X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 16 Nov 2010 19:11:08 -0500 Message-ID: X-Original-Return-Path: Received: from elasmtp-curtail.atl.sa.earthlink.net ([209.86.89.64] verified) by logan.com (CommuniGate Pro SMTP 5.3.10) with ESMTP id 4581040 for lml@lancaironline.net; Tue, 16 Nov 2010 10:17:38 -0500 Received-SPF: none receiver=logan.com; client-ip=209.86.89.64; envelope-from=douglasbrunner@earthlink.net DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=dk20050327; d=earthlink.net; b=hwa0HbLNEKIAm63GJ2L+4tzYFypCi0dhIcsiI4Wtbsa83YiMOzsInJxS0vXBfVF7; h=Received:From:To:References:In-Reply-To:Subject:Date:Message-ID:MIME-Version:Content-Type:X-Mailer:thread-index:Content-Language:X-ELNK-Trace:X-Originating-IP; Received: from [74.93.196.177] (helo=DougsLaptop) by elasmtp-curtail.atl.sa.earthlink.net with esmtpa (Exim 4.67) (envelope-from ) id 1PINHK-0006h4-3H for lml@lancaironline.net; Tue, 16 Nov 2010 10:17:02 -0500 From: "Douglas Brunner" X-Original-To: "'Lancair Mailing List'" References: In-Reply-To: Subject: RE: [LML] Re: Electronic Ignition X-Original-Date: Tue, 16 Nov 2010 10:17:17 -0500 X-Original-Message-ID: <002001cb85a1$5b294010$117bc030$@net> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0021_01CB8577.72533810" X-Mailer: Microsoft Office Outlook 12.0 thread-index: AcuFmhOS5VYcC/pXRm++LBCRarq5aAABvimQ Content-Language: en-us X-ELNK-Trace: ad85a799c4f5de37c2eb1477c196d22294f5150ab1c16ac0f2b12df0f75675a4d9b651e3945cb53cb7b1476fac3a9e33350badd9bab72f9c350badd9bab72f9c X-Originating-IP: 74.93.196.177 This is a multi-part message in MIME format. ------=_NextPart_000_0021_01CB8577.72533810 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable You make a persuasive case for the advantages of electronic ignition = when cruising LOP at reduced manifold pressures. =20 I guess my reservations are what the electronic ignition does in other = regimes of flight. =20 From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of = Gary Casey Sent: Tuesday, November 16, 2010 9:25 AM To: lml@lancaironline.net Subject: [LML] Re: Electronic Ignition =20 I certainly agree with the statements below from Mr. Brunner. A few = reinforcing comments: Back in the old days when everyone flew at 8,000 feet or less, the mag = with its fixed timing worked quite well. At takeoff the mixture was so = rich that combustion slowed and the peak cylinder pressure could end up = at 16 degrees ATC, as suggested below. When at a cruising altitude the = mixture was leaned, probably to about peak EGT (carbureted systems) and = that sped up the combustion so that even with the lower manifold = pressure the peak pressure was still near 16 ATC. Then we started to = fly above 10,000 feet and wanted to go LOP. Lower manifold pressures = slow the combustion as does LOP mixtures. Now the spark was definitely = retarded from optimum. The solution? An ignition system that advances = the timing as the manifold pressure drops. But that still doesn't = compensate for LOP operation - the Prism system will do that. =20 And, yes, the electronic system only increases power when it advances = timing over the fixed mag AND the peak cylinder pressure occurs after 16 = ATC. When is that? Probably at any mixture when flying at = significantly over 10,000 feet (manifold pressures less than 20). And = especially when at low manifold pressures AND running LOP. So, in my = opinion the advantage is real when typical cruising is done over 10,000 = and LOP. Otherwise the benefits are not all that persuasive. What = about turbocharged engines? How often are they operated at less than 20 = inches? The only problem I see with mags (on turbocharged engines) is = potential for cross-firing within the distributor cap, eliminated by = most electronic systems. TBO? Certainly any time the peak cylinder = pressure is increased TBO is reduced. But I think a 10:1 engine = operated like it was turbocharged (avoid peak EGT like the plague) could = last as long as a standard engine operated more casually. And the lower = EGT produced by the higher compression is likely to increase exhaust = valve life. Gary Casey ES N224SG, IO-540, 10:1, single Lightspeed, always cruising at 12,000+, = LOP =20 At the risk of starting a =E2=80=9Ctheological=E2=80=9D controversy, I = would like to raise some reservations about electronic ignition systems = (other than reliability and loss of electrical power) =20 Peak intracylinder pressure (the point in the combustion cycle at which = pressure in the cylinder is highest =3D effective timing) is related to = 3 things; spark timing, rpm and MIXTURE.=20 =20 Why mixture? Because air and fuel mixtures burn at different rates = depending on how rich or lean they are. So at a given RPM, MAP and = spark advance you can vary your effective timing by changing the = mixture.=20 =20 =C2=B7 Want to advance your timing? Change your mixture to a 50 = deg ROP mixture =E2=80=93 which is the fastest burning. =C2=B7 Want to retard your timing? Make your mixture richer or = leaner from 50 deg ROP. =20 And since optimal power is achieved at an effective timing of 16 deg = ATDC, advancing the spark timing may or MAY NOT increase horsepower = depending on the mixture. But advancing the timing will likely increase = the magnitude of peak intracylinder pressure leading to higher = intracylinder pressures, higher cylinder head temperatures and greater = stress =3D shorter enging life. =20 For those of you who are using electronic ignition (I am not): =C2=B7 Are you sure you are getting more horsepower? How do you = know? =C2=B7 If you are getting more horsepower, are you getting it = during all modes of engine operation? Rich of peak, lean of peak, high = MAP, low MAP, etc =C2=B7 What is happening to your TBO? =20 D. Brunner =20 ------=_NextPart_000_0021_01CB8577.72533810 Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: quoted-printable

You make a persuasive case for the advantages of electronic ignition = when cruising LOP at reduced manifold pressures.

 

I guess my reservations are what the electronic ignition does in = other regimes of flight.

 

From:= = Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of = Gary Casey
Sent: Tuesday, November 16, 2010 9:25 = AM
To: lml@lancaironline.net
Subject: [LML] Re: = Electronic Ignition

 

I certainly agree with the = statements below from Mr. Brunner.  A few reinforcing = comments:

Back in the old days when everyone = flew at 8,000 feet or less, the mag with its fixed timing worked quite = well.  At takeoff the mixture was so rich that combustion slowed = and the peak cylinder pressure could end up at 16 degrees ATC, as = suggested below.  When at a cruising altitude the mixture was = leaned, probably to about peak EGT (carbureted systems) and that sped up = the combustion so that even with the lower manifold pressure the peak = pressure was still near 16 ATC.  Then we started to fly above = 10,000 feet and wanted to go LOP.  Lower manifold pressures slow = the combustion as does LOP mixtures.  Now the spark was definitely = retarded from optimum.  The solution?  An ignition system that = advances the timing as the manifold pressure drops.  But that still = doesn't compensate for LOP operation - the Prism system will do = that.

 

And, yes, the electronic system = only increases power when it advances timing over the fixed mag AND the = peak cylinder pressure occurs after 16 ATC.  When is that? =  Probably at any mixture when flying at significantly over 10,000 = feet (manifold pressures less than 20).  And especially when at low = manifold pressures AND running LOP.  So, in my opinion the = advantage is real when typical cruising is done over 10,000 and LOP. =  Otherwise the benefits are not all that persuasive.  What = about turbocharged engines?  How often are they operated at less = than 20 inches?  The only problem I see with mags (on turbocharged = engines) is potential for cross-firing within the distributor cap, = eliminated by most electronic systems.  TBO?  Certainly any = time the peak cylinder pressure is increased TBO is reduced.  But I = think a 10:1 engine operated like it was turbocharged (avoid peak EGT = like the plague) could last as long as a standard engine operated more = casually.  And the lower EGT produced by the higher compression is = likely to increase exhaust valve life.

Gary Casey

ES N224SG, IO-540, 10:1, single = Lightspeed, always cruising at 12,000+, LOP

 

At the risk of starting a =E2=80=9Ctheological=E2=80=9D controversy, I = would like to raise some reservations about electronic ignition systems = (other than reliability and loss of electrical = power)

 

Peak intracylinder pressure (the point in the combustion cycle at which = pressure in the cylinder is highest =3D effective timing) is related to = 3 things; spark timing, rpm = and MIXTURE. 

 

Why mixture? Because air and fuel mixtures burn at different rates = depending on how rich or lean they are.  So at a given RPM, MAP and = spark advance you can vary your effective timing by changing the = mixture. 

 

=C2=B7=      &nb= sp;   Want to advance your timing? Change your mixture to a 50 deg ROP = mixture =E2=80=93 which is the fastest burning.

=C2=B7=      &nb= sp;   Want to retard your timing?  Make your mixture richer or leaner = from 50 deg ROP.

 

And since optimal power is achieved at an effective timing of 16 deg = ATDC, advancing the spark timing may or MAY = NOT increase horsepower depending on the mixture.  But = advancing the timing will likely increase the magnitude of peak = intracylinder pressure leading to higher intracylinder pressures, higher = cylinder head temperatures and greater stress =3D shorter enging = life.

 

For those of you who are using electronic ignition (I am = not):

=C2=B7=      &nb= sp;   Are you sure you are getting more horsepower?  How do you = know?

=C2=B7=      &nb= sp;   If you are getting more horsepower, are you getting it during all modes = of engine operation?  Rich of peak, lean of peak, high MAP, low = MAP, etc

=C2=B7=      &nb= sp;   What is happening to your TBO?

 

D. Brunner

 

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