Return-Path: Received: from relay03.roc.ny.frontiernet.net ([66.133.131.36] verified) by logan.com (CommuniGate Pro SMTP 4.1.4) with ESMTP id 2602821 for flyrotary@lancaironline.net; Wed, 24 Sep 2003 23:42:06 -0400 Received: (qmail 27237 invoked from network); 25 Sep 2003 03:42:05 -0000 Received: from unknown (HELO frontiernet.net) ([67.50.169.163]) (envelope-sender ) by relay03.roc.ny.frontiernet.net (FrontierMTA 2.3.6) with SMTP for ; 25 Sep 2003 03:42:05 -0000 Message-ID: <3F725683.95EBF33D@frontiernet.net> Date: Wed, 24 Sep 2003 22:44:19 -0400 From: Jim Sower X-Mailer: Mozilla 4.77 [en] (Win98; U) X-Accept-Language: en MIME-Version: 1.0 To: Rotary motors in aircraft Subject: Re: [FlyRotary] more (interesting but useless) turbo math References: Content-Type: multipart/alternative; boundary="------------E49A204E924A17EA4A845A1D" --------------E49A204E924A17EA4A845A1D Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit <... when the engine compresses it before ignition. My thought was that a 100 degrees could be small potatoes by comparison ...> TT says CHARGE TEMP IS EVERYTHING. You need to keep that thought. The reason you're turbocharging in the first place is to get more (greater mass of) air into the combustion chamber. That done, the magic happens and the prop turns faster. The hotter the intake temp, the less charge you deliver to the chamber. You don't give a rat's ass what compression temps are (so long as they don't detonate - but that's another issue). Compression temps are the rotor's job. Delivering the greatest amount of air you can with the least effort on the part of the engine is your job. Just keep on delivering the mostest, coldest air you can to the chamber. That's your job. The rest of that stuff is the rotor's job, and we'd do well to leave him alone and let him do it. Just tryin' to stay focused .... Jim S. Russell Duffy wrote: > Still have the old turbo bug but haven't run it in 8 years as > I have an airplane to fly now. Ken WelterAre we going to have > to call you Herbie now :-) Thanks for the real world (if you > can call 100" MAP real world) failure modes. Hopefully, I'll > be a little safer at half that.And now, for more turbo math. > With all the talk of intake temps, I was wondering just how > hot the mixture gets when the engine compresses it before > ignition. My thought was that a 100 degrees could be small > potatoes by comparison. Calling on all of my vast memory from > Physics about an eon ago, I searched internet until someone > handed me the formula on a silver platter :-)The formula is: > (intake temp in Kelvin) * (compression ratio) ^ (gamma > -1)gamma is listed as 1.4 for gas engines.For a 90F day, and > 9.7 cr, we have 305 * 9.7 ^.4 = 757 K or 903 degrees F > (ouch)At first, I though this was good news, until I found out > that raising intake temp 100 degrees, raises the compression > temp much more than 100. At my 5 psi intake temp of 214, the > compression temp is 1210 F.This is all interesting, but > doesn't tell me diddly. First, the actual intake temp is > probably a good bit lower, since fuel atomization will lower > the charge temp from what we measure before the throttle > body. Second, octane, timing, mixture and engine cooling have > a large part to play in where detonation will occur. The > lesson to be learned here is that you should just delete my > posts when you see them :-)Cheers, Turbo Rusty -- Jim Sower Crossville, TN; Chapter 5 Long-EZ N83RT, Velocity N4095T --------------E49A204E924A17EA4A845A1D Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit <... when the engine compresses it before ignition. My thought was that a 100 degrees could be small
potatoes by comparison ...>
TT says CHARGE TEMP IS EVERYTHING. You need to keep that thought. The reason you're turbocharging in the first place is to get more (greater mass of) air into the combustion chamber. That done, the magic happens and the prop turns faster. The hotter the intake temp, the less charge you deliver to the chamber. You don't give a rat's ass what compression temps are (so long as they don't detonate - but that's another issue). Compression temps are the rotor's job. Delivering the greatest amount of air you can with the least effort on the part of the engine is your job. Just keep on delivering the mostest, coldest air you can to the chamber. That's your job. The rest of that stuff is the rotor's job, and we'd do well to leave him alone and let him do it.

Just tryin' to stay focused .... Jim S.

Russell Duffy wrote:

Still have the old turbo bug but haven't run it in 8 years as I have an airplane to fly now. Ken WelterAre we going to have to call you Herbie now :-) Thanks for the real world (if you can call 100" MAP real world) failure modes. Hopefully, I'll be a little safer at half that.And now, for more turbo math. With all the talk of intake temps, I was wondering just how hot the mixture gets when the engine compresses it before ignition. My thought was that a 100 degrees could be small potatoes by comparison. Calling on all of my vast memory from Physics about an eon ago, I searched internet until someone handed me the formula on a silver platter :-)The formula is: (intake temp in Kelvin) * (compression ratio) ^ (gamma -1)gamma is listed as 1.4 for gas engines.For a 90F day, and 9.7 cr, we have 305 * 9.7 ^.4 = 757 K or 903 degrees F (ouch)At first, I though this was good news, until I found out that raising intake temp 100 degrees, raises the compression temp much more than 100. At my 5 psi intake temp of 214, the compression temp is 1210 F.This is all interesting, but doesn't tell me diddly. First, the actual intake temp is probably a good bit lower, since fuel atomization will lower the charge temp from what we measure before the throttle body. Second, octane, timing, mixture and engine cooling have a large part to play in where detonation will occur. The lesson to be learned here is that you should just delete my posts when you see them :-)Cheers, Turbo Rusty

--
Jim Sower
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T
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