From: gary@ke4zv.uucp (Gary Coffman)
Subject: Re: Continuing Steam-Car Discussion
Reply-To: gary@ke4zv.UUCP (Gary Coffman)
Organization: Gannett Technologies Group
Date: Fri, 20 Nov 1992 08:50:59 GMT

In article <1992Nov19.090350.12088@bsu-ucs> 01crmeyer@leo.bsuvc.bsu.edu (Craig Meyer) writes:
>
>> Steam engines normally use the wet steam as a cylinder lubricant. 
>> No additional oils are required. The "rings" are normally leather
>> wetted by the steam. In old locomotives, they lasted 6 months of
>> *continous* hard pulling between servicing. Remember that a piston
>> steam engine develops maximum torque at stall and is a low RPM 
>> device. Bearing lubrication can be a simple drip oiler.
>
>All I know is that the passage about the GM SE 101 steam car (in an
>industrical-arts textbook) said that they had to mix the lubricants with the
>steam at "elevated temperatures and pressures" and then separate it from the
>steam before heating.
>
>And that thing ran at just 370C (My mistake saying it was 700C)
>
>This may be good news, though, in that they WERE able to deal with it.  It may
>have been tricky, but they were SUCCESSFUL in lubricating the engine, albeit
>further development could perfect the system.
>
>Does this offset one of the big problems of 800C steam--lubrication?

Well stationary plants that operate at 800C don't use lubricants in the
steam because they use turbines. Hopefully there's no metal to metal
contact in areas reachable by the steam. In old piston plants, as I noted, 
they used the wet steam as a lubricant. I suspect that GM was trying to use
ordinary IC engine rings and thus needed lubricants in the steam.

>Could corrosion be successfully fought with newer corrosion-resistant
>materials?

Sure. Exotic materials are available, but using them in a mass produced
auto engine probably should be avoided for cost reasons. Ford did some
work on a *ceramic* engine that might be useful here. It was able to
operate without cooling. That's another issue with high superheats,
800C is in the annealing range for steel. Operating an iron engine in
that temperature range would reduce the hardness of the materials 
enough to markedly increase wear. 

The other issue with high superheats is how do you generate them?
A flash boiler probably won't do. That means the boiler and the
superheat exchanger would be much larger, startup time would go
from 30 seconds to several minutes, and much more live steam would
be in the system making it more dangerous in a collision.

>> That's hard to say. The very best superheat compound cycle steam plants
>> have an efficiency of around 50% while the best IC engines have an 
>> efficiency around 28%. To approach a big compound plant in a car though,
>> that would be really tough. I'd *guess* from what I've read that the
>> steam plant would be about 30% worse than the IC plant for the same
>> peak horsepower. One thing should be noted, however, the characteristics
>> of the two engines are wildly different and a lower peak horsepower steam
>> plant should offer the same driving characteristics as a bigger IC plant.
>
>That looks like a prescription for delivery vehicles & buses.
>
>Big-rigs would be big business, though.  I know the Carnot equasion and all,
>but practically, would raising the working temperature from 370C to 800C have
>a drastic effect on efficiency.  Carnot ideal for 370C: 36.7%  Carnot ideal for
>800C: 65.2%.  (But if even the stationary plants have trouble cracking 50%, why
>should we do any better, eh?)

Well naturally the higher the ideal value, the easier it is to approach
some lower practical value. But there are other issues to consider. For
mass production reasons, you want something simple, rugged, and reliable
that doesn't use exotic materials or difficult manufacturing techniques.
You'd also like it to run for at least 5 years with no major troubles.
You don't want it to fly apart until after you've collected the final
payment. :-)


Gary

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