X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 29 Nov 2010 14:50:17 -0500 Message-ID: X-Original-Return-Path: Received: from web57515.mail.re1.yahoo.com ([66.196.100.82] verified) by logan.com (CommuniGate Pro SMTP 5.3.10) with SMTP id 4594705 for lml@lancaironline.net; Sun, 28 Nov 2010 08:19:30 -0500 Received-SPF: none receiver=logan.com; client-ip=66.196.100.82; envelope-from=casey.gary@yahoo.com Received: (qmail 20417 invoked by uid 60001); 28 Nov 2010 13:18:54 -0000 DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=UKhENrHXwv/ehbUVf3jA398Z3F0RmcZg3qNNWY4YcVF4rkzxeC0EDC9fqH8ZTMOmIw4xr9htNpiE/3Mogkk5gcdXpHFqb4ihTYfLRJ8jDWaqT0p5gFSwHVmcpP6j2dpidU8T/aq4zyqoW8FZb+k4Sc/7CkuLMWJmi0hB3D/l3b8=; X-Original-Message-ID: <268698.19102.qm@web57515.mail.re1.yahoo.com> X-YMail-OSG: MViY.2oVM1mZ09TFmHGTeXqGuQ3cDzb_wmJXD1BAbjL7tRb 13wJ6HgIaBAYDtzNKSa.mlhW1dAASEI8jQmc6cGyXS9QSDgQuOAy7Jm9J7ms AaQ.Nc5O0tTL_rfaS.MyDIMK7YffYeirCZbhykIGJvDg.ZJJNVsP_fTPjcqp BIbLTtC.4Dal.wVbozUpU2Ue5Zg5y7EmsIbLps4bkJ766H0retKbqSEACc6Q WtF22wqqQEZNM7cHvbC7cusqxM8fPYe1JEoynK6FTeTXxN.tWds3uYqSGF2K U_f2vs_L13exXaqvgJIU. Received: from [97.122.152.1] by web57515.mail.re1.yahoo.com via HTTP; Sun, 28 Nov 2010 05:18:54 PST X-Mailer: YahooMailRC/553 YahooMailWebService/0.8.107.285259 References: X-Original-Date: Sun, 28 Nov 2010 05:18:54 -0800 (PST) From: Gary Casey Subject: Re: Critical Turbo Altitude (LIVP) with TSIO550E? X-Original-To: Lancair Mailing List In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii I've been reading this thread with interest - and difficulty. For some reason only emails from this mail list (I'm in the digest mode) have been coming through garbled. My son the IT expert says it is being sent as http instead of text, but why only from this source and why only since a few days ago? Anyway, something Brent said got me to thinking. He said the compressor inlet pressure drop had a significant effect on the critical altitude, especially the air filter pressure drop. So I went through some calculations. A typical air filter drop at sea level might be 4 inches of water (makes my math easier :-), or 1% of an atmosphere. As you go up in altitude the inlet density drops, but at the same power the mass air flow remains roughly the same. With turbulent flow through an orifice (the air filter) it turns out that the pressure drop is inversely proportional to the density. The density at the altitudes we're talking about might be 1/3 that at sea level. So the pressure drop is 3 TIMES the seal level pressure drop. The compressor operates at a given pressure RATIO at critical altitude (waste gate closed) - in this case the pressure ratio is about 3:1. Bottom line? Instead of a 1% power reduction at sea level, the same air filter would create a 9% reduction at altitudes over 25K. Which says that anything you can do to reduce the compressor inlet restriction will make a big difference in critical altitude. The same argument can be made for exhaust restriction after the turbine, but this is less of an issue because the exhaust restriction is already very low. Other considerations: If the divergent geometry of the compressor discharge could be extended past the compressor, more pressure recovery could be realized. The same is true of a divergent section after the turbine. Often the flow "refinements" in a turbo design are neglected, as I suppose the idea is that as long as boost can be maintained by closing the wastegate there is no problem. In reality, any flow improvements can make a big difference, mostly in lower engine inlet temperatures, lower exhaust back pressure, and yes, higher critical altitude. At "normal" altitudes these improvements will result in more power for a given fuel flow. Gary Casey From: "Rick Titsworth" To: ""

Technically, the compressor inlet pressure is normally ALWAYS below ambient