Return-Path: Sender: "Marvin Kaye" To: lml@lancaironline.net Date: Wed, 23 Mar 2005 13:59:55 -0500 Message-ID: X-Original-Return-Path: <210flyer@earthlink.net> Received: from smtpauth03.mail.atl.earthlink.net ([209.86.89.63] verified) by logan.com (CommuniGate Pro SMTP 4.3c3) with ESMTP id 817450 for lml@lancaironline.net; Wed, 23 Mar 2005 13:47:57 -0500 Received-SPF: pass receiver=logan.com; client-ip=209.86.89.63; envelope-from=210flyer@earthlink.net Received: from [68.166.244.246] (helo=marauder) by smtpauth03.mail.atl.earthlink.net with asmtp (Exim 4.34) id 1DEAso-0002mT-T7 for lml@lancaironline.net; Wed, 23 Mar 2005 13:47:11 -0500 DomainKey-Signature: a=rsa-sha1; q=dns; c=simple; s=test1; d=earthlink.net; h=Reply-To:From:To:Subject:Date:MIME-Version:Content-Type:X-Mailer:X-MimeOLE:Thread-Index; b=FfnyqkhQaeYnjkczi8lDWOJrDqpzN/qx+yuqq3Vngf/zt28qO0DvsGSrKDLV8SBx; Reply-To: <210flyer@earthlink.net> From: "210flyer" <210flyer@earthlink.net> X-Original-To: "Lancair Mailing List" Subject: Superchargers X-Original-Date: Wed, 23 Mar 2005 11:47:19 -0700 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0029_01C52F9E.11C55350" X-Mailer: Microsoft Office Outlook, Build 11.0.6353 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2527 Thread-Index: AcUv2L1vOIrNG+2eQtmHNQLKOk8Q8A== X-ELNK-Trace: 96606e18df264d301aa676d7e74259b7b3291a7d08dfec79cfb76d9e9944cd1633e36d147ceaccd5350badd9bab72f9c350badd9bab72f9c350badd9bab72f9c X-Originating-IP: 68.166.244.246 X-Original-Message-ID: This is a multi-part message in MIME format. ------=_NextPart_000_0029_01C52F9E.11C55350 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Hi Rob, I have been watching your dialogue with George on this topic with great interest. I was quite surprised, however, when you responded to George on intercoolers. George said: >>4)To get the air temperature back down to tolerable (detonation margins) ranges requires an intercooler Rob said: All sorts of engines run without intercoolers, without damage. Detonation is a function of temperature AND pressure in the cylinder at, or near, full compression, not the temperature in the intake. Besides, if you are flying up high, where an add on system makes sence, the air starts out colder so it isn't all that much warmer than it would have been at ground level.[emphasis mine] The principle reason for adding an intercooler is the same as for adding a supercharger, to make the intake air denser and increase the mass flow through the engine. In particular, I take issue with your suggestion that intercoolers are not needed at altitude. Let's take a look at a supercharger (mechanical or exhaust driven) installation on a 7.5:1 compression ratio engine providing 30" MAP at 20'000 pressure altitude and 20C above ISA. While a perfect supercharger (100% efficient) might only raise the adiabatic (no heat added or lost in the process) motored (no spark or fuel, just air) compression temperature 9%, a real world supercharger (76% efficient) would raise the motored compression temperature over 31% (using the Rankine temperature scale). I think that is a significant number. By way of example, this Christmas, I was flying in Texas at 17,000' with a pressure altitude of nearly 20,000' (13.8") and an OAT +22C over ISA (my Density Altitude was 23,500'). My Compressor Discharge Temperature ("CDT") was 212F at 33" MAP with a pressure ratio of 2.4 for a compressor efficiency of 76% (TSIO-520R). This is an 180F temperature increase over ambient! I think that is a significant number. An intercooler with only 60% efficiency would have reduced my inlet and turbine temperatures by over 100F ! That would have moved my TIT from 1622 to 1522, well below my max TIT. Similarly, it would decrease the heat rejection requirements of the engine and improve my CHTs a bit. Furthermore, it would result in decreased peak combustion pressures and a slight delay in the pressure peak, resulting in less stress on the engine. All of these factors significantly increase the detonation margin between safe operation and engine damage. More importantly, the lower temperatures substantially reduce the probability of preignition, and this is the real killer. Having said all this, I must conclude by commenting that my aircraft does not have an intercooler. As far as I know, I have not damaged the engine by operating without an intercooler. On the other hand, I also realize that I am close to a number of the thermal limits for my engine and that I must limit the HP output in cruise so as not to exceed these limits and cause damage to the engine or turbo. I really wish I had an intercooler for my engine. Best Regards, Mike Hutchins Forever struggling to find a loophole around the Laws of Thermodynamics ------=_NextPart_000_0029_01C52F9E.11C55350 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Hi Rob,

 

I have been watching your dialogue with George on = this topic with great interest. I was quite surprised, however, when you responded = to George on intercoolers.

 

George said:

>>4)To get the air = temperature back down to tolerable (detonation margins) ranges requires an = intercooler

 

Rob said:

All sorts of engines run without intercoolers, = without damage. Detonation is a function of temperature AND pressure in the cylinder at, or near, full compression, not the temperature in the = intake. Besides, if you are flying up high, where an = add on system makes sence, the air starts out colder so it isn't all that much = warmer than it would have been at ground level.[emphasis = mine]

 

The principle reason for adding an intercooler is = the same as for adding a supercharger, to make the intake air denser and increase = the mass flow through the engine.

 

 

In particular, I take issue with your suggestion that intercoolers are not needed at altitude. Let’s take a look at a = supercharger (mechanical or exhaust driven) installation on a 7.5:1 compression ratio = engine providing 30” MAP at 20’000 pressure altitude and 20C above = ISA. While a perfect supercharger (100% efficient) might only raise the adiabatic = (no heat added or lost in the process) motored (no spark or fuel, just air) = compression temperature 9%, a real world supercharger (76% efficient) would raise = the motored compression temperature over 31% (using the Rankine temperature = scale). I think that is a significant number.

 

By way of example, this Christmas, I was flying in = Texas at = 17,000’ with a pressure altitude of nearly 20,000’ (13.8”) and an = OAT +22C over ISA (my Density Altitude was 23,500’). My Compressor = Discharge Temperature (“CDT”) was 212F at 33” MAP with a = pressure ratio of 2.4 for a compressor efficiency of 76% (TSIO-520R). This is an 180F temperature increase over ambient! I think that is a significant = number.

 

An intercooler with only 60% efficiency would have = reduced my inlet and turbine temperatures by over 100F ! That would have moved = my TIT from 1622 to 1522, well below my max TIT. Similarly, it would decrease the = heat rejection requirements of the engine and improve my CHTs a bit. = Furthermore, it would result in decreased peak combustion pressures and a slight delay = in the pressure peak, resulting in less stress on the engine. All of these = factors significantly increase the detonation margin between safe operation and = engine damage. More importantly, the lower temperatures substantially reduce = the probability of preignition, and this is the real = killer.

 

Having said all this, I must conclude by commenting = that my aircraft does not have an intercooler. As far as I know, I have not = damaged the engine by operating without an intercooler. On the other hand, I also = realize that I am close to a number of the thermal limits for my engine and that = I must limit the HP output in cruise so as not to exceed these limits and cause = damage to the engine or turbo. I really wish I had an intercooler for my = engine.

 

Best Regards,

Mike = Hutchins

 

Forever struggling to find a loophole around the = Laws of = Thermodynamics

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