Path: santra!tut!draken!kth!mcvax!uunet!tektronix!sequent!mntgfx!mbutts From: mbutts@mntgfx.mentor.com (Mike Butts @ APD x1302) Newsgroups: alt.fusion,sci.space,rec.autos.tech Subject: Stirling engines & fusion, rev. 2 Keywords: stirling engines fusion Message-ID: <1989Apr25.132913.1300@mntgfx.mentor.com> Date: 25 Apr 89 20:29:10 GMT Organization: Mentor Graphics Corporation, Beaverton Oregon Lines: 79 Xref: santra alt.fusion:643 sci.space:9430 Several have pointed out that my earlier posting was wider than 80 columns. Sorry about that. Here's a narrower version with a few technical points refined and with references. The subject of Stirling engines has come up in sci.space and alt.fusion. I found a very good article in the McGraw-Hill Encyclopedia of Science and Technology, complete with diagrams of several forms, graphs of power and efficiency vs. temperature difference, photos of actual engines, and references. I'll try to summarize here, but it's worth looking at the article. The Stirling Engine converts any form of heat differential into mechanical work. It has a cold end and a hot end, with a sealed working fluid (hydrogen) which is put through a pressure/volume/temperature cycle: Compress it on the cold end, shift that compressed gas to the hot end, where it expands against the piston, shift the hot uncompressed gas to the cold end where it is cooled and compressed again. The work from hot expansion exceeds the work of cold compression. The efficiency depends primarily on the difference between the hot and cold temperatures, according to the Carnot cycle, and secondarily on a large number of engineering factors. Actual engines have been built in the 10HP to 500HP range per cylinder. Pictures of two engines are shown, one built by Philips in Holland and the other by GM. Since they work from steady heat, these engines have a burner at one end, burning anything from gasoline to olive oil. Cooling is done with water and a radiator, as in a car. The efficiency- temperature curve shows up to 40% efficiency has been measured on an actual engine, with a burner temperature of 800 degrees C. This drops below 5% at 250 degrees C. Coolant temperature is 15 degrees C. Raising the coolant to 60 degrees C lowers max efficiency (as I read the curves) to 35%. The working fluid cycles between 800 degrees and 150-200 degrees C at max efficiency. The approximate heat balance is 40% work, 10% burner exhaust, and 50% into the cooling system. Since the engine has a closed cycle, far more heat is dissipated by the cooling system than with internal combustion, where the exhaust carries away most of the waste heat. Thus the cooling system must be much larger than in cars. The torque is nearly constant per rotation and over speed for four-cylinder engines. Speed is controlled by varying the pressure of the working fluid. The engine is completely balanced, the pistons move according to sinusoids, and there are no explosive power events, so it is extremely smooth and quiet in operation. (I want to drive one of these!) We can easily imagine a palladium fusion reactor mounted to the head of a Stirling engine. The operating temperature is extremely important, as that determines efficiency. 800 degrees C is below the melting point of palladium, so we may hope that such an engine will come to pass. If the cost and efficiency are right, we might see fusion-driven Stirling engines running cars (which are very clean and quiet and have enormous grilles). An engine like that would also be ideal for a home power station, generating electricity from the crankshaft and heating the house with the coolant. If such a device could be manufactured economically, it would be a tremendous boon to developing nations, who could get high-grade power where and when needed, without big capital investments in power stations and distribution systems, and without the pollution and economic miseries of oil. If and only if Pons is right, if enough palladium or a substitute can be found, cheap enough, if it's as free of radiation as Pons says it is, if it can be made to run at a high enough temperature for thermal efficiency, if it can be engineered, if it is appropriate for intermittent use, etc. Very big ifs, but we will certainly see! Please followup to alt.fusion. References (from McGraw-Hill Encyclopedia): M.J.Collie, Stirling Engine Design and Feasability for Automotive Use, 1979. G. Walker, The Stirling Engine, Scientific American, 229(2):80-87, 8/73. G. Walker, Stirling Engines, 1980. -- Michael Butts, Research Engineer KC7IT 503-626-1302 Mentor Graphics Corp., 8500 SW Creekside Place, Beaverton, OR 97005 ...!{sequent,tessi,apollo}!mntgfx!mbutts OR mbutts@pdx.MENTOR.COM Opinions are my own, not necessarily those of Mentor Graphics Corp.