Handbook of Turbomachinery Second Edition Revised - Ventech!

740 ft/sec. The turbine pressure ratio at these conditions is approximately
1.4.
Expander cycle engines have been designed, built, and successfully
operated by several major rocket engine manufacturers. One of these is (to
this author) of particular interest. The engine in question is a prototype built
by the Liquid Rocket Division of Aerojet General. This engine is powered
by LOX/LH 2 and is in the 3,750-lb thrust class, to be used for an orbital
transfer vehicle-type application. To obtain weight savings and reduce
complexity in the LOX pump, an extension of the expander cycle known as
the dual expander is employed (see Fig. 5). In this concept, the main
combustion chamber is constructed separately from the nozzle. These two
sections are mechanically joined together. As can be seen in Fig. 5, each
section employs a separate regenerative cooling circuit. In this implementation,
LOX is heated to a supercritical state in the main combustion chamber
cooling circuit, while LH 2 is heated to supercritical conditions in the nozzle
jacket. The resulting gaseous oxygen (GOX) (at a temperature of 860 8R) is
used for turbine drive in the LOX turbopump, and GH2 for fuel pump
turbine drive. The advantage here is derived from the fact that the oxidizer
turbopump is being driven by the same fluid as is being pumped. Whereas in
oxidizer pumps being driven by a hot-gas turbine (where the hot gas is
generally hot fuel) an elaborate shaft sealing system with inert gas purges is
necessary to isolate pump and turbine fluids, the dual expander cycle
eliminates this requirement.
The other example of a closed engine cycle that we wish to discuss is
the staged combustion cycle. At the time of this writing (January 1993) the
only example of this type of engine that is in production in the United States
is the Space Shuttle main engine. Japan is in the final stages of development
of a staged combustion engine (the LE-7, which is also powered by LOX/
LH2). Actually, it appears (to this author) that the former Soviet Union
possesses the greatest experience with this type of engine cycle, having been
in production of at least three different models for a period of nearly
30 years.
The staged combustion cycle is shown schematically in Fig. 3. Please
note that this cycle, like the expander cycle, places the turbine(s) in series
with the main combustion chamber. However, unlike the expander, the
staged combustion cycle also places a gas generator (referred to in this cycle
as a preburner) between the pump discharge and the turbine package. Also
note that two independent preburners may be employed, as is done in the
Space Shuttle main engine. Together with LOX throttling valves at the inlets
of both preburners, this arrangement gives independent control of both
main combustion chamber pressure and engine mixture ratio. When coupled
with a high main combustion chamber pressure target, this cycle can place
Copyright © 2003 Marcel Dekker, Inc.