Hybrid staged combustion-expander topping cycle engine

A thrust engine is disclosed in the form of a hybrid staged combustion-expander topping cycle engine. The engine comprises a mixed cycle, one cycle being an expander cycle (14) operating at low temperatures and the other being a staged combustion cycle (12) operating at a higher temperature. A portion of liquid hydrogen from a fuel pump (16) is passed in heat exchange relation with the engine nozzle (22) for cooling same and heating the hydrogen, and the heated hydrogen is passed to an oxidizer turbine (28) for driving a liquid oxygen pump (81). Another portion of the liquid hydrogen from the fuel pump is passed in heat exchange relation with the engine thrust chamber (21) and combustor (20), and a portion of the resulting heated hydrogen is introduced, together with a portion of the pressurized liquid oxygen from the liquid oxygen pump, into a preburner (20) for combustion therein, and passage of the combustion gasses to a fuel turbine (26) for driving the fuel pump. A portion of the liquid hydrogen discharged from heat exchange relation with the thrust chamber and combustor is introduced into the combustor, together with a portion of the liquid oxygen discharged from the liquid oxygen pump, for combustion and passage of the combustion gases to the thrust chamber and expansion in the nozzle. The combustion gases discharged from the fuel turbine are mixed with the hydrogen gases discharged from the oxidizer turbine, and such mixture is also introduced into the combustor.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to thrust engine systems, and is particularly 
directed to a hybrid staged combustion-expander topping cycle engine. 
2. Description of the Prior Art 
In the thrust engine, basically a set of propellants is pumped through a 
combustor and burn therein to provide thrust. Some of these engines are 
known as gas generators and some are staged combustion cycle engines. 
Staged combustion cycle engines are very high chamber pressure engines 
providing a large thrust. Thus they operate at very high system pressure 
and very high system temperatures. 
In a typical staged combustion cycle engine, both the fuel turbine and the 
oxidizer turbine are driven by preburners employing very high temperature 
gasses, of the order of 1900.degree. R. In such fully staged combustion 
cycles there is thus employed two preburners, one for each of the 
respective turbines. The gasses discharged from the turbines are combined 
and are introduced at very high temperatures into the thrust chamber of 
the engine. 
As between the gas generator cycle engine and the staged combustion engine, 
the latter is of higher performance. However, because of the high 
temperatures and pressures involved in the staged combustion engine and 
due to the presence of more components in such engines and high thermal 
stresses in the turbines, a greater potential for failure is present, thus 
reducing the reliability potential for such engines. 
SUMMARY OF THE INVENTION 
There is accordingly provided according to the present invention concept a 
mixed cycle engine, utilizing an expander cycle operating at relatively 
low temperatures and a staged combustion cycle operating at a higher 
temperature. Thus, the expander cycle is combined with the staged 
combustion cycle to gain greater reliability over the conventional staged 
combustion cycle engine without adversely affecting its performance to any 
substantial degree. 
In the resulting hybrid cycle engines, according to one embodiment thereof, 
preburner gasses are fed directly to the fuel turbine of the staged 
combustion cycle without dilution of such gases, and according to another 
embodiment the preburner combustion gasses are diluted with gasses 
discharged from the oxidizer turbine of the expander cycle, prior to 
introduction of the preburner combustion gasses into the fuel turbine of 
the staged combustion cycle. In the case of the latter hybrid staged 
combustion topping cycle embodiment, preburner gas dilution is used to 
develop required turbine power in a moderate thrust engine system with 
turbine operating temperatures substantially lower, e.g. of the order of 
1000.degree. R, lower than those of the conventional staged combustion 
cycle. 
To accomplish the cycle power balance at the lower temperatures, the main 
turbines of the expander cycle and the staged combustion cycle are run in 
series, with the low-power oxidizer turbine of the expander cycle upstream 
of the fuel turbine of the staged combustion cycle. A portion of the fuel, 
e.g. hydrogen, heated, e.g. to 600.degree. R by passage initially through 
the nozzle coolant jacket of the thrust engine is used to drive the 
oxidizer turbine. Another portion of the hydrogen fuel, after passage in 
heat exchange relation with the engine thrust chamber and combustor, is 
passed to the preburner of the staged combustion cycle, where it is 
combusted with oxygen to increase the fuel turbine flow rate and to 
provide high temperature combustion gases, to the inlet of the fuel 
turbine. In the dilution embodiment the preburner combustion gasses are 
cooled through mixing with the oxidizer turbine exhaust hydrogen to obtain 
a lower temperature hydrogen-rich mixture, e.g. of about 900.degree. R and 
of high enthalpy, before being introduced into the fuel turbine. The 
temperatures of the drive gasses are in all cases low enough to 
significantly reduce the thermal stresses and cooling requirements of the 
oxidizer turbine, fuel turbine and turbine exhaust collection manifolds. 
OBJECTS OF THE INVENTION 
It is accordingly one object of the present invention to provide an 
improved hybrid staged combustion-expander topping cycle engine. 
Another object is to combine a staged combustion cycle engine with an 
expander cycle engine which operates with lower turbine temperatures. 
A further object is the provision of an engine of the above type wherein 
the turbines operate at reduced temperatures without substantially 
reducing chamber pressures. 
A still further object of the invention is the provision of a hybrid cycle 
engine of the above type having greater reliability and reduced thermal 
stresses as compared to the fully staged conventional combustion cycle 
engine, with performance only somewhat lower to moderately lower than the 
conventional staged combustion cycle engine.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS 
FIG. 1 of the drawing is directed to one embodiment of the invention 
directed to an expander/staged combustion hybrid cycle engine without 
preburner dilution, indicated at 10. The engine is comprised of a staged 
combustion cycle, indicated generally at 12, in combination with an 
expander topping cycle, indicated generally at 14. The staged combustion 
cycle 12 comprises a fuel pump 16 for pressurizing the fuel, hydrogen in 
the present embodiment, and the expander cycle 14 comprises an oxidizer 
pump 18 for pressurizing oxidizer, oxygen in the present embodiment to a 
high pressure. Thus, as described in greater detail hereinafter, hydrogen 
and oxygen are pressurized to a high pressure and are conducted to a 
combustor 20 for combustion therein to a high temperature, and the 
resulting combustion gasses are passed through an associated thrust 
chamber 21 and into a nozzle 22 for expansion therein to generate thrust 
power. 
The staged combustion cycle 12 includes a fuel-rich preburner 24 to 
generate combustion gasses for the fuel turbine 26 which drives the fuel 
pump 16. 
The expander topping cycle 14 includes an oxidizer or liquid oxygen turbine 
28 driven by hydrogen gasses heated to a temperature lower than the 
temperature of the combustion gasses from the preburner 24, for driving 
the liquid oxygen pump 18. 
More particularly, for driving the staged combustion cycle 12 of the 
engine, hydrogen fuel at 30 is introduced into a fuel boost pump 32 and 
the initially pressurized fuel is introduced via a conduit at 34 into the 
fuel pump 16. Pressurized liquid hydrogen at a pressure of 8380 psi is 
discharged at 36 from fuel pump 16 and the major portion of such hydrogen 
at 38 is divided into two streams 40 and 42. A minor portion of 
pressurized liquid hydrogen at 36 is by-passed at 44 to the inlet of a 
fuel boost pump turbine 46 for driving the fuel boost pump 32, and the 
expanded hydrogen at 48 is combined with the pressurized hydrogen 
discharged from the fuel boost pump at 34. As an alternative to the liquid 
hydrogen by-pass at 44, a gaseous hydrogen drive may be employed for the 
fuel boost pump turbine 46. 
The stream of liquid hydrogen in a conduit at 40, constituting about 31.6% 
of the main hydrogen stream 36 passes through a first main fuel valve 50 
and then passes through a coolant jacket 52 of engine nozzle 22 for 
cooling the nozzle. The hydrogen gasses discharge from the coolant nozzle 
jacket and heated to a temperature of about 600.degree. R are conducted at 
54 to the inlet of the liquid oxygen turbine 28 for driving same. Thus, 
the expander cycle engine 14 is operated by a turbine 28 driven by heated 
hydrogen at a much lower temperature rather than by combustion gasses used 
to drive the fuel turbine 26 of the staged combustion cycle 12, and which 
are generally at a much higher temperature of the order of about 
1900.degree. R. 
The liquid hydrogen stream at 42 passes through another main fuel valve 56 
and is conducted at 58 in heat exchange relation with the thrust chamber 
21 and combustor 20, for cooling same, and the heated hydrogen gasses at a 
temperature of 229.degree. R are introduced at 60 into the preburner 24. 
Referring now to the expander topping cycle 14, oxidizer, specifically 
oxygen, at 62 is fed to a liquid oxygen boost pump 64 and the pressurized 
oxygen at 66 is introduced into the liquid oxygen pump 18 for further 
pressurization therein. Pressurized liquid oxygen discharged at 68 from 
pump 18 is divided into three streams. A minor stream of liquid oxygen at 
70 is introduced into a liquid oxygen boost turbine 72 which is used to 
drive the boost pump 64, and the expanded discharged oxygen stream at 74 
is mixed with the pressurized stream of liquid oxygen at 66 discharged 
from the liquid oxygen boost pump 64. 
The second liquid oxygen stream at 76 is introduced into a liquid oxygen 
kick or boost pump 78, and the pressurized liquid oxygen discharged at 80 
from pump 78, and at a pressure of about 9136 psi, which is substantially 
at the same pressure as the hydrogen stream 60, is introduced, together 
with such hydrogen stream, into the preburner 24. It is noted that the 
liquid oxygen turbine 28 drives the liquid oxygen kick pump 78, as well as 
the main liquid oxygen pump 18. 
Thus, liquid oxygen at 80 passes through preburner oxygen valve 82, and 
liquid hydrogen at 60, both at high pressure, are introduced into the 
fuel-rich preburner 24. In the preburner, the hydrogen and oxygen are 
combusted and the combustion gasses discharged at 84 from the preburner 
are at high temperature of about 1600.degree. R. These combustion gasses 
are introduced into the fuel turbine 26 for driving fuel pump 16, and the 
expanded combustion gasses are discharged at 86. These gasses are mixed at 
88 with hydrogen gas discharged at 90 from the liquid oxygen turbine 28. 
Since heated hydrogen at 54, from the nozzle coolant jacket 52, at moderate 
temperature, is used to drive the oxidizer turbine 28, the total enthalpy 
(flow rate x enthalpy per pound) of the hydrogen is comparable to the 
enthalpy of the liquid oxygen/hydrogen preburner combustion products at 84 
because of the difference of heat capacity of the two gasses, so that 
sufficient oxidizer pump power can be derived with a fraction of the 
thrust chamber hydrogen coolant flow. The combustor hydrogen coolant flow 
at 60 and combusted with oxygen in the preburner 24 increases turbine flow 
rate and temperature of the combustion gasses to approximately 
1600.degree. R. 
The mixture at 88 of expanded combustion gasses 86 from the fuel turbine 26 
and expanded hydrogen gasses at 90 from the oxidizer turbine 28 are 
conducted at 96, at a temperature of about 1090.degree. R and 3300 psi 
pressure, to the combustor 20 and thrust chamber 21. Also, the third 
stream of pressurized liquid oxygen 98 from the liquid oxygen pump 18 is 
passed through main oxygen valve 100 and into the combustor 20. Further, a 
portion of the liquid hydrogen 60 previously passed in heat exchange 
relation at 58 with the thrust chamber 21 and combustor 20, and at 
substantially the same pressure as the liquid oxygen at 98 and the mixed 
gasses at 96, is also introduced at 102 into the combustor 20 and thrust 
chamber 21. A flow orifice (not shown) allows for equalization of these 
pressures. Thus, the liquid oxygen and liquid hydrogen introduced into the 
combustor 20 together with the mixed gasses introduced at 96, are 
combusted therein, and such combustion gasses are passed into the nozzle 
22 for expansion therein and delivery of thrust power. 
It will be noted that a portion of the hydrogen stream 54 to the oxidizer 
turbine 28 is by-passed at 92 through an expansion valve 94 and mixed with 
the expanded oxidizer turbine exhaust at 90 to provide mixture ratio 
control trim, with the main oxidizer valve 100 providing the primary 
mixture ratio control function. 
It is thus seen that the hybrid engine 10 of the invention is driven by a 
mixed cycle, one being an expander cycle as shown at 14 using low 
temperatures and the other one being a staged combustion cycle at 12 at a 
higher temperature. As compared to the conventional staged combustion 
cycle engine employing two turbines, the fuel turbine and the oxidizer 
turbine, both of which are driven by preburners generating combustion 
gasses at very high temperature of the order of about 1900 to 2000.degree. 
R, the advantage of the concept of the present invention is that one of 
the turbines, requires non-combustion driving gasses, namely hydrogen 
gasses, at relatively low temperatures, and requires less power than the 
other turbine. Since the hydrogen gasses used to power one of the turbines 
are relatively cooler gasses this means that the turbine driven thereby 
will be exposed internally to lower temperatures, resulting in longer and 
more reliable life. 
FIG. 2 of the drawing illustrates schematically another embodiment of the 
hybrid engine of the invention employing a staged combustion cycle 103 in 
combination with an expander topping cycle 105, similar to 12 and 14 
respectively, of the embodiment of FIG. 1, but employing preburner gas 
dilution. In the engine of FIG. 2, the components common to the components 
of FIG. 1 bear the same reference numbers as in FIG. 1. 
In the embodiment of FIG. 2, instead of mixing the expanded hydrogen 
discharge gas at 90 from the liquid oxygen turbine 28, with the expanded 
combustion gas discharge at 86 from the fuel turbine 26, as in FIG. 1, the 
expanded hydrogen gas at 90 is mixed with the hot preburner combustion 
gasses at 84 to cool same prior to their introduction into the fuel 
turbine 26. Thus, a mixture of hydrogen gasses at about 420.degree. R is 
mixed with preburner combustion gasses at about 1600.degree. R to dilute 
same and form a gas mixture at 104 of a lower intermediate temperature of 
about 900.degree. R which is introduced into the fuel turbine 26. The 
expanded mixture of combustion gasses and hydrogen from the fuel turbine 
26, at a temperature of about 1100.degree. R, is then introduced at 106 
into the combustor 20 and the thrust chamber 21, together with the liquid 
oxygen at 98 and the liquid hydrogen at 102, for combustion to provide the 
mixture of drive gasses in the thrust chamber 21. Thus, while the 
introduction of the expanded hydrogen gasses at 90 into the preburner 
combustion gasses at 84 has the advantage of reducing the temperature in 
the fuel turbine 26, the expanded gasses therefrom at 106 and introduced 
into the combustor 20 are substantially at the same temperature as the 
mixture of gasses at 96 introduced into the combustor 20 in FIG. 1. 
The lower temperatures at the main turbines, and collection manifolds in 
the hybrid staged combustion-expander topping cycle engine of the 
invention, provide the hybrid cycle engine with essentially equal 
reliability potential as the expander topping cycle per se. With proper 
control, the invention engine, particularly as exemplified in the 
embodiment of FIG. 2, can be started and brought to intermediate mainstage 
thrust levels in the expander cycle mode without any possibility of large 
temperature overshoots of the combustion gases at 104, as in the 
conventional staged combustion cycle. The hybrid cycle of the invention 
can then be staged into full thrust by opening the preburner oxidizer 
valve 82 to achieve full power, thus avoiding the steeper start transient 
flow gradients and preburner mixture ratio deviations. 
It has been found that the hybrid expander-staged combustion cycle of the 
invention in its most reliable configuration, with preburner gas dilution 
as in FIG. 2, provides performance 8 seconds higher than the gas generator 
cycle and only 4 second lower than the staged combustion cycle. The hybrid 
cycle without dilution, as in FIG. 1, provides performance only 2 seconds 
lower than the staged combustion cycle. Typical engine perameters for the 
hybrid cycle without dilution illustrated in FIG. 1 and for the hybrid 
cycle with dilution illustrated in FIG. 2 are shown in the table below: 
TABLE 
______________________________________ 
HYBRID HYBRID 
WITHOUT WITH 
ENGINE DILUTION DILUTION 
AMETER (FIG. 1) (FIG. 2) 
______________________________________ 
Fuel Turbine 1600 904 
Inlet Temp, 
.degree.R. 
Oxidizer Turbine 
597 460 
Inlet Temp. 
.degree.R. 
Fuel Main Pump 8380 9084 
Outlet Pres., 
psia 
Oxidizer Main Pump 
4593 3811 
Outlet Pres., 
psia 
Oxidizer Kick Pump 
9136 7664 
Outlet Pres., 
psia 
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From the foregoing, it is seen that the invention provides an improved 
hybrid staged combustion-expander topping cycle engine comprised of a 
mixed cycle including an expander cycle operating at low temperatures and 
a staged combustion cycle operating at a higher temperature, and reducing 
the overall temperatures of operation as well as the thermal stresses and 
cooling requirements of the oxidizer turbine, fuel turbine, and turbine 
exhaust collection manifolds. 
It is to be understood that what has been described is merely illustrative 
of the principles of the invention and that numerous arrangements in 
accordance with this invention may be devised by one skilled in the art 
without departing from the spirit and scope thereof.