专利汇可以提供Pulse detonation engine having an aerodynamic valve专利检索,专利查询,专利分析的服务。并且A pulse detonation engine (10) is provided with an aerovalve (14) for controlling the pressure of injected propellants (Ox, Fuel) in an open-ended detonation chamber (26). The propellants are injected at such pressure and velocity, and in a direction generally toward a forward thrust wall end (16) of the detonation chamber (26), an aerovalve (14) is formed which effectively inhibits or prevents egress of the propellant from the detonation chamber (26). A shock wave (34) formed by the injected propellant acts, after reflection by the thrust wall end (16) and in combination with the aerovalve (14), to compress and conserve, or increase, the pressure of the injected propellant. Carefully timed ignition (28) effects a detonation pulse under desired conditions of maintained, or increased, pressure. Termination of the propellant injection serves to “open” the aerovalve (14), and exhaust of the combusted propellants occurs to produce thrust. Alternate embodiments of propellant injection mechanisms (12, 112) provide pulse valves (24, 122, 124) each having a fixed slotted disk (40, 140, 240) and a rotating slotted disk (42, 142, 242) to provide the desired high speed valving of discrete pulses of propellant for injection.,下面是Pulse detonation engine having an aerodynamic valve专利的具体信息内容。
What is claimed is:1. A pulse detonation engine (10, 110) having an aerodynamic valve (14), comprising:a detonation chamber (26), having a thrust wall end (16) and an opposite exit end (18); anda valved fluid injection mechanism (12) associated with the detonation chamber (26) and located intermediate the thrust wall end (16) and the exit end (18), an outlet portion (30,30′; 32,32′) oriented generally toward the thrust wall end, for delivering a charge of at least fluid propellant at a high velocity and pressure into and directed generally toward, the thrust wall end (16) of the detonation chamber (26) in a charge filling process that further serves as an aerodynamic valve (14) to temporarily contain the fluid charge in the detonation chamber (26) during the charge filling process.2. The pulse detonation engine (10, 110) of claim 1 further including an ignition mechanism (28) associated with the detonation chamber (26) for effecting detonation of the fluid propellant charge in the detonation chamber (26).3.The pulse detonation engine (10, 110) of claim 2 wherein the ignition mechanism (28) is timed to initiate detonation of the fluid propellant charge at a desired instant in the charge filling process.4.The pulse detonation engine (10, 110) of claim 3 wherein:the fluid injection mechanism (12) injects the charge of fluid propellant to the detonation chamber (26) at an injection station (30′, 32′) along the detonation chamber (26);the injected charge of fluid propellant establishes a shock wave that is reflected by the thrust wall end (16);the detonation of the fluid propellant charge results in the creation of a rapidly propagating detonation wavefront; andthe ignition mechanism (28) is timed to initiate detonation of the fluid propellant charge at such instant as will result in the propagated detonation wave front and the reflected shock wave arriving at the injection station (30′, 32′) substantially in unison.5. The pulse detonation engine (10, 110) of claim 1 wherein the detonation chamber (26) is tubular and has a longitudinal centerline, and the fluid injection mechanism (12) injects the charge of fluid propellant into the detonation chamber (26) at an angle &bgr; to the centerline, which angle is less than about 45°.6. The pulse detonation engine (10, 110) of claim 5 wherein the angle &bgr; at which propellant is injected is no greater than about 30°.7. The pulse detonation engine (10, 110) of claim 1 wherein:the detonation chamber (26) is tubular and has a longitudinal centerline, and the fluid injection mechanism (12) injects the charge of fluid propellant into the detonation chamber (26) at an angle &bgr; to the centerline; andthe propellant injected includes gaseous fuel and gaseous oxidizer, the fuel and oxidizer being injected into the detonation chamber (26) at substantially the same angle &bgr; and at substantially the same station (30/32, 30′/32′) longitudinally of the detonation chamber (26).8. The pulse detonation engine (10, 110) of claim 1 wherein:the detonation chamber (26) is tubular and has a longitudinal centerline, and the fluid injection mechanism (12) injects the charge of fluid propellant into the detonation chamber (26) at an angle &bgr; to the centerline; andthe propellant injected into the detonation chamber (26) is injected at two discrete stations (30/32, 30′/32′; 130/132, 130′/132′) spaced longitudinally a significant distance from one another along the detonation chamber (26), thereby to increase the rate of the charge filling process and reduce leakage by the aerodynamic valve (14).9. The pulse detonation engine (10, 110) of claim 1 wherein the charge of propellant injected into the detonation chamber (26) is injected as a discrete charge and at a pressure, velocity, and angle toward the thrust wall end (16), such that the aerodynamic valve (14) sufficiently retains the charge for the pressure of the propellant in the detonation chamber (26), prior to detonation, to be at least nearly as great as the pressure of the propellant as injected.10. The pulse detonation engine (10, 110) of claim 9 wherein the charge of propellant is injected at a pressure, velocity, and angle toward the thrust wall end (16), such that the aerodynamic valve (14) sufficiently retains the charge for the pressure of the propellant in the detonation chamber (26), prior to detonation, to exceed the pressure of the propellant as injected.11. The pulse detonation engine (10, 110) of claim 1 wherein the fluid injection mechanism (12, 112) comprises at least one fuel injection valve (24, 124, 122), the fuel injection valve (24, 124, 122) comprising a plenum chamber (74, 174, 274), means (76, 78, 178, 278) for supplying propellant under pressure to the plenum chamber (74, 174, 274), a pair of members (40, 42; 140, 142; 240; 242) mutually juxtaposed in close, facing relation and having respective slots (44, 46; 144, 146; 244, 246) therein, one member (42, 142, 242) of the pair of slotted members (40, 42; 140, 142; 240, 242) being adapted to rotate relative to the other (40, 140, 240) to successively align and unalign, and thus port and unport, the slots (44, 46; 144, 146; 244, 246) in the two members, the pair of members (40, 42; 140, 142; 240, 242) defining a boundry of the plenum (74, 174, 274), and means (70, 54, 52; 194) for rotatingly driving one member (42, 142, 242) of the pair relative to the other (40, 140240) to provide successive pulses of propellant for injection into the detonation chamber (26).12. A pulse detonation engine (10, 110) having an aerodynamic valve (14), comprising:a detonation chamber (26), having a thrust wall end (16) and an opposite exit end (18) substantially without an axially-reflective surface; andfluid injection mechanism (12) associated with the detonation chamber (26) and located intermediate the thrust wall end (16) and the exit end (18), for delivering a charge of at least fluid propellant at a high velocity and pressure into and directed generally toward, the thrust wall end (16) of the detonation chamber (26) in a charge filling process that further serves as an aerodynamic valve (14) to temporarily contain the fluid charge in the detonation chamber (26) during the charge filling process.
This invention was made with United States Government support under Contract Number NAS8-98-035 awarded by the National Aeronautics and Space administration. The Government has certain rights in this invention.
TECHNICAL FIELD
This invention relates generally to pulse detonation engines, and more particularly to the fluid dynamics of such engines. More particularly still, the invention relates to the valving of fluids employed in pulse detonation engines.
BACKGROUND ART
Pulse detonation engines (PDE) represent an energy conversion device that has existed for some time, but which have recently received increased attention. Such engines generally combust fuel and an oxidant in a chamber, or combustor, to provide a component of thrust or force in an intended direction. The combustion occurs in the manner of discrete, i.e. pulsed, detonations. The present invention is concerned with configurations that employ an open-ended chamber, such as a rocket nozzle, that may be employed for a component of thrust. A principal application for such engines is as a thrust source to propel an aerospace vehicle in the atmosphere or the vacuum of space. In such instance, the PDE is also a rocket engine.
The development of PDE's requires the ability to quickly fill an open-ended chamber with a detonatable mixture while purging the exiting exhaust gases with minimal mixing. For pulse detonation rocket engine applications where the open end of the chamber is likely to be exposed to a vacuum, the fresh charge of detonatable mixture must be contained in the chamber for several milliseconds before the detonation is initiated. Further, the mixture must be pressurized to levels on the order of 50-1000 psi with the chamber open to vacuum in order to generate thrust competitive with conventional rocket engines. Moreover, the process must be done at rates approaching or exceeding 100 Hz.
Two alternative concepts that may be used to control chamber pressure are mechanical valves and fixed throats, but each has significant limitations. The complexity and weight of a mechanical valve, combined with durability and sealing requirements in the hot exhaust flow, suggest that it would be difficult and/or impractical to implement in this application and environment. A fixed throat near the chamber exit would restrict the flow, allowing the chamber to be pressurized with high propellant flow rates while some propellant is lost through the exit. This arrangement suffers from the loss of efficiency due to propellant leakage during the fill process and from thrust reduction due to the reduced exit area of the throat.
A further discussion of the physics and operation of PDE's is contained in several U.S. Patents by T. R. Bussing, including U.S. Pat. Nos. 5,513,489; 5,353,588; and 5,345,758. These patents discuss the use of a rotary valve, but only to control the admission of propellant and oxidant to each of multiple combustor chambers rather than to also control the pressure developed in the chamber. They rely upon an approach that uses multiple chambers each feeding into a common, restricted throat.
Accordingly, it is an object of the invention to provide an arrangement that is durable, relatively efficient, and simple, for controlling the pressure of fluids, such as propellants, in the chamber of a pulse detonation engine.
It is a further object to provide a pulse detonation engine in which the timing of detonation is optimized or tuned in accordance with the present invention.
It is a still further object to provide improved fluid injection mechanism for use with the pulse detonation engine in accordance with the invention.
DISCLOSURE OF INVENTION
A pulse detonation engine (PDE) is provided with an aerodynamic valve (aerovalve) for controlling the pressure of injected fluids, typically gases, but also including liquids, such as fuel or fuel and oxidizer, referred to as propellants, in an open-ended detonation chamber. The PDE includes a detonation chamber closed at a thrust wall end and open at the opposite, exhaust, end. A fluid injection mechanism injects pressurized propellant fluid into and directed toward the thrust wall end of, the detonation chamber. The propellant fluid is injected in a pulsed manner by the injection mechanism, and with sufficient pressure and velocity and such direction as to effectively restrict or prevent rearward flow of the injected fluid, thus forming a closed aerovalve. Moreover, the injected propellant fluid establishes a shock wave which, when moving rearward in the detonation chamber toward the exhaust end after reflection by the thrust wall end, serves in combination with the closed aerovalve to increase, or at least sufficiently conserve, the pressure of the fluid in the chamber, such that it is a pressure preferably greater than, or at least nearly as great as, that at which it entered. At the appropriate instant, the injected and pressurized propellant is detonated, as by an ignition device, to rapidly combust the injected propellants. Because the exhaust end of the detonation chamber is not mechanically constricted, as by a mechanical valve, and the aerovalve is open because injection has ceased, the resulting combustion products readily exit to produce thrust. Such configuration avoids the concerns of a mechanical valve structure for controlling exhaust from the detonation chamber and does not require a mechanically-constricted throat structure which would otherwise impede exhaust flow.
The PDE is preferably tuned to optimize the specific impulse or thrust. This is accomplished by coupling the timing of the fluid propellant injection and the subsequent ignition to maximize performance. More specifically, the mass average chamber temperature and pressure are at a maximum as the reflected shock wave nears the injection mechanism. The ignition is timed and positioned such that the resulting detonation wave, which moves at a velocity greater than the reflected shock wave, arrives at the injection mechanism at the same instant as the reflected shock wave.
The propellant injection mechanism is a high frequency pulse valve which delivers and injects pressurized pulses of propellant, typically fuel and oxidizer, to the detonation chamber of the PDE. Various arrangements may be used for providing such pressurized pulses of propellant. However, in the propellant injection mechanism of the preferred embodiment, each propellant component is supplied, at pressure, to a respective slotted disk type of valve. The slotted disk valve includes at least one rotating disk having a plurality of slots, and a complementary slotted disk, typically stationary, such that the slots of the two disks port (open) and unport (close) in rapid succession. The propellant pulses are delivered from the disk valves to the detonation chamber via injection ducts which are positioned and directed to provide the aerovalve of the invention.
One embodiment of the propellant injection mechanism comprises one or more injection valves offset from the axis of the detonation chamber and in which the rotating disk is driven by a spring-biased drive member at the axis of the disk, but offset from the detonation chamber axis.
Another embodiment of the propellant injection mechanism comprises a pair of annular injection valves that encircle the detonation chamber and in which annular fixed and rotating slotted disks are disposed coaxially with the detonation chamber to provide the pulsed injections.
The foregoing features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments thereof as illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1
is a simplified, cross-sectional view of a pulse detonation engine (PDE) employing an aerodynamic valve (aerovalve) in accordance with the invention;
FIGS. 2A
,
2
B and
2
C are simplified diagrammatical depictions of the PDE of
FIG. 1
showing, respectively, initial injection of propellant fluid to establish and close an aerovalve and also create a shock wave, detonation of propellant fluid at appropriate timing of the reflected shock wave, and final exhaust and venting of combusted propellant fluid through relaxed, or opened, aerovalve;
FIG. 3
is a graphical depiction of the filtered and normalized pressure histories at various locations in the PDE during a representative cycle of pulse operation, but omitting actual detonation;
FIG. 4
is a graphical depiction of the chamber pressure, temperature and leakage during a representative cycle of pulse operation, but omitting actual detonation;
FIG. 5
is a graphical depiction of a single pulse pressure trace from multiple repetitive detonations;
FIG. 6
is a graphical plot of the aerovalve performance metrics of pressure and leakage as a function of the injection angle (&bgr;) of the propellant fluid;
FIG. 7
is a simplified diagrammatical depiction of a PDE in accordance with the invention, illustrating multiple axially-spaced stations for the injection of propellant fluid;
FIG. 8
is a sectional view of one embodiment of a slotted-disk pulse valve for metering and injecting propellant fluid to the PDE chamber to provide the aerovalve in accordance with the invention;
FIGS. 9A and 9B
depict, respectively, the rotating disk and the stationary disk of the pulse valve of
FIG. 8
;
FIG. 10
is a simplified sectional view of a second embodiment of a pair of slotted-disk pulse valves for metering and injecting propellant and oxidant fluids to the PDE chamber to provide the aerovalve in accordance with the invention; and
FIG. 11
is an exploded view of the major elements of the slotted-disk pulse valve assembly of FIG.
10
.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring to FIGS.
1
and
2
A-
2
C, there is illustrated in
FIG. 1
a simplified, somewhat diagrammatic, cross-sectional view of a pulse detonation engine (PDE)
10
employing fluid injection mechanism
12
to provide the aerodynamic valve (aerovalve)
14
depicted diagrammatically through the use of gas flow arrows in
FIGS. 2A-2C
in accordance with the invention. The PDE
10
is typically an elongate tubular structure
11
having a closed thrust wall end
16
and an opposite exit, or exhaust, end
18
that is open. A fluid injection mechanism
12
is located intermediate the opposite ends
16
and
18
, relatively toward the exhaust end
18
, and may typically include an annular injector member
20
and associated fluid pulse injection valves
22
and
24
. The annular injector member
20
may conveniently be included as a structural portion of the tubular PDE structure. The region of the PDE between the injector member
20
and the thrust wall end
16
comprises the detonation, or combustion, chamber
26
. An active ignition source, such as spark plug
28
, is located in a wall of the PDE in communication with the detonation chamber
26
.
The PDE
10
is provided with a supply of fuel, such as hydrogen gas or liquid, via the fluid pulse injection valve
24
, and with a supply of oxidizer, such as oxygen gas or liquid, via the fluid pulse injection valve
22
. The fuel and the oxidizer, in liquid or gas phase, are injected into the detonation chamber
26
via fuel injection ducts
30
and oxidizer injection ducts
32
, respectively, in the annular injector member
20
. The inner ends of the ducts
30
and
32
define respective fuel injection ports
30
′ and oxidizer injection ports
32
′ at their interface with the detonation chamber
26
. The fuel injection ducts
30
and the oxidizer injection ducts
32
are oriented such that, at least at their respective ports
30
′ and
32
′, they form an angle &bgr; with the axis, or centerline, of the detonation chamber
26
and the tubular structure
11
of the PDE
10
. This orientation is selected so as to inject the fuel and oxidizer relatively forward toward the thrust wall end
16
of the PDE
10
. In this way, the advantages of the aerovalve
14
of the invention are obtained, as will be explained in greater detail. Although the fuel injection ducts
30
and the fuel injection ports
30
′ are depicted in
FIG. 1
as being displaced longitudinally slightly from the oxidant injection ducts
32
and the oxidant injection ports
32
′ for convenience of illustration, it will be appreciated that they may also be at substantially the same longitudinal position, as will become evident later herein. In that latter instance, they may collectively appear as a single, nominally continuous, annular entry port.
Referring to the diagrammatical illustrations of
FIGS. 2A-2C
, there is depicted a cycle of operation of the PDE
10
, including the associated aerovalve
14
.
FIG. 2A
shows the fuel and oxidizer propellants being injected into the detonation chamber
26
under high pressure and speed via ducts
30
and
32
respectively. Assuming the PDE
10
is operating at high altitude or in space, the initial pressure in the detonation chamber
26
may be at a near-vacuum condition. The propellant flow expands as it is injected toward the thrust wall end
16
. A shock wave
34
is formed at the leading edge of the advancing propellant flow. Importantly also, the high velocity of the flow toward the thrust wall end
16
limits its ability to turn toward the exhaust end
18
and leakage, represented by arrows
36
, is thereby minimized or prevented. This latter characteristic results in the formation and relative closing of an aerodynamic valve, identified by the independent reference numeral
14
, and thus aids in containing and compressing the injected propellants. Referring to
FIGS. 2A and 2B
, when the supersonic flow of the shock wave
34
contacts the thrust wall end
16
, it is reflected back through the detonation chamber
26
toward the injection region and the exhaust end
18
. This reflected shock wave
34
travels back over the injected propellant gas, both stagnating and heating the gas, as well as recovering pressure. The resulting pressure in detonation chamber
26
is seen to increase significantly, as will later be illustrated graphically. At the appropriate instant, the compressed and heated propellant gas is detonated, as by the firing of the spark plug
28
represented in FIG.
2
B. The resulting detonation also produces a detonation wave front (not separately shown) which advances in all directions from its source at a velocity greater than the reflected shock wave
34
. The timing of ignition and resulting detonation are preferably selected such that the reflected shock wave
34
and the detonation wave front arrive at the region of the injector ducts
30
and
32
at substantially the same time, at which time the mass average pressure and temperature in detonation chamber
26
are a maximum.
Referring to
FIG. 2C
, the PDE
10
is illustrated shortly after the detonation of
FIG. 2B
has occurred. It will be noted that because there is no further injection of fuel and oxidant, the aerovalve
14
has relatively opened or relaxed, to permit the rapid and thorough egress of the combusted propellants and the associated development of the desired thrust impulse. Following the opening of the aerovalve
14
and the exhaust of the combusted propellants, the PDE
10
is ready to begin a new pulse cycle by receiving a new injection of propellant, as depicted in FIG.
2
A. In the interest of maximizing the cycle-average thrust, it is desirable to both fill, and later exhaust, the detonation chamber
26
as rapidly as possible. Cycle rates of 100 Hz are typical, resulting in cycle times of about 10 ms. It should be noted that cycle rates vary inversely as a function of the length of the detonation chamber
26
and thus, may be controlled and varied to some extent by the selection of the length of the detonation chamber
26
. A further understanding of the invention is obtained with reference to the graphical depictions of
FIGS. 3 and 4
, which represent data obtained from an instrumented PDE
10
during a cycle of operation, but without ignition or detonation. The pulse detonation chamber
26
was cylindrical, having a diameter of about 4 inches and a length of about 40 inches, with the injection mechanism
12
, and particularly the injection ducts
30
and
32
, being located at the aft end of the detonation chamber, just forward of the exhaust end
18
of the PDE
10
. The operating environment at the exhaust end
18
of PDE
10
was at a pressure less than 1 psia.
Referring to
FIG. 3
, the normalized value of pressure, p/Pt
inject
, for each of several locations at, or in, the PDE
10
, is plotted as a function of Time (in milliseconds). In the expression for the normalized value of pressure, p is static pressure and Pt
inject
represents the injected total pressure. It will be seen that, as would be expected, the injection pressure, Pt
inject
, at the injection ports
30
′ and
32
′ is substantially at unity. However, the pressure within the detonation chamber
26
is seen to experience a rapid increase from near zero to a maximum that is, in accordance with the invention, greater than the injected pressure, in this instance about 1.15, or 15% greater. The lowermost trace is representative of the ambient pressure at or near the exhaust end
18
of the PDE
10
, and is indicative of a low, near-vacuum pressure except immediately following exhaust of the injected propellants. The remaining trace is that of Pt
leak
, which is commensurate with the pressure of the leakage flow from the aerovalve
14
, represented by the leakage arrows
36
of
FIGS. 2A-2c
.
Referring to
FIG. 4
, the pressure, temperature, and leakage in detonation chamber
26
are displayed in a normalized form for one fill and exhaust cycle. The time base &tgr; is normalized time, and represents ta/l
t
, where “t” is time, “a” is the speed of sound and “l
c
” is the length of detonation chamber
26
as measured between the injection ports
30
′/
32
′ and the thrust end wall
16
. The values along the ordinate are normalized and dimensionless. The normalized value of the pressure of the injected propellant(s) is seen to increase until about &tgr;=2.75, at which time it is about 1.2. or 20% greater than the injected pressure, Pt
inject
, which in turn is typically about 50 times greater than the ambient pressure. Similarly, the temperature in the chamber
26
increases until about &tgr;=2.75, at which time it is about 1.3, or 30% greater than the temperature at the moment of initial injection. At, or shortly before, &tgr;=2.75, detonation would normally occur, however detonation is omitted in this example and the pressure is seen to drop rapidly, with the temperature also dropping at a lesser rate. Further, the leakage of fluids, initially undetonated injectant, is seen to be relatively low until about &tgr;=2.75, being only about 0.15, or 15%. Thereafter, the leakage of previously injected gases increases rapidly because further injection has terminated and the aerovalve
14
relaxes, or opens. Had detonation occurred, the combusted gases would rapidly exit the detonation chamber
26
as they produce thrust. In the foregoing example, the fuel and oxidant were injected at an angle, &bgr;, of 30°.
Referring to
FIG. 5
, there is provided a graphical depiction of a single pulse pressure trace from a 25 Hz run with repetitive detonations. The initiation of fuel injection is seen at the left side origin of the trace and the normalized pressure remains relatively constant for a little longer than 1 ms as the shock wave
34
travels toward the thrust wall end
16
. Then, at T=1.29 on the graph scale, the shock wave is reflected and the pressure in the detonation chamber
26
rapidly and significantly increases until, at about T=1.294, detonation occurs and the pressure increases very rapidly and very significantly. Shortly thereafter, the combustion products exhaust and produce the desired thrust, as indicated by the rapid decline in pressure between the detonation and initiation of the next injection of propellant about 2 ms later.
Referring to
FIG. 6
, the aerovalve performance metrics of pressure and leakage are displayed as a function of the injection angle &bgr; of the propellant fluid. The ordinate represents normalized values for the performance of aerovalve
14
for the various injection angles &bgr; measured along the abscissa. The maximum normalized mass-average total pressure per fill cycle is Max Pt
m
/Pt
inject
, where Pt
m
is the chamber mass-average total pressure and Pt
inject
is the injected total pressure. This parameter is important because the total impulse imparted to the system during a detonation blowdown is directly proportional to the post-detonation mass-average total pressure; the higher the fill pressure, the higher the post-detonation pressure. It will be noted that the normalized mass-average total pressure is greatest when the injection angle &bgr; is smallest, as when &bgr; is 0°. In that instance, the propellant would be directed parallel to the axis of detonation chamber
26
in the direction of the thrust wall end
16
, and the maximum could theoretically be 60% greater than the injected pressure. Conversely, if the propellant is injected at an angle &bgr; of 90° to the chamber's axis, there is essentially no increase in the pressure over the injected pressure. This analysis indicates the desirability of making the injection angle &bgr; as small as possible in order to maximize the pressure increase. It will be appreciated, however, that the mechanics of injecting propellant at an angle of 0° may be difficult or impractical in an operating configuration, and angles in the range of about 20° to 45° are practicably obtainable and are seen to provide significant pressure increases, as for instance 50% and 25%, respectively. Further, the leakage parameter M
leak
/M
inject
is a ratio of the mass of propellant gas leaked to the mass injected during fill. It will be seen that such leakage is less for a small injection angle &bgr;, and is significantly greater as the angle increases toward 90°. It is thus again desirable to keep the injection angle &bgr; as small as practicably possible. In the foregoing analysis, the pressure of the injected propellant, Pt
inject
, is 50 times greater than the ambient pressure, and the ratio of the area of the injector ports
30
′/
32
′ is the same as the cross-sectional area of the detonation chamber
26
.
A further variable that may be introduced to affect performance of the PDE is the addition of a second propellant injector, or a second set of propellant injectors, as part of the fluid injection mechanism
12
′ (shown in broken line), at a location intermediate the initial injector, or injector set,
30
/
32
, and the thrust wall end
16
. In the embodiment depicted in a simplified diagrammatic form in
FIG. 7
, the initial injector ducts
30
/
32
, depicted for simplicity as a single duct, are at, or near, one end of detonation chamber
26
of a PDE
110
and the thrust wall end
16
is at the opposite end. The second set of injectors is represented by injector ducts
130
/
132
and respective ports
130
′/
132
′, which are located approximately midway between the initial injector ducts
30
/
32
and the thrust wall end
16
. Such arrangement provides for the injection of propellants from the two locations at substantially the same time, which has been seen to result in a substantially faster filling rate and with substantially less leakage by the aerovalve
14
. Under similar conditions and differing only in the number of injector sets, the single injector set configuration was seen to have a relative leakage value of 0.14 and fill time value of 2.94, whereas those same values for the two injector set configuration are 0.10 and 1.51, respectively. The advantages of including a second injector set are tempered by added complexity and slightly decreased pressure and temperature values, the latter believed being due to interference between the reflected shock wave from the added injector set and the advancing shock wave from the initial injector set. Also, as mentioned previously, some further advantage is derived if the injection angle &bgr; is kept relatively small, as for instance 45° or less, and preferably about 30°.
Attention is now given to a detailed consideration of one embodiment of a representative propellant injection valve, such as the fluid pulse injection valve (PIV)
24
for injecting fuel, such as hydrogen liquid or gas. Referring to
FIGS. 8
,
9
A and
9
B, there is illustrated a slotted-disk pulse injection valve
24
, including the fixed disk
40
and rotating disk
42
which form parts thereof. The PIV
24
is designed to start and stop the flow of fluids, such as liquids or particularly gases, at high frequencies, without the shortcomings of prior devices that were frequency limited. The PIV
24
employs two circular disks, one being a fixed disk
40
and the other being a rotating disk
42
. The faces of the disks
40
and
42
are ground to precision flatness and surface finish. The disks
40
and
42
, respectively, have radial slots
44
and
46
, respectively, cut into their faces such that when they are in facing mated engagement and rotated on a concentric axis, the slots
44
and
46
port (open) and unport (close). The frequency of the porting and unporting action is a function of the number of radial slots
44
/
46
in the faces of disks
40
and
42
and the relative rotational speed of those disks. Because the number of slots
44
/
46
can be relatively large, i.e., 10 to 20, high frequency operation can be achieved at relatively low rotational speeds. The angular extent of the slots
44
/
46
is typically constant from the radially innermost to the radially outermost portion of a respective slot, though the angular extent of the slots
44
may differ somewhat from that of slots
36
. In either event, the angular extents are typically less than about 5°-10° and there may be, for example, 10 to 20 such slots per disk. In the instance of 20 slots, a frequency of 100 Hz is obtained at a rotational speed of 300 rpm. The faying surfaces between the rotating disk
42
and the stationary disk
40
are coated with a dry film lubricant compatible with the fluid being injected, to facilitate relative motion and sealing. Depending on the relative positioning of the disks
40
and
42
, that face of the disk closest to the ducts
30
/
32
and the detonation chamber
26
(seen in
FIG. 1
) may be protected with a thermal barrier coating to minimize distortion from thermal gradients and transients. Further protection may be obtained by recessing the valve from the detonation flow path, as by ducts
30
/
32
and/or supplying a bleed fluid such as air, if available, over the sensitive surface.
Referring to the PIV
24
in greater detail, a housing
50
provides structural support for the PIV assembly, and includes mounting flanges
51
for mounting it in fixed relation to the structure
11
of the PDE
10
. The housing
50
includes a generally cylindrical through-bore and coaxial counter bores. An electric motor
52
or similar actuator for providing rotary motion, is mounted to the outboard end of the PIV housing
50
, and a rotary drive shaft
54
is connected thereto by a suitable coupling
56
for transmitting rotary torque and motion from the motor
52
to the drive shaft
54
. The drive shaft
54
extends forwardly into the bore in housing
50
in radially-spaced relation, and is centered and rotatably supported therein by bearings
58
. The bearings
58
are axially spaced from one another by spacer
60
, and are retained at their ends against axial movement by snap rings
62
seated in the housing
50
, and possibly additional snap rings in the shaft
54
. The outside diameter of the drive shaft
54
is increased in a step at its inboard end to create a shoulder portion
64
against which the forward bearing
58
may axially bear and against which the inner diameter of a seal
66
may radially bear. The drive shaft
54
contains an axially-extending, blind, hexagonally-shaped (hex) recess
68
formed, as by machining, in its forward, or inboard, end for receiving a ball hex driver
70
in axially-sliding relationship therein. The shank of ball hex driver
70
is formed in a complementary hex shape with the recess
68
in the drive shaft
54
to prevent relative rotation there between. Of course other complementary geometries containing flats to prevent rotation would also suffice. The ball hex driver
70
has a ball hex driver head
71
formed at its forward, distal or inboard, end for driving engagement with the rotating disk
42
via a hex shaped recess
71
′ centered in the disk
42
. A compression spring
72
is seated in the recess
68
in drive shaft
54
, and acts against the rearward, proximal or outboard, end of the ball hex driver
70
to urge it forward and into engagement with the rotating disk
42
, as will be described.
The forward, or inboard, end of the PIV housing
50
includes a relatively large counterbored region forming a plenum
74
. A fitting
76
on housing
50
serves to admit propellant, in this instance fuel, to the plenum
74
via a conduit
78
in the housing. The rearward end of the plenum is closed by the seal
66
, which extends radially from the shoulder
64
on drive shaft
54
to the radially inner wall of housing
50
. The disks
40
and
42
are mounted in the forward end of PIV housing
50
such that they define the forward end of the plenum
74
. The fixed disk
40
is axially forwardmost in housing
50
, and is statically mounted therein in a sealed manner that prevents motion relative to the housing, axially, circumferentially, and radially, as by weld, braze, thread, or the like, or by machining. The faying surface of fixed disk faces rearwardly. The rotating disk
42
is positioned immediately rearward of the fixed disk
40
, with the former's faying surface facing forward in opposition to that of the latter. The rotating disk
42
is free to rotate when driven by the ball hex driver
70
. The ball hex driver head
71
is urged forward by compression spring
72
, into mated driving engagement with the rotating disk
42
in, and via, the hex shaped recess
71
′ in the disk. This coupling and driving arrangement compensates for fore and aft angular misalignment (wobble) between fixed disk
40
and rotating disk
42
by allowing the faying surfaces of the disks to float with limited axial and wobble displacement and thereby maintain intimate contact during rotation. In addition to the nominal preload that the compression spring
72
provides, the propellant pressure in the plenum
74
applies a force load to the rotating disk
42
to maintain sealing contact between it and the fixed disk
40
. The forward end of plenum
74
is sequentially opened and closed by means of the slots
44
and
46
in disks
40
and
42
, respectively, thus successively porting and unporting. In this way, propellent admitted to the plenum
74
under pressure is discharged (injected) to the detonation chamber
26
as discrete, high frequency, pressurized pulses for providing the benefits attainable with such operation.
Referring now to
FIGS. 10 and 11
, there is depicted a second embodiment of a fluid injection mechanism
112
comprising a pair of annular injection valves
122
and
124
that serve to inject pulses of the oxidant and the fuel, respectively. Unlike the injection valve arrangement
24
of
FIG. 8
wherein the axis(es) of the fixed disk(s)
40
and the rotating disk(s)
42
are offset from the axis of the detonation chamber
26
of the PDE
10
, the present fluid injection mechanism
112
provides a ganged pair of annular injection valves
122
and
124
having fixed annular disks
240
and
140
respectively, and rotating annular disks
242
and
142
respectively, all of which are concentric and coaxial with the axis of detonation chamber
26
. The fixed disks
240
and
140
have radial slots
244
and
144
respectively, and the rotating disks
242
and
142
have radial slots
246
and
146
, respectively. The injection valves
122
and
124
are axially spaced by a common annular injector member
120
that is positioned therebetween adjacent to the respective rotating disks
242
and
142
. The annular injector member
120
has a lobed mixing tang
190
that defines, in cooperation with the rotating disks
142
and
242
and their slots
146
and
246
, the fuel injection ducts
130
and the oxidant injection ducts
132
that extend radially inward and axially forward from the disks at the desired injection angle, &bgr;. The annular injector member
120
, and the rotating disks
142
and
242
are all mounted for rotation coaxially about the detonation chamber
26
, with at least part the injector member
120
defining an annular portion of the wall of the detonation chamber. The rotating disks
142
and
242
are connected to the annular injector member
120
, as by a key, pin, or spline-type coupling arrangement
192
that allows limited relative axial motion but prevents relative circumferential motion, such that the three elements rotate in unison but some limited axial angular or “wobble” motion therebetween is permitted to allow each rotating disk to “float” relative to its associated fixed disk.
The fixed disks
240
and
140
are each further mated with fixed, plenum-forming members
240
′ and
140
′, respectively, to define plenums
274
and
174
, respectively, and include fluid inlet passages
278
and
178
, respectively, for supplying the oxidant and fuel. As with the
FIGS. 8
,
9
a
, and
9
B embodiment, the faying surfaces of the fixed and the rotating disks are in sliding contact with one another and thus, are machined and processed to a fine finish and receive lubricants, such as a dry film and grease, to facilitate operation. To assure that the flat mating faying surfaces of the rotating and fixed disks come together and mate without any angular mismatch in the axial direction to insure good running and sealing, the rotating disks
142
and
242
are permitted to float a small amount relative to the respective fixed disks
140
and
240
. More specifically, as noted above, the coupling arrangement
192
allows the rotating disks
142
and
242
to move axially angularly, or “wobble”, relative to the annular injector member
120
that is positioned therebetween. A number of compression springs
172
are interposed and arranged circumferentially, under preload, between the injector member
120
and the outer rims of the respective rotating disks to resiliently bias the rotating disks
142
and
242
into close mating and sealing contact with the respective faying surfaces of the fixed disks
140
and
240
.
In operation, the annular injector member
120
and the associated rotating disks
142
and
242
are rotated, as by a motor driven friction belt
194
or geared drive (not shown) engaging the injector member
120
, and the slots
144
,
244
146
and
246
port and unport as earlier described. Assuming about 20 slots on the disks, pulses of fuel and oxidant are provided at 100 Hz when the rotating portion of the fluid injection mechanism
112
is driven at 300 rpm.
Although the invention has been described and illustrated with respect to the exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made without departing from the spirit and scope of the invention. For instance, the fluid propellants injected may each be in either the liquid or gaseous phase; the pressure of the propellants in the detonation chamber at the moment of detonation may be less than, but nearly as great as, the pressure of the propellant as injected; the fluid injection mechanism for the pulse detonation engine may employ suitable fluid pulse injection arrangements other than the slotted disks of the preferred embodiment; and the use of PDE's is not limited to aeronautical and space applications, but may be used for power generation in other applications, including land-based machinery, either linear or rotary.
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