Alternative engines

[M. Jones]

Use a two-spool machine, like a PT-6.  The gas producer screams along at 
20,000-30,000 rpms, while the power turbine spins at a leisurely 6,000 or 
something.  For automotive use, hydrostatic drive from there.  Most turboprop 
aircraft spin the prop at something less than 2,700 rpms max (geared only), so 
it's obviously do-able.  BUT would you want to?   Not for anything other than 
fun.

By way of example, with the industrial gas turbines I'm most familiar with (I 
manage power plants for a living) the gas producer spins at 11,270 rpms, the 
power turbine at 8550 rpms and is then geared to 1800 rpm generator speed. 
 Works great, with excellent efficiency at full load (especially in 
cogeneration service with a steam turbine in service).  Heat rate drops like a 
rock at anything below 90% load.  Fully 67% of the energy produced by a gas 
turbine goes solely to keep itself sustained and internally cooled.  Most gas 
turbines will not self-sustain below 60% gas producer speed.

Gas turbines may find use in a hybrid scenario -- start and run at max tilt to 
charge a battery bank or flywheel, then off when not needed.  But I strongly 
doubt you'll ever see gas turbines used directly in automotive applications.

Mike Jones


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From: 	William T Wilson[SMTP:fluffy at snurgle.org]
Reply To: 	diy_efi at efi332.eng.ohio-state.edu
Sent: 	Thursday, April 22, 1999 6:43 PM
To: 	'diy_efi at efi332.eng.ohio-state.edu'
Subject: 	RE: Alternative engines

On Thu, 22 Apr 1999, Kurek, Larry wrote:

> Huh? How does it accelerate if it has no torque? Maybe they just
> didn't gear it correctly. Maybe a CVT type of transmission is needed
> to keep the rpm up and multiply the torque accordingly. With
> electronic controls, it would be

Maybe.  Don't most turbines spin something like 30,000 RPM?  It's a lot.
And they don't really produce any torque at all until they get up to a
substantial portion of that.  You'd need a 20:1 final drive ratio to get
"normal" performance, so that won't do.  What I would recommend is a
reduction before you feed into the transmission.  Before the clutch, even.
I wouldn't trust most transmissions to take that much RPM on the input.