X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 2 [X] Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 29 Mar 2007 16:50:56 -0400 Message-ID: X-Original-Return-Path: Received: from mta11.adelphia.net ([68.168.78.205] verified) by logan.com (CommuniGate Pro SMTP 5.1.7) with ESMTP id 1949957 for lml@lancaironline.net; Thu, 29 Mar 2007 10:21:53 -0400 Received-SPF: pass receiver=logan.com; client-ip=68.168.78.205; envelope-from=glcasey@adelphia.net Received: from [75.82.254.207] by mta11.adelphia.net (InterMail vM.6.01.05.02 201-2131-123-102-20050715) with ESMTP id <20070329142102.PDOZ2195.mta11.adelphia.net@[75.82.254.207]> for ; Thu, 29 Mar 2007 10:21:02 -0400 Mime-Version: 1.0 (Apple Message framework v752.2) In-Reply-To: References: Content-Type: multipart/alternative; boundary=Apple-Mail-15--697633767 X-Original-Message-Id: <61C3DEB7-E6A9-4211-8E83-F82198077B96@adelphia.net> From: Gary Casey Subject: Re: Thielert Diesel Centurion 4.0 X-Original-Date: Thu, 29 Mar 2007 07:21:01 -0700 X-Original-To: "Lancair Mailing List" X-Mailer: Apple Mail (2.752.2) --Apple-Mail-15--697633767 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=WINDOWS-1252; delsp=yes; format=flowed As usual, George hit the nail squarely on the head. In order to get =20 power up on a diesel the peak cylinder pressures are much higher than =20= on a spark-ignition engine - something like 2,000 psi, compared to =20 1,000. The structure of the engine is proportional to the peak =20 pressure, so the engine almost has to be heavier. Most of the =20 combustion chamber is in the piston, so piston cooling becomes the =20 limiting factor and a great deal of heat is rejected to the oil as a =20 result. Heat rejection during combustion is roughly proportional to =20 the pressure TIMES the temperature difference, so the heat rejection =20 into the cylinder head is also very high. This means large heat =20 exchangers and more cooling drag. A diesel at full power requires =20 about 10% excess air, so the filter (if any) and muffler (if any) has =20= to be larger, as does all the associated plumbing. There was a =20 comment about the power of the engine rolling off above 15,000 ft. =20 The reason is that the engine is running very high manifold pressure =20 - I'm guess at least 60 inches and more likely 90 inches or even more =20= - in order to get the desired power. Turbocharger technology just =20 isn't up to the task of producing the required pressure ratios above =20 a fairly low altitude. You could go to series turbochargers, but =20 that would add more weight. It would certainly produce plenty of =20 cabin pressure, except that the critical altitude would be even lower =20= if some air is taken off for pressurization. And then there is the =20 fuel - it produces more BTU's per gallon, but fewer BTU's per pound =20 than gasoline (about 5% in both cases). Depends on whether you are =20 buying the fuel (per gallon) or carrying the fuel (per pound). =20 Another little detail - many diesel fuel system really, really don't =20 like air in the fuel and some don't self-prime. And if you're flying =20= in the flight levels, don't let the fuel get too cold (of course, =20 that's why jet-A is different from diesel fuel). I like diesels, but =20= for a 300-hp aircraft application the big-bore air-cooled gasoline =20 engines are remarkably good. Gary Casey ES N224SG > There is =93another whole issue=94 with diesel engines . > > One that NOBODY has discussed in public. It is so =93silent=94 that =20= > it almost appears that to bring up the subject may be like =20 > breaking wind in church. > ... > > Because that heat has to be dissipated - - - some way. > > HOW ? Either through air cooling through cylinder fins or through =20= > a radiator. > > EITHER WAY - - - you end up with an ENGINE that may have a BSFC =20 > of around 0.36 to 0.37 (compared to 0.38 to 0.39 for a same =20 > horsepower spark ignition engine ) . > > However - - whatever fuel efficiency is realized - - - is most =20 > likely MORE THAN OFFSET by the additional cooling drag requirements. > > End result - - - it likely takes more pounds of fuel to get you =20 > from A to B - - or more Hp to get you the same air speed. > > Regards, George --Apple-Mail-15--697633767 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=WINDOWS-1252
As usual, George hit = the nail squarely on the head.=A0 In order to get power up on a diesel = the peak cylinder pressures are much higher than on a spark-ignition = engine - something like 2,000 psi, compared to 1,000.=A0 The structure = of the engine is proportional to the peak pressure, so the engine almost = has to be heavier.=A0 Most of the combustion chamber is in the piston, = so piston cooling becomes the limiting factor and a great deal of heat = is rejected to the oil as a result.=A0 Heat rejection during combustion = is roughly proportional to the pressure TIMES the temperature = difference, so the heat rejection into the cylinder head is also very = high.=A0 This means large heat exchangers and more cooling drag.=A0 A = diesel at full power requires about 10% excess air, so the filter (if = any) and muffler (if any) has to be larger, as does all the associated = plumbing.=A0 There was a comment about the power of the engine rolling = off above 15,000 ft.=A0 The reason is that the engine is running very = high manifold pressure - I'm guess at least 60 inches and more likely 90 = inches or even more - in order to get the desired power.=A0 Turbocharger = technology just isn't up to the task of producing the required pressure = ratios above a fairly low altitude.=A0 You could go to series = turbochargers, but that would add more weight.=A0 It would certainly = produce plenty of cabin pressure, except that the critical altitude = would be even lower if some air is taken off for pressurization.=A0 And = then there is the fuel - it produces more BTU's per gallon, but fewer = BTU's per pound than gasoline (about 5% in both cases).=A0 Depends on = whether you are buying the fuel (per gallon) or carrying the fuel (per = pound). =A0Another little detail - many diesel fuel system really, = really don't like air in the fuel and some don't self-prime. =A0And if = you're flying in the flight levels, don't let the fuel get too cold (of = course, that's why jet-A is different from diesel fuel).=A0 I like = diesels, but for a 300-hp aircraft application the big-bore air-cooled = gasoline engines are remarkably good.

Gary Casey
ES = N224SG=A0

There is =93another whole issue=94=A0= with diesel engines .

=A0One that NOBODY has discussed in public.=A0 It is so =93silent=94= that it almost appears that to bring up the subject may be=A0 like = breaking wind in = church.

...

Because that heat =A0has to be = dissipated - - - some way.

HOW ?=A0=A0 Either through air = cooling through cylinder fins or through a radiator.

EITHER WAY=A0 - = - -=A0 you end up with an ENGINE that may have a BSFC of around 0.36 to = 0.37=A0 (compared to 0.38 to 0.39 for a same horsepower spark ignition = engine ) .

However - - whatever fuel = efficiency is realized - - - is most likely MORE THAN OFFSET=A0 by the = additional cooling=A0 drag requirements.

End result - - = - it likely takes more pounds of fuel to get you from=A0 A to B - - or = more Hp to get you the same air speed.

Regards,=A0 = George

= --Apple-Mail-15--697633767--