Return-Path: <13brv3@bellsouth.net> Received: from imf22aec.mail.bellsouth.net ([205.152.59.70] verified) by logan.com (CommuniGate Pro SMTP 4.1.4) with ESMTP id 2602556 for flyrotary@lancaironline.net; Wed, 24 Sep 2003 21:25:50 -0400 Received: from rad ([68.212.13.204]) by imf22aec.mail.bellsouth.net (InterMail vM.5.01.05.27 201-253-122-126-127-20021220) with ESMTP id <20030925012549.SLAX1849.imf22aec.mail.bellsouth.net@rad> for ; Wed, 24 Sep 2003 21:25:49 -0400 From: "Russell Duffy" <13brv3@bellsouth.net> To: "'Rotary motors in aircraft'" Subject: more (interesting but useless) turbo math Date: Wed, 24 Sep 2003 20:25:49 -0500 Message-ID: <000001c38303$f405fec0$0201a8c0@rad> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C382DA.0B2FF6C0" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.4510 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C382DA.0B2FF6C0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Still have the old turbo bug but haven't run it in 8 years as I have an airplane to fly now. Ken Welter=20 =20 Are we going to have to call you Herbie now :-) =20 =20 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. =20 =20 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 :-) =20 The formula is: (intake temp in Kelvin) * (compression ratio) ^ (gamma = -1) =20 gamma is listed as 1.4 for gas engines. =20 For a 90F day, and 9.7 cr, we have 305 * 9.7 ^.4 =3D 757 K or 903 = degrees F (ouch) =20 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. =20 =20 At my 5 psi intake temp of 214, the compression temp is 1210 F. =20 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. =20 =20 The lesson to be learned here is that you should just delete my posts = when you see them :-) =20 Cheers,=20 Turbo Rusty=20 ------=_NextPart_000_0001_01C382DA.0B2FF6C0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Message
 Still have the old turbo bug but haven't run it in 8 years as = I have=20 an airplane to fly now.

 Ken Welter 
 
Are we going=20 to have to call you Herbie now :-)  
 
Thanks for=20 the real world (if you can call 100" MAP real world) failure = modes. =20 Hopefully, I'll be a little safer at half = that.
 
 
And now, for=20 more turbo math.  With all the talk of intake temps, I was = wondering=20 just how hot the mixture gets when the engine compresses it before=20 ignition.  My thought was that a 100 degrees could be small=20 potatoes by comparison.  Calling on all of my vast memory from = Physics=20 about an eon ago, I searched internet until someone handed me the = formula on a=20 silver platter :-)
 
The formula=20 is:  (intake temp in Kelvin) * (compression ratio) ^ (gamma=20 -1)
 
gamma is=20 listed as 1.4 for gas engines.
 
For a 90F=20 day, and 9.7 cr, we have  305 * 9.7 ^.4 =3D 757 K or  903 = degrees=20  F (ouch)
 
At first, I=20 though this was good news, until I found out that raising intake temp = 100=20 degrees, raises the compression temp much more than 100. =20
 
At my 5 psi=20 intake temp of 214, the compression temp is 1210 F.
 
This is all=20 interesting, but doesn't tell me diddly.  First, the actual intake = temp is=20 probably a good bit lower, since fuel atomization will lower the charge = temp=20 from what we measure before the throttle body.  Second, octane, = timing,=20 mixture and engine cooling have a large part to play in where detonation = will=20 occur.  
 
The lesson to=20 be learned here is that you should just delete my posts when you see = them=20 :-)
 
Cheers, 
Turbo=20 Rusty 
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