Aeronautics and astronautics – Spacecraft – With fuel system details
Reexamination Certificate
1998-09-29
2001-04-10
Poon, Peter M. (Department: 3644)
Aeronautics and astronautics
Spacecraft
With fuel system details
C244S199100, C060S204000
Reexamination Certificate
active
06213431
ABSTRACT:
This application claims the benefit of the filing of South African provisional application No. 978749, filed Sep. 30, 1997.
BACKGROUND OF THE INVENTION
The invention relates to rocket engines and, in particular, to an aerospike rocket engine.
Conventional rocket engines use round, bell-shaped nozzles. These nozzles, however, have an inherent limitation in that the combustion gas, or plume inside the nozzle can expand only as far as the shape and length of the nozzle allow, resulting in substantial under and/or over expansion, with a resulting loss of thrust and instability/vibration of the expanding plume. Bell nozzles are, therefore, typically designed for specific applications, e.g., take-off, high altitude, or outer space. However, even within the confines of these applications, under/over expansion invariably occurs due to 1) changes in atmospheric pressure, and 2) a finite expansion capability of approximately 1:400 (where infinite expansion is theoretically required in space), which may result in up to 5% loss of thrust. See, e.g.,
Missile Engineering Handbook,
van Nostrand, FIG. 7.1.1, 1957;
Aviation Week
&
Space Technology,
p. 130, Aug. 10, 1987). Therefore, a bell nozzle having a given size and shape can reach peak efficiency only at an altitude where the plume expansion within the nozzle equals the theoretical expansion that would be permitted by the atmospheric pressure at that altitude.
To overcome the bell nozzle's limitation, Rocketdyne Propulsion and Power (“Rocketdyne”), a subsidiary of the Boeing Co., developed a nozzle which resembles a bell nozzle turned inside-out called an “aerospike” nozzle. More specifically, a linearized version of the aerospike nozzle called a “linear” aerospike nozzle was developed for the proposed X33/VentureStar single-stage-to-orbit (“SSTO”) space plane project. The linear aerospike engine resembles a bell-shaped nozzle that has been split in half and the two halves put back-to-back to each other, and the end of nozzle clipped or truncated. In some cases, however, the linear aerospike engine may have only one of the two halves, i.e., a single-sided engine. Because the plume of the aerospike nozzle is manifested on the peripheral of the nozzle, it is free to expand, limited only by atmospheric pressure. As a rocket using the aerospike nozzle climbs higher and higher, the plume is able to expand continuously against the decreasing atmospheric pressure, albeit at a cost to the thrust vector which diverges progressively sideways.
Referring to
FIG. 1
, there is shown a bank numerical reference
11
of five linear aerospike engines
10
arranged side-by-side. Each aerospike engine
10
comprises a rectangular wedge or tapered body
12
, a slanted or curved reaction surface or plane
14
, a leading end
16
and a trailing end
18
. Each engine
10
has at least one injector
20
or, more typically, a set of injectors
20
adjacent the leading end
16
and arranged to direct a propellant or fuel down the reaction plane
14
towards the trailing end
18
. Upon combustion of the propellant or fuel from the injector
20
, the combustion gas, or plume, travels down the reaction plane
14
and exerts propulsive pressure on the reaction plane
14
, which provides the thrust for the space plane.
As can be seen, turning to
FIGS. 2A-2C
, the linear aerospike design allows the plume to expand freely against atmospheric pressure. At low altitude, the exhaust plume
24
is held in a fairly narrow band
26
by the high atmospheric pressure as shown in FIG.
2
A. However, referring to
FIG. 2B
, at high altitude and low atmospheric pressure, the plume
24
is able to expand. Shock waves produced by the supersonic speed of the space plane at high altitude provides a shock front
28
that can assists in resisting the expansion of the plume
24
. As the space plane
22
climbs into outer space, the vacuum of space may tend to pull the plume
24
away from the reaction plane
14
, as shown in FIG.
2
C. This may result in “divergence,” wherein the plume's
24
thrust vectors becomes misaligned with the direction of flight, resulting in a decrease in net thrust and, hence, engine efficiency.
One solution to this divergence syndrome is to extend the reaction plane
14
so as to facilitate full expansion of the plume
24
. However, because the plume
24
is unconfined, the boundary layer may tend to separate from the reaction plane
14
. Boundary layer separation is a lifting off or peeling away of the plume
24
from the reaction plane
14
. According to Bernoulli's law, as long as the boundary layer remains sufficiently energized, the plume
24
will adhere to the reaction plane
14
by virtue of the negative pressure between the high-speed boundary layer and the reaction plane
14
. As the plume
24
travels along the reaction plane
14
, the boundary layer may run out of energy and separate from the reaction plane
14
. The effects of boundary layer separation include instability or turbulence which can produce severe mechanical vibrations that can damage the space plane
22
. In addition, boundary layer separation may result in a loss of thrust and engine efficiency. Separation usually starts at the end of the boundary layer where the energy of the boundary layer is low. Atmospheric pressure can help to hold the plume
24
against the reaction plane
14
. Therefore, separation is more likely to occur at high altitude where the atmospheric pressure is low.
One way of preventing boundary layer separation is by truncating the reaction plane
14
so that the reaction plane
14
is shorter (as can be seen in published illustrations of the X33). This allows the boundary layer to traverse the entire length of the reaction plane
14
before running out of energy. The trade-off, however, is that there is a reduction in thrust and engine efficiency relative to an untruncated reaction plane due to 1) under expansion, and 2) thrust vector diversion/deflection. Furthermore, the shorter reaction plane
14
may not allow the propellant or fuel sufficient time to completely combust/accelerate before reaching the end of the reaction plane
14
, which can result in reduced thrust on the reaction plane
14
. This reduction in thrust may be critical at high altitudes where the space plane needs to attain very high velocity.
Over and above the truncation limitation of the X33 implementation of the aerospike engine, scaling up of the aerospike plan form to suit larger space plane applications (e.g., the proposed VentureStar heavy lift shuttle) may additionally require cascaded or staged propellant/fuel injection in lieu of the impact of dimensional scaling.
SUMMARY OF THE INVENTION
As mentioned above, a conventional linear aerospike engine may be inefficient for powering very large space planes or other vehicles because of the reduction or loss of pressure due to truncation of the engine wedge. The present invention provides means for maintaining and/or increasing the pressure across the reaction plane to thereby enhance the thrust of the engine, and for reducing the divergence or deflection of the thrust vectors. The present invention also provides means for preventing or inhibiting boundary layer separation from the reaction plane.
In general, in one aspect, the invention is related to a rocket engine comprising a tapered body, a slanted reaction plane on the body, and means for increasing propulsive pressure on the reaction plane. In one embodiment, the means for increasing propulsive pressure on the reaction plane may be a first fuel injector adjacent a leading end of the engine and injecting a first fuel on the reaction plane and a second fuel injector between the leading end and a trailing end of the engine and injecting a second fuel on the reaction plane. The first fuel and the second fuel may be cascaded on the reaction plane, and may be of the same type, or two different types of fuels.
In another embodiments, the means for increasing propulsive pressure on the reaction plane may be a means for inducing a vortex on the reaction plane substanti
Palo Francis T.
Poon Peter M.
Rosenthal & Osha L.L.P.
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