EP3290798B1 - Method for controlling a fuel/air ratio in a heating system and a control unit and a heating system - Google Patents

Description

The invention relates to a method for setting and regulating a fuel-air ratio in a heating system. The invention also relates to a control unit which is designed to carry out the method according to the invention and to a heating system with the control unit according to the invention.

State of the art

To ensure optimal combustion, it is necessary to ensure the correct fuel-air ratio when operating gas burners. For this purpose, the gas burner is regulated on the basis of a combustion parameter measured by a sensor system, in which this combustion parameter is matched to a target combustion parameter. The correct functioning of the sensors used to determine the combustion parameter must be guaranteed. Gas burners are known from the prior art, which for this purpose execute methods for calibrating the corresponding sensors. As a rule, the target combustion parameter is adapted to changing internal and / or external conditions. In such calibration procedures, the gas burner is largely operated over its entire power range. This has the disadvantage that more pollutants can be emitted during such a calibration. The duration of such a calibration is in the range from several seconds to minutes. That has the added bonus Disadvantage that during this time the gas burner is not available for normal operation. Prior art calibration methods are disclosed in US Pat EP0770824 and the EP1750058 known.

Disclosure of the invention benefits

• Erzeugen einer vorübergehenden, zeitlichen Fluidzufuhränderung einer Fluidzufuhrkenngröße, wobei eine Zeitdauer der Fluidzufuhränderung pulsartig und kurz gegenüber im üblichen Betrieb des Heizsystems vorgesehenen zeitlichen Variationen der Fluidzufuhrkenngröße ist,
• Versuch, ein Signalmaximum einer mit der zeitlichen Fluidzufuhränderung korrelierten zeitlichen Änderung von mindestens einer Verbrennungskenngröße zu ermitteln,
• Ermitteln einer Sollverbrennungskenngröße auf Basis des Signalmaximums, falls ein Signalmaximum ermittelt wurde,
• Regeln des Heizsystems auf Basis der Sollverbrennungskenngröße, falls ein Signalmaximum ermittelt wurde,

und wobei die Fluidzufuhränderung so gewählt ist, dass bei der zeitlichen Änderung von der mindestens einen Verbrennungskenngröße ein Verbrennungskenngrößenmaximum mindestens zwei Mal angenommen wird, und wobei in einem zusätzlichen Schritt überprüft wird, ob die zeitliche Änderung der mindestens einen Verbrennungskenngröße eine Doppelpeakstruktur aufweist, und wenn festgestellt wird, dass die zeitliche Änderung der mindestens einen Verbrennungskenngröße keine Doppelpeakstruktur aufweist, die Fluidzufuhränderung in den nächsten Schritten vergrößert wird, hat den Vorteil, dass die Sollverbrennungskenngröße im laufenden, regulären Betrieb des Heizsystems ermittelt werden kann. Das Verfahren stellt nur einen kurzzeitigen Eingriff in die Regelung des Heizsystems dar, bei dem nur kleine Fluidzufuhränderungen vorgenommen werden im Vergleich zu möglichen gesamten Fluidzufuhränderungen im Betrieb des Heizsystems. Auf diese Weise wird das Heizsystem stets mit einem vorgesehenen, optimierten Brennstoff-Luft-Verhältnis betrieben. Das Brennstoff-Luft-Verhältnis wird auch als Lambdawert bezeichnet. So wird eine vorgesehene Leistung des Heizsystems unter einem minimalen Schadstoffausstoß erzeugt. Zusätzlich entfällt die Notwendigkeit, spezielle Kalibrierzyklen zur Einstellung der Sollverbrennungskenngröße zu fahren. Das hat den Vorteil, dass keine weiteren Emissionen entstehen und das Heizsystem weitgehend immer in einem Regelbetrieb operieren kann, sodass es stets im vollen Umfang zur Verfügung steht. Dadurch, dass die Fluidzufuhränderung so gewählt ist, dass bei der zeitlichen Änderung von der mindestens einen Verbrennungskenngröße das Verbrennungskenngrößenmaximum mindestens zweimal angenommen wird, wird das Signalmaximum besonders zuverlässig erkannt. Das ermöglicht eine besonders präzise Bestimmung der Sollverbrennungskenngröße.The method according to the invention for setting and regulating a fuel-air ratio in a heating system, which comprises the following steps:

• Generating a temporary, temporal change in fluid supply of a fluid supply parameter, with a duration of the fluid supply change being pulse-like and short compared to the temporal variations of the fluid supply characteristic provided in normal operation of the heating system,
• Attempt to determine a signal maximum of a change in time of at least one combustion parameter that is correlated with the change in fluid supply over time,
• Determination of a target combustion parameter based on the signal maximum, if a signal maximum was determined,
• Control of the heating system on the basis of the target combustion parameter, if a signal maximum has been determined,

and wherein the fluid supply change is selected such that a combustion parameter maximum is assumed at least twice for the change over time of the at least one combustion parameter, and in an additional step it is checked whether the change over time of the at least one combustion parameter has a double-peak structure, and if it is determined If the change over time of the at least one combustion parameter does not have a double peak structure, the fluid supply change is increased in the next steps, has the advantage that the target combustion parameter can be determined during ongoing, regular operation of the heating system. The method represents only a short-term intervention in the regulation of the heating system, in which only small fluid supply changes are made compared to possible total fluid supply changes during operation of the heating system. That way it becomes Heating system always with an intended, optimized fuel-air ratio operated. The fuel-air ratio is also known as the lambda value. In this way, the intended output of the heating system is generated with minimal pollutant emissions. In addition, there is no need to run special calibration cycles to set the target combustion parameter. This has the advantage that there are no further emissions and that the heating system can largely always operate in regular operation so that it is always fully available. The fact that the change in fluid supply is selected in such a way that the maximum combustion parameter is assumed at least twice when the at least one combustion parameter changes over time means that the signal maximum is detected particularly reliably. This enables a particularly precise determination of the target combustion parameter.

"Heating system" is understood to mean at least one device for generating thermal energy, in particular a heating device or heating burner, in particular for use in a building heating system and / or for generating hot water, preferably by burning a gaseous or liquid fuel. A heating system can also consist of several such devices for generating thermal energy and other devices that support heating, such as hot water and fuel storage tanks.

A "fluid supply parameter" is to be understood in particular as a scalar parameter which is correlated in particular with at least one fluid, in particular a combustion air flow, a fuel flow and / or a mixed flow, in particular consisting of a combustion air and a fuel, that is fed to a burner unit of the heating system . Advantageously, in particular by means of a control and / or regulating unit of the heating system, at least based on the fluid supply parameter, a volume flow and / or a mass flow of the at least one fluid are closed and / or the volume flow and / or the mass flow of the at least one fluid are determined. An example of a fluid supply parameter is the specification of an opening width of a fuel valve. A “temporary, temporal change in fluid supply” is to be understood as a temporally restricted variation in the fluid supply parameter, so that it deviates from the value of the fluid supply parameter before the fluid supply change begins. The fluid supply parameter is preferably increased or decreased over the period of the fluid supply change. Preferably, the fluid supply parameter is first monotonically increased and then monotonically decreased, or first monotonically decreased and then monotonically increased. The duration of the fluid supply change is preferably pulse-like and short compared to the time variations of the fluid supply parameter provided in normal operation of the heating system.

A “pulse”, a “pulse-like change” or a “pulse-shaped signal” is to be understood as a characteristic of a characteristic which is brought from a first value to at least a second value different from the first value within a limited period of time. A "pulse" is sometimes referred to as an "impulse", especially in electrical engineering.

A “combustion parameter” is to be understood in particular as a scalar parameter which is correlated in particular with the combustion, in particular the mixture, in particular from the combustion air and the fuel. An example of a combustion parameter is an ionization current, which is measured on a flame of the heating system. Advantageously, in particular by means of the control and / or regulating unit of the heating system, at least the combustion parameter can be used to infer the presence and / or quality of the combustion and / or the presence and / or the quality of the combustion can be determined. Advantageously, a measure for the quality of the combustion can be clearly assigned on the basis of the combustion parameter at least in partial intervals and at least in certain operating states of the heating system. An example of a measure for the quality of combustion is the fuel-air ratio. The combustion parameter advantageously corresponds to at least one or exactly one measured value that depicts and / or characterizes the combustion, such as a combustion signal, in particular light intensity, pollutant emissions, temperature and / or advantageously an ionization signal, or the combustion parameter can be clearly assigned to such a measured value A "signal maximum" is to be understood as the maximum amplitude of the combustion parameter in a period of time that is correlated with the change in the fluid supply parameter over time. A signal maximum is in particular the maximum amplitude of a pulse of the fluid supply parameter. A “combustion parameter maximum” should be understood to mean a maximum possible value of the combustion parameter with a constant burner output parameter in at least certain operating states of the heating system. The combustion parameter maximum can advantageously be assigned unambiguously to a well-defined value of the fuel-air ratio. A combustion parameter maximum is a maximum possible value of the combustion parameter with a constant burner output parameter.

“Burner output parameter” is to be understood in particular as a parameter which is correlated with the output, in particular a heating output, of the heating system. The power, in particular the heating power, of the heating system can advantageously be determined, in particular by the control and / or regulating unit of the heating system, at least on the basis of the burner power parameter. Advantageously corresponds to Burner output parameters at least one or exactly one measured value representing the output or can be clearly assigned to such a measured value. Such a measured value can be, for example, a temperature, an air flow rate, a fan control signal or a fan speed.

An "attempt" to determine a signal maximum of a temporal change in at least one combustion parameter correlated with the temporal fluid supply change is to be understood as a method step in which a signal maximum of a temporal change in at least one combustion parameter correlated with the temporal fluid supply change is measured or determined . Depending on the result or value of the signal maximum, different following steps can optionally be selected in the further course of the method, if this is necessary and / or desired.

"Control of the heating system" means the one-time or repeated, in particular periodic, setting of operating parameters of the heating system so that the heating system can always fulfill the specified and / or requested performance to the full extent, especially under changing internal and external conditions, in particular with Wear processes and changing boundary and environmental conditions. "Operating parameters" are to be understood as parameters that are used by the control of the heating system to control and monitor processes taking place in the heating system. Examples of “operating parameters” are the fan speed or the fan speed characteristic, a flame ionization characteristic or an opening width of a fuel control valve.

“Setpoint combustion parameter” is to be understood in particular as a scalar parameter which describes the desired size of the combustion parameter. If the combustion parameter assumes the value of the set combustion parameter, the combustion has the intended properties, in particular with regard to pollutant emissions. With "regulating the heating system on the basis of the nominal combustion parameter" is meant an operation of the heating system in which the operating parameters are set so that the combustion parameter largely assumes the value of the nominal combustion parameter.

The features listed in the subclaims allow advantageous developments of the method according to the main claim.

If the heating system is regulated on the basis of a standard combustion parameter, if no signal maximum has been determined, this has the advantage that the heating system remains functional even with a signal maximum that cannot be determined. This will ensure the reliability of the heating system.

If a first error reaction is carried out if no signal maximum is determined, the reliability of the method increases. If no signal maximum can be determined, the heating system is in an unfavorable operating state which is corrected by the first error reaction or to which the first error reaction is used.

If the change in fluid supply is selected as a function of a burner output parameter, this enables the required change in the fluid supply parameter to be precisely adapted in order to assume the combustion parameter maximum at least twice. In this way, the required fluid supply change can be minimized, so that the required amount of fluid, preferably fuel, is saved and so emissions are reduced.

If, in an additional step, a temporary additional fluid supply change is generated, this additional fluid supply change opposing the fluid supply change, this has the advantage that the additional heating power and the additional emissions caused by the fluid supply change are compensated. As a mean over time over the change in fluid supply and the additional change in fluid supply, the fluid supply parameter has the value provided in regular operation.

According to the invention, it is checked in an additional step whether the change over time of the at least one combustion parameter has a double peak structure. This has the advantage that it is reliably verified whether the signal maximum corresponds to the maximum combustion parameter. "Double peak structure" is to be understood as a time course of the combustion parameter in a period of time correlated with the time change in the fluid supply parameter, which has at least two maxima, possibly with largely the same amplitude.

If a first error reaction is carried out if no double peak structure is recognized, the method becomes more robust and reliable in this way. In this way, the precision and reliability of the determination of the target combustion parameter is improved.

If it is established that the change over time of the at least one combustion parameter does not have a double peak structure, the fluid supply change is increased in the next steps in order to enable the detection of a double peak structure in the further course of the method. This makes the method for setting and regulating a fuel-air ratio particularly robust and reliable. Are there by "next steps" thereafter to understand the following steps of the method in which a fluid supply change is generated. In particular, “next steps” are to be understood as meaning steps that belong to a next iteration of the method.

If the target combustion parameter is determined by forming the product of the signal maximum with a calibration factor, a particularly simple and reliable method for determining the target combustion parameter is implemented. In addition, in this way, all relevant influences on the combustion are automatically taken into account when selecting the target combustion parameter which have an influence on the combustion parameter maximum. This saves the need for additional sensors to take these influences into account.

If the fluid supply parameter corresponds to a control signal for metering a fuel and / or the combustion air and / or a mixture of a fuel and combustion air, no measurement of the fuel and / or the combustion air and / or a mixture of a fuel and combustion air or a Flow rate of these fluids required. This simplifies the process and makes it robust against malfunctions.

If the at least one combustion parameter is determined by an ionization current measurement on a flame of the heating system, this is particularly advantageous since there is a functional relationship between the ionization current on a flame and the fuel-air ratio, which can be evaluated particularly favorably. In particular, the ionization stream has a combustion parameter maximum which is at a fuel-air ratio of 1.

The method is further improved if the burner output parameter is a fan speed or depends on it and / or a mass flow of combustion air and / or a mixture of fuel and combustion air is or depends on this and / or a volume flow of combustion air and / or a mixture is composed of a fuel and combustion air or depends on this and / or a running time of a combustion air and / or a mixture of a fuel and combustion air is or depends on this. The fan speed can be determined easily and reliably and provides a good estimate of the burner output. A mass flow and / or a volume flow of a combustion air and / or a mixture of a fuel and combustion air allow a particularly precise estimation of the burner output. A running time of a combustion air and / or a mixture of a fuel and combustion air can be determined particularly simply and inexpensively.

If the change in fluid supply over time has an at least largely rectangular shape, this has the advantage that the change over time in the at least one combustion parameter can be detected particularly easily. In this way the reliability of the method is further increased. Here, “largely rectangular shape of the fluid supply change” is to be understood as a time course of the fluid supply parameter in which the fluid supply parameter initially has a normal value. The fluid supply parameter is then quickly increased to a largely constant maximum supply value. The fluid supply parameter is then quickly reduced to the normal value. This time course of the fluid supply parameter has the shape of a rectangular function to a good approximation. Such a time course of the fluid supply parameter is usually referred to as a square-wave signal.

The use of a control unit for a heating system, the control unit being set up to carry out the method according to the invention for checking and regulating a fuel-air ratio in a heating system, has the advantage that, by operating the heating system with the correct setting of the fuel Air ratio, the durability of the heating system is increased, malfunctions are avoided and thus safety is increased.

A heating system with a control unit according to the invention, with a metering device for a fuel and / or for combustion air and / or for a mixture of a fuel and combustion air, as well as with an ionization probe on a flame and with a fan with variable fan speed has the advantage that in Operation of the heating system an incorrect setting of the fuel-air ratio is largely prevented. In this way, unforeseen, heavy loads on the heating system due to, for example, too high burner temperatures and / or too high fan speeds and / or too high soot emissions and / or too strong vibrations are avoided. This enables the heating system to be manufactured inexpensively. In addition, the fuel consumption is reduced and the service life of the heating system is increased or the time interval between the required inspection intervals is reduced.

If the heating system has at least one metering device for a fuel and / or for combustion air and / or for a mixture of a fuel and combustion air, a change in a fluid supply parameter over time can thus be generated particularly easily.

In this context, a “metering device” is to be understood as meaning in particular an, in particular electrical and / or electronic, unit, in particular actuator unit, advantageously actuating unit, which is provided to feed the at least one fluid, in particular the combustion air flow, the fuel flow and / or to influence the mixture flow, in particular from the combustion air and the fuel. In particular, the at least one metering device is provided to set, regulate and / or promote a volume flow and / or a mass flow, in particular the combustion air and / or the fuel. The metering device for combustion air can advantageously be designed as a fan, in particular with a variable speed, and / or preferably as a blower, in particular with a variable speed. The metering device for fuel can advantageously be designed as a, in particular throughput variable, fuel pump and / or preferably as, in particular throughput variable, fuel valve. In particular, the metering device for combustion air and / or the metering device for fuel are provided to modulate a heating output of the heater device.

If the heating system has an ionization probe on the flame of the heater, a particularly inexpensive and reliable sensor for measuring a combustion parameter is implemented. Ionization detectors are usually used in heating devices for flame detection.

If the heating system has a fan with a variable fan speed, a simple and robust means for setting and determining the output of the heater can be implemented in this way.

drawings

• Figur 1 eine schematische Darstellung des erfindungsgemäßen Heizsystems mit der erfindungsgemäßen Steuereinheit,
• Figur 2 das erfindungsgemäße Verfahren zum Regeln und/oder Kalibrieren eines Heizsystems,
• Figur 3 eine schematische Darstellung einer Fluidzufuhränderung und einer zeitlichen Änderung von einer Verbrennungskenngröße,
• Figur 4 eine schematische Darstellung einer Abhängigkeit des Ionisationsstroms vom Brennstoff-Luft-Verhältnis,
• Figur 5 schematische Darstellungen von Fluidzufuhränderungen und zeitlichen Änderungen von einer Verbrennungskenngröße bei unterschiedlichen Messungen und
• Figuren 6 bis 8 Varianten des Verfahrens zum Regeln und/oder Kalibrieren eines Heizsystems.

In the drawings, exemplary embodiments of the method according to the invention for regulating and / or calibrating a heating system, the control unit according to the invention and the heating system according to the invention are shown and explained in more detail in the following description. Show it

• Figure 1 a schematic representation of the heating system according to the invention with the control unit according to the invention,
• Figure 2 the method according to the invention for regulating and / or calibrating a heating system,
• Figure 3 a schematic representation of a change in fluid supply and a change in a combustion parameter over time,
• Figure 4 a schematic representation of a dependence of the ionization current on the fuel-air ratio,
• Figure 5 schematic representations of fluid supply changes and changes over time of a combustion parameter with different measurements and
• Figures 6 to 8 Variants of the method for regulating and / or calibrating a heating system.

description

In the different embodiment variants, the same parts or steps are given the same reference numbers.

In Figure 1 a heater 10 is shown schematically, which is arranged on a memory 12 in the exemplary embodiment. The heater 10 has a housing 14 which accommodates different components depending on the level of equipment.

The essential components are a heat cell 16, a control unit 18, one or more pumps 20 as well as piping 22, cables or bus lines 24 and holding means 26 in the heater 10. The number and complexity of the individual components also depends on the degree of equipment of the heater 10.

The heat cell 16 has a burner 28, a heat exchanger 30, a fan 32, a metering device 34 and an air supply system 36, an exhaust system 38 and, when the heat cell 16 is in operation, a flame 40. An ionization probe 42 protrudes into the flame 40. The metering device 34 is designed as a fuel valve 44. A fan speed 80 of the fan 32 is variably adjustable. The heating device 10 and the memory 12 together form a heating system 46. The control unit 18 has a data memory 48, a computing unit 50 and a communication interface 52. The components of the heating system 46 can be controlled via the communication interface 52. The communication interface 52 enables data to be exchanged with external devices. External devices are, for example, control devices, thermostats and / or devices with computer functionality, for example smartphones.

Figure 1 shows a heating system 46 with a control unit 18. In alternative embodiments, the control unit 18 is located outside the housing 14 of the heater 10. The external control unit 18 is designed in special variants as a room controller for the heating system 46. In preferred embodiments, the control unit 18 is mobile. The external control unit 18 has a communication link to the heating device 10 and / or other components of the heating system 46. The communication connection can be wired and / or wireless, preferably a radio connection, particularly preferably via WLAN, Z-Wave, Bluetooth and / or ZigBee. In further variants, the control unit 18 can consist of several components, in particular components that are not physically connected. In special variants, at least one or more components of the control unit 18 can be partially or entirely in the form of software that is executed on internal or external devices, in particular on mobile computing units, for example smartphones and tablets, or servers, in particular a cloud. The communication links are then corresponding software interfaces.

In Figure 2 the method 54 according to the invention for checking and regulating a fuel-air ratio 56 in a heating system 46 is shown. In the exemplary embodiment, a fluid supply change 60 over time of a fluid supply parameter 62 is generated in a step 58. In the exemplary embodiment, the fluid supply parameter 62 is a control signal 64 to the doser 34 (see FIG Figure 3 ). The control signal 64 is characterized by an indication of a current strength. The control signal 64 is sent to the fuel valve 44 by the control unit 18. A relationship between a fuel flow that has passed through the fuel valve 44 and a control signal 64 required for this is stored in the control unit 18.

The fluid supply change 60 in the exemplary embodiment is shown in FIG Figure 3 pictured. The first axis of abscissa 66 represents a time. On the first axis of ordinate 68, the fluid supply parameter 62 is shown. The fluid supply change 60 runs in a largely rectangular pulse. Initially, the control signal 64 has a largely constant normal supply value 70. The control signal 64 is then increased to a maximum supply value 72 as quickly as possible. The control signal 64 is then reduced to the normal value 70 as quickly as possible. One in Figure 3 pulse height 74 shown is 65 mA. One in Figure 3 the pulse width 76 shown is 40 ms.

In the exemplary embodiment, the fluid supply change 60 is selected in step 58 as a function of a burner output parameter 78. The burner output parameter 78 is a fan speed 80 (see Figure 2 ). The fan speed 80 is a characteristic value determined by the control unit 18, which determines a fan control signal. The fan control signal is sent from the control unit 18 to the fan 32 and determines a speed of the fan 32. The pulse height 74 is selected in the exemplary embodiment as a function of the fan speed 80. The pulse height 74 increases linearly with the Fan speed 80 on. Between a minimum fan speed and a maximum fan speed, the pulse height assumes 74 values in an interval between 10 mA and 1000 mA. During regular operation of the heating system 46, the pulse height 74 preferably assumes values between 40 mA and 100 mA. In the exemplary embodiment, the pulse width 76 is selected as a function of the fan speed 80. The pulse width 76 increases linearly with the fan speed 80. Between a minimum fan speed and a maximum fan speed, the pulse width assumes 76 values in an interval between 1 ms and 2000 ms. During regular operation of the heating system 46, the pulse width 76 assumes values between 10 ms and 200 ms, preferably 100 ms.

In a following step 82 (see Figure 2 ) an attempt is made to determine a signal maximum 84 of a temporal change of a combustion parameter 86 that is correlated with the temporal change in fluid supply 60. In the exemplary embodiment, the combustion parameter 86 is an ionization flow 88 (see Figure 3 ). The ionization current 88 is determined by the ionization probe 42 at the flame 40 and transmitted to the control unit 18. After the change in fluid supply 60, the time profile of the ionization current 88 has the signal maximum 84. In the exemplary embodiment, the signal maximum 84 from the ionization current 88 is assumed twice.

The signal maximum 84 is determined in the exemplary embodiment in that the control unit 18 checks whether the ionization current 88 increases more than signal noise above the ionization current normal value 90. The normal ionization current value 90 is determined in the exemplary embodiment in which the mean ionization current 88 measured over the duration of the pulse width 76 is determined. In alternative variants, the ionization current normal value 90 is determined in which the mean ionization current 88 between the fluid supply change 60 and the temporal change of the at least one combustion parameter correlated with the temporal fluid supply change 60 86 is determined. In further variants, a value of the ionization current 88 which was recorded before the temporal change of the at least one combustion parameter 86 correlated with the temporal change in fluid supply 60, for example at the beginning of the fluid supply change 60, is used as the normal ionization current value 90.

The signal maximum 84 is assumed by the ionization current 88 twice. The signal maximum 84 corresponds to a combustion characteristic maximum 92. The reason for this is the configuration of the fluid supply change 60 and the relationship between the ionization flow 88 and the fuel-air ratio 56. The fuel-air ratio 56 is calculated from an air volume divided by a fuel volume in a mixture of the fuel and the combustion air, which is fed to the burner 28. Figure 4 illustrates the relationship between the ionization flow 88 and the fuel-air ratio 56 at a constant fan speed 80. The ionization flow 88 is plotted on the first axis of ordinate 68. The fuel-air ratio 56 is shown on a second abscissa axis 94. Different measurements 96, 98, 100, 102 and 104 are marked on the graph of the ionization current 88. These measurements each have the same fan speed 80 and different fuel-air ratios 56. The individual measurements are discussed later. The course of the ionization current 88 has a combustion characteristic maximum 92 with a fuel-air ratio 56 of 1 (measurement 98). When the fuel-air ratio 56 is increased or decreased, starting from the combustion parameter maximum 92, the ionization current 88 decreases. The heating system 46 is preferably operated with an excess of air, that is to say with a fuel-air ratio 56 greater than 1. The heating system 46 is particularly preferably operated with a fuel-air ratio 56 between 1.2 and 1.4, preferably 1.3 (measurement 102). Procedure 54 ensures that the heating system 46 is operated with a predetermined fuel-air ratio 56.

Due to the change in fluid supply 60, the fuel-air ratio 56 is reduced for a short time. If the fuel-air ratio 56 is greater than 1, the fuel-air ratio 56 is reduced to a value less than 1 by increasing the fluid supply parameter 62 to the maximum supply value 72. The subsequent lowering of the fluid supply parameter 62 to the normal value 70 causes the fuel-air ratio 56 to rise to the original value greater than 1. In this way, as a result of the fluid supply change 60, the fuel-air ratio 56 assumes the value 1 twice. The ionization current 88 assumes the combustion parameter maximum 92 twice. The ionization current 88 has two local maxima, which represents a double peak structure 106 (see FIG Figure 3 ).

In the exemplary embodiment, the lowering of the fuel-air ratio 56 to a value less than 1 is ensured in that a sufficiently large fluid supply change 60 is selected for each burner output parameter 78 by laboratory tests, so that this fluid supply change 60 always occurs as a result of this fluid supply change 60 in all operating states and under largely all environmental conditions the fuel-air ratio 56 is reduced to below 1, in particular when the fuel-air ratio 56 is greater than 1, in particular when the fuel-air ratio 56 is greater than 1.3. For this purpose, the relationships between the required pulse height 74 or the required pulse width 76 are stored in the control unit 18 as a function of the fan speed 80.

In the exemplary embodiment, the signal maximum 84 is determined by the control unit 18 in that the maximum ionization current 88 is determined in a period of time that is correlated with the change in the ionization current 88 over time. The one with The period of time correlated with the temporal change in the ionization current 88 is determined by the fact that this begins with a first deviation of the ionization current 88 from the ionization current normal value 90 beyond signal noise and ends with a return of the ionization current 88 to the ionization current normal value 90 within the limits of the signal noise. If a period of time correlated with the change in ionization current 88 over time cannot be determined within a determination time, no signal maximum 84 can be determined. The determination time has the length of a time threshold stored in the control unit 18. The determination time begins with the fluid supply change 60. In alternative embodiments, the determination time begins with the end of the fluid supply change 60 or with the end of a time delay after the fluid supply change 60. The time delay takes into account a flow duration of the fluid from the doser 34 to the burner 28. In the exemplary embodiment, this is Time threshold 2 seconds. In variants, a time threshold between 1 second and 5 seconds is selected. In alternative embodiments, the signal maximum 84 is determined in which the control unit 18 identifies the two maxima of the double-peak structure 106. The signal maximum 84 results from the arithmetic mean of the two maxima of the double-peak structure 106. In further embodiments, the signal maximum 84 is determined by measuring the ionization current 88 over the determination time. If the ionization current 88 assumes a value greater than the normal ionization current value 90 over the determination time beyond signal noise, the greatest value of the ionization current 88 over the determination time is selected as the signal maximum 84. If the ionization current 88 does not take on a value greater than the normal ionization current value 90 beyond signal noise during the determination time, no signal maximum 84 can be determined.

In a further step 108, a target combustion parameter 110 is determined based on the signal maximum 84 if a signal maximum 84 was determined in step 82 (path A in Figure 2 ). In the exemplary embodiment, the nominal combustion parameter 110 is determined as the product of the signal maximum 84 and a calibration factor 112. The calibration factor 112 is a value between 0 and 1 stored in the control unit 18. In the exemplary embodiment, the calibration factor 112 is 0.75. In alternative variants, the calibration factor 112 takes values between 0.6 and 0.9. In special embodiments, the calibration factor 112 is dependent on the burner output parameter 78.

In a further step 114, the heating system 46 is regulated on the basis of the target combustion parameter 110 determined in step 108 if a signal maximum 84 was determined in step 82. For this purpose, the nominal combustion parameter 110 is stored in the data memory 48 of the control unit 18. With the nominal combustion parameter 110 determined in step 108, a flame ionization characteristic curve stored in the control unit 18 is updated. The flame ionization characteristic describes the relationship between the burner output parameter 78 and the target combustion parameter 110. The control unit 18 assigns the target combustion parameter 110 to a predetermined burner output parameter 78 with the aid of the flame ionization characteristic. The flame ionization characteristic is determined empirically and is stored in the control unit 18. In the exemplary embodiment, the flame ionization characteristic is updated by method 54 if this is necessary.

In alternative embodiments, the heating system 46 is controlled without using a flame ionization curve. The regulation of the heating system 46 is based solely on the target combustion parameter 110 determined in step 108.

In the exemplary embodiment, the normal value 70 of the control signal 64 is selected by the control unit 18 or transmitted to the fuel valve 44 in such a way that the ionization flow 88 assumes the value of the setpoint combustion parameter 110. For this purpose, a closed control loop is used in the exemplary embodiment, the ionization current 88 being a controlled variable, the control signal 64 being a manipulated variable and the set combustion parameter 110 being a reference variable. In this way, the intended fuel-air ratio 56 is achieved. In variants of the method, different flame ionization characteristics are stored in the control unit 18 for different desired fuel-air ratios 56.

If no signal maximum 84 can be determined in step 82, the method continues on path B. In this case, a first error response 116 and a step 115 are carried out. In the case of the first error response 116, a first error counter variable stored in the control unit 18 is increased by 1. If the first error counting variable exceeds a maximum value, the method 54 is ended, the heating system 46 is shut down and an error message is output. In the exemplary embodiment, the maximum value has the value 7. In alternative embodiments, the maximum value assumes values between 1 and 10. If a signal maximum 84 is determined in step 82, the error count variable is decreased by 1 if its value is greater than 0. In variants, the first error count variable is set to the value 0 if a signal maximum 84 is determined in step 82. In step 115, the heating system 46 is regulated on the basis of a standard combustion parameter 117. The standard combustion parameter 117 is stored in the control unit 18 on the basis of the burner output parameter 78 Flame ionization characteristic determined. In alternative variants, the position of steps 116 and 115 can be swapped.

Figure 5 illustrates the sequence of the method 54 for the different measurements 96, 98, 100, 102 and 104, each with different fuel-air ratios 56 (see Figure 4 ). The same time is shown on the first abscissa axes 66 for each measurement. The second ordinate axes 118 each represent the fluid supply parameter 62. The third ordinate axes 120 each depict the ionization flow 88. During the measurement 102, the fuel-air ratio 56 is the intended value 1.3. The nominal combustion parameter 110 determined by the method 54 is the same as the nominal combustion parameter 110 already used by the control unit 18. The fluid supply parameter 62 and the ionization flow 88 are therefore not changed.

In measurement 104, the fuel-air ratio 56 is 1.45. The target combustion parameter 110 stored in the control unit 18 is too low. For comparison, a comparison ionization stream 122 is shown as a dashed line in FIG Figure 5 which corresponds to the course of the ionization current 88 from measurement 102. The target combustion parameter 110 newly determined by the method 54 is greater than the ionization current normal value 90. In step 114, the control signal 64 is increased so that the fuel valve 44 opens further. The ionization current normal value 90 increases. When measuring 100, the fuel-air ratio 56 is 1.15. The target combustion parameter 110 newly determined by the method 54 is smaller than the ionization current normal value 90. In step 114, the control signal 64 is reduced so that the fuel valve 44 reduces its passage.

In the measurement 98, the fuel-air ratio 56 has the value 1. As a result of the fluid supply change 60, the ionization current 88 falls. The method 54 cannot determine a signal maximum 84. The first error response 116 is carried out. The heating system 46 is shut down. In the measurement 96, the fuel-air ratio 56 has the value 0.85. The change in fluid supply 60 causes the ionization current 88 to drop. This means that no signal maximum 84 can be determined and the first error response 116 is carried out, and the heating system 46 is shut down.

In alternative embodiments, a signal minimum is additionally determined in step 82. This is determined in a manner analogous to the determination of the signal maximum 84 via a lowering of the ionization current 88 that can be distinguished sufficiently from the signal noise. If the signal minimum is large enough or if the distance between the signal minimum and the ionization current normal value 90 falls below a maximum deviation value stored in the control unit 18, then the signal maximum 84 is set to the value of the ionization current normal value 90. If the distance between the signal minimum and the ionization current normal value 90 is small enough, the ionization current normal value 90 largely corresponds to the combustion parameter maximum 92.

The method 54 is repeated periodically in the exemplary embodiment. Figure 5 In measurements 100, 102 and 104, FIG. 8 shows a fluid supply change 60 following the change in ionization current 88, which change belongs to a next iteration of method 54. A time interval between the iterations of the method 54 is selected depending on the operating state of the heating system 46 and on the external conditions. In the exemplary embodiment, the time interval is between 1 second and 20 seconds, preferably 2 seconds.

In the exemplary embodiment, the change in fluid supply 60 is selected as a function of the fan speed 80. The pulse height 74 and the pulse width 76 depend in each case linearly from the fan speed 80. In alternative embodiments, a fluid supply change characteristic curve is stored in the control unit 18, which assigns a fluid supply change 60 to the burner output parameter 78. The fluid supply change characteristic is defined at least at intervals of the parameter range of the burner output parameter 78. The fluid supply change characteristic is determined by laboratory tests and is selected in such a way that the fluid supply change 60 selected on the basis of the fluid supply change characteristic always reduces the fuel-air ratio 56 to below 1 in all operating states and under largely all environmental conditions, in particular when the fuel-air ratio is present 56 greater than 1, in particular with an existing fuel-air ratio 56 greater than 1.3.

In alternative embodiments, an additional fluid supply change 126 is generated in an additional step 124. The additional fluid supply change 126 is largely opposite to the fluid supply change 60. In this way, the mean fluid supply parameter 62 over a period of time which includes the fluid supply change 60 and the additional fluid supply change 126 largely corresponds to the normal supply value 72. In preferred embodiments, the graph of the temporal course of the fluid supply parameter 62 of the additional fluid supply change 126 largely resembles that reflected in the normal supply value 72 Time-shifted graphs of the time course of the fluid supply parameter 62 of the fluid supply change 60. If, for example, the fluid supply change 60 is implemented by a largely rectangular pulse with a certain positive pulse height 74 and a certain pulse width 76, the additional fluid supply change 126 is achieved by a largely rectangular pulse with a largely the same pulse width 76 and an additional pulse height, which depends on the magnitude of the pulse height 74 of the first largely rectangular pulse of the fluid supply change 60 largely corresponds and is negative. Step 124 can be carried out at any point in method 54. In Figure 6 a variant is shown in which step 124 is carried out after step 82. In preferred embodiments, the step 124 is positioned such that the additional fluid supply change 126 does not influence the change in the combustion parameter 86 that is correlated with the fluid supply change 60. Step 124 is preferably carried out after step 58, particularly preferably after step 82.

In variants of the method 54, an additional step 128 checks whether the change over time of the at least one combustion parameter 86 has a double-peak structure 106. Step 128 is preferably carried out after step 58 and preferably before step 108. Figure 7 shows a variant in which step 128 is executed on path A after step 82. If it is determined in step 128 that a double peak structure 106 is present, the method is continued on path C with step 108. If there is no double peak structure 106, the method is continued on path D and the first error response 116 is carried out. The heating system 46 is regulated in step 115 based on the standard combustion parameter 117. In step 128, the time profile of the change in the combustion parameter 86 stored in the control unit 18 as a result of the fluid supply change 60 is examined for the existence of at least two local maxima. In alternative variants, step 128 is carried out before step 82.

In special variants, a second error reaction 130 is carried out if no double peak structure 106 is present. In the case of the second error reaction 130, a second error counter variable 132 is increased by 1 (see Figure 8 ).

In preferred variants in which the second error reaction 130 is carried out, if the second error count variable 132 has been increased by one, the fluid supply change 60 is increased in the next iteration of the method 54 in step 58. The fluid supply change 60 is limited upwards by a maximum fluid supply change which is dependent on the burner output parameter 78 and which is stored in the control unit 18. In this way, an insufficient fluid supply change 60 can be corrected. If the fluid supply change 60 is insufficient, the fuel-air ratio 56 is not decreased below the value 1. Figure 8 shows a variant in which the second error reaction 130 is carried out on the path after the first error reaction 116. The second error count variable 132 influences the selection of the fluid supply change 60, which is made in step 58 of the following iteration of the method 54. In alternative embodiments, the sequence of steps 116, 130 and 115 on path D can be changed as desired.

In the exemplary embodiment, the target combustion parameter 110 is determined by forming the product of the signal maximum 84 with the calibration factor 112. In alternative variants, the calibration factor 112 depends on the operating state of the heating system 46. In preferred variants, the calibration factor 112 depends on the burner output parameter 78. In further variants, a nominal combustion characteristic is stored in the control unit 18. With the aid of the nominal combustion parameter characteristic curve, the nominal combustion parameter 110 is assigned to the signal maximum 84. The target combustion characteristic curve is dependent on the operating state of the heating system 46. In particular, the setpoint combustion characteristic depends on the desired fuel-air ratio 56 and / or on the burner output parameter 78.

In the exemplary embodiment, the fluid supply parameter 62 is a control signal 64 to the fuel valve 44. In alternative embodiments, the fluid supply parameter 62 is a scalar value that can be derived from the control signal 64. In further embodiments, the fluid supply parameter 62 is an opening width selection of the fuel valve 44. On the basis of the opening width selection, the control unit 18 determines and transmits a control signal 64 to the fuel valve 44. In further variants, the fluid supply parameter 62 corresponds to a control signal 64 for metering a combustion air and / or a mixture of a fuel and a combustion air. The control signal 64 sent by the control unit 18 contains at least one control command to at least one metering device 34. The at least one metering device 34 is at least one fuel valve 44 and / or at least one fan 32. In alternative embodiments, a metering value of the metering device 34 is measured and used as a fluid supply parameter 62 used. "Dosage value" is to be understood as a characteristic value which describes the state of the dosing device 34 and which allows conclusions to be drawn about the amount of substance supplied and / or allowed through by the dosing device 34. An example of a dosage value is a measured opening width of the fuel valve 44 and / or a measured fuel flow.

In the exemplary embodiment, the combustion parameter 86 is an ionization current 88. The ionization current 88 is determined by measuring the ionization current on a flame 40 of the heating system 46. The ionization current 88 is determined by the ionization probe 42 and transmitted to the control unit 18. In further embodiments, the combustion parameter 86 is a light intensity, a spectrum, a lambda value, a pollutant emission and / or a temperature. The light intensity and / or the spectrum at the flame 40 is determined by at least one photodiode. The lambda value is measured with a lambda probe in an exhaust gas. The exhaust system 38 has the lambda probe. The pollutant emissions will determined by a sensor device which is located on the flame 40 and / or in the exhaust system 38. The temperature is determined by a contact thermometer and / or a non-contact thermometer, in particular a pyrometer. The thermometer can be located in the exhaust system 38 and / or measure the flame 40.

In the exemplary embodiment, the burner output parameter 78 is the fan speed 80. The fan speed 80 is a characteristic value determined by the control unit 18, which determines a fan control signal. In alternative embodiments, the burner performance parameter 78 is a measured fan speed and / or a temperature and / or an air flow rate and / or a flow rate of the air-fuel mixture. The air flow rate or the flow rate of the air-fuel mixture can be determined as a volume flow or as a mass flow. In further embodiments, the burner output parameter 78 is a run time of a combustion air and / or a mixture of a fuel and combustion air. In special variants, a running time is determined as the time difference between the fluid supply change 60 and the time change in the combustion parameter 86 correlated with the fluid supply change 60. The running time corresponds to the time which the mixture of fuel and combustion air needs to get from the fuel valve 44 to the ionization probe 42. The running time is a measure of the flow rate of the air-fuel mixture. These parameters can also be used in combination. The temperature in the exhaust system 38 and / or by the flame 40 can be determined.

In the exemplary embodiment, the fluid supply change 60 has a largely rectangular shape. In alternative embodiments, the fluid supply change 60 has largely the shape of a ramp and / or largely a triangular shape and / or largely the shape of a sine and / or largely in the form of a Gaussian curve. In the exemplary embodiment, the change in fluid supply 60 is selected as a function of the burner output parameter 78. The pulse height 74 and pulse width 76 each depend linearly on the fan speed 80. In this way, it is ensured that the heating system 46 is not disturbed too much in its regular operation by the fluid supply change 60. In alternative embodiments, the fluid supply change 60 has a functional relationship with the burner output parameter 78. The functional relationship is selected so that good detection of the signal maximum 84 is possible, taking into account the technical properties of the heating system 46. If, for example, resonances occur at certain fan speeds 80, which increase the signal noise of the ionization current 88, then at these fan speeds 80 the fluid supply change 60 is increased.

Claims (13)

1. Method (54) for setting and controlling a fuel/air ratio (56) in a heating system (46) which comprises the following steps:

   • generating a temporary change (60) over time in the fluid supply of a fluid supply characteristic variable (62), wherein a time period of the change in the fluid supply is pulse-like and short in comparison with variations over time in the fluid supply characteristic variable which is provided during the customary operation of the heating system,

   • attempt to determine a signal maximum (84) of a change over time, correlated with the change over time (60) in the fluid supply, in at least one combustion characteristic variable (86),

   • determining a setpoint combustion characteristic variable (110) on the basis of the signal maximum (84) if a signal maximum (84) has been determined,

   • controlling the heating system (46) on the basis of the setpoint combustion characteristic variable (110) if a signal maximum (84) has been determined,
   wherein the change (60) in the fluid supply is selected in such a way that during the change over time in the at least one combustion characteristic variable (86) a combustion characteristic variable maximum (92) is accepted at least twice, wherein in an additional step it is checked whether the change over time in the at least one combustion characteristic variable (86) has a double peak structure (106), and if it is detected that the change over time in the at least one combustion characteristic variable (86) has no double peak structure (106), the change (60) in the fluid supply is increased in the next steps.
2. Method (54) for setting and controlling a fuel/air ratio (56) in a heating system (46) according to Claim 1, characterized in that in an additional step the heating system (46) is controlled on the basis of a standard combustion characteristic variable (117) if the signal maximum (84) has not been determined.
3. Method (54) for setting and controlling a fuel/air ratio (56) in a heating system (46) according to one of the preceding claims, characterized in that a first fault reaction (116) is carried out if a signal maximum (84) has not been determined.
4. Method (54) for setting and controlling a fuel/air ratio (56) in a heating system (46) according to one of the preceding claims, characterized in that the change (60) in the fluid supply is selected as a function of a burner output parameter (78).
5. Method (54) for monitoring and controlling a fuel/air ratio (56) in a heating system (46) according to one of the preceding claims, characterized in that in an additional step a temporary additional change (126) over time in the fluid supply is generated, wherein this additional change (126) in the fluid supply is largely opposed to the change (60) in the fluid supply.
6. Method (54) for monitoring and controlling a fuel/air ratio (56) in a heating system (46) according to one of the preceding claims, characterized in that a first fault reaction (116) is carried out if a double peak structure (106) is not detected.
7. Method (54) for monitoring and controlling a fuel/air ratio (56) in a heating system (46) according to one of the preceding claims, characterized in that the setpoint combustion characteristic variable (110) is determined by a product formation of the signal maximum (84) with a calibration factor (112).
8. Method (54) for monitoring and controlling a fuel/air ratio (56) in a heating system (46) according to one of the preceding claims, characterized in that the fluid supply characteristic variable (62) corresponds to a control signal (64) for metering a fuel and/or the combustion air and/or a mixture composed of a fuel and combustion air.
9. Method (54) for monitoring and controlling a fuel/air ratio (56) in a heating system (46) according to one of the preceding claims, characterized in that the at least one combustion characteristic variable (86) is determined by an ionization current measurement at a flame (40) of the heating system (46).
10. Method (54) for monitoring and controlling a fuel/air ratio (56) in a heating system (46) according to one of the preceding claims, characterized in that the burner output parameter (78) is a blower rotational speed (80) or depends thereon and/or a mass flow of combustion air and/or a mixture of a fuel and combustion air or depends thereon and/or a volume flow of combustion air and/or a mixture of a fuel and combustion air or depends thereon and/or a running time of combustion air and/or a mixture of a fuel and combustion air or depends thereon.
11. Method (54) for monitoring and controlling a fuel/air ratio (56) in a heating system (46) according to one of the preceding claims, characterized in that the change over time (60) in the fluid supply has an at least largely square-wave shape.
12. Control unit (18) for a heating system (46), wherein the control unit (18) is configured in such a way that a method (54) for monitoring and controlling a fuel/air ratio (56) in a heating system (46) can be carried out according to one of the preceding claims.
13. Heating system (46) with a control unit (18) according to Claim 12, with a metering device (34) for a fuel and/or for combustion air and/or for a mixture of a fuel and combustion air, and with an ionization probe (42) at a flame (40) and with a blower (32) with a variable blower rotational speed (80).

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