Device and method for operating a fuel burner

Abstract

Method for operating a fuel burner (100), wherein at least one operating parameter which characterizes a system natural frequency of the fuel burner (100) is determined (402), characterized by supplying a fuel combustion chamber (108) with air and supplying a fuel for combustion in the fuel combustion chamber (108) via an injection valve (106), wherein, depending on the at least one operating parameter, a setpoint value is determined (404), which characterizes an injection frequency which differs from the system natural frequency and whose integer multiples differ from the system natural frequency, wherein, depending on the setpoint value, a control signal for supplying the fuel through the injection valve with the injection frequency is determined (406), and the injection valve is controlled (408), in particular in a pulsed or clocked manner, depending on the control signal.

Description

[0001] The invention relates to a device and a method for operating a fuel burner.

[0002] In this regard, DE 10 2004 051 905 A1 discloses an exhaust gas burner whose injection valve is operated with an injection frequency higher than 30 Hz in order to prevent the burner flame from extinguishing.

[0003] DE 42 41 729 A1 discloses an actuator that, in combination with a control loop, enables active control of combustion stability in liquid-fuel burners by imposing mass flow or pressure fluctuations in a frequency range of approximately 50 to 1000 Hz on pressurized liquid flows. The actuator is located between a delivery device and a nozzle. As a control strategy for suppressing combustion vibrations, a corresponding anticyclical fuel supply is determined as a control signal from sound pressure and / or power fluctuations as the input signal.

[0004] DE 33 19 124 C2 discloses a fuel injection pump unit for an internal combustion engine that influences the fuel combustion process, particularly with regard to minimizing nitrogen oxide formation at low engine loads and ensuring appropriate power output at higher engine loads. For this purpose, valves are controlled with a duty cycle determined based on the accelerator pedal position, engine speed, and engine coolant temperature in order to adapt the fuel injection time and fuel injection quantity to the given load.

[0005] Due to its design, such a fuel burner forms a resonance system in which resonance effects occur due to the superposition of a vibration with a system natural frequency of the fuel burner and a vibration with an injection frequency or an integer multiple of the injection frequency of an injector. These resonance effects negatively impact the combustion stability of the fuel burner.

[0006] By a method and a device for operating a fuel burner according to the independent claims, the combustion stability is improved.

[0007] The method for operating the fuel burner comprises supplying a fuel combustion chamber with air and supplying a fuel for combustion in the fuel combustion chamber via an injection valve, wherein at least one operating parameter that characterizes a system natural frequency of the fuel burner is determined, wherein a target value is determined depending on the at least one operating parameter that characterizes an injection frequency that differs from the system natural frequency and whose integer multiples differ from the system natural frequency, wherein a control signal for supplying the fuel through the injection valve with the injection frequency is determined depending on the target value, and the injection valve is controlled in a pulsed or clocked manner depending on the control signal. As a result, combustion stability of the fuel burner is stabilized by targeted control of the injection valve.

[0008] Preferably, the target value is determined such that the injection frequency and / or at least one of the integer multiples of the injection frequency differs from the system's natural frequency by at least a predetermined value. This maintains a safety margin between the system's natural frequency and an injection frequency critical with respect to resonance or the harmonics related to the injection frequency.

[0009] Preferably, the at least one operating parameter characterizes a temperature, a pressure, a speed of sound, a composition of a gas mixture, and / or an air / fuel ratio during operation of the fuel burner. These parameters influence resonance behavior and are therefore particularly suitable for determining the setpoint.

[0010] Preferably, the setpoint characterizes a target damping for a vibration in the fuel burner that is smaller than the actual damping caused by the control at the injection frequency. As a result, the component of the superimposed vibration generated by the injection frequency has a damping effect on the superimposed vibration.

[0011] Preferably, the setpoint is determined as a function of a characteristic curve or a characteristic map that assigns the setpoint to the at least one operating parameter.

[0012] It can be provided that a system natural frequency is determined depending on the at least one operating parameter, the injection frequency is determined depending on the system natural frequency and the control signal is determined depending on the injection frequency.

[0013] Preferably, at least one target damping is determined depending on the system's natural frequency, which maximizes the damping, in particular a target damping from a damping range closest to the system's natural frequency, wherein the injection frequency is determined depending on the target damping. This achieves a particularly effective damping effect on the superimposed vibration.

[0014] A device for operating the fuel burner comprises a control device which is designed to control the fuel burner in order to supply a fuel combustion chamber with air, to supply fuel for combustion in the fuel combustion chamber via an injection valve, to determine at least one operating parameter which characterizes a system natural frequency of the fuel burner, to determine a setpoint value which characterizes an injection frequency which differs from the system natural frequency and whose integer multiples differ from the system natural frequency, depending on the setpoint value, to determine a control signal for supplying the fuel through the injection valve at the injection frequency and to control the injection valve depending on the control signal, in particular in a pulsed or clocked manner.

[0015] The control device is preferably designed to determine the setpoint value such that the injection frequency and / or at least one of the integer multiples of the injection frequency differs from the system natural frequency by at least a predetermined value.

[0016] The device preferably comprises at least one sensor for detecting the at least one operating parameter, wherein the at least one operating parameter characterizes a temperature, a pressure, a speed of sound, a composition of a gas mixture and / or an air / fuel ratio during operation of the fuel burner.

[0017] Preferably, the control device is designed to determine a setpoint value that characterizes a setpoint damping for a vibration in the fuel burner that is smaller than an actual damping by the control with the injection frequency.

[0018] The control device can be designed to determine the setpoint value depending on a characteristic curve or a characteristic map that assigns the setpoint value to the at least one operating parameter.

[0019] The control device can be designed to determine a system natural frequency depending on the at least one operating parameter, to determine the injection frequency depending on the system natural frequency and to determine the control signal depending on the injection frequency.

[0020] Preferably, the control device is designed to determine at least one target damping depending on the system natural frequency, which maximizes the damping, in particular a target damping from a damping range closest to the system natural frequency, and to determine the injection frequency depending on the target damping.

[0021] Further advantageous embodiments will become apparent from the following description and the drawing. The drawing shows: Fig. 1 a schematic representation of a fuel burner, Fig. 2 a temporal progression of unstable combustion, Fig. 3 a temporal course of a stable combustion, Fig. 4 aspects of a method for operating the fuel burner, Fig. 5 a time course of pressure and temperature during operation of the fuel burner, Fig. 6 a Campbell diagram with a temporal progression of frequencies and their amplitudes for the fuel burner, Fig. 7 a Bode diagram with a curve of attenuation plotted against the frequencies.

[0022] In Fig. 1, a fuel burner 100 is shown schematically.

[0023] The fuel burner 100 includes an optional air filter 102 through which air can be supplied from outside the fuel burner 100 via an air supply 104. The fuel burner 100 includes an injection valve 106 configured to supply fuel. The fuel burner 100 includes a fuel combustion chamber 108. In the example, the air is supplied to the fuel combustion chamber 108 through the air supply 104, with the injection valve 106 being arranged such that the fuel is injected into the fuel combustion chamber 108 to generate a fuel / air mixture. The injection valve 106 can also be arranged such that the fuel can be injected between the air supply 104 and the fuel combustion chamber 108 to generate the fuel / air mixture. Exhaust gas produced during combustion of the fuel / air mixture in the fuel combustion chamber 108 is discharged through an outlet section 110.

[0024] The air supply 104 can be an air pump or a vane that feeds into a supply line to supply the fuel combustion chamber 108. The fuel is metered, for example, using a timed fuel injector that includes the injection valve 106. The exhaust gases from the fuel combustion chamber 108 discharge into the outlet section 110, for example, into one or more exhaust pipes, and flow out into the surroundings of the fuel burner 100.

[0025] The described structure, based on the principle of a vibrating tube or a Helmholtz resonator, forms a resonant system with vibrations having one or more distinct system natural frequencies and corresponding damping behavior. The system natural frequency(s) and the damping behavior are determined by the geometric design of the fuel burner 100. Once excited, the resonant system can exhibit pronounced pulsations, which can lead to unstable combustion and / or extinction in the fuel burner 100, i.e., in the fuel combustion chamber 108. This is particularly the case when the vibrations propagate through the entire structure between the air filter 102 and the outlet section 110, i.e., through a supply and exhaust side. A basic excitation of the vibration occurs primarily during an initial ignition of the fuel burner 100.Additionally, air supply through air supply 104 and cyclic fuel metering can represent further excitations. Each injection and subsequent combustion of the fuel / air mixture leads to pressure pulsation, which can negatively impact the resonant system and its combustion stability. In particular, a superposition of the system's natural frequency or one of the system's natural frequencies with the injection frequency or a harmonic of the injection frequency can cause harmful resonance effects.

[0026] To mitigate harmful resonance effects or to influence resonance behavior so that pressure pulsations do not impair or improve combustion stability, a targeted injection frequency selection is beneficial. Two strategies can be used for this purpose.

[0027] A first strategy for stabilizing combustion consists in selecting the injection frequency of the injector such that neither this nor its harmonics can interfere with the system's natural frequency or one of the system's natural frequencies of the resonant system in such a way that resonance occurs. The system's natural frequency depends on geometric boundary conditions of the resonant system, for example, a diameter or length of the tubes or a volume of the fuel combustion chamber 108. The system's natural frequency also depends on the speed of sound in the combustion gas. Combustion gas here means the gas mixture in the respective section of the fuel burner 100, e.g., the exhaust gas resulting from the combustion of the fuel / air mixture or a mixture of fuel, air, and exhaust gas.

[0028] Since the speed of sound increases with rising temperature, the system's natural frequency also increases with rising temperature of the gas mixture. At the same time, the speed of sound depends on the gas composition and thus on the air / fuel ratio during operation. The injection frequency is adapted to the operation, as described below, so that a sufficient safety margin can be guaranteed between the system's natural frequency, the injection frequency, and its harmonics under all operating conditions. If the injection frequency or one of its harmonics and the system's natural frequency or frequencies can no longer overlap in such a way that a resonance occurs excited by the injection frequency or one of its harmonics, then significantly more stable, extinction-resistant combustion behavior is achieved.

[0029] A device 112 for operating the fuel burner 100 according to a first strategy comprises a control device 114 which is designed to control the fuel burner 100 in order to supply the fuel combustion chamber 108 with air and to supply fuel for combustion in the fuel combustion chamber 108 via the injection valve 106.

[0030] The control device 114 is configured to determine at least one operating parameter 116 that characterizes a system natural frequency of the fuel burner 100. In the example, the device 112 comprises at least one sensor 118 for detecting the at least one operating parameter 116. In the example, the sensor 118 transmits the at least one operating parameter 116 to the control device 114. The at least one operating parameter 116 can characterize a temperature, a pressure, a speed of sound, and / or a composition of a gas mixture or an air / fuel ratio during operation of the fuel burner.

[0031] The control device 114 is designed to determine, depending on the at least one operating parameter 116, a setpoint value which characterizes an injection frequency which differs from the system natural frequency and whose integer multiples, ie harmonics, differ from the system natural frequency.

[0032] The control device 114 is configured to determine, depending on the setpoint, a control signal 120 for supplying the fuel through the injection valve 106 at the injection frequency and to control the injection valve 106, in particular in a pulsed or clocked manner, depending on the control signal 120. In the example, the control device 114 is also configured to output a control signal 122 for controlling the air supply 104 in order to generate a fuel / air mixture for combustion.

[0033] The fuel / air mixture for combustion is adjusted, for example, depending on setpoints for controlling the air supply 104 and the injection valve 106. The control device 114 comprises, for example, a microcontroller and an output stage for outputting the control signal 120 and the control signal 122. A characteristic curve or characteristic map configured as described below can be stored in a memory, for example in the microcontroller.

[0034] The control device 114 can be designed to determine the setpoint value depending on a correspondingly data-enabled characteristic curve or a correspondingly data-enabled characteristic map, which assigns a specific setpoint value to each value of the at least one operating parameter 116.

[0035] In the example, the control device 114 is designed to determine the setpoint value for the injection frequency with which the injection valve 106 is to supply fuel.

[0036] The control device 114 can also be designed to determine the system natural frequency as a function of the at least one operating parameter 116 and to determine the setpoint value as a function of the system natural frequency in such a way that injection takes place at the injection frequency.

[0037] The control device 114 is designed to determine the control signal 120 therefor depending on the setpoint value for the injection frequency.

[0038] In one aspect, the control device 114 is configured to determine the setpoint value such that, for the setpoint value, the injection frequency and / or at least one of the integer multiples of the injection frequency differs from the system's natural frequency by at least a predetermined value. Thus, the safety margin according to the first strategy is maintained.

[0039] In Fig. 2 is a time profile of an air mass flow m for an unstable combustion in the fuel burner 100, shown with a solid line In Fig. 2 shows a time course of a temperature T with a dashed line. In the Fig. In the steady-state operation shown in Figure 2, the injection frequency has a fixed value that is specified independently of the system's natural frequencies. Due to the superposition of the injection frequency and its integer multiples with one of the system's natural frequencies, the entire system oscillates due to strong pressure pulsations. This occurs after initial ignition, particularly in the period between seconds 10 and 45. Fig. 2. From second 45 onwards, an area of stable combustion follows.

[0040] In Fig. 3 shows a time profile of a stable combustion achievable by the control device 114 in the fuel burner 100. In Fig. 3 shows the time course of the air mass flow ṁ, shown with a solid line. In Fig. 3 shows the time course of the temperature T with a dashed line. Fig. With the injection frequency selection shown in Figure 3, there is no superposition of the injection frequency or an integer multiple thereof with the system's natural frequency. This extends the stable operating range of the entire system after initial ignition to the range between 10 seconds and 45 seconds.

[0041] Based on the Fig. 4, a method for operating the fuel burner according to the first strategy is described below.

[0042] The method provides for supplying air to the fuel combustion chamber 108 and supplying the fuel for combustion in the fuel combustion chamber 108 via the injection valve 106.

[0043] In a step 402, the at least one operating parameter 116 is determined. The at least one operating parameter 116 characterizes the system natural frequency of the fuel burner 108. In the example, the at least one operating parameter 116 is a temperature detected by the sensor 118. The pressure, the speed of sound, and / or the composition of the gas mixture or the air / fuel ratio can also be used during operation of the fuel burner.

[0044] It may be provided to use one or more of these operating parameters. Instead of or in addition to the sensor 118, a modeling of one or more operating parameters depending on measured sensor data may be used.

[0045] A step 404 is then executed.

[0046] In step 404, the setpoint is determined depending on the at least one operating parameter 116. The setpoint characterizes the injection frequency, which differs from the system's natural frequency and whose integer multiples differ from the system's natural frequency. The setpoint can be determined such that the injection frequency differs from the system's natural frequency by at least a predetermined value. The setpoint can be determined such that, additionally or alternatively, at least one of the integer multiples of the injection frequency differs from the system's natural frequency by a predetermined value. The predetermined value is specified, for example, as a safety margin.

[0047] The setpoint can be determined depending on the characteristic curve or the characteristic map that assigns the setpoint to the at least one operating parameter 116. For implementation, for example, a parameterizable characteristic map for the injection frequency of the injector 106 is used. In the example, the characteristic map is dependent on operating parameters such as temperature and air / fuel ratio, independent of the geometry of the fuel burner, and assigns the injection frequency to these parameters independently of the geometry. The fuel burner 100 can thus be operated stably, regardless of the design of the resonance bodies in the fuel burner 100.

[0048] In contrast, it can also be provided that in step 404 the system natural frequency is determined depending on the at least one operating parameter 116 and the injection frequency is determined as a target value depending on the system natural frequency.

[0049] A step 406 is then executed.

[0050] In step 406, the control signal 120 for supplying fuel through the injection valve 106 at the injection frequency is determined depending on the setpoint. The control signal 120 is determined, for example, depending on a design of the injection valve 106 such that the injection valve 106 is controlled in a pulsed or clocked manner, in the example, so that the injection frequency is adjusted.

[0051] A step 408 is then executed.

[0052] In step 408, the injection valve 106 is controlled, in particular in a pulsed or clocked manner, depending on the control signal 120. This stabilizes the combustion stability of the fuel burner 100 through targeted control of the injection valve 106. This prevents disruptive resonance behavior induced by the superposition of the injection frequency and the system's natural frequency.

[0053] These steps are performed in this or another order to control the fuel burner 100 in its operation.

[0054] A second strategy for stabilizing combustion is to use the injection frequency to influence the system's resonance frequency during operation. If the fuel is delivered at an injection frequency that is very close to the system's natural frequency, the entire system tends to adopt the injection frequency. In this respect, the injector 106 assumes a synchronization function. It is thus possible to slightly shift an unfavorable oscillation frequency of the overall system. This can be used to synchronize an already oscillating system to a frequency with high damping. The amplitudes of the pressure pulsations decrease as a result of the damping, and the system operates more smoothly and stably.

[0055] In this aspect, the control device 114 may be configured to determine a setpoint value that characterizes a setpoint damping for a vibration in the fuel burner 100 that is smaller than an actual damping due to the control with the injection frequency.

[0056] The control device 114 can be configured to determine, depending on the system's natural frequency, at least one desired damping that maximizes the damping. Preferably, the control device 114 is configured to determine a desired damping from a damping range closest to the system's natural frequency and to determine the injection frequency depending on the desired damping.

[0057] The setpoint characterizes a setpoint damping for a vibration in the fuel burner 100, which is smaller than an actual damping due to the control with the injection frequency.

[0058] A method for operating the fuel burner 100 according to the second strategy, in contrast to the method described for the first strategy, provides that in step 404 the target value is determined as the injection frequency as a function of the system's natural frequency. For this purpose, at least one target damping is determined that maximizes damping of the system's natural frequency with the injection frequency. In the example, the target damping is determined from the damping range closest to the system's natural frequency, and the target value for the injection frequency is determined as a function of the target damping. The injection frequency is specifically selected in the damping range closest to the system's natural frequency. This can be specifically specified in the characteristic map.

[0059] An example of the second strategy can be found in the Fig. 5 to 7.

[0060] In Fig. 5, a temporal progression of pressure pulsations is shown as an envelope with a solid line. A temporal progression of an air mass flow ṁ at the outlet section 110 is shown with a dashed line. A temporal progression of a temperature T, for example, at the outlet section 110, is shown with a dash-dot line.

[0061] In Fig. Figure 6 shows a Campbell diagram for an injection frequency of 150 Hz and a 3rd harmonic of the injection frequency at 450 Hz and a curve of the superimposed oscillation.

[0062] In Fig. Figure 7 shows a Bode diagram for a frequency response of damping through the injection frequency, in which an area of maximum damping at a frequency of 450 Hz is marked by an arrow.

[0063] In summary, the Fig.5 to 7, that after an initial ignition from second 54 a maximum damping by the third harmonic of the injection frequency with 450 Hz a synchronization of the superimposed oscillation to a frequency of 450 Hz takes place, at which an amplitude of the pressure pulsation is significantly reduced.

Claims

[1] Method for operating a fuel burner (100), wherein at least one operating parameter characterizing a system natural frequency of the fuel burner (100) is determined (402), characterized by supplying a fuel combustion chamber (108) with air and supplying a fuel for combustion in the fuel combustion chamber (108) via an injection valve (106), wherein a setpoint value is determined (404) as a function of the at least one operating parameter, which characterizes an injection frequency which differs from the system's natural frequency and whose integer multiples differ from the system's natural frequency, wherein a control signal for supplying the fuel through the injection valve with the injection frequency is determined (406) as a function of the setpoint value, and the injection valve is controlled (408) in a pulsed or clocked manner as a function of the control signal. [2] Method according to claim 1, characterized bythat the setpoint is determined such that the injection frequency and / or at least one of the integer multiples of the injection frequency differs from the system natural frequency by at least a predetermined value. [3] Method according to one of the preceding claims, characterized by that the at least one operating parameter characterizes a temperature, a pressure, a speed of sound, a composition of a gas mixture and / or an air / fuel ratio during operation of the fuel burner. [4] Method according to one of the preceding claims, characterized by that the setpoint characterizes a setpoint damping for a vibration in the fuel burner, which is smaller than an actual damping due to the control with the injection frequency. [5] Method according to one of the preceding claims, characterized bythat the setpoint is determined (404) as a function of a characteristic curve or a characteristic map which assigns the setpoint to the at least one operating parameter. [6] Method according to one of the preceding claims, characterized by that a system natural frequency is determined (404) depending on the at least one operating parameter, the injection frequency is determined (404) depending on the system natural frequency and the control signal is determined (406) depending on the injection frequency. [7] Method according to claim 6, characterized by that, depending on the system natural frequency, at least one target damping is determined which maximizes the damping, in particular a target damping from a damping range closest to the system natural frequency, wherein the injection frequency is determined depending on the target damping. [8] Device (112) for operating a fuel burner (100), which is designed to determine at least one operating parameter (116) which characterizes a system natural frequency of the fuel burner, characterized bythat the device (112) comprises a control device (114) which is designed to control the fuel burner (100) in order to supply a fuel combustion chamber (108) with air, to supply fuel for combustion in the fuel combustion chamber (108) via an injection valve (106), to determine a setpoint value as a function of the at least one operating parameter, which characterizes an injection frequency which differs from the system's natural frequency and whose integer multiples differ from the system's natural frequency, to determine a control signal (120) for supplying the fuel through the injection valve (106) at the injection frequency as a function of the setpoint value and to control the injection valve (106) as a function of the control signal (120), in particular in a pulsed or clocked manner. [9] Device according to claim 8, characterized bythat the control device (114) is designed to determine the setpoint value such that the injection frequency and / or at least one of the integer multiples of the injection frequency differs from the system natural frequency by at least a predetermined value. [10] Device (112) according to claim 8 or 9, characterized by that the device (112) preferably comprises at least one sensor (118) for detecting the at least one operating parameter (116), wherein the at least one operating parameter (116) characterizes a temperature, a pressure, a speed of sound, a composition of a gas mixture and / or an air / fuel ratio during operation of the fuel burner (100). [11] Device (112) according to one of claims 8 to 10, characterized bythat the control device (114) is designed to determine a setpoint value which characterizes a setpoint damping for a vibration in the fuel burner (100) which is smaller than an actual damping due to the control with the injection frequency. [12] Device (112) according to one of claims 8 to 11, characterized by that the control device (114) is designed to determine the setpoint value as a function of a characteristic curve or a characteristic map which assigns the setpoint value to the at least one operating parameter (116). [13] Device (112) according to one of claims 8 to 12, characterized by that the control device (114) is designed to determine a system natural frequency depending on the at least one operating parameter (116), to determine the injection frequency depending on the system natural frequency and to determine the control signal (120) depending on the injection frequency. [14] Device (112) according to one of claims 8 to 13, characterized bythat the control device (114) is designed to determine, depending on the system's natural frequency, at least one desired damping which maximizes the damping, in particular a desired damping from a damping range closest to the system's natural frequency, and to determine the injection frequency depending on the desired damping.

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