X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from poplet2.per.eftel.com ([203.24.100.45] verified) by logan.com (CommuniGate Pro SMTP 5.3.7) with ESMTP id 4341182 for flyrotary@lancaironline.net; Wed, 09 Jun 2010 03:55:37 -0400 Received-SPF: none receiver=logan.com; client-ip=203.24.100.45; envelope-from=lendich@aanet.com.au Received: from sv1-1.aanet.com.au (mail.aanet.com.au [203.24.100.34]) by poplet2.per.eftel.com (Postfix) with ESMTP id C8C6D1736A2 for ; Wed, 9 Jun 2010 15:54:58 +0800 (WST) Received: from ownerf1fc517b8 (203.171.92.134.static.rev.aanet.com.au [203.171.92.134]) by sv1-1.aanet.com.au (Postfix) with SMTP id 1CB3EBEC064 for ; Wed, 9 Jun 2010 15:54:53 +0800 (WST) Message-ID: From: "George Lendich" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: high/low pressure pumps question Date: Wed, 9 Jun 2010 17:54:56 +1000 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0009_01CB07FC.DF456090" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5931 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5931 X-Antivirus: avast! (VPS 100608-1, 06/08/2010), Outbound message X-Antivirus-Status: Clean This is a multi-part message in MIME format. ------=_NextPart_000_0009_01CB07FC.DF456090 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Steve, Thanks for the response. How important is it to have this percentage of dissolved air in the = fuel. George (down under) George, If I understand your question correctly, I would expect that the fuel = radiator would be useful in keeping the fuel cool and help with respect = to the potential problems 1 & 2 mentioned below. It would not help much = with respect to #3 since the dissolution of the air back into the fuel = seems to be relatively slow. If the header tank is small enough, the = air may remain dispersed and be drawn into the pump supply as small = bubbles to be compressed even smaller and some of them injected with the = fuel. Then the air would not accumulate in the small header tank like = it could in a large one where the mixing is not so effective. In other = words, Ed's header tank may work well partly because of its small = volume. This is just speculation on my part, though. Steve Boese=20 RV6A, 1986 13B NA, RD1A, EC2 -------------------------------------------------------------------------= ----- From: Rotary motors in aircraft [flyrotary@lancaironline.net] On = Behalf Of George Lendich [lendich@aanet.com.au] Sent: Tuesday, June 08, 2010 4:01 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: high/low pressure pumps question Steve, How would you assume the small fuel radiator (before header tank) = would work in the circumstances you describe. George (down under)=20 In the reference provided by Ed, there is mention of the fuel = temperature being monitored to allow compensation for changes in fuel = viscosity with changes in temperature. The ECU might be changing = injector pulse width in response to the fuel temperature rather than = changing the fuel pressure in an attempt to avoid vapor lock. When I first assembled my fuel system, I put a section of glass = tubing in the return line after the pressure regulator. I did this = because I saw bubbles in the fuel being returned to the tank and assumed = that there was an air leak somewhere in the system, most likely in the = suction section between the tank and the pumps. I never found an air = leak after many hours of searching. The bubbles I saw were air bubbles = that separated from the fuel during the rapid pressure drop through the = regulator. The formation of the air bubbles takes place quickly whereas = the dissolution back into the fuel is much slower. The solubility of = air in fuel is much greater than the solubility of air in water, and we = all have seen the air bubbles that form on the walls a container of = water as it warms up and the solubility decreases. When returning the = fuel to the tank, eventually the air would be purged from the liquid = fuel and out the vent. I observed the elimination of the air bubbles in = the return line after about 10 minutes of recurculation when using a = vented fuel tank of only a gallon in volume. I don't know how long this = would take in the case of a large wing tank. Returning the fuel from the regulator to the supply line orto a = small header tank feeding the fuel pumps seems to me to have the = potential for problems in at least three ways: 1) from increasing fuel = vapor pressure as temperature rises, 2) decreased solubility of air in = the fuel as temperature rises, 3) the accumulation of air as a result = of the formation of air bubbles in the pressure regulator which occurs = even without an increase in temperature. All of these things could = contribute to vapor lock. =20 These are just my observations. There is also the indisputable = observation of the success of Ed's system for many years of operation. Steve Boese=20 RV6A, 1986 13B NA, RD1A, EC2 ------=_NextPart_000_0009_01CB07FC.DF456090 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Steve,
Thanks for the response.
How important is it to have = this percentage=20 of dissolved air in the fuel.
George (down under)
 
George,
 
If I understand your question = correctly, I would=20 expect that the fuel radiator would be useful in keeping the fuel cool = and=20 help with respect to the potential problems 1 & 2 mentioned = below. =20 It would not help much with respect to #3 since the dissolution = of the=20 air back into the fuel seems to be relatively slow.  If the = header tank=20 is small enough, the air may remain dispersed and be drawn into the = pump=20 supply as small bubbles to be compressed even smaller and some of them = injected with the fuel.  Then the air would not accumulate in the = small=20 header tank like it could in a large one where the mixing is not so=20 effective.  In other words, Ed's header tank may work well partly = because=20 of its small volume.  This is just speculation on my part,=20 though.
 
 Steve=20 Boese=20
RV6A, 1986 13B NA, RD1A,=20 EC2
 
 
From: Rotary = motors in aircraft=20 [flyrotary@lancaironline.net] On Behalf Of George Lendich=20 [lendich@aanet.com.au]
Sent: Tuesday, June 08, 2010 4:01=20 PM
To: Rotary motors in aircraft
Subject: = [FlyRotary] Re:=20 high/low pressure pumps question

 
Steve,
How would you assume the small fuel = radiator=20 (before header tank) would work in the circumstances you = describe.
George (down under) 
 
In the reference provided by Ed, there is mention of the fuel=20 temperature being monitored to allow compensation for changes in = fuel=20 viscosity with changes in temperature.  The=20 ECU might be changing injector pulse = width in=20 response to the fuel temperature rather than changing the fuel = pressure in=20 an attempt to avoid vapor lock.
 
When I first assembled my fuel = system, I put a=20 section of glass tubing in the return line after the pressure=20 regulator.  I did this because I saw bubbles in the fuel being = returned=20 to the tank and assumed that there was an air leak somewhere in the = system,=20 most likely in the suction section between the tank and the = pumps.  I=20 never found an air leak after many hours of searching.  The = bubbles I=20 saw were air bubbles that separated from the fuel during the rapid = pressure=20 drop through the regulator.  The formation of the air bubbles = takes=20 place quickly whereas the dissolution back into the fuel is much=20 slower.  The solubility of air in fuel is much greater than the = solubility of air in water, and we all have seen the air = bubbles that=20 form on the walls a container of water as it warms up and the=20 solubility decreases.  When returning the fuel to the tank, = eventually=20 the air would be purged from the liquid fuel and out the vent.  = I=20 observed the elimination of the air bubbles in the return line after = about=20 10 minutes of recurculation when using a vented fuel tank of only a = gallon=20 in volume.  I don't know how long this would take in the case = of a=20 large wing tank.
 
Returning the = fuel from the=20 regulator to the supply line orto a small header tank feeding the = fuel pumps=20 seems to me to have the potential for problems in at least three=20 ways: 1)  from increasing fuel vapor pressure as = temperature=20 rises,  2)  decreased solubility of air in the fuel as = temperature=20 rises,  3)  the accumulation of air as a result of the = formation=20 of air bubbles in the pressure regulator which occurs even without = an=20 increase in temperature.  All of these things could contribute = to vapor=20 lock. 
 
These are just = my=20 observations.  There is also the indisputable = observation of the=20 success of Ed's system for many years of operation.
 
Steve = Boese=20
RV6A, 1986 13B NA, RD1A,=20 EC2
 
 
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