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| Re: Here's the problem with gas-turbine trains (321856) | |||
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Re: Here's the problem with gas-turbine trains |
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Posted by WillD on Tue Oct 10 03:24:09 2006, in response to Re: Here's the problem with gas-turbine trains, posted by RonInBayside on Tue Oct 10 01:05:19 2006. Axial flow turbojets of the type used were the worst in that they were most efficient at high altitude.I've always wondered how these trains would have worked out if they'd gone with a centrifugal flow turbine which may have been better suited to this role. Chrystler built a gas turbine powered car which used a single stage compressor and turbine with a pair of regenerators to both increase incoming post compressor temperatures and decrease exhaust gas temperatures. I've always wanted to see something like that increased in size and power to the point where it could power a train, but we keep using helicopter engines which are utterly unsuited to the task. That's not to say the Chrystler turbine was not without problems, in the 1960s it may have had better fuel economy and better emissions than gasoline engines of the day, but today it'd look like a fuel hog and smoke belcher. There also were technical problems with sealing the regenerators and apparantly they had a tendancy to break down under the heat, something that could possibly be remedied with modern materials technology. The Navy uses gas turbines to power ships because there's no other way, short of a nuclear reactor, to get a big warship up to 30+ knots. An oil fired steam powerplant will get a warship up to 30 knots, after all that's what the battleships and cruisers in WWII used, it just requires a large plant which takes up more room and possible payload. The same thing applies to nuclear powerplants, where a significant portion of the belowdeck area of nuclear powered cruisers had to be given to their powerplant. The gas turbine powerplant had a siginificant impact because it allowed a fairly lightweight powerplant which could be placed fairly high in the hull with only an increase in the stack requirements. Gas turbines are also extremely quiet in terms of noise radiated into the water and that noise can be reduced to nearly zero by turning off the gas turbines without a significant impact on the system's response time. This is unlike a steam plant, either conventional or nuclear, which always has to be running to maintain a head of steam, and that operation creates noises which are harder to isolate from the sea. The first US Navy ships with gas turbine powerplants, the Spruance class destroyers, were renowned for 'sneaking up' on submarines and at times operating offensively against submerged targets in exercises. Incidentally it's unlikely that a diesel powerplant could be designed to deliver the kind of power modern US cruisers and destroyers have while fitting into the hull. However, navies which maybe desire a bit better fuel efficiency or don't want to be cruising around with gas turbines all the time go with a Combined Diesel and Gas or CODAG powerplant arrangement. Here a fairly fuel efficient set of diesels provides power for cruising, while gas turbines supplement them for high speed or other high power applications. Here in the states the USCG's Polar Star class ice breakers use CODAG with something like 18000hp available from the diesels and 75,000hp from the gas turbines. http://en.wikipedia.org/wiki/Combined_diesel_and_gas Similarly, the Abrams tank can shoot accurately while rolling 40 mph over open ground, which makes it an incredibly powerful weapon, and the gas turbine is hat allows 70+ tons to get to that speed relatively quickly. But it sucks fuel like it's going out of style! Right on the second part, somewhat incorrect on the first part. The M1's ability to shoot accurately at relatively high speeds is quite independent of the gas turbine powerplant. The British Challenger II uses a V-12 powerplant, uses a similar gun, and by all accounts has every bit the lethality as the M1. Also the German Leopard 2 uses the exact same gun as the M1, and is widely regarded as its equal, but it uses a 1500hp V-12 diesel. The US Army may be regretting the use of gas turbines in the M1s since it creates an enormous maitenance tail in terms of both fuel and spare parts. I did see something on FAS.org that the possible M1A3 or M9/10/11/12 (or whatever they're up to) replacement for the M1A2 would use a hybrid powerplant with either a diesel or gas turbine powerplant to reduce the tremendous fuel demand the M1 brings to the battle. |
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