---- START NEW MESSAGE --- Received: from cherry.ease.lsoft.com [209.119.0.109] by dpmail10.doteasy.com with ESMTP (SMTPD32-8.05) id A37680D01FC; Tue, 27 Jan 2004 23:23:34 -0800 Received: from PEAR.EASE.LSOFT.COM (209.119.0.19) by cherry.ease.lsoft.com (LSMTP for Digital Unix v1.1b) with SMTP id <10.00CC094B@cherry.ease.lsoft.com>; Wed, 28 Jan 2004 2:23:26 -0500 Received: from MITVMA.MIT.EDU by MITVMA.MIT.EDU (LISTSERV-TCP/IP release 1.8e) with spool id 2685 for PICLIST@MITVMA.MIT.EDU; Wed, 28 Jan 2004 02:23:19 -0500 Received: from MITVMA (NJE origin SMTP@MITVMA) by MITVMA.MIT.EDU (LMail V1.2d/1.8d) with BSMTP id 1089; Wed, 28 Jan 2004 02:22:58 -0500 Received: from linda-3.paradise.net.nz [202.0.58.22] by mitvma.mit.edu (IBM VM SMTP Level 430) via TCP with ESMTP ; Wed, 28 Jan 2004 02:22:57 EST X-Comment: mitvma.mit.edu: Mail was sent by linda-3.paradise.net.nz Received: from smtp-2.paradise.net.nz (smtp-2a.paradise.net.nz [202.0.32.195]) by linda-3.paradise.net.nz (Paradise.net.nz) with ESMTP id <0HS600CAHV6AKT@linda-3.paradise.net.nz> for PICLIST@MITVMA.MIT.EDU; Wed, 28 Jan 2004 20:22:58 +1300 (NZDT) Received: from Paradise (202-0-40-43.adsl.paradise.net.nz [202.0.40.43]) by smtp-2.paradise.net.nz (Postfix) with SMTP id E75969E208 for ; Wed, 28 Jan 2004 20:22:57 +1300 (NZDT) MIME-version: 1.0 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 X-Mailer: Microsoft Outlook Express 6.00.2800.1158 Content-type: text/plain; charset=Windows-1252 Content-transfer-encoding: 7bit X-Priority: 3 X-MSMail-priority: Normal Message-ID: <003701c3e56f$a163aae0$7b01a8c0@Paradise> Date: Wed, 28 Jan 2004 20:23:27 +1300 Reply-To: pic microcontroller discussion list Sender: pic microcontroller discussion list From: Russell McMahon Subject: [OT:] Stirling engines To: PICLIST@MITVMA.MIT.EDU Precedence: list X-RCPT-TO: Status: U X-UIDL: 371856045 A response I wrote for another list that may be of passing interest here: Subject was whether existing internal combustion engines could readily be replaced by alternatives. _______________ > Turbines are far simpler, lighter per horsepower, and vastly more > reliable - but they do so at the cost of less thermal efficiency. > Reciprocating engines, at least to my limited knowledge, wring more > mechanical energy from every BTU than just about anything else out > there. I suspect, though I do not know this to be the case, that a > small turbine driving a generator and charging a large capacitor bank > could drive an AC induction motor for a system that *might* do better > than an all-mechanical drive train connected to a piston engine. Best of all, theoretically, is the "external combustion" Stirling engine which runs on the Carnot cycle, unlike standard internal combustion engines which use the theoretically non-ideal Otto Cycle. An ideal Carnot cycle engine is as efficient as can be achieved thermodynamically. However, a very good xxx cycle engine can of course be more efficient than a bad Stirling engine. Modern diesel engines do a very good job of making an inferior thermodynamic cycle look quite good. In practice, practical compact and power-dense Stirling engines have, so far, proved too hard to implement economically except in niche applications where cost is secondary. The main barriers are the extremely high sealing pressures and high temperatures which the engine needs to run at. Ideally a Stirling engine would use Hydrogen as the working gas but as this has the bad habit of diffusing out through the engine castings and leaking out through everywhere else at the temperatures and pressures involved, people usually compromise and use Helium, which is good but not as good as Hydrogen. Starting soon after WW2 Philips spent many tens of millions of dollars trying to commercialise this technology. They built vehicular demonstrators in conjunction with various automotive people including a van with Ford and a bus with ??AEG??. All attempts proved to have insurmountable problems with sealing. Along the way they did produce a very successful line of Stirling cryocoolers. This business was sold off when they rationalised their activities a decade or two ago. AFAIR Philips estimated that IF/ONCE the problems were solved that the payback time for the investment based on world petroleum savings would be about 4 months !!!!!!!!!!!!!!!!! :-). However, they also placed a rather large figure on the estimated cost of getting it right ($14 billion comes to mind but it was basically "heaps".) So far nobody has seriously risen to the challenge of multiplying their money several times over every year. A NZ designed & modestly successful Stirling combined-cycle heat and power system is selling internationally. Known as the "Whispergen" it produces approaching 1 kW of electricity and about ?4 kW of heat and is targeted at small off-grid applications. The price ($10,000 or so?) makes it unattractive financially compared to grid power where it is readily available. I believe the Swedes make/made a Stirling powered submarine run from heat of crystallisation from a thermal store. The major advantage is presumably very low noise operation. Various military applications exist. A niche market exists for free piston solar Stirling engines and various people have made 10 kW plus solar engines using large dish concentrators and typically liquid sodium as the heat transfer fluid. Russell McMahon -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics .