Return-Path: Received: from fed1rmmtao09.cox.net ([68.230.241.30] verified) by logan.com (CommuniGate Pro SMTP 4.2.9) with ESMTP id 711882 for flyrotary@lancaironline.net; Mon, 07 Feb 2005 20:57:08 -0500 Received-SPF: none receiver=logan.com; client-ip=68.230.241.30; envelope-from=daveleonard@cox.net Received: from davidandanne ([68.101.147.215]) by fed1rmmtao09.cox.net (InterMail vM.6.01.04.00 201-2131-117-20041022) with SMTP id <20050208015536.YHOT8811.fed1rmmtao09.cox.net@davidandanne> for ; Mon, 7 Feb 2005 20:55:36 -0500 From: "DaveLeonard" To: "Rotary motors in aircraft" Subject: RE: [FlyRotary] Re: Heating the Fuel Date: Mon, 7 Feb 2005 17:55:41 -0800 Message-ID: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0054_01C50D3E.3CE63360" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook IMO, Build 9.0.2416 (9.0.2910.0) X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 Importance: Normal In-Reply-To: This is a multi-part message in MIME format. ------=_NextPart_000_0054_01C50D3E.3CE63360 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit [FlyRotary] Re: Performance coatings- bearing damage?Al, thanks for the input. My tank is not pressurized (no check valve on the vent) and any vapor bubble formed after the heat exchanger would flow harmlessly back to the wing tank. As long as the fuel will not be boiling at 200F at ambient pressure at 18,000 ft (which it may be, I should look it up) then I should be ok. Todd has a good point that only the lower side of the wing can be counted on for cooling, but I still feel it should be adequate. I was beginning to fear that the problem would simply be inadequate fuel flow, as Tracy seems to have found through experience. That small amount of fuel (about 40 gal/hr) is simply not enough to cause any significant cooling of the coolant flowing at what? about 20 gal/min? Assuming the fuel went from 70 to 170F, and that fuel has about the same specific heat as Evans Coolant. That means that the coolant temp would drop by 3.3 deg. I could turn on the aux pump and bring the return fuel flow up to 80gal/hr in which case I could see a 6.6 deg drop in coolant temp which is almost enough to be worth it - but not quite. It sure would be nice to make use of all that drag-free surface area of the wings. Evans coolant may just the stuff to design a cooling system around. Simply route the heated coolant out to the wing tips where it could passively drain back through shallow bays on the lower surface of the wing and into a sump where an EWP could pump it back to the engine pump. The bays in the wings would be very shallow to minimize weight, they would be sealed but need not be pressurized. Evans is the perfect stuff because it need not be pressurized, is very non-corrosive and non-toxic. Then there would be no need for a radiator at all. Probably enough capacity there for a coolant/oil heat exchanger and whala, zero cooling drag... Tracy, is it too late to make your RV-8 with zero cooling drag? :-) Dave Leonard Dave; Normally efforts are made to cool the gasoline to prevent vapor lock and improve performance. My old XJS has a fuel cooler that is cooled by the Freon from a AC pump. The average vapor pressure of gasoline at room temps is already fairly high, like 9 psia (absolute), which is below atmospheric pressure and not much of a problem. You may want to look up somewhere what it is at higher pressures, but I'd guess two things, one is that as it increases directly with temp it is likely go increase the pressure in the tank much more rapidly than the fuel is fed out of the tank, and at temps of about 190 the pressure could be quite high. I referred to average vapor pressure because gasoline is a mix of stuff, some of which has much higher VP than others. They usually refer to the 'Reid' vapor pressure which is computed by some complex formula. So you also run the risk of altering the compostion; e.g., the n-Pentane coming off much more rapidly than the iso-octane or some other stuff. At those temps, anywhere in the line upstream from the pump a vapor bubble is almost assured. Not to discourage experimentation, but my opinion would be - maybe not the best idea. Al Subject: [FlyRotary] Heating the Fuel In anticipation of the new turbo, I am considering ways to improve coolant cooling. Besides the obvious more air, more ducting, more radiator; I have been again toying with the idea of a heat exchanger. This time coolant to fuel. The plan would be to use a typical oil/water exchanger but use fuel instead of oil. I would use the fuel on the way back to the tank, and the coolant after it has already been cooled by the radiator. The fuel would then go back to the nice metal tank of the RV. I am looking for input on the implications of heating the fuel. I expect it would reach max temps of about 190 (usually a little cooler) but quickly cool once in the tank. Can the fuel tolerate that temp without vaporizing? It will probably expand in the tank but I don't expect that will occur faster than it is used up. I have no guess as to what temp will become steady state for the fuel pumped out of the tank. My guess is that it will not be much warmer than normal, but a slight increase in temp may help with vaporization. The last question is how much will it cool the coolant. My hope is about 10 deg but I doubt it will be quite that much. I know others have considered using the fuel to cool (Tracy) and I would appreciate your thoughts. Dave Leonard ------=_NextPart_000_0054_01C50D3E.3CE63360 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable [FlyRotary] Re: Performance coatings- bearing = damage?
Al, thanks for the input.  My tank is not = pressurized (no check valve on the vent) and any vapor bubble = formed after=20 the heat exchanger would flow harmlessly back to the wing tank.  As = long as=20 the fuel will not be boiling at 200F at ambient pressure at 18,000 ft = (which it=20 may be, I should look it up) then I should be ok.  Todd has a good = point=20 that only the lower side of the wing can be counted on for cooling, but = I still=20 feel it should be adequate.
 
I was=20 beginning to fear that the problem would simply be inadequate fuel = flow, as=20 Tracy seems to have found through experience.  That small amount of = fuel=20 (about 40 gal/hr) is simply not enough to cause any = significant=20 cooling of the coolant flowing at what? about 20 gal/min?  Assuming = the=20 fuel went from 70 to 170F, and that fuel has about the same = specific=20 heat as Evans Coolant. That means that the coolant temp would drop = by 3.3=20 deg.  I could turn on the aux pump and bring the return fuel = flow up=20 to 80gal/hr in which case I could see a 6.6 deg drop in coolant = temp which=20 is almost enough to be worth it - but not = quite.
 
It sure would=20 be nice to make use of all that drag-free surface area of the=20 wings.
 
Evans coolant=20 may just the stuff to design a cooling system around.  Simply route = the=20 heated coolant out to the wing tips where it could passively = drain=20 back through shallow bays on the lower surface of the wing and into a = sump where=20 an EWP could pump it back to the engine pump.  The bays in the = wings would=20 be very shallow to minimize weight, they would be sealed but need not be = pressurized.  Evans is the perfect stuff because it need not be=20 pressurized, is very non-corrosive=20 and non-toxic.
 
Then there=20 would be no need for a radiator at all.   Probably enough = capacity=20 there for a coolant/oil heat exchanger and whala, zero cooling=20 drag...
 
Tracy, is it=20 too late to make your RV-8 with zero cooling drag? =20 :-)
 
Dave=20 Leonard
 

Dave;

 

Normally efforts are = made to cool=20 the gasoline to prevent vapor lock and improve performance.  My = old XJS=20 has a fuel cooler that is cooled by the Freon from a AC pump. =20

 

The average vapor = pressure of=20 gasoline at room temps is already fairly high, like 9 psia (absolute), = which=20 is below atmospheric pressure and not much of a problem.  You may = want to=20 look up somewhere what it is at higher pressures, but I’d guess = two things,=20 one is that as it increases directly with temp it is likely go = increase the=20 pressure in the tank much more rapidly than the fuel is fed out of the = tank,=20 and at temps of about 190 the pressure could be quite high.  I = referred=20 to average vapor pressure because gasoline is a mix of stuff, some of = which=20 has much higher VP than others.  They usually refer to the = ‘Reid’ vapor=20 pressure which is computed by some complex formula.  So you also = run the=20 risk of altering the compostion; e.g., the n-Pentane coming off much = more=20 rapidly than the iso-octane or some other stuff. =20  

 

At those temps, = anywhere in the=20 line upstream from the pump a vapor bubble is almost assured.=20  

 

Not to discourage=20 experimentation, but my opinion would be – maybe not the best=20 idea.

 

Al

 

Subject:=20 [FlyRotary] Heating the Fuel

 

In=20 anticipation of the new turbo, I am considering ways to improve = coolant=20 cooling.  Besides the obvious more air, more ducting, more = radiator; I=20 have been again toying with the idea of a heat exchanger.  This = time=20 coolant to fuel.  The plan would be to use a typical oil/water = exchanger=20 but use fuel instead of oil.  I would use the fuel on the way = back to the=20 tank, and the coolant after it has already been cooled by the = radiator. =20 The fuel would then go back to the nice metal tank of the=20 RV.

 

I am=20 looking for input on the implications of heating the fuel.  I = expect it=20 would reach max temps of about 190 (usually a = little cooler) but=20 quickly cool once in the tank.  Can the fuel tolerate that temp = without=20 vaporizing?  It will probably expand in the tank but I don't = expect that=20 will occur faster than it is used up.  I have no guess as to what = temp=20 will become steady state for the fuel pumped out of the tank.  My = guess=20 is that it will not be much warmer than normal, but a slight increase = in temp=20 may help with vaporization.

 

The last=20 question is how much will it cool the coolant.  My hope is about = 10 deg=20 but I doubt it will be quite that much.  I know others have = considered=20 using the fuel to cool (Tracy) and I = would=20 appreciate your thoughts.

 

Dave=20 Leonard

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