outlet is usually sized smaller than the pipe that it is = sized for in=20 order to provide adequate back pressure to the pump to prevent = cavitation. If=20 you drill out this outlet, then bubbles can/will form in the impellor = and the=20 resulting cavitation will result in less flow and quite possibly the = vapour=20 lock that we are trying to avoid. This restriction does not diminish = the=20 requirement for a proper sized tube to be plumbed to it in order to = achieve=20 rated flow.
   =20 Just my 2 bits = worth
Cheers
Todd

So I just can't see what the = size of an=20 attached pipe has to do with the flow rate through a  "vena = contracta"=20 ("vena constricta"??).  You also say "but much of this pressure = is=20 recovered downstream"  Hmmmmmm, ... I say "so what"??.  We = aren't=20 interested in pressure drops or pressure recovery, ... it's = flow rates=20 that are the SOLE issue,  and the capacity of an open=20 flow 1/4 inch line to get rid of the fuel dumped by the=20 regulator. 
 
 
Leon =20
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