This invention relates to pulse detonation systems, and more particularly, to a pulse detonation combustor (PDC) with at least one plenum for lowering the peak of the pressure pulse and extending the duration of the plateau and blowdown time.
With the recent development of pulse detonation combustors (PDCs) and pulse detonation engines (PDEs), various efforts have been underway to use PDC/Es in practical applications, such as combustors for aircraft engines and/or as means to generate additional thrust/propulsion in a post-turbine stage. Further, there are efforts to employ PDC/E devices into “hybrid” type engines that use a combination of both conventional gas turbine engine technology and PDC/E technology in an effort to maximize operational efficiency.
One of the key advantages of a pulse detonation engine (PDE) is the pressure-rise combustion that leads to increased performance by attaining a quasi-constant volume thermodynamic cycle. The challenge is that practical PDE applications require pulsed operation due to the unsteady nature of detonations. The pressure-rise is, therefore, attained for only a very brief period of time. A typical pressure-trace shows a very high pressure spike (lasting approximately 5 microseconds), followed by a plateau that can last 2-3 milliseconds, followed by a blowdown to a lower ambient (or fill) pressure. The duration of the plateau and blowdown is largely a function of the tube volume and exit nozzle area ratio. It is desirable to lower the ‘peak’ of the pressure pulse (which can be harmful to upstream and downstream components) and extend the duration of the plateau and blowdown.
The inventors have solved the problem of lowering the peak of the pressure pulse and extending the duration of the plateau and blowdown time for a PDC by providing at least one plenum along the length of the PDC. The plenum can either be upstream or downstream of the fuel injection port and ignition source. The plenum can be used instead of, or in conjunction with, a downstream exit nozzle that also assists in extending the blowdown time.
In one aspect of the invention, a pulse detonation combustor having a wall and comprising at least one plenum along a length of the pulse detonation combustor for controlling one of a mechanical loading on the wall, a velocity of fluid flowing within the combustor, and a pressure generated by the pulse detonation combustor.
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. cross-fire).
As used herein, a “detonation” is understood to mean either a detonation or a quasi-detonation.
As used herein, “engine” means any device used to generate thrust and/or power.
As used herein, a “plenum” means an enclosed chamber where fluid can collect that has a cross-sectional area that is larger than the remainder of the pulse detonation combustor.
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:
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.
In general, the operation and function of the pulse detonation combustor 10 is in accordance with any known or conventional means and methods. The present invention is not limited, in any way, to the operation and configuration of the pulse detonation combustor. The flow of the primary air into the combustor 10 may be controlled by the valve 12 to provide the proper fuel-air ratio conditions for sustainable detonations. The flow control may be achieved by any known or conventional means.
Alternatively, a premixed air/fuel mixture can be provided to the combustor 10 instead of airflow 16, and the fuel injector port 18 is not required and can be eliminated. An ignition source 20, such as a spark plug, and the like, ignites the fuel/air mixture within the PDC 10. The PDC 10 may also include an obstacle field 22 that impart turbulence and or swirl to enhance mixing of the fuel/air mixture within the PDC 10, thereby promoting detonation formation within the PDC 10. A benefit is to achieve a nearly uniform temperature profile that facilitates optimum energy conversion and robust design life of the downstream device. The obstacle field 22 can be in the form of spirals, blockage plates, ramps, and the like.
One aspect of the invention is that the PDC 10 includes a plenum 24 having a cross-sectional area that is larger than the cross-sectional area of the remainder of the PDC 10. For example, the plenum 24 can have a cross-sectional area that is between about 1.1 to about 2.0 times larger than the cross-sectional area of the remainder of the PDC 10. In one specific embodiment, the plenum 24 has a cross-sectional area that is approximately 1.4 times larger than the cross-sectional area of the remainder of the PDC 10.
One benefit of the additional volume provided by the plenum 24 is that the peak of the pressure pulse, which can be harmful to upstream (and downstream) components is lowered, and the duration of the plateau and blowdown of the pressure pulse is extended. Referring now to
The plenum 24 serves several purposes, which can be selectively adjusted by locating the plenum 24 at different locations along the PDC 10. These purposes include, but are not limited to:
Each of these purposes is discussed below.
Mechanical Loading Control
A sudden change in cross-sectional area change from a small diameter to a larger diameter helps weaken detonation wave or shock wave, thereby reducing the dynamic impact load, which results in very high transient peak stresses, and also lowers the “average pressure” in the larger volume section. However, this larger diameter cross-sectional area results in a larger surface area for pressure to act on, so it could result in a higher static load (so there is a trade-off of dynamic load vs static load).
In general, the best location of the plenum 24 for mechanical loading is proximate the air valve 12. If the plenum 24 is upstream of the fuel injector port 18 and ignition source 20, then fuel does not enter the plenum 24 (i.e., the plenum is unfueled). At this location, there are multiple benefits:
Flow Velocity Control
Much of the flow processes, for example, fuel fill, detonation initiation, blowdown, and the like, are impacted by the bulk flow velocity. At a high level, the bulk-flow velocity in the PDC 10 is principally controlled by the mass flow rate, density (e.g., P and T), the diameter of the PDC 10, and the throat area of the exit nozzle 14. The local bulk flow velocity can be adjusted along the length of the PDC 10 by selectively adjusting the local diameter of the PDC 10. This could be helpful in at least two areas:
Pressure Control
In general, the larger the tube volume, the higher the average pressure-rise will be achieved. Having locally larger diameters anywhere can help increase the pressure-rise and extend the blowdown time (trade-offs are with nozzle throat diameter and frequency of operation).
It is envisioned that the plenum 24 can be located at five (5) different locations along the PDC 10. These locations include, but are not limited to,
Each location 1) through 5) impacts the mechanical loading control, flow velocity control and the pressure rise control of the PDC 10 in a different manner. In the illustrated embodiment shown in
Referring now to
Referring now to
Referring now to
It will be appreciated that the invention can have multiple plenums 24 along the length of the PDC 10 to accomplish tailoring of the pressure, velocity and/or mechanical loading as needed.
In the illustrated embodiment, the transition between the plenum 24 and the remainder of the combustor 10 is an abrupt angle 26 of about ninety degrees (i.e., perpendicular to the wall of the PDC 10). However, it will be appreciated that the invention is not limited by the transition angle 26 between the wall of the combustor 10 and the plenum 24, and that the invention can be practiced with any desirable angle between zero and ninety degrees. For example, the transition angle 26 can be less than ninety degrees, as shown in
As described above, the plenum 24 lowers the “peak” of the pressure pulse, which can be harmful to downstream (and upstream) components, and extends the duration of the plateau and blowdown in the pulse detonation combustor 10.
While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.