Patent Application
20110146232
The invention relates generally to pulse detonation engines (PDEs), and more particularly to operational techniques for controlling outputs of multi-tube PDEs in response to control of corresponding pulse detonation combustor outputs.
Pulse detonation combustors create high pressure and temperature detonation waves by combusting a mixture of gas (typically air) and a hydrocarbon fuel. The detonation waves exit pulse detonation tubes as pulses, thus providing thrust or temperature and pressure rise.
With the recent development of pulse detonation technology, various efforts have been underway to use this technology in practical applications. An example of such a practical application is the development of a pulse detonation engine (PDE) where the hot detonation products are directed through an exit nozzle to generate thrust for aerospace propulsion. Another example is the development of a “hybrid” engine that uses a combination of both conventional gas turbine engine technology and pulse detonation (PD) technology to maximize operation efficiency. These pulse detonation turbine engines (PDTE)s can be used for aircraft propulsion or as a means to generate power in ground-based power generation systems.
It is for either of these applications that the following discussion will be directed. It is noted that the following discussion will be directed to “pulse detonation engines” (i.e. PDEs). However, the use of this term is intended to include pulse detonation engines, pulse detonation turbine engines, and the like.
Today, no known control system has been demonstrated to regulate the output of a PDTE. The PDTE is envisioned to replace existing gas turbine engines, which are used to operate machinery, generate electrical power or provide aerospace propulsion. These engines need the ability to operate at different operating points as required by the user in order to be useful. This may include, for example, different shaft speeds, power levels due to increased load, or targeted emission levels. Further, gas turbine engines need to be robust against variations in inlet conditions such as inlet temperature or variations in fuel supply pressure.
In view of the foregoing, it would be advantageous to provide one or more robust operational techniques to reliably control/regulate the output of a complete PDTE system.
Briefly, in accordance with one embodiment of the invention, a pulse detonation turbine engine (PDTE) comprises:
As used above, a plurality of controllable peripheral PDC components may include, for example, and without limitation, one or more fuel valves, one or more air valves, and one or more ignition elements.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
While the above-identified drawing figures set forth alternative embodiments, other embodiments of the present invention are also contemplated, as noted in the discussion. In all cases, this disclosure presents illustrated embodiments of the present invention by way of representation and not limitation. Numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention.
As used herein, a pulse detonation combustor is understood to mean any device or system that produces both a pressure rise and velocity increase from a series of repeated detonations or quasi-detonations within the tube. 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 pulse detonation tubes 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 or quasi-detonation. 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 quasi-detonation.
The primary means of control for existing gas turbine engines includes fuel flow and inlet guide vanes. These control means typically use simple maps that correlate fuel-flow and inlet guide vane (IGV) position with heat-release in the combustor or output power. Control of a PDTE may require use of these same handles, and will require additional control of PDC component timing The PDC components to be timed include, without limitation, the air valve, fuel valve, and igniter (such as spark igniter). These components may be timed to affect fuel and/or air fill fraction, purge fraction, equivalence ratio distribution within the pulse detonation tubes, skip firing (i.e., the timing can be arranged such that air is passed through the tube, but no fuel and no ignition), and tube-to-tube relative timing (i.e., firing pattern).
As used herein, PDC is considered the overall combustor for the engine. It can be arranged in a can-annular arrangement, in which case it may include an array of one or more pulse detonation bundles (PDB), each of which can include one or more pulse detonation combustor chambers (PDCC)s. The PDCCs often take the form of pulse detonation tubes (PDT)s or pipes, but they can have other shapes as well. Alternatively, the entire PDC may be arranged in a different manner, such as a full-annular arrangement or a rotating detonation type arrangement. Regardless, the term tube as used herein also includes the tubular or cylindrical openings within a full-annular or rotating detonation type combustor. The PDC can be the combustor for a pulse detonation turbine engine (PDTE) or for a pulse detonation engine (PDE).
Embodiments of the invention described herein include single-loop and hierarchical controller designs comprising two or more control loops. Use of a hierarchical control system accommodates the significant difference in controller rates required by the PDC versus the controller rate required by the compressor-turbine portion of the PDTE.
The inner control loop regulates the PDC and the outer control loop regulates the output of the turbine for a two loop controller design. The outer control loop provides the reference to the inner control loop.
The innermost control loop regulates the individual tubes of the PDC for a three-loop controller design, while the intermediate loop regulates the PDC, and the outer control loop regulates the output of the turbine. The outer loop provides the references to the intermediate loop, and the intermediate loop provides the references to the innermost loop. A hierarchical structure advantageously enables modularization of the control hardware, facilitates controller tuning since the controller may be tuned loop-by-loop, and allows the loops to operate at different rates.
The outer control loop, for example, may convert commanded shaft speed, power, or emissions to one or more target turbine inlet conditions to be used by the inner loop as a reference. The inner control loop regulates the PDC 12 in response to desired overall commanded PDTE output characteristics 14 such as, without limitation, shaft speed, power, or emissions output. The inner control loop uses component timing as control handles. The component timing affects operation parameters such as, without limitation, fuel and/or air fill fraction, purge fraction, equivalence ratio distribution and tube-to-tube relative timing Further, either the outer or inner control loops may use, without limitation, fuel flow, fuel pressure, and IGV position as additional control handles.
It can be appreciated that fuel-flow for a PDTE is not as simple as existing gas turbine engines. Fuel-flow for existing engines is regulated simply by operating a control valve to modulate the fuel-flow for more/less power, and to compensate for any variations in fuel supply pressure. The fuel-flow for a PDTE is controlled by either varying the fuel supply pressure or turning on/off additional fuel-valves on PD tubes 18, both of which change the equivalence ratio in the PD tubes 18. Further, fuel flow for a PDTE can be varied by changing the fuel-valve timing, as well as skip firing or completely shutting-down an entire PD combustor 12 or bundles of PD combustors. Consider for example, an optimum firing sequence represented by 1-2-3-4-5-6-1-2-3-4-5-6-1-2- . . . . One skip firing sequence for this embodiment is 1-2-3-4-5-6-wait-wait-wait-wait-wait-wait-1-2-3-4-5-6 that skips an entire firing cycle. Another skip firing sequence embodiment may be represented as, for example, 1-2-3-4-5-6-wait-wait-1-2-3-4-5-6. Yet another embodiment may be represented as 1-2-wait-4-5-6-1-2-wait-4-5-6. It can be appreciated that many other skip firing embodiments which are too numerous to describe herein are also encompassed by the principles described herein.
Further, fuel flow for a PDTE can be varied by changing the firing pattern and/or firing pattern repetition rate of a plurality of pulse detonation tubes. Consider for example, an optimum firing pattern represented by 1-2-3-4-5-6-1-2-3-4-5-6-1-2- . . . . A different firing pattern may look like 1-3-2-4-5-6-1-3-2-4-5-6 . . . , while another firing pattern may be represented as, for example, 2-1-6-5-4-3-2-1-6-5-4-3 . . . . Any firing pattern can be repeated a desired number of times before repeating itself to achieve a desired repetition rate. It can be appreciated that many other firing pattern embodiments which are too numerous to describe herein are also encompassed by the principles described herein.
Programmable controller 52 is thus directed by the algorithmic software integrated therein to regulate the controllable PDC 54 including pulse detonation tubes 18 such that commanded PDTE output characteristics 14 are met in order to achieve, without limitation, a desired overall PDTE shaft speed, power, or emissions output 16.
PDTE 60 further includes a programmable controller 52 configured with algorithmic software to regulate a plurality of controllable peripheral PDC components that may include, for example, and without limitation, one or more fuel valves 74, one or more air valves 72, and one or more ignition devices 88. The controllable multi-tube pulse detonation combustor (PDC) 62 is configured to initiate firing of one or more PD tubes 70 in response to operation of the plurality of controllable peripheral PDC components to regulate PDTE output characteristic such as, and without limitation, PDTE shaft speed, PDTE output power, and PDTE output emissions. Programmable controller 52 directed by algorithmic software operates to control operation timing parameters for the plurality of controllable peripheral PDC components in response to PDTE input conditions, such that one or more PD tube operating conditions can be different for at least one PD tube relative to another PD tube within the multi-tube PDC 62, and further such that detonation timing can be different for at least one PD tube relative to another PD tube within the multi-tube PDC 62.
Programmable controller 52 is thus directed by the algorithmic software integrated therein to regulate the controllable PDC 62 including pulse detonation tubes 70 such that turbine inlet conditions are met in order to achieve the desired overall PDTE output conditions such as, without limitation, shaft speed, power, or emissions output 16.
In summary explanation, PDTE rotational shaft speed, output power and output emissions commands are first transmitted to a PDTE according to one embodiment. A corresponding PDC including pulse detonation tubes is then regulated in response to the input commands in order to achieve the commanded PDTE shaft speed, output power and output emissions. A corresponding PDC controller generates component timing signals in response to the commanded PDTE shaft speed, output power and output emissions, to affect operation parameters such as, without limitation, fuel and/or air fill fraction, purge fraction, equivalence ratio distribution in the detonation tubes, and tube-to-tube relative timing to achieve the desired PDTE operation characteristics. Finally, the air inlet valve open time period, the fuel fill time period and the time of detonation for each PD tube is adjusted in response to the respective controller signals to achieve the commanded output, while the PDTE is operating in an acceleration mode, deceleration mode, or at a constant output. Sensing variables used by the algorithmic software may include, without limitation, fuel fill length, fuel supply pressure, fuel flow rates, and generated power.
The power generated via the PDTE can be determined and controlled using one or more control limit techniques familiar to those skilled in the art of power generation engines. These control limits may include, without limitation, speed limits, pressure limits, temperature limits, and/or mass flow limits Further details of such known control limit techniques are not discussed herein for brevity and to improve clarity regarding the principles described herein.
In further summary explanation, several different operational techniques have been described to modulate output conditions for a PDTE. The commanded shaft speed, output power, and/or output emissions, for example, can be achieved by varying the firing pattern repetition rate (e.g. frequency), skip firing, fill fraction, equivalence ratio, detonation versus quasi-detonation, exit nozzle area, and inlet mass flow of individual PDC tubes or groups of PDC tubes such that operating parameters can vary from tube-to-tube, or from one group of tubes to another group of tubes, and further such that tube-to-tube relative ignition timing can vary between tubes or groups of tubes.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
