Note: Descriptions are shown in the official language in which they were submitted.
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PLENUM AIR PREHEAT FOR COLD STARTUP OF LIQUID-FUELED PULSE
DETONATION ENGINES
BACKGROUND OF THE INVENTION
The present invention relates to pulse detonation engines, and in particular
to
liquid-fueled pulse detonation engines and using plenum air preheat for
startup.
Current research in the area of aviation propulsion has led to the
development of pulse detonation combustors (PDCs). Pulse detonation combustors
produce pressure rise from periodically pulsed detonations in fuel-air
mixtures,
resulting in a relatively high operational efficiency when compared to the
operational
efficiency of a conventional gas turbine engine.
As the use of pulse detonation engines/combustors grows, they are being
used in a wider variety of applications. Many of those applications involve
starting
pulse detonation engines from startup and/or in cold environments. This is
true in
either power generation or aviation applications. However, because of the
nature of
the operation of PDCs, in particular those using liquid fuel, combustor
initiation
(startup) can be difficult, especially in cold environments.
SUMMARY OF THE INVENTION
In an embodiment of the present invention, a power generation system
contains a compressor stage which compresses a flow passing through the
compressor
stage, a plenum stage downstream of the compressor stage which receives a
first
amount of the flow from the compressor stage, wherein the plenum stage
comprises at
least one pre-burner which receives a second amount of the flow from the
compressor
stage and uses the second amount of the flow to burn a fuel within the plenum
stage;
and a combustor stage positioned downstream of the plenum stage and having at
least
one pulse detonation combustor positioned therein. At least some of the first
amount
of the flow and at least some of the combusted second flow from the plenum is
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directed to the combustor stage and combined with a second fuel to create
either a
deflagration or a detonation within the combustion stage.
As used herein, a "pulse detonation combustor" PDC (also including PDEs)
is understood to mean any device or system that produces both a pressure rise
and
velocity increase from a series of repeating detonations or quasi-detonations
within
the device. A "quasi-detonation" is a supersonic turbulent combustion process
that
produces a pressure rise and velocity increase higher than the pressure rise
and
velocity increase produced by a deflagration wave. Embodiments of PDCs (and
PDEs) include a means of igniting a fuel/oxidizer mixture, for example a
fuel/air
mixture, and a detonation chamber, in which pressure wave fronts initiated by
the
ignition process coalesce to produce a detonation wave. Each detonation or
quasi-
detonation is initiated either by external ignition, such as spark discharge
or laser
pulse, or by gas dynamic processes, such as shock focusing, auto ignition or
by
another detonation (i.e. a cross-detonation tube). The geometry of the
detonation
chamber is such that the pressure rise of the detonation wave expels
combustion
products out of the pulse detonation combustor and produces a high speed, high
temperature and high pressure exhaust stream. Useful work and power are
extracted
from this exhaust stream, using a downstream multi-stage turbine. As known to
those
skilled in the art, pulse detonation may be accomplished in a number of types
of
detonation chambers, including detonation tubes, shock tubes, resonating
detonation
cavities and annular detonation chambers.
BRIEF DESCRIPTION OF THE DRAWINGS
The advantages, nature and various additional features of the invention will
appear more fully upon consideration of the illustrative embodiment of the
invention
which is schematically set forth in the figures, in which:
FIG. 1 is a diagrammatical representation of a pulse detonation combustion
system in accordance with an exemplary embodiment of the present invention;
FIG. 2 is a diagrammatical representation of a pulse detonation combustion
system in accordance with another exemplary embodiment of the present
invention; and
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FIG. 3 is a diagrammatical representation of a pulse detonation combustion
system in accordance with a further exemplary embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be explained in further detail by making reference
to the accompanying drawings, which do not limit the scope of the invention in
any
way.
FIG. 1 depicts a diagrammatical representation of an exemplary embodiment
of the power generation system 100 of the present invention. As shown, this
embodiment of the invention includes a compressor stage 101, a plenum stage
103
which contains pre-burners 105, an inlet valve portion 107, a combustor stage
109
which contains one or more PDCs 113 and a turbine stage 111.
As used herein, the power generation system 100 is not limited to any type of
power generation application. It is contemplated that embodiments of the
present
invention can be employed as ground based power generation machines such as
electrical power generators and the like, and propulsion type devices such as
turbofans, turbojets, ramjets or scramjets and the like. The present invention
is not
limited in this regard.
The compressor stage 101 is a conventionally known or used compressor
stage which uses an amount of work to create a pressure rise of the fluid flow
through
it. In an embodiment of the present invention, the fluid is air. The
compressor stage
101 can be made up of multiple stages or a single stage. The present invention
is not
limited in this regard.
Downstream of the compressor stage 101 is a plenum stage 103, which
receives the compressed fluid from the compressor stage 101. In an exemplary
embodiment of the present invention a percentage of the compressor flow enters
the
plenum stage 103, whereas a remaining percentage is used by the pre-burners
105. In
the embodiment shown in Fig. 1 three (3) pre-burners are shown. However, the
present
invention is not limited in this regard as it is contemplated that more or
less pre-
burners 105 can be utilized depending on performance and operational
parameters.
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The pre-burners 105 are employed to add additional heat to the compressor
flow (the temperature of the compressor flow does increase due to the
compression
process) prior to entering the inlet valve 107 or combustion stage 107.
Due to the operational nature of PDCs it is difficult to start PDCs in cold
environments or from a dead stop. This is particularly true in PDCs which use
liquid
fuel because the compressor flow temperature, by itself, is often insufficient
to
vaporize the liquid fuel. Fuel vaporization is beneficial to the PDC process,
particularly in startup conditions. To aid in this process, the present
invention pre-
heats the compressor flow to a level which makes it easier to start the pulse
detonation
process.
In an embodiment of the present invention, the pre-burners 105 are constant
pressure deflagration devices which use a portion of the compressor flow FPB
combined with a fuel to heat a remaining portion of the compressor flow within
the
plenum stage 103. The fuel used can be any known or used fuel, and depending
on
the embodiment, may or not come from the same fuel source used for the
combustion
stage 109. In an embodiment of the invention, the pre-burners 105 can be
similar to
v-gutter designs used in existing afterburners on aircraft propulsion systems
or could
be discrete burners (similar to DACRS burners). It is contemplated that each
of these
types of burners would be located within the flow path as described.
In an exemplary embodiment of the present invention, a portion of the
compressor flow is directed to the pre-burners 105 (FPB) via a manifold
structure. In a
further embodiment of the invention, the amount of compressor flow to the pre-
burners FPB is regulated by a control device (not shown), such that the heat
produced
by the pre-burners 105 is controlled based on operational parameters. In a
further
exemplary embodiment, after PDC startup or initiation, the pre-burners 105 are
shut
down and the compressor flow simply bypasses the pre-burners 105.
During operation of an embodiment of the present invention, at the startup of
the system 100, the pre-burners 105 are operating, using a portion of the
compressor
flow FPB, while a remaining portion of the compressor flow F is directed to
the
plenum 103 directly. In an exemplary embodiment of the invention, the majority
of
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the compressor flow F is directed directly to the plenum 103 and a smaller
amount of
the flow FPB is used by the pre-burners 105. Within the plenum 103 the
compressor
flow F is mixed with the combustion gas from the pre-burners 105. This mixing
raises the overall temperature of the fluid flow through the plenum 103 and
into the
inlet valve(s) 107. In an embodiment of the invention, the temperature of the
fluid
within the plenum 103 is raised to a temperature which facilitates and/or aids
in the
vaporization of the fuel used in the combustion stage 109 of the system 100.
Lobed
mixer elements, vortex generators or other mixing geometric features can be
used to
help promote mixing of the main flow with the combustion gas from the pre-
burners
105.
In an embodiment of the present invention, the temperature of the fluid
within the plenum 103 is raised to approximately 700 degrees F using the pre-
burners
105. In another embodiment of the present invention approximately 5 to 10% of
the
compressor flow is directed to the pre-burners 105, whereas the remaining flow
is
directed directly to the plenum 105.
In an embodiment of the present invention the overall percentage of the flow
to the pre-burners 105 FPB can be increased or decreased to achieve the
desired
temperature increase within the plenum 103. However, it is noted that the
percentage
of the flow FPB should not be such that there is an insufficient amount of the
remaining flow F to facilitate combustion/detonation within the combustion
stage 109.
In a further exemplary embodiment of the present invention, alternative
heating mechanism can be employed. For example, in an embodiment electrical
heating or arc heating can be employed. The heating mechanism can be employed
to
heat the flow through the plenum and/or the heat the fuel. Of course, it is
also
contemplated that additional heating mechanisms, such as electrical heating
mechanisms can be employed with the embodiment discussed above.
As shown in the embodiment depicted in Fig. 1 downstream of the plenum
103 is an inlet valve portion 107. The inlet valve portion 107
controls/regulates the
flow of the fluid into the combustion stage 109. In Fig. 1 the inlet valve
portion 107
is depicted simply, as its structure and configuration is dictated by the
inlet valving
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needs of the combustion stage 109. It is also contemplated that in a further
embodiment of the present invention the combustion stage 109 is immediately
downstream of the plenum 103 such that the inlet valving mechanisms are
located
within the combustion stage 109.
In an exemplary embodiment of the present invention, a fuel injection system
(not shown) is located within the inlet valve portion 107 of the system 100.
In such
an embodiment, a fuel is injected into the flow by any commonly known or used
methodology such that fuel vaporization is enabled as the flow enters into the
combustion stage 109. The fuel injection system employed is to be such that
proper
operation of the combustion devices 113 located within the combustion stage
109 is
ensured.
In an embodiment of the present invention, the combustion stage 109
comprises a plurality of combustion devices 113. In one embodiment of the
invention, which is a PDC-hybrid configuration, at least one of the devices
113 is a
PDC and the remaining devices are standard deflagration/constant pressure
combustion devices. In a further embodiment, which is a non-hybrid
configuration,
all of the devices 113 are PDCs. Additionally, although Fig. 1 depicts a
plurality of
combustion devices 113 in the combustion stage 109, it is contemplated that in
an
embodiment of the invention only a single PDC is placed in the combustion
stage 109.
The quantity, structure and operational characteristics of the combustion
devices 113
and PDC(s) in the combustion stage 109 is a function of operational and
performance
criteria. Any known PDC configuration can be used as a combustion device 113.
Following the combustion stage 109 of the system 100 is a turbine stage 111.
The turbine stage 111 can be of any commonly known or used turbine
configuration
used to extract work energy from the combustion stage 109. The present
invention is
not limited in this regard.
Fig. 2 depicts another exemplary embodiment of the present invention. (It is
noted that like components are numbered the same as shown in Fig. 1).
Specifically,
Fig. 2 depicts a system 200 which is similar to that shown in Fig. 1 except
that a fuel
injection system 220 is shown coupled to the inlet valve portion 107.
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In the embodiment shown in Fig. 2, the fuel injection system 220 comprises a
fuel tank 221, a fuel line 223, a fuel heating system 225 and fuel injectors
227. It is
noted that the present invention is not limited to the specific structure or
configuration
shown in either Figs. 1 or 2 and that the figures are exemplary
representations.
The embodiment shown in Fig. 2 employs an electrical heating system to
heat the fuel contained in the fuel system 220. In such an embodiment, the
fuel is
heated to a temperature which aids in facilitating vaporization of the fuel
during
startup or in cold environments. In an embodiment of the invention, the
electrical
heating system 225 heats the fuel in the tank 221 as well as during its travel
through
the fuel line 223. Although an electrical fuel heating system 225 is
discussed, the
present invention is not limited in this regard and any known or conventional
means
of heating fuel can be employed. Further, the fuel system 220 is depicted as
using the
fuel injectors 227 to inject the fuel in the inlet valve stage 107 of the
system 200. The
present invention is equally not limited in this regard as the fuel can be
introduced
into the system 200 by any conventional methodology using any known system or
structure.
Further, the Fig. 2 embodiment depicts a system 200 having both the plenum
preheat of the compressor flow as shown in Fig. 1 coupled with a fuel heating
system
225. However, an alternative embodiment of the present invention only employs
the
fuel preheat system 225 as described above.
The fuel heating system 225 heats up the fuel to a sufficient temperature such
that only a partial evaporation or flash vaporization of the fuel occurs
during the fuel
injection process. In general, heating of the incoming fuel aids cold startup.
IN a
further alternative embodiment (not shown) the fuel lines can be run through
the
plenum stage such that the fuel is heated by the preheating occurring in the
plenum
stage 103. For example the fuel lines can run along the inner surface of the
plenum
was (so as to not obstruct flow significantly) to allow the fuel to be heated
in this
fashion. Of course, the present invention is not limited to running the fuel
lines
through the plenum stage 103, but also the inlet valve 107, or other structure
where
the fuel would be heated.
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In an embodiment of the invention, during startup or during cold start, at
least one of the PDCs used in the combustion stage 109 can be operated in
constant
pressure deflagration mode - using either plenum preheat, fuel preheat, or
both - until
such time that the overall system temperature reaches such a level that
transition to
pulse detonation operation can proceed effectively. If the combustion devices
113 are
all PDCs then all or some can be operated in constant pressure deflagration
mode until
system pressure is sufficiently high so that transition to pulse detonation
can be
sustained in all or some of the devices 113. By using any one or a combination
of the
embodiments described above the transition to detonation mode is quicker.
Fig. 3 depicts another exemplary embodiment of the present invention. (It is
noted that like components are numbered the same as shown in Fig. 1).
Specifically,
Fig. 3 depicts a system 200 which is similar to that shown in Fig. 1 except
that the
pre-burners 105 are positioned out of the main flow F. In this embodiment,
rather
than being obstructions within the flow path, the pre-burners 105 are
positioned along
the side of the structure (for example the plenum stage 103). By moving the
pre-
burners 105 out of the main flow path, pressure losses due to dry-loss may not
be
experienced. Stated differently, it is contemplated that the pre-burners 105
may only
be used during engine start up. Accordingly, after start-up the pre-burners
105 will be
shut down, and if they remain in the flow path they will merely be
obstructions in the
flow path. This embodiment moves the pre-burners 105 out of the main flow
path, for
example along the wall of the plenum stage 103, so that once the pre-burners
105 are
shut down they do not act as mere obstructions in the main flow F.
As shown, in an exemplary embodiment the pre-burners can be fed via pre-
burner bypass ducts 301. These ducts direct pre-burner flow FPB to the pre-
burners
105 but also separate the main flow F from the pre-burner flow in the plenum
stage
103. Additionally, the bypass flow ducts 301 can have an upstream bypass valve
303
which controls the flow to the ducts 301. For example, during start up the
valves 303
can be opened to allow flow to the pre-burners 105, and then as the engine
reaches
operational power such that the need for pre-heated flow is diminished. For
example,
this can occur when the plenum stage 103 reaches an operational temperature.
When
this occurs the valves 303 can be closed causing all of the flow to go through
with the
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primary flow F. With the per-burners 105 not being in the direct flow path no
(or a
reduced) pressure drop will be incurred because of flow obstructions. Of
course, it is
also contemplated that based on operational and performance parameters the
valves
303 can be positioned at any suitable position to direct an amount of flow to
the pre-
burners 105. The valves do not have to be in a full open or full closed
position.
Further, the exact location of the pre-burners 105 with respect to the flow F,
the plenum stage 103 or the remaining structure is to be based on operational
and
design parameters. In fact, it is also contemplated that at least some or all
of the pre-
burner flow to the pre-burners 105 comes from a source outside the engine,
such that
they are not fed from the main flow F.
In a further embodiment, various flow direction or flow mixers can be
positioned downstream of the pre-burners 105 to maximize or at least promote
mixing
the preheated flow with the main flow.
Because the operation and structure of transitioning a combustion device
from constant pressure deflagration combustion to pulse detonation combustion
is
known to those of skill in the art, a detailed discussion is not included
herein.
In another embodiment of the invention the combustion devices 113 are
made up of a combination of constant pressure deflagration combustors and
PDCs.
When such a combination is used, the constant pressure deflagration combustors
are
operated until such time that the system temperature permits the PDCs to
operate. In
this embodiment of the invention, once the PDCs begin to operate the constant
pressure deflagration combustors can either stop functioning or continue
functioning
depending on the desired operational and performance parameters.
Moreover, it is noted that although both FIGs. 1 and 2 depict the system as
co-axially configured, this is intended to merely exemplary in nature as the
present
invention is not limited in this regard. In an embodiment of the present
invention, it is
contemplated that the system is configured co-axially, whereas in an alternate
embodiment various components are not positioned co-axially. For example, it
is
contemplated that the compressor and turbine portions are not positioned co-
axially,
or along the same drive shaft (not shown).
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It is noted that although the present invention has been discussed above
specifically with respect to power generation and aircraft applications, the
present
invention is not limited to this and can be employed in any application in
which
efficient power or work generation is required.
While the invention has been described in terms of various specific
embodiments, those skilled in the art will recognize that the invention can be
practiced with modification within the spirit and scope of the claims.
