X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fmailhost05.isp.att.net ([207.115.11.55] verified) by logan.com (CommuniGate Pro SMTP 5.3.7) with ESMTP id 4340541 for flyrotary@lancaironline.net; Tue, 08 Jun 2010 15:12:51 -0400 Received-SPF: none receiver=logan.com; client-ip=207.115.11.55; envelope-from=bbradburry@bellsouth.net Received: from desktop (adsl-85-113-162.mco.bellsouth.net[98.85.113.162]) by isp.att.net (frfwmhc05) with SMTP id <20100608191201H0500rokoae>; Tue, 8 Jun 2010 19:12:01 +0000 X-Originating-IP: [98.85.113.162] From: "Bill Bradburry" To: "'Rotary motors in aircraft'" References: In-Reply-To: Subject: RE: [FlyRotary] Re: high/low pressure pumps question Date: Tue, 8 Jun 2010 15:12:02 -0400 Message-ID: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0021_01CB071C.F3603B80" X-Mailer: Microsoft Office Outlook 11 Thread-Index: AcsHJ/lt93qz1/suQmeen90l9x0UjQAFF4VQ X-MimeOLE: Produced By Microsoft MimeOLE V6.0.6001.18049 This is a multi-part message in MIME format. ------=_NextPart_000_0021_01CB071C.F3603B80 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit The fuel pressure regulator should act like the evaporator in an air conditioning system. When the fuel pressure drops suddenly, it should cool the fuel. If you were getting bubbles in the line it could have been because the hose was not filled totally and some of the fuel flashed to vapor when the pressure dropped. Not because it was hotter, but because of the suddenly lower pressure. However, Al is right. You should not plumb your fuel from the regulator back to the intake of the pump. The combination of lower pressures (suction from the pump and the pressure drop coming from the regulator) could cause a lot of vapor to build in the system and could cause a greater tendency for vapor lock. YMMV While we are on the subject, that fuel cooler would be much more effective for preventing engine shutdown from vapor lock if it were ahead of the fuel rail instead of after it. It would also provide a denser fuel which would reduce the duty cycle needed for the injectors. Bill B _____ From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Steven W. Boese Sent: Tuesday, June 08, 2010 12:30 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: high/low pressure pumps question 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. 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 RV6A, 1986 13B NA, RD1A, EC2 _____ From: Rotary motors in aircraft [flyrotary@lancaironline.net] On Behalf Of Al Wick [alwick@juno.com] Sent: Tuesday, June 08, 2010 8:59 AM To: Rotary motors in aircraft Subject: [FlyRotary] Re: high/low pressure pumps question Hi Ed. You often make significant contributions that help improve flight safety. If you share your fuel design, at least do the calculations and let users know how close this is to vapor lock. We're talking about life risk here. You are glossing over my point and changing the topic. Returning fuel to pump inlet is very risky and should not be done unless you desire to operate on the threshold of vapor lock. I agree, there is one exception. That's if you have one of the new fuel pump controllers that measures fuel parameters and alters pump speed. I looked into that one years ago. Talk about added complexity! On with the good stuff! -al wick ------=_NextPart_000_0021_01CB071C.F3603B80 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

The fuel pressure regulator should = act like the evaporator in an air conditioning system.  When the fuel = pressure drops suddenly, it should cool the fuel.  If you were getting = bubbles in the line it could have been because the hose was not filled totally and = some of the fuel flashed to vapor when the pressure dropped.  Not because = it was hotter, but because of the suddenly lower = pressure.

However, Al is right.  You = should not plumb your fuel from the regulator back to the intake of the pump.  = The combination of lower pressures (suction from the pump and the pressure drop coming = from the regulator) could cause a lot of vapor to build in the system and could = cause a greater tendency for vapor lock.

YMMV

 

While we are on the subject, that = fuel cooler would be much more effective for preventing engine shutdown from = vapor lock if it were ahead of the fuel rail instead of after it.  It = would also provide a denser fuel which would reduce the duty cycle needed for the injectors.

 

Bill B

 

 

From: = Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Steven W. Boese
Sent: Tuesday, June 08, = 2010 12:30 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: = high/low pressure pumps question

 

 

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.  =

 

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 =

RV6A, 1986 13B NA, RD1A, = EC2

 

From: = Rotary motors in aircraft [flyrotary@lancaironline.net] On = Behalf Of Al Wick [alwick@juno.com]
Sent: Tuesday, June 08, = 2010 8:59 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: = high/low pressure pumps question

Hi Ed. You often make significant contributions that help improve flight safety. If you share your fuel = design, at least do the calculations and let users know how close this is to = vapor lock. We're talking about life risk here. You are glossing over my point = and changing the topic. Returning fuel to pump inlet is very risky and = should not be done unless you desire to operate on the threshold of vapor = lock.

 

I agree, there is one exception. = That's if you have one of the new fuel pump controllers that measures fuel parameters and alters pump speed. I looked into that one years ago. Talk = about added complexity!

 

On with the good = stuff!

 

-al wick

 

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