X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from cdptpa-omtalb.mail.rr.com ([75.180.132.120] verified) by logan.com (CommuniGate Pro SMTP 5.4.1) with ESMTP id 5087170 for flyrotary@lancaironline.net; Tue, 09 Aug 2011 15:45:41 -0400 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.120; envelope-from=eanderson@carolina.rr.com Return-Path: X-Authority-Analysis: v=1.1 cv=SOlsIBN44tkg4MqIq+y2aLZdhoA3kHpmiRsLue6rfnM= c=1 sm=0 a=Qjvt2ncigrUA:10 a=rPkcCx1H5rrOSfN0dPC7kw==:17 a=arxwEM4EAAAA:8 a=r1ClD_H3AAAA:8 a=TlGmdTreKYMyw_K_-lEA:9 a=aczJdIo_DzuA6wtL2A8A:7 a=pILNOxqGKmIA:10 a=6kds3Yh_lZATna66:21 a=M-DHY2Bi4HuMTBCB:21 a=E93lBu2AAAAA:8 a=CHk-hiqc1IUZXVjkfJwA:9 a=7wDbMtAuDXtIJZxg7VYA:7 a=MpuOTR30KwMA:10 a=FOUTPhXFUAcA:10 a=zgjei8Deq7QA:10 a=NWVoK91CQyQA:10 a=rPkcCx1H5rrOSfN0dPC7kw==:117 X-Cloudmark-Score: 0 X-Originating-IP: 174.110.167.5 Received: from [174.110.167.5] ([174.110.167.5:58193] helo=EdPC) by cdptpa-oedge01.mail.rr.com (envelope-from ) (ecelerity 2.2.3.46 r()) with ESMTP id CD/1B-15242-24E814E4; Tue, 09 Aug 2011 19:45:06 +0000 Message-ID: <6E025086B3E64840876FD2E20C7DF903@EdPC> From: "Ed Anderson" To: "Rotary motors in aircraft" Subject: Have you checked your gasoline's RVP lately? Date: Tue, 9 Aug 2011 15:43:58 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_001A_01CC56AB.270028E0" X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 14.0.8117.416 X-MimeOLE: Produced By Microsoft MimeOLE V14.0.8117.416 This is a multi-part message in MIME format. ------=_NextPart_000_001A_01CC56AB.270028E0 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable Reid Vapor Pressure (RVP)=20 RVP Low =3D Poor Cold Weather Starting but good "vapor Lock" resistance RVP High =3D Good cold weather starting characteristics but poor "vapor = Lock" resistance Vapor Pressure / Volatility The Reid Vapor Pressure (RVP) is a number expressed in pounds per square = inch (PSI). It represents the fuel's volatility at its initial boiling = point. Any restrictions in fuel lines, pumps, injectors, etc., will lead to an = acceleration of fuel velocity and a lowering of its pressure. That=92s = why engines with fuel pumps and injection systems are more susceptible = to vapor lock, however the problem can occur even on naturally aspirated = engines if things get too hot or the RVP is too high for the conditions = around fuel systems. Simple things like a kink or pinch in a fuel line = between the gascolator and a carburetor are sufficient to cause = localized phase change of a fluid, bubbles of fuel vapor, and a = rough-running engine. While the higher vapor pressure helps the cars to start, it can lead to = vapor lock. Gasolines with RVP of 12 to 14 are highly volatile. If the = fuel line is routed close to a heat source, like the headers, and if the = ambient air conditions are right, the fuel could physically boil in the = fuel line. When this happens, vapor, not liquid, makes its way to the = fuel pump and the engine dies. Most racing fuels have an RVP between 5 and 7 pounds. THe lower the = number, the more difficult it is to start a cold engine because it = doesn't vaporize as well. In a race car, the ignition is generally hot = enough to vaporize the fuel inthe combustion chamber, so starting the = engine is not a problem. :=20 The other prime requirement is RVP, which controls both cold start = volatility (RVP too low is bad) and vapor lock resistance (RVP too high = is bad). Those limits are narrower for aircraft (5.5 to 7.0 psi) than = they are for automotive use.=20 I must admit, I had never paid any attention to the RVP of gasoline = (mainly because it didn't seem like truly useful information), but it = might be time to get an RVP tester {:>) Ed Edward L. Anderson Anderson Electronic Enterprises LLC 305 Reefton Road Weddington, NC 28104 http://www.andersonee.com http://www.eicommander.com ------=_NextPart_000_001A_01CC56AB.270028E0 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable
Reid Vapor Pressure (RVP)
 
RVP Low =3D Poor Cold Weather Starting but good = "vapor Lock"=20 resistance
 
RVP High =3D Good cold weather starting = characteristics but=20 poor "vapor Lock" resistance
 
Vapor Pressure / Volatility
 
The Reid Vapor Pressure (RVP) is a number expressed in pounds = per=20 square inch (PSI). It represents the fuel's volatility at its initial = boiling=20 point.
 
 Any restrictions in fuel lines, pumps, injectors, etc., will = lead to=20 an acceleration of fuel velocity and a lowering of its pressure. = That=92s why=20 engines with fuel pumps and injection systems are more susceptible to = vapor=20 lock, however the problem can occur even on naturally aspirated engines = if=20 things get too hot or the RVP is too high for the conditions around fuel = systems. Simple things like a kink or pinch in a fuel line between the=20 gascolator and a carburetor are sufficient to cause localized phase = change of a=20 fluid, bubbles of fuel vapor, and a rough-running engine.
 
While the higher = vapor=20 pressure helps the cars to start, it can lead to vapor lock. Gasolines = with RVP=20 of 12 to 14 are highly volatile. If the fuel line is routed close to a = heat=20 source, like the headers, and if the ambient air conditions are right, = the fuel=20 could physically boil in the fuel line. When this happens, vapor, not = liquid,=20 makes its way to the fuel pump and the engine = dies.

  Most=20 racing fuels have an RVP between 5 and 7 pounds. THe lower the number, = the more=20 difficult it is to start a cold engine because it doesn't vaporize as = well. In a=20 race car, the ignition is generally hot enough to vaporize the fuel = inthe=20 combustion chamber, so starting the engine is not a=20 problem.

:

The other prime = requirement is=20 RVP, which controls both cold start volatility (RVP too low is bad) and = vapor=20 lock resistance (RVP too high is bad). Those limits are narrower for = aircraft=20 (5.5 to 7.0 psi) than they are for automotive use.

I must admit, I had = never paid any=20 attention to the RVP of gasoline (mainly because it didn't seem like = truly=20 useful information), but it might be time to get an RVP tester=20 {:>)

Ed

 

 

 Edward L. Anderson
Anderson Electronic = Enterprises=20 LLC
305 Reefton Road
Weddington, NC 28104
http://www.andersonee.com
http://www.eicommander.com

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