Kevin Crosby said the following to Jim Dunmyer on the subject of
RE: ENGINE DESIGN (16 Oct 97  20:06:06)
 KC> Turbines have their own unique problems also.  A turbine is
 KC> inefficient at low speeds, so you have to factor in the added weight of
 KC> gear reduction to reuce the uotput to a usable RPM.
 KC> Also, the higher speed causes some difficulties with coolant and oil
 KC> circulation.  Generally, coolant and oil pumps operate at a relatively
 KC> low RPM, requiring yet more complexity to drive them at appropriate
 KC> speeds. Higher shaft speed will also result in accelerated bearing
 KC> wear, unless the lubricating oil is kept scrupulously clean and
 KC> continuously fed.
 KC> Turbines generally run at a much higher temperature, with accompanying
 KC> problems created for the cooling system.  Exhaust temperatures may
 KC> also be rather high.
 KC> I will admit that my turbine experience has been with steam and gas
 KC> turbine marine propulsion, so I may not be aware of methods by which
 KC> these problems can be solved in an automotive application.
 KC> Kevin
You have the right idea, Kevin. The marine turbines you delt with had
really huge horsepower ratings though with a relatively low load factor.
The car is much less demanding since maybe only 1/1000'th of that amount
of power is needed.
Taking for example lubrication it then becomes a much simpler problem.
An air bearing can be used and entirely side step the problem. This is
not a new idea and is currently used in a number of devices such as for
example your computer's hard disk which is rated to withstand quite a
few G's of shock.
As for the power transmission problem, it can also be side stepped by
using an electric drive system. This means torque is also no longer a
problem either. Remember diesel-electric trains can't use a mechanical
transmission because metals won't withstand the huge torque involved.
It is entirely common sense that the technology must be scaled to the
application. To make an assumption from your previous experience with
huge marine turbines and then apply it to the personal car is not quite
being realistic. After all we're not putting a ship's engines in a car.
With this skewed image it's really no wonder then that we all uphold a
somewhat negative bias against the use of a turbine in a car.
I see the problem as simply a question of scale not the technology.
For example a rocket motor is a rocket motor no matter what size it is.
However the payload is what dictates how much propulsion is needed.
 Mike
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