Bruce Simpson wrote in message . ..
On 22 Jan 2004 08:46:18 -0800, (robert arndt) wrote:



SNIP

Incorrect -- a gas-turbine is a constant combustion device,like a
ramjet and whereas a turbine has a rotating compressor, the ramjet
achieves an increase in static pressure by using a diffuser (go read
up on Bernoulli's theorum to see how that works.


During the 1920s and 1930s a German engineer called Holzworth deigned
and built for the German railways several "constant volume combustion"
gas turbines.

Also von Ohain while working at Heinkel also inspired the construction
of a 60kg thrust constant volume combustion jet engine that produced
60kg thrust. It was damaged in testing and not pursued because of the
urgency of other war time work.

Holzworths gas turbine consisted of a large water jacketed chamber
that was filled with compressed air via a large hydraulically
opperated poppet valve. The Hydraulic poppet valve was then closed,
the mixture ignited and then a second hydraulicaly opperated poppet
valve was opened to exhaust the mixture over a large water cooled
power turbine.

The whole thing opperated at about 50 cycles a second. A pair of
chambers and tubines coupled to a common shaft was used to provide
smooth power. The advantage being that the device was much less
sensitive to turbine and compressor efficiency, the combustion was at
a higher temperature becuase the intermittant nature allowed cooling.

Holzworths engines worked quite well on gas, liquid fuels. They
worked quite well on powdered coal though the abrasion on the turbines
was fairly high.

At one point it seemed that constant volume combustion would win out
over constant pressure combustion. Several projects were looked at by
the Germans as they seemed superior at both generating thrust and gas.
Some used conventional compresseors and systems of poppet valves and
spark plugs that needed to be elaborately sequenced. (this
comblicated things)

Von Ohain engine relied upon a sort of rotating combustion chamber
consisting of blades which partitioned the chamber into sections.
von Ohains engine does have a name (after the town it was built in)
can't recall right now.

All covered in Anthony Kay's book "German Jet Engine and Gas Turbine
development 1930 to 1945"


A lot of these things are worth looking at again.