Power plants – Combustion products used as motive fluid
Reexamination Certificate
1999-08-06
2001-03-27
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
C060S725000, C431S114000
Reexamination Certificate
active
06205764
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for the active damping of combustion oscillation in a combustion chamber and to a corresponding combustion apparatus.
An article entitled “Aktive Dampfung selbsterregter Brennkammerschwingungen (AIC) bei Druckzerstäuberbrennern durch Modulation der flüssigen Brennstoffzufuhr” [Active Damping of Self-Excited Combustion-Chamber Oscillations (AIC) in Pressure Atomizer Burners by Modulating the Liquid Fuel Supply] by J. Herrmann, D. Vortmeyer and S. Glei&bgr;, in VDI Reports No. 1090, 1993, describes how combustion oscillation occurs in a combustion chamber and how it can be actively damped. During combustion, in a combustion chamber, for example of a turbine, self-excited combustion oscillation may occur, which is also referred to as combustion instability. Such combustion oscillation arises as a result of interaction between a fluctuating release of power during combustion and acoustics of the combustion chamber. Combustion oscillation is often accompanied by high noise emission and mechanical load on the combustion chamber, which may lead to structural parts being destroyed. Active damping of combustion oscillation is achieved by modulation through the use of an actuating member (piezoelectric actuator). The actuating member modulates a fuel quantity which is supplied to a burner. A microphone records the acoustic oscillations in the combustion chamber. A regulating signal for regulating the modulation of the fuel quantity being supplied is derived from a microphone signal in such a way that the modulation of the fuel quantity being supplied takes place anti-cyclically to the combustion oscillation.
International Publication No. WO93/10401 has disclosed a burner configuration with two burners in a common combustion chamber. Each of the burners can be supplied with fuel through a fuel line. An acoustically acting element is coupled to a fuel line. It is preferably a passive element, in the form of a Helmholtz resonator, for example, which modifies the acoustic properties of the fuel line, i.e. which acoustically detunes the fuel line. In another configuration, the acoustically acting element is a loudspeaker which acts on fuel flowing through the fuel line. According to the single embodiment disclosed, the loudspeaker is driven through the use of a microphone disposed outside the combustion chamber.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a simple method for the active damping of combustion oscillation in a combustion chamber and a combustion apparatus in which the active damping of the combustion oscillation is possible in a simple manner, which overcome the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for the active damping of combustion oscillation, which comprises supplying each of at least two burners of a combustion chamber with at least one medium for combustion; damping combustion oscillation by control of at least two actuating members each influencing a regulating variable being a quantity of the at least one medium supplied to one of the burners; determining measured variables characterizing the combustion oscillation at least at one measuring point; and controlling the actuating members through a number of the measured variables being smaller than the number of the actuating members.
This method makes it possible, at a low outlay in terms of measurement, to carry out regulation for the active damping of combustion oscillation. The term “regulating variable” means a system variable which is described by a physical variable, for example a fuel quantity supplied at a specific point. In this sense, another regulating variable would, for example, be a fuel quantity supplied at another point or, for example, a quantity of combustion air supplied. An actuating member is accordingly not necessarily to be interpreted as a unit of equipment. The term “actuating member” may also embrace two or more devices which jointly influence a regulating variable, for example two loudspeakers that jointly modulate a combustion-air mass flow.
In accordance with another mode of the invention, fuel and combustion air are supplied for combustion, and a quantity of fuel supplied for combustion and/or a quantity of combustion air supplied for combustion is preferably used as a regulating variable, although other regulating variables may also be used at the same time. The fuel mass flow and/or the combustion-air mass flow is preferably modulated. It is consequently possible to carry out the active damping of combustion oscillation through the modulation of the fuel quantity supplied and/or of the combustion-air quantity supplied.
In combustion oscillation, natural acoustic oscillation or a sound field forms in the combustion chamber. A sound field is characterized by characteristic sound-field variables, such as, for example, sound pressure and sound velocity, the time profiles of which have particular periodic regularities. A sound field typically has spatial regions, within which the soundfield variables oscillate periodically at different amplitudes. Sound-field variables in different spatial regions of the sound field are shifted relative to one another in time in their oscillations in a manner which is characteristic of the sound field. In other words, they have a characteristic phase shift. If the spatial regions described have some regularity in their features, this is referred to as symmetry of the sound field.
In accordance with a further mode of the invention, exactly as many measured variables as are necessary for characterizing the natural oscillation are determined.
In accordance with an added mode of the invention, the control of at least one actuating member is preferably determined through the symmetry of the natural acoustic oscillation. The natural acoustic oscillation is characterized with the aid of a number of measured variables. The regulation of the actuating members is derived from this knowledge of the existing sound field through the symmetry of the natural acoustic oscillation in the combustion chamber. This is accomplished by taking into account the respective spatial position in which an actuating member influences the combustion oscillation. The phase and amplitude of the combustion oscillation at the point of action of an actuating member are known from the characterization of the natural acoustic oscillation. The regulation of each actuating member, as is necessary for damping the combustion oscillation, is thus obtained. The number of measuring points is therefore determined solely by the number of measuring points necessary for characterizing the natural oscillation.
In accordance with an additional mode of the invention, the actuating members are controlled anti-cyclically to the combustion oscillation. Anti-cyclic control brings about particularly efficient damping of the combustion oscillation. Anti-cyclic control denotes a regulating variable fluctuation which is inverted in relation to the self-excited combustion oscillation. In the case of harmonic combustion oscillation, this means that the regulating variable is applied with the same frequency, but in phase opposition.
In accordance with yet another mode of the invention, the method is employed in an annular combustion chamber of a gas turbine. An annular combustion chamber of a gas turbine has a relatively large number of burners which may each excite combustion oscillation. It is desirable to have the possibility of carrying out active damping of combustion oscillation for each burner through the use of its own actuating member. The number of measured variables to be determined for these actuating members may be kept small.
With the objects of the invention in view there is also provided a combustion apparatus, comprising a combustion chamber having at least two burners each to be supplied with at least one
Hantschk Carl-Christian
Hermann Jakob
Orthmann Armin
Vortmeyer Dieter
Zangl Peter
Casaregola Louis J.
Greenberg Laurence A.
Lerner Herbert L.
Stemer Werner H.
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