gas turbine load / speed questions

[schwee]

I hate to belabor the point, and please pardon my stupidity, but:

Why aren't gas turbines widely used in cars?

From what I can gather, it's because they have a narrow load/speed range, because they have poor throttle response, and because they really eat fuel at idle.

OK. Let's say I had a way of varying the pressure and volume of air coming into the power turbines, though, independent of the compressor. Say, a big steam accumulator.

Say I have a turbine that idles at 60,000 rpm and delivers its best power at 80,000 to 95,000 rpm. I don't even know what this means, exactly.

If I load the output shaft of the turbine at 80,000 rpm, could I not continue to increase my steam flow such that I kept at 80,000 rpm at that load? And if so, at what load would no amount of increased steam flow be sufficient to hold the speed? What determines that?

Similarly, if I started at 80,000 rpm and loaded the shaft at a slower rate than I increased the steam flow, it would stand to reason that I would increase turbine speed, to say, 95,000 rpm. What limits how fast I can go?

Taking that argument further, why couldn't I start loading right from 60,000 rpm, or from zero?

Say the power turbine is stalled. I direct a jet of steam at it, and at the same time apply a load. Why can't I get any decent power out of it, even if I'm blasting a large volume of steam at high speed and pressure at it?

The propeller on a 100 hp outboard boat motor gives pretty good power from 0 rpm to 2000 or 7000 or whatever it is rpm. There are no gears. Isn't this situation analogous to a turbine, except it's in water rather than air, and it's shaft turning propeller, rather than propeller (turbine) turning shaft?

Again, sorry to be so stupid.

-- Schwee

 

[balu1]

Gas turbines (GT) are used on modern tanks. They have been used on some locomotives and trucks but never a steam turbine (ST) has been used (except maybe for some experimental purposes). They are used only on large ships as well as gas turbines on smaller battle ships. Obviously size of a practical ST power plant is an un-resolving obstacle.

Car usage is impractical due to transmission size (reduction from 80,000-100,000 down to 1,000 rpm), efficiency-high specific fuel consumption (higher than Otto engine) and minimum power output which is rather high (the smaller GT power the worse efficiency). Price is also high but mass production would probably solve that problem.

If you care to browse turboshafts (helicopter GTs) and turboprops (those would be appropriate for automobile applications) the smallest units are well in excess of 200 SHP. Therefore GTs may be used on Rolls-Royce and similar cars where price and economy do not matter.

Additional problem is a noise but that I believe can be reduced to acceptable level if there is enough money.

 

[zqew05]

Decades ago General Motors had a gas turbine show car but it sucked up so much fuel. An AVCO Lycoming TF40 turbine was being researched for use on a locomotive, it was feasable and economical on long distance routes with minimum stops, and it also met tough emmission standards better than diesels. The Abrams tank is the only tank with turbine power packs. There never was a gas turbine on battleships, there were gas turbines on Navy destroyers. Battleships had steam turbines. Abrams tanks probably have the best noise silencers around because it is no noiser than a diesel.