X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 07 Aug 2005 11:22:43 -0400 Message-ID: X-Original-Return-Path: Received: from mta11.adelphia.net ([68.168.78.205] verified) by logan.com (CommuniGate Pro SMTP 4.3.6) with ESMTP id 626624 for lml@lancaironline.net; Sat, 06 Aug 2005 08:23:23 -0400 Received-SPF: pass receiver=logan.com; client-ip=68.168.78.205; envelope-from=glcasey@adelphia.net Received: from [70.34.82.20] by mta11.adelphia.net (InterMail vM.6.01.04.01 201-2131-118-101-20041129) with ESMTP id <20050806122229.MGSH24042.mta11.adelphia.net@[70.34.82.20]> for ; Sat, 6 Aug 2005 08:22:29 -0400 Mime-Version: 1.0 (Apple Message framework v730) In-Reply-To: References: Content-Type: multipart/alternative; boundary=Apple-Mail-8--1005144257 X-Original-Message-Id: <764E85BD-0142-4711-BD89-C1CC7C4B8BFC@adelphia.net> From: Gary Casey Subject: Re: Lower Cowl Air Temperature - Induction Air - Heater Air Temp X-Original-Date: Sat, 6 Aug 2005 05:22:23 -0700 X-Original-To: "Lancair Mailing List" X-Mailer: Apple Mail (2.730) --Apple-Mail-8--1005144257 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed The theoretical temperature drop of the mixture due to fuel evaporation is about 70F with a normal mixture, correlating closely to Walter's measurement. But he suggested there is a temperature drop due to the carburetor venturi - not quite true as the temperature drops in the venturi throat, but during the diverging portion is rises again - very little net drop. The temperature drop is due to fuel evaporation and the result is a positive. In other words a given volume of air/fuel mixture contains more oxygen if the fuel is evaporated than if it is in liquid form as long as the latent heat comes from the air. A fuel-injected engine gains very little from fuel evaporation as most of the latent heat comes from the cylinder head and intake valve. The fuel is mostly splattered on the metal surfaces, which being very hot, evaporate the fuel very quickly but not at any significant air temperature drop. One can increase power by moving the injectors upstream from the intake port so that the latent heat is taken from the air, but that introduces other problems. Someone else discussed placement of the throttle body - where in the intake system the throttle body is placed has a different effect depending on whether you are using a "Bendix" (air-flow) system or Continental (throttle angle) system. The Bendix system, made by Precision Airmotive, probably gives more consistent air/fuel ratios if placed downstream of the intercooler. Gary Casey > As an example, in my Twin Beech, when the OAT is 92dF, the > temperature AFTER the venturi in the carburetor is 35dF. That > temperature drop across the venturi is not there in an injected > engine. Now add another 100dF so that the IAT is 192 and the carb > temp is 135. That is not a good thing. At high powers, with > higher CHTs, the detonation margin is quite a bit narrower. This > isn't too much of a problem in the lower compression engines but > can quickly cross the threshold in the higher compression engines. > > > > Walter > --Apple-Mail-8--1005144257 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=ISO-8859-1

The theoretical temperature = drop of the mixture due to fuel evaporation is about 70F with a normal = mixture, correlating closely to Walter's measurement.=A0 But he = suggested there is a temperature drop due to the carburetor venturi - = not quite true as the temperature drops in the venturi throat, but = during the diverging portion is rises again - very little net drop. =A0The= temperature drop is due to fuel evaporation and the result is a = positive. =A0In other words a given volume of air/fuel mixture contains = more oxygen if the fuel is evaporated than if it is in liquid form as = long as the latent heat comes from the air. =A0A fuel-injected engine = gains very little from fuel evaporation as most of the latent heat comes = from the cylinder head and intake valve.=A0 The fuel is mostly = splattered on the metal surfaces, which being very hot, evaporate the = fuel very quickly but not at any significant air temperature drop.=A0 = One can increase power by moving the injectors upstream from the intake = port so that the latent heat is taken from the air, but that introduces = other problems.

Someone else discussed = placement of the throttle body -=A0 where in the intake system the = throttle body is placed has a different effect depending on whether you = are using a "Bendix" (air-flow) system or Continental (throttle angle) = system.=A0 The Bendix system, made by Precision Airmotive, probably = gives more consistent air/fuel ratios if placed downstream of the = intercooler.

Gary = Casey

As an example, in my Twin Beech, when the OAT is 92dF, = the temperature AFTER the venturi in the carburetor is 35dF.=A0 That temperature drop across = the venturi is not there in an injected engine.=A0 Now add another 100dF so that = the IAT is 192 and the carb temp is 135.=A0 That is not a good = thing.=A0 At high powers, = with higher CHTs, the detonation margin is quite a bit narrower.=A0 This isn't too much of a = problem in the lower compression engines but can quickly cross the = threshold in the higher compression engines.

Walter

= --Apple-Mail-8--1005144257--