JPH04121425A - Active controller inhibiting instability resulting from combustion - Google Patents

Abstract

PURPOSE: To control combustion-induced instabilities in low frequency without entailing drop in engine performance by installing a phase shifting means which connects a pressure transducer means to a servovalve means, thereby reducing the amount of fuel supplied for combustion during pressure peaks and lenssening the extent of pressure flunctuations in a combustion chamber. CONSTITUTION: In a turbojet engine 1 provided with an active control 3 which adjusts a flow of fuel fed to one of combustor fuel nozzles 5, a dynamic pressure transducer 43 constituting this active control is set up in a combustion chamber 17 at the downstream of the spray nozzle 5, measuring the pressure fluctuations in the combustion chamber. After feeding to a measuring phase shifter 47, here a time-lag to be induced by the position of a sensor to the fuel nozzles, a time-lag to be induced by a servovalve 53 and a time-lag for fuel's evaporation and combustion are all adjusted. A phase signal is transmitted to the servovalve 53 through an amplifier 51. Subsequently the servovalve 53 is inserted into a fuel line, adjusting a partial flow of fuel to be fed through this line.

Description

[Detailed description of the invention]

[0001]

[Industrial application field]

The present invention relates to an active control system that suppresses low frequency instability caused by combustion in an engine, combustor, and afterburner. [0002]

[Conventional technology]

Most aircraft engines, afterburners, and stationary gas and liquid combustion combustors exhibit some combustion-induced instability, depending on operating conditions. Instabilities in aircraft main engines and stationary combustors are usually in the low frequency range and are characterized by burls/grackles.
The instability seen in afterburners consists of both low frequency oscillations (baul/grackle) and high frequency oscillations called screech. Traditionally, high frequency speech leaks have been addressed by passive treatment with acoustic liners and other similar means. However, these devices are not efficient enough to suppress low frequency vibrations. [0003] Depending on the conditions, the combustor, afterburner, and turbine combustor of an aircraft main engine may experience vibrations (oscillations) caused by unstable combustion as a result of a combination of unstable heat dissipation vibrations and sound pressure fluctuations. occurs. If such vibrations are not suppressed, in extreme cases they can become extremely large and cause physical collapse of the equipment. At a minimum, such vibrations are undesirable because they lead to undesirable metal fatigue. Conventional means of suppressing such vibrations in practical devices are limited to passive devices such as acoustic liners and Helmholtz resonators. Most devices of this type are not very effective at suppressing low frequency (below 500 Hz) vibrations. Current devices have a limited effective operating envelope and do not exhibit optimal performance in avoiding potentially damaging vibrations. [0004] Active control efforts using loudspeakers as actuators to change the acoustic boundary conditions in the combustor have been conducted in laboratory studies. Active control methods based on loudspeakers are extremely attractive as research subjects, but the relatively low energy output of loudspeakers and their large physical dimensions make practical speech-reach control difficult. It is not a means. [0005] Research has been conducted to achieve active control by adjusting the rate of gaseous fuel flow in the immediate vicinity of a flame holder. Sound pressure level reductions of up to 10 dB have been reported for laboratory scale combustors by using on-off actuators in feedback mode to adjust gas flow. However, the use of gaseous fuels is limited to gas turbine combustors, and for most practical devices such as aircraft combustors and afterburners using liquid fuels, active control methods are applied to control the combustion by adjusting the fuel flow. There is no known research on suppressing the vibrations that occur. The invention is applicable to main combustors and afterburners of aircraft engines as well as stationary main combustors using liquid fuel. Generally, in all such devices, the fuel is injected in the form of a liquid spray just upstream of the flame holder or stabilizer, with some type of air swirl-based atomization. Stabilize the flame with a recirculating wake or thin stream downstream of a flame holder or swirl stabilizer. [0006]

[Problem to be solved by the invention]

An object of the present invention is to provide an active control system that suppresses instability caused by low-frequency combustion in an engine, combustor, and afterburner without reducing performance. [0007]

[Means to solve the problem]

According to the present invention, an active control device is provided that suppresses instability caused by combustion in a combustion chamber having a fuel injection means therein. The active control device includes pressure transducer means for measuring pressure fluctuations in the combustion chamber and servo valve means for regulating the amount of fuel supplied to the fuel injection means. Phase shifting means connect the pressure transducer means to the servo valve means. The phase shift means adjusts the amount of fuel supplied for combustion at peak pressure times to reduce pressure fluctuations in the combustion chamber. [0008]

【Example】

In order to further clarify the purpose and effect of this invention,
Preferred embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same reference numerals indicate the same elements. [0009] FIG. 1 shows a turbojet engine 1 provided with an active control device 3 for regulating the fuel flow supplied to one of the combustor fuel nozzles 5. The engine 1 includes a generally cylindrical housing 7 that is open at both ends. The rotor of the compressor 11 and the rotor of the turbine 13 are provided on a common shaft. Compressor 11 and turbine 13 are arranged within housing 7 . Air is introduced into the compressor inlet through an inlet diffuser and duct 15 located at one end of the housing. Next, the air is compressed by a dynamic compressor 11,
into the annular combustion chamber 17. A plurality of fuel nozzles 5 arranged at the center of the swirl cup 21 introduce fuel to be mixed with air and combusted. Downstream of the combustion chamber 17, the heated air expands as it passes through a turbine, producing power to drive the compressor. The air can be further heated by further combustion with additional fuel in the combustion chamber 23, called an afterburner. The afterburner 23 is located near the other end of the housing 7 and includes a diffuser cone 25 and a plurality of fuel sprayers 27 extending radially inward through the housing. A first set of spray bars surrounds the diffuser cone 25 and a second set of spray bars extends radially inwardly downstream thereof. The orifices in each spray bar 27 are oriented perpendicular to the airflow, and as the fuel exits the spraybar, it is atomized and vaporized by the airflow. Immediately downstream of the fuel injected from the first set of spray bars, a first annular flame holder (frame holder) 31 with a V-shaped cross section, also called a gutter, is arranged. The apex of ■ is facing upstream. Arrow 33 indicates the direction of air flow. The second annular flame holder 35 with a V-shaped cross section is the first flame holder 31
and immediately downstream of the fuel injected from the second set of spray bars. The second flame stabilizer 35 is supported by a support member 37 in the housing 7 . The first flame holder 31 and the second flame holder 35 are supported by a support member 41 . [0010] A dynamic pressure transducer 43 constituting an active control device is placed in the combustion chamber downstream of the spray nozzle 5 to measure pressure fluctuations. pressure transducer 43
sends the electrical signal generated by the block 45 to a filter and preamplifier indicated by block 45. The filter removes high frequency noise and DC components from the signal. The filtered and amplified signal is sent to a phase shifter, indicated by block 47. Phase shifter 47 adjusts for the time delay introduced by the position of the sensor relative to the fuel nozzle, the time delay introduced by the servo valve, and the time delay in which the fuel evaporates and burns. Adjustment of the phase shifter can be done by adjusting the amount of phase shift required during actual operation, or by using an adaptive controller that provides the appropriate phase shift at different frequencies. You can also do it. Block the phase shifted signal 5
It is sent to a servo valve 53 through an amplifier indicated at 1. The servo valve 53 is inserted into a fuel line 55 that supplies one of the fuel nozzles 5 with fuel. Servo valve 53 regulates a portion of the fuel flow routed through the line. The feedback control response is mainly limited by the response of the servo valve 53. For example, a servo valve with a response frequency of 150Hz is
It is available as the 73 series manufactured by Ioog Inc., East Aurora, New York, USA. [0011] According to the present inventors' idea, the main mechanism that causes suffrage is the interaction between unstable heat dissipation vibration and sound pressure fluctuation, and the interaction that occurs in this way affects the equipment. It represents the extremely delicate balance between energy human power and the energy lost by equipment. In order for combustion instability to persist,
Lord Rayleigh was the first to point out that the unstable heat dissipation and the unstable pressure must, on average, be in phase per cycle.
ayleigh). Most commercial combustors have very little damping, and the balance between the energy input to the device as a result of unstable heat dissipation and pressure being in phase and the energy lost to the device due to acoustic and other viscous losses is extremely poor. It's subtle. Therefore, even a slight phase shift in the unstable heat dissipation in response to sound pressure vibrations in an appropriate direction is sufficient to disrupt this delicate balance and suppress such vibrations. The active controller regulates the fuel flow and therefore the unstable heat dissipation by a few percentage points in a feedback mode, thus effectively decoupling the unstable heat dissipation from the unstable pressure fluctuations. Therefore, sufficient phase shift occurs to suppress vibrations. Regulation of fuel flow by servo valves reduces the fuel flow available for combustion during pressure peaks. [0012] Referring now to FIG. 2, a turbojet 1 and active control device 3 of the type shown in FIG. 1 is shown. The dynamic pressure transducer 43 is placed in the afterburner 23 rather than in the combustion chamber 17 as in the previous example. Servo valve 53 regulates fuel flow to spray bar 27 rather than to fuel nozzle 5 . In operation, liquid fuel is injected through small orifice ports in the fuel spray bar just upstream of the flame holders 31 and 35 (in this example, the gutter) into a stream of hot air flowing therethrough. The fuel is thus mixed with the hot air flowing with it, atomized and vaporized as it travels downstream. As the partially mixed fuel-air mixture flows to the lip of the flame holder, a spanwise vortex is created. The axis of rotation of the spanwise vortex is perpendicular to the flow direction. These sludge migrate downstream, entraining hot recycle products, grow together, and then after some time delay (depending on fuel velocity, etc.) burn, releasing heat and thus This heat changes the dynamic pressure field within the afterburner 23. The resulting pressure fluctuations at the lip of the V-gutter, in turn, cause another set of dips, thus repeating the process. When the frequency with which this process occurs matches the acoustic resonance mode of the afterburner (geometry dependent), coupling occurs and a spurfreach occurs. The thin film serves to mix the relatively cool reactants with the hot recycle products and is therefore critical to flame maintenance. However, even though the fuel is injected in a steady state upstream of the flame stabilizer, the same flame holder also continues to vibrate due to unstable combustion. [0013] The active control device 3 adjusts the fuel injected upstream of the flame stabilizer by a small amount with an appropriate phase shift, so that the combustion occurs in-phase with the pressure oscillations, but slightly out of phase. Contains less fuel (and therefore releases slightly less energy). The result of this solution is that the heat dissipation is "on average" sufficiently "out of phase" with the pressure oscillations, so that the oscillations are suppressed. However, since the time delay is not known, the appropriate amount of phase shift required cannot be calculated in advance. The controller therefore operates in feedback mode. [0014] Afterburner action was simulated using a 3 x 3 inch spur reach combustor. The flame holder is a V gutter type (3
(3% occlusion), the fuel was injected 6 inches upstream of the flame holder using a conventional swirl spray nozzle. Preheat the air to about 600F with an electric preheater to help atomize the liquid fuel (kerosene). Without active control, the combustor operates at a main frequency of 13
It showed an unstable mode of quarter longitudinal wave at 0 Hz. FIG. 3 is a power spectrum measured by a dynamic pressure transducer placed 24 inches upstream of the flame holder. [0015] The active control feedback loop consisted of a pressure transducer placed 24 inches upstream of the flame holder, a Krohnhite-type high-order bandpass filter, a Tektronix
) amplifier, a PAR lock-in amplifier as a phase shifter, and an electronically controlled move servo valve as an actuator. The servovalve regulated fuel flow in response to the processed input signal. With appropriate amplification in the feedback loop and an appropriate amount of phase shift, a significant reduction in combustor dynamic activity was observed. FIG. 4 shows the power spectrum measured at the same location on the combustor with the active controller turned "ON". As can be seen from the figure, there is a significant decrease in dynamic activity at the main frequency of vibration. We found that turning the active control system ONJ reduced the overall sound pressure level in the combustor by approximately 4 dB, with minimal energy input to the system and adjusting the fuel flow by 5% of the average fuel flow. Higher order modes also appear to have been significantly reduced, even though they are outside the actuator's bandwidth. [0016] Feedback control shown in FIGS. 1 and 2 The device can be implemented as a digital or analog circuit.Although only one fuel nozzle has been shown regulating the fuel supply, it is possible to regulate the fuel supplied to several fuel nozzles. The fuel supplied to the spray bar can be similarly adjusted. [0017]

【Effect of the invention】

The above describes an active control device that suppresses low-frequency combustion-induced instability in the engine, combustor, and afterburner without degrading performance. [0018] Having described this invention with respect to several embodiments thereof, it will be apparent to those skilled in the art that various changes may be made therein in form and detail without departing from the spirit of the invention.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a typical turbojet engine equipped with an active control system for suppressing low frequency combustion-induced instability within the combustion chamber in accordance with one embodiment of the present invention.

FIG. 2 is a cross-sectional view of a representative turbojet engine incorporating an active control system for suppressing low frequency combustion-induced instability within the combustion chamber in accordance with another embodiment of the present invention.

FIG. 3 is a graph showing the power spectrum (in logarithmic volts) measured by a dynamic pressure transducer as a function of frequency for a simulated afterburner with the active control device of the invention turned off;

FIG. 4 is a graph showing the power spectrum (in logarithmic volts) measured by a dynamic pressure transducer as a function of frequency for a simulated afterburner with the active control device of the invention turned on;

[Explanation of symbols]

1 Turbojet engine 3 Control system 5 Fuel nozzle combustion chamber afterburner spray bar pressure transducer Filter/Preamp phase shifter amplifier servo valve fuel line

[Document person]

[Figure 1] drawing

[Figure 2]

[Figure 3]

[Figure 4]

Claims (6)

[Claims] 1. An active control device for suppressing instability caused by combustion in a combustion chamber having fuel injection means therein, comprising: pressure transducer means for measuring pressure fluctuations in the combustion chamber; and a pressure transducer means for measuring pressure fluctuations in the combustion chamber; and phase shifting means connecting said pressure transducer means to said servo valve means, said phase shifting means reducing the quantity of fuel supplied for combustion at pressure peaks. active control device that adjusts the combustion chamber to reduce pressure fluctuations in the combustion chamber. 2. The active control system of claim 1, wherein said servo valve means regulates approximately 5% of the total fuel delivered to the combustion chamber. 3. The active control device according to claim 1, further comprising filter means inserted between said pressure transducer means and said phase shift means for removing noise and DC components of the signal. 4. The apparatus of claim 3 further comprising amplifying means inserted between said phase shifting means and said servo valve means for increasing the gain of a signal from said phase shifting means driving said servo valve means. active control device. 5. A combustion chamber, a fuel injection means disposed within the combustion chamber, a pressure transducer means for measuring pressure fluctuations in the combustion chamber, a servo valve means for regulating fuel supplied to the fuel injection means, and the above. phase shifting means connecting a pressure transducer means to said servo valve means, said servo valve means being configured to reduce the amount of fuel supplied for combustion at pressure peaks to reduce pressure fluctuations in the combustion chamber. A jet engine that suppresses combustion instability. 6. The jet engine according to claim 5, wherein the combustion chamber constitutes an afterburner.