EP3715716A1 - Method for controlling a fuel/air ratio in a heating system and a control unit and a heating system - Google Patents

Abstract

The invention relates to a method (54) for setting and regulating a fuel-air ratio (56) in a heating system (46) with a sensor for detecting a combustion parameter (84), in particular an ionization current (86), which comprises the following steps : • Generating (58) a temporary, temporal fluid supply change (60) of a fluid supply parameter (62) which is provided to generate a temporal change in the combustion parameter (84), the fluid supply change (60) being selected so that the temporal change of the Combustion parameter (84) has a double peak structure (94) which has at least a first peak (88), a first dip (90) and a second peak (92), • determining (80) the first peak (88) and the second peak (92) from the temporal change in the combustion parameter (84) correlated with the temporal change in fluid supply (60), • determining (101) an oxygen concentration (103) as a function of a Qu otients from the first peak (88) and the second peak (92), • Determining (102) a first burner output parameter (104), • Determining (116) a target combustion parameter (130) based on the oxygen concentration (103) and the first burner output parameter ( 104), • regulating the heating system (46) on the basis of the nominal combustion parameter (130). The invention also relates to a control unit (18) which is designed to carry out the method (54) according to the invention, as well as a heating system (46) with the control unit ( 18).

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. This has the additional disadvantage that the gas burner is not available for normal operation during this time.

Disclosure of the invention benefits

• Erzeugen einer vorübergehenden, zeitlichen Fluidzufuhränderung einer Fluidzufuhrkenngröße, welche dazu vorgesehen ist, eine zeitliche Änderung der Verbrennungskenngröße zu erzeugen, wobei die Fluidzufuhränderung so gewählt ist, dass die zeitliche Änderung der Verbrennungskenngröße eine Doppelpeakstruktur aufweist, welche zumindest einen ersten Peak, eine erste Senke und einen zweiten Peak aufweist
• Ermitteln des ersten Peaks und des zweiten Peaks von der mit der zeitlichen Fluidzufuhränderung korrelierten zeitlichen Änderung der Verbrennungskenngröße,
• Ermitteln einer Sauerstoffkonzentration in Abhängigkeit von einem Quotienten aus dem ersten Peak und dem zweiten Peak,
• Ermitteln eines ersten Brennerleistungsparameters,
• Ermitteln einer Sollverbrennungskenngröße auf Basis der Sauerstoffkonzentration und des ersten Brennerleistungsparameters,
• Regeln des Heizsystems auf Basis der Sollverbrennungskenngröße.

The present invention provides a method for setting and regulating a fuel-air ratio in a heating system. The procedure consists of the following steps:

• Generating a temporary, temporal fluid supply change of a fluid supply parameter, which is provided to generate a temporal change in the combustion parameter, the fluid supply change being selected so that the temporal change in the combustion parameter has a double peak structure, which has at least a first peak, a first sink and a has second peak
• Determining the first peak and the second peak from the change in the combustion parameter over time correlated with the change in fluid supply over time,
• Determination of an oxygen concentration as a function of a quotient from the first peak and the second peak,
• Determining a first burner output parameter,
• Determination of a target combustion parameter based on the oxygen concentration and the first burner output parameter,
• Regulation of the heating system based on the target combustion parameter.

With the help of the method, the nominal 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. In this way, the heating system is always operated with an intended, optimized fuel-air ratio. 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.

Because the change in fluid supply is selected such that the change over time in the combustion parameter has at least a double peak structure, the existing combustion conditions can be identified particularly reliably. This enables a particularly precise determination of the target combustion parameter.

Because an oxygen concentration is determined and taken into account when determining the target combustion parameter, the quality of the previously used target combustion parameter can be taken into account. If the oxygen concentration deviates from a desired value, this is an indication that the previously used target combustion parameter was not set correctly. This can be taken into account when setting and regulating the fuel-air ratio, in particular by adapting the new 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, a volume flow and / or a mass flow of the at least one fluid can be inferred and / or the volume flow and / or the mass flow of the at least one fluid can be determined, in particular by a control and / or regulating unit of the heating system, at least on the basis of the fluid supply parameter.

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 / or short compared to the usual Operation of the heating system provided time variations of the fluid supply parameter, for example when a change in heating power.

A “pulse”, a “pulse-like change” or a “pulse-shaped signal” is to be understood as a time profile of a parameter 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 the control and / or regulating unit of the heating system, at least based on the combustion parameter, the presence and / or quality of the combustion can be inferred 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. Another example is an oxygen concentration, in particular an oxygen concentration in a fuel-air mixture and / or in combustion exhaust gases. The oxygen concentration is correlated with 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 .

“Double peak structure” is to be understood as a time course of the combustion parameter in a time period correlated with the time change in the fluid supply parameter, which has at least two maxima, possibly with largely the same amplitude. The first two maxima of the double peak structure are referred to as the “first peak” and “second peak”, and the minimum between them is referred to as the “first dip”.

"Determining" a first peak and a second peak of the temporal change in the combustion parameter correlated with the change in fluid supply over time is to be understood as a method step in which a first peak and second peak of a temporal change in the combustion parameter correlated with the change in fluid supply over time are measured or is detected. Methods of data processing or data evaluation can also be provided here. Depending on the result or value of the first peak and / or second peak, different subsequent steps can optionally be selected in the further course of the method, if this is necessary and / or desired.

“Burner output parameter”, a “first burner output parameter” or a “second burner output parameter” is to be understood as meaning, in particular, 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. The burner output parameter advantageously corresponds to 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 or can be derived from these measured parameters. The first burner output parameter preferably depends on a different measured value representing the output than the second burner output parameter or the first burner output parameter is determined using a different method than the second burner output parameter.

“Determining” a first burner output parameter should be understood to mean a method step in which a variable that is directly or indirectly correlated with an output is measured or determined. Methods of data processing or data evaluation can also be provided here. Depending on the result or value of the first burner output parameter, different following steps can optionally be selected in the further course of the method, if this is necessary and / or desired.

“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. For example, a fuel supply and / or a combustion air supply can be set with a control system such that the combustion parameter assumes or at least largely assumes the value of the target combustion parameter.

“Determining” a target combustion parameter is to be understood as a method step in which the target combustion parameter is determined or established as a function of the signal maximum, the first burner output parameter and optionally other parameters, in particular operating parameters of the heating system. In particular, methods of data processing or data evaluation can also be provided, in particular using a computing unit.

"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 fully meet the specified and / or requested output, especially under changing internal and external conditions, especially 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.

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

The heating system is calibrated if the determined oxygen concentration exceeds a stored critical maximum value or falls below a stored critical minimum value, this has the advantage that a particularly safe and clean operation of the heating system is possible. Too high or too low an oxygen concentration is an indication that an earlier setting of the target combustion parameter was incorrect, so that the heating system was not operated with the desired fuel-air ratio (but with a fuel-air mixture that was too lean if the fuel-air ratio was too low high oxygen concentration or too rich a fuel-air mixture with too low an oxygen concentration).

If the deviation from the desired fuel-air ratio is low enough or the oxygen concentration is below the critical maximum value and above the critical minimum value, this deficiency can probably be corrected by adapting the new target combustion parameter according to the present method. However, if the deviation from the desired fuel-air ratio is large or if the oxygen concentration is above the critical maximum value or below the critical minimum value, this can be an indication that a new calibration of the heating system is necessary.

A calibration of the heating system is to be understood in particular as a special operating state which interrupts the regular operation of the heating system and in which the operating parameters - for example combustion parameters, target combustion parameters or characteristics - of the heating system are reset. For example, different powers or heating powers can be run through during calibration. It is conceivable that maintenance steps are also carried out during calibration, such as, for example, an in particular automated cleaning of an ionization probe. It is also conceivable that calibrating the heating system means that the heating system is shut down or operated in a restricted mode - which is intended to protect the heating system, for example by restricting the heating output - and a calibration and / or inspection is requested, for example by sending a corresponding request to the user of the heating system.

If a signal maximum is determined from the first peak and the second peak and taken into account when determining the target combustion parameter, this has the advantage that a particularly precise and reliable determination of the target combustion parameter is possible. For example, the signal maximum is taken as the mean value from the first peak and the second peak, temperature-dependent effects on a measuring device of the combustion parameter can be taken into account in this way, for example a temperature-dependent conductivity of an oxidation layer on an ionization probe.

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 can in particular be the maximum amplitude of a pulse of the combustion parameter. If the change in the combustion parameter over time has a double peak structure, this is an indication that the signal maximum corresponds to the combustion parameter maximum. 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.

In a further embodiment of the invention, a correction value for correcting the signal maximum is taken into account, which depends on the first burner output parameter and optionally a second burner output parameter. This has the advantage that the determination of the target combustion parameter is particularly precise. In particular, a power dependency of the target combustion parameter on the signal maximum can be taken into account.

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. The calibration factor advantageously has a value between 0 and 1, preferably between 0.5 and 0.9, particularly preferably between 0.6 and 0.8, in particular 0.7.

If the calibration factor is determined as a function of the first burner power parameter and / or of the or a second burner power parameter, a power dependency of the target combustion parameter on the signal maximum can be taken into account.

If the change in fluid supply over time largely has the shape of a ramp and / or largely a triangular shape, it can be ensured particularly reliably that the change in the combustion parameter over time has a double-peak structure. In this context, “largely the shape of a ramp” 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 increased linearly. When a maximum supply value is reached, the fluid supply parameter is quickly reduced to the normal value, in particular as quickly as possible. In the case of a "largely triangular shape", the fluid supply parameter is increased linearly as in the case of the ramp shape. If the maximum supply value is reached, the fluid supply parameter is reduced linearly until the normal value is reached. The linear increase in the fluid supply parameter can take place at a largely identical or different speed as the linear decrease in the fluid supply parameter.

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 for. 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.

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, in this way no measurement of the fuel and / or the combustion air and / or a mixture of a fuel and combustion air or a flow of these fluids is required. This simplifies the process and makes it robust against malfunctions.

If the combustion parameter is determined by an ionization current measurement on a flame of the heating system, this is particularly advantageous because between the ionization current at a flame and the fuel-air ratio, there is a functional relationship 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.

In a further embodiment of the invention, the first burner output parameter is determined from a first time difference between the generation of the fluid supply change and the determination of the temporal change in the combustion parameter that is correlated with the fluid supply change. The first time difference is a measure of a running time or a transport speed of a combustion air and / or a mixture of a fuel and combustion air. This embodiment has the advantage that the first time difference can be determined particularly simply and inexpensively.

If the first burner output parameter is determined from the double peak structure, in particular from a second time difference between the first peak and the first sink and / or from a third time difference between the first peak and the second peak, this has the advantage that a reliable estimate of an instantaneous burner output is possible is possible. The second time difference and the third time difference are shorter than the first time difference in preferred embodiments.

In a preferred variant, the second burner output parameter is a fan speed or depends on it. The fan speed can be determined easily and reliably and provides a good estimate of the burner output. In addition, a second burner output parameter determined in this way allows the first burner output parameter to be checked if this was determined using a different method, for example via a transit time measurement or an analysis of the double peak structure.

If the change in fluid supply is selected as a function of the first and / or the or a second burner output parameter, this enables the required change in the fluid supply parameter to be precisely adjusted, so that the combustion parameter can assume the combustion parameter maximum at least twice or has a double peak structure. In this way, the required change in fluid supply can be minimized, so that a quantity of fluid, in particular fuel, is saved and the emissions are thus reduced.

The use of a control unit for a heating system, wherein the control unit is 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 in this way 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 for the at least one fluid, in particular the combustion air flow, the fuel flow and / or 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 used as a fuel pump, in particular with a variable flow rate and / or preferably be designed as a fuel valve, in particular with a variable flow rate. 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 an output of the heater can be implemented in this way.

drawings

• Figur 1 eine schematische Darstellung des Heizsystems mit der Steuereinheit,
• Figur 2 das Verfahren zum Regeln des Heizsystems,
• Figur 3 eine schematische Darstellung einer Fluidzufuhränderung und einer zeitlichen Änderung von einer Verbrennungskenngröße,
• Figur 4 eine schematische Darstellung einer Abhängigkeit des lonisationsstroms vom Brennstoff-Luft-Verhältnis,
• Figur 5 eine schematische Darstellung eines Zusammenhangs zwischen einer Sauerstoffkonzentration und einem Quotienten aus einem ersten Peak und einem zweiten Peak und einem zweiten Peak,
• Figur 6 eine schematische Darstellung einer Zeit-Brennerleistung-Funktion,
• Figur 7 eine schematische Darstellung einer Flammenionisationskennlinie und
• Figur 8 eine schematische Darstellung eines Zusammenhangs zwischen der Sauerstoffkonzentration und einem Kompensationsfaktor.

In the drawings, exemplary embodiments of the method for setting and regulating a fuel-air ratio in a heating system according to the present invention, the control unit according to the present invention and the heating system according to the present invention are shown and explained in more detail in the following description. Show it

• Figure 1 a schematic representation of the heating system with the control unit,
• Figure 2 the procedure for regulating the 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 a schematic representation of a relationship between an oxygen concentration and a quotient of a first peak and a second peak and a second peak,
• Figure 6 a schematic representation of a time-burner output function,
• Figure 7 a schematic representation of a flame ionization characteristic and
• Figure 8 a schematic representation of a relationship between the oxygen concentration and a compensation factor.

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 by way of example, 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 96 of the fan 32 is variably adjustable. The heater 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 not physically connected Components. 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 the 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 an intended opening width 64 of the metering device 34 (see FIG Figure 3 ). The opening width 64 is an example of a percentage, an opening width 64 of 0% corresponding to a completely closed fuel valve 44 and an opening width 64 of 100% describing a completely open fuel valve 44. A relationship between the opening width 64 and a control signal required for this is preferably stored in the control unit 18. The intended opening width 64 is implemented in the exemplary embodiment by selecting the control signal and transmitting this control signal to the fuel valve 44 by the control unit 18. The opening width 64 describes a request which is transmitted to the fuel valve 44.

The fluid supply change 60 is, for example, 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 and an ionization flow 86 are shown. The fluid supply change 60 preferably runs in a largely ramp-shaped pulse. Initially, the control signal 64 has a largely constant normal value 70. At a first point in time 72, the control signal 64 is increased linearly, for example, with a largely constant gradient. As soon as the control signal 64 reaches a maximum feed value 74, the control signal 64 is lowered to the normal value 70 as quickly as possible. One in Figure 3 The pulse height 76 shown is, for example, 30%. One in Figure 3 The pulse width 78 shown is, for example, 1 s.

In the exemplary embodiment, the fluid supply change 60 is selected in step 58 as a function of a second burner output parameter 95. In the exemplary embodiment, the second burner output parameter 95 is derived from the fan speed 96 determined (see Figure 2 ). The fan speed 96 is preferably a characteristic value determined by the control unit 18, which determines a fan control signal. In the exemplary embodiment, the fan control signal is sent from the control unit 18 to the fan 32 and determines a speed of the fan 32. In the control unit 18, for example, a fan speed characteristic is stored, which assigns a fan speed 96 to a corresponding second burner output parameter 95. The pulse height 76 is selected in the exemplary embodiment as a function of the fan speed 96. The pulse height 76 preferably increases linearly with the fan speed 96. In the exemplary embodiment, the pulse height 76 is selected as a function of the normal value 70. Between a minimum fan speed and a maximum fan speed, the pulse height 76 assumes values in a preferred interval between 5% and 90%. During regular operation of the heating system 46, the pulse height 76 preferably assumes values between 20% and 60%, particularly preferably between 35% and 45%. The pulse width 78 is selected in the exemplary embodiment as a function of the fan speed 96. The pulse width 78 preferably increases linearly with the fan speed 96. Between a minimum fan speed and a maximum fan speed, the pulse width 78 assumes values in an interval between 10 ms and 5000 ms, for example. In regular operation of the heating system 46, the pulse width 78 preferably assumes values between 50 ms and 2000 ms, particularly preferably between 250 ms and 1000 ms.

In a following step 80 (see Figure 2 ) a first peak 88 and a second peak 92 as well as a signal maximum 82 of a temporal change of a combustion parameter 84 correlated with the temporal fluid supply change 60 are determined. In the exemplary embodiment, the combustion parameter 84 is the ionization flow 86 (see Figure 3 ). The ionization current 86 is determined, for example, by the ionization probe 42 on the flame 40 and transmitted to the control unit 18. After the fluid supply change 60, the time course of the ionization current 86 has the first peak 88, a first dip 90 and the second peak 92. These two local maxima represent a double peak structure 94.

The reason for the double peak structure 94 is the configuration of the fluid supply change 60 and a relationship between the ionization flow 86 and the fuel-air ratio 56. The fuel-air ratio 56 is calculated from an amount of air divided by an amount of fuel 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 86 and the fuel-air ratio 56 at a constant fan speed 96. The ionization flow 86 is plotted on the first axis of ordinate 68. The fuel-air ratio 56 is shown on a second abscissa axis 97. The course of the ionization stream 86 has a maximum combustion parameter 98 with a fuel-air ratio 56 of 1. When the fuel-air ratio 56 is increased or decreased, starting from the combustion parameter maximum 98, the ionization current 86 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. The method 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 74. 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 stream 86 assumes the maximum combustion parameter 98 twice. The ionization stream 88 has in Figure 3 two local maxima 88, 92, which represents the double peak structure 94.

In the in Figure 3 The double peak structure 94 shown, the first peak 88 and the second peak 92 have a different ionization current value. In general, the at least two local maxima of the double peak structure 94 can be the same or of different sizes or have different ionization current values. One reason for different values of the maxima of the double peak structure 94 is the dependence of the combustion parameter maximum 98 on operating parameters and / or further, internal and / or external parameters which can change in the period between the occurrence of the first peak 88 and the second peak 92. Examples of operating parameters are in particular a flame temperature, fuel quality or fuel calorific value. Examples of further, internal and / or external parameters are a flame height or flame geometry, in particular a contact area between the flame 40 and the ionization probe 42, air pressure, or outside temperature. In particular, some of these operating parameters or further parameters can also be changed indirectly or directly by changing the fluid supply 60, for example the flame geometry.

Another reason for generally different values of the maxima of the double peak structure 94 is that the in Figure 4 The illustrated idealized relationship between the fuel-air ratio 56 and the ionization flow 86 generally has a hysteresis. A hysteresis is to be understood here as meaning that the ionization current is dependent on a previous history, that is to say that a current value of the ionization current 86 does not depend solely on a current value of the fuel-air ratio 56, but also on a previous time course of the value of the fuel-air ratio 56. This is due, for example, to temperature-dependent interaction processes between the ionization probe 42 and the flame 40. An important influencing factor for the strength of this hysteresis is an existing oxygen concentration 103. An oxidation layer which has a temperature-dependent ohmic resistance can be present on the ionization probe 42. In the in Figure 3 The double peak structure 94 shown, the combustion parameter maximum 98 is assumed twice, it has a different value of the ionization current.

In step 80, for example, the double peak structure 94 is evaluated in the exemplary embodiment. The control unit 18 checks whether the ionization current 86 detected and stored by the ionization probe 42 is stronger than signal noise via a normal ionization current value 100 (see FIG Figure 3 ) increases. The normal ionization current value 100 is determined in the exemplary embodiment in which the mean ionization current 86 measured over the duration of the pulse width 78 is determined. To determine a double peak structure 94, the control unit 18 checks whether the stored time profile of the change in the combustion parameter 84 as a result of the fluid supply change 60 has at least two local maxima, which differ significantly from the signal noise. The value of the ionization current 86 of the two maxima occurring first is recorded as a first peak 88 and second peak 92, respectively. The signal maximum 82 results from the arithmetic mean of the first peak 88 and second peak 92. In alternative embodiments, the signal maximum 82 can correspond to the first peak 88 and / or the second peak 92 and / or the smaller or larger maximum of the double peak structure 94. To this In this way, a characteristic or technical peculiarities of a device provided for recording the combustion parameter 84 can be taken into account. It is also conceivable that the signal maximum 82 using a function or rule from the first peak 88 and / or the second peak 90 and / or further characteristic points of the double peak structure 94, for example the first sink 90, and / or points one with the temporal fluid supply change 60 correlated temporal change in the combustion parameter 84 is determined. For example, the signal maximum 82 can be determined from a weighted arithmetic mean of the first peak 88 and second peak 92.

In the exemplary embodiment, the occurrence of a double peak structure 94 or the reduction in the fuel-air ratio 56 to a value less than 1 is ensured in that a sufficiently large fluid supply change 60 is selected by laboratory tests for every second burner performance parameter 95, so that as a result of this fluid supply change 60 in In all operating states and largely under all environmental conditions, the fuel-air ratio 56 is always reduced 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. The relationships between the required pulse height 76 and the required pulse width 78 are stored in the control unit 18 as a function of the fan speed 96.

It is conceivable that the fluid supply change 60 in alternative embodiments is selected as a function of at least one operating parameter and / or a measured value, in particular of a parameter describing the performance of the heating system 46. In such embodiments, the relationships between the required fluid supply change 60 determined in laboratory tests, for example characterized by the pulse height 76 and / or the pulse width 78, are stored in the control unit 18 as a function of the at least one operating parameter and / or measured value.

If a double peak structure 94 cannot be determined within a determination time, no signal maximum 82 can be determined. The determination time has the length of a predetermined time threshold stored in the control unit 18. The determination time begins with the fluid supply change 60 or with the first point in time 72. 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 size of the determination time is determined beforehand in laboratory tests and takes into account a flow duration of the fluid from the doser 34 to the burner 28. It is conceivable that the determination time depends on the performance of the Heating system 46 describing parameters is determined or selected. If no signal maximum 82 can be determined, in the exemplary embodiment the heating system 46 is regulated with the aid of a flame ionization characteristic curve 124 (see explanations below and Figure 7 ). It is conceivable that in variants of the method 54, the fluid supply change 60 is increased in the next iteration step if no signal maximum 82 or no double peak structure 94 could be determined.

In a step 101 (see Figure 2 ) the oxygen concentration 103 is determined. For this purpose, for example, the quotient is calculated from the value of the first peak 88 and the value of the second peak 92. The oxygen concentration 103 is then assigned to the quotient determined. In the exemplary embodiment, a linear function is stored in the control unit 18 for this purpose, which assigns the associated oxygen concentration 103 to the quotient.

In alternative embodiments, a table is stored in the control unit 18, in which value pairs from quotients and the associated oxygen concentration are stored. If a determined quotient is not stored in the table, the associated oxygen concentration can be interpolated from the two closest value pairs stored in the table, in particular linearly interpolated. A table stored in the control unit with pairs of values composed of quotients and oxygen concentrations has the advantage that in this way, in particular, non-linear relationships between the quotient and the oxygen concentration can be taken into account.

Figure 5 illustrates by way of example a relationship between the quotient and the oxygen concentration 103. The quotient is plotted on the second ordinate axis 105. The oxygen concentration 103 is plotted on the third abscissa 107. The in Figure 5 The depicted course of the relationship between the quotient and the oxygen concentration 103 is largely linear. In Figure 5 three pairs of values 109 from quotient and oxygen concentration 103 are shown by way of example. A first pair of values 109a shows a quotient of 0.95 and an oxygen concentration 103a of 2.7%. A second pair of values 109b shows one Quotient of 0.92 and an oxygen concentration 103b of 3.5%. A third pair of values 109c shows a quotient of 0.68 and an oxygen concentration 103c of 6.2%.

In a step 102 (see Figure 2 ) a first burner output parameter 104 is determined. The control unit 18 determines, for example, a second point in time 106 at which the ionization current 86 assumes the first peak 88 (see FIG Figure 3 ).

In the exemplary embodiment, the control unit 18 preferably stores a time profile of the ionization current 86. A first time difference 108 between the first point in time 72 and the second point in time 106 is advantageously determined. The first time difference 108 determined in this way describes, in particular, a time interval between the generation of the fluid supply change 60 and the determination of the resulting time change in the combustion parameter. The first time difference 108 is a measure of a flow rate of a fuel-air mixture flowing to the burner 28. Due to the known and largely constant dimensions of the piping 22 transporting the fuel-air mixture, the first time difference 108 is a measure of a volume flow of the fuel-air mixture. The first time difference 108 is thus a parameter describing the performance of the heating system 46. A time / burner output function 110 is stored in the control unit 18, which assigns the first burner output parameter 104 to the first time difference 108. In the exemplary embodiment, the time / burner output function 110 is a rational functional specification, on the basis of which the control unit 18 calculates the first burner output parameter 104 from the first time difference 108. The time-burner output function 110 is determined by laboratory tests. In the exemplary embodiment, the time-burner output function 110 is selected such that the values of the first burner output parameter 104 lie in the value range of the second burner parameter 95 and correspond to one another. In this way, the first burner output parameter 104 and the second burner output parameter 95 can be compared with one another, in particular one of the burner output parameters can be used to control or check the other burner output parameter. Figure 6 shows the time / burner output function 110. A fourth axis of abscissa 112 represents the first burner output parameter 104. The first time difference 108 is shown on a third axis of ordinate 114. The first burner output parameter 104 is greater, the smaller the first time difference 108 is.

In alternative variants, the time / burner output function 110 is stored as a value table in the control unit 18. A value range for the first time difference 108 is subdivided at least into intervals and the value table assigns a first burner output parameter 104 to each of these intervals. The value range for the first time difference 108 advantageously has such values for first time differences 108 which represent an at least largely complete power range of the heating system 46. In further embodiments, the first time difference 108 is determined between the first point in time 72 and a third point in time 118 at which the ionization current 86 assumes the first sink 90, or between the first point in time 72 and a fourth point in time 120 at which the ionization current 86 ends second peak 92 assumes, or the first point in time 72 and a point in time at which it is determined for the first time that the ionization current 86 deviates from the ionization current normal value 100 more than a signal noise. It is also conceivable that the generation of the fluid supply change 60 is described with a point in time at which the fluid supply parameter 62 reaches the maximum supply value 74 or assumes the normal value 70 again.

In a further step 116, a target combustion parameter 130 is determined based on the oxygen concentration 103 and on the first burner output parameter 104 (see FIG Figure 2 ). In the exemplary embodiment, the signal maximum 82 determined in step 80 from the double peak structure 94 is corrected for this purpose. A correction value 122 is determined from the first burner output parameter 104 in conjunction with the second burner output parameter 95. Figure 7 shows the flame ionization characteristic 124 stored in the control unit 18. The flame ionization characteristic 124 describes the relationship between the second burner output parameter 95 and the ionization flow 86 at a given fuel-air ratio 56. A fifth abscissa axis 126 shows the second burner output parameter 95 and the first burner output parameter 104 The ionization current 86 is shown on the first ordinate axis 68. Figure 7 shows a flame ionization characteristic curve 124 for a fuel-air ratio 56 of 1. The flame ionization characteristic curve 124 is determined empirically and is stored in the control unit 18. A plurality of flame ionization characteristic curves 124 for different fuel-air ratios 56 are stored in the control unit 18. In the exemplary embodiment, the flame ionization characteristic curves are 124 rational functional rules. In the exemplary embodiment, the flame ionization characteristic curves 124 are updated by the method 54 if this is necessary (see step 134).

In step 116, a power difference 128 between the second burner power parameter 95 and the first burner power parameter 104 is determined. The control unit 18 assigns the correction value 122 to the power difference 128. For this purpose, with the aid of the flame ionization characteristic curve 124 for a fuel-air ratio 56 of 1 at the position of the current second burner output parameter 95, the output difference 128 is assigned a difference in the ionization flow 86, which represents the correction value 122. Alternatively, a first ionization value can be assigned to the current second burner power parameter 95 with the aid of the flame ionization characteristic curve 124 for a fuel-air ratio 56 of 1, and a second ionization value can be assigned to the first burner power parameter 104. The correction value 122 is determined from the difference between the first ionization value and the second ionization value. The signal maximum 82 is corrected in that the correction value 122 is added to its value. The correction value 122 and / or the power difference can in each case assume positive or negative values or the value zero. An advantage of the correction value 122 is explained below.

In the exemplary embodiment, the target combustion parameter 130 is determined as the product of the corrected signal maximum 84, a calibration factor 132 and a compensation factor. The calibration factor 132 is a value between 0 and 1 stored in the control unit 18. In the exemplary embodiment, the calibration factor 132 is 0.75. In alternative variants, the calibration factor 132 takes values between 0.6 and 0.9. In the exemplary embodiment, the calibration factor 132 is an empirically determined constant. The nominal combustion parameter 130 is stored in the data memory 48 of the control unit 18.

The compensation factor depends on the value of the oxygen concentration 103 determined in step 101. A rational function is advantageously stored in the control unit 18 which assigns the compensation factor to the oxygen concentration 103. The compensation factor advantageously has a value which is between 0.6 and 1.4, preferably 0.8 and 1.2, particularly preferably between 0.9 and 1.1. The compensation factor advantageously increases steadily with the oxygen concentration 103. The compensation factor preferably has the value 1 or a value close to 1, if the oxygen concentration 103 is in a desired range. If the oxygen concentration 103 is below a desired range, the compensation factor preferably has a value less than 1. Because if the oxygen concentration 103 is too low, this indicates that the value of the fuel-air ratio 86 is too low. According to the representation in Figure 4 this indicates that the previously used target combustion parameter 130 is too large. Therefore, in such a case, a compensation factor smaller than 1 is preferably selected in order to correct the new setpoint combustion parameter 130 downwards. Accordingly, the compensation factor preferably has a value greater than 1 when the oxygen concentration 103 is above a desired range.

In Figure 8 a relationship between the oxygen concentration 103 and the compensation factor is shown as an example. The compensation factor is plotted on the fourth ordinate axis 131. The oxygen concentration 103 is plotted on the third abscissa axis 107. From the im Figure 8 The applied functional relationship is preferably assigned to the determined oxygen concentration 103 of the compensation factor. As an example, three pairs of values 133 from the compensation factor and oxygen concentration 103 of the functional relationship are shown. A first pair of values 133a shows a compensation factor of 0.82 and an oxygen concentration 103d of 2.0%. A second pair of values 133b shows a compensation factor of 1.00 and an oxygen concentration 103e of 4.21%. A third pair of values 133c shows a compensation factor of 1.30 and an oxygen concentration 103f of 6.4%. The second pair of values 133b represents a preferred oxygen concentration 103e, at which no compensation or correction is necessary, so the compensation factor has the value 1.0. Oxygen concentrations 103 lying below the preferred oxygen concentration 103e, such as 103d for example, are assigned a compensation factor smaller than one. Oxygen concentrations 103 above the preferred oxygen concentration 103e, such as 103c, for example, are assigned a compensation factor greater than one.

A functional relationship between the oxygen concentration and the compensation factor, as for example in FIG Figure 8 mapped, depending on the first burner output parameter 104 and / or second burner output parameter 95 and / or another parameter which the Performance of the heater characterized, deposited or saved. This relationship can in particular be in the form of a rational function and / or a table of values, with values between the entries in the table of values preferably being interpolated, for example being linearly interpolated.

In variants of the exemplary embodiment, in an optional step, which preferably immediately follows the determination 101 of the oxygen concentration 103, it is checked whether the determined oxygen concentration 103 exceeds a stored critical maximum value or falls below a stored critical minimum value. For example, the critical maximum value and / or the critical minimum value are stored in the control unit 18, preferably in the data memory 48. For example, the critical maximum value of the oxygen concentration 103c is between 4% and 9%, preferably between 5% and 8%, particularly preferably between 6%. and 7%. For example, the critical minimum value of the oxygen concentration 103 is between 1% and 6%, preferably between 2% and 5%, particularly preferably between 3% and 4%. The stored critical minimum value is smaller than the stored critical maximum value.

If the determined value of the oxygen concentration 103 falls below the critical minimum value or if the determined value of the oxygen concentration 103 exceeds the critical maximum value, the heating system is preferably calibrated. In particular, the method 54 can be interrupted or canceled in order to carry out the calibration.

In a further step 134, the heating system 46 is regulated on the basis of the target combustion parameter 130 determined in step 116. In the exemplary embodiment, the heating system 46 is regulated with the aid of the flame ionization characteristic curve 124 stored in the control unit 18. A flame ionization characteristic curve 124 is used for a fuel-air ratio 56 of 1.3. If necessary, the flame ionization characteristic curve 124 for a fuel-air ratio of 56 1.3 is updated by the target combustion parameter 130 determined in step 116. For this purpose, a value of the ionization current 86 is assigned to the current fan speed 96 using the flame ionization characteristic curve 124 for a fuel-air ratio 56 of 1.3 and compared with the nominal combustion parameter 130 determined in step 116. If the relative deviation exceeds a predetermined tolerance value, the flame ionization characteristic curve 124 is updated by adding the associated rational Functional rule is changed. In the exemplary embodiment, this rational functional rule is changed in such a way that the updated values of the ionization current 86 assigned to the second burner power parameter 95 are multiplied by a correction factor. The correction factor is equal to the nominal combustion parameter 130 divided by the corresponding value of the ionization current 86 before the update.

If the fan speed 96 is changed in the exemplary embodiment and if there is no target combustion parameter 130 determined in a step 116 for this changed second burner output parameter 95, then the target combustion parameter 130 from the flame ionization curve 124 is used for a fuel-air ratio 56 of 1.3. If the desired fuel-air ratio 56 changes and if there is no target combustion parameter 130 determined in a step 116 for this changed operating parameter, then the target combustion parameter 130 from the flame ionization characteristic curve 124 stored in the control unit 18 is used for the corresponding fuel-air ratio 56 . In alternative embodiments, regardless of the currently present second burner output parameter 95 and / or operating parameters, the target combustion parameter 130 determined last in a step 116 is used for regulating the heating system 46.

In the exemplary embodiment, the heating system 46 is regulated on the basis of a target combustion parameter 130, which is determined as a function of the second burner output parameter 95 and the appropriate flame ionization characteristic 124 if a target combustion parameter 130 cannot be determined in step 116, for example because no signal maximum 82 can be determined in step 80 .

In step 134, 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 current 86 assumes the value of the setpoint combustion parameter 130. For this purpose, a closed control loop is used in the exemplary embodiment, the ionization current 86 being a controlled variable, the control signal 64 being a manipulated variable and the target combustion parameter 130 being a reference variable.

The method 54 is repeated in the exemplary embodiment. A time interval between the iterations of the method 54 is dependent on the operating state of the Heating system 46 and selected by external conditions. In the exemplary embodiment, the time interval is between 2 seconds and 240 seconds, preferably between 10 seconds and 120 seconds, particularly preferably 30 seconds. In variants of the exemplary embodiment, the method 54 is carried out largely periodically. A time interval between the iterations of the method 54 is largely constant. In further embodiments, the execution of the method 54 is triggered by an event, in particular as a function of an operating parameter of the heating system 46. For example, the method 54 can be used in the event of an incorrect measurement of the combustion parameter 84 and / or when the heating system 46 is restarted and / or in the event of unusual changes from recorded measured values, in particular measured values dependent on the combustion. In preferred variants, the method 54 is carried out at least largely once every 24 hours.

In the exemplary embodiment, steps 80 and 102 are carried out largely in parallel. These can also be carried out one after the other in any order. The sequence of steps 80 and 102 is irrelevant for method 54. In the exemplary embodiment, the first burner output parameter 104 is determined in step 102 as a function of the fluid supply change 60. In alternative embodiments, the first burner output parameter 104 can be determined independently of the fluid supply parameter 60, for example by measuring the temperature at the flame 40 and / or by measuring a fuel flow by a mass flow sensor. In these embodiments, step 102 can be carried out at any position before step 116, in particular before step 58.

It is conceivable that in variants of the embodiment, the flame ionization characteristic curve 124 (see Figure 7 ) describes the relationship between the first burner power parameter 95 and the ionization current 86. In these variants, the regulation of the heating system or the method 54 determines the output of the heating system 46 by ascertaining the first burner output parameter 95 sufficiently frequently. The second burner output parameter 95 is used for correction, for example via the output difference 128.

Furthermore, it is conceivable that in further variants of the embodiment, in step 116 for correcting the signal maximum 82, the correction value 122 is obtained from the Power difference 128 and a flame ionization characteristic 124 stored in the control unit 18 for a fuel-air ratio 56 of 1.3 or for a desired value of the fuel-air ratio 56 is determined. In other embodiments, the correction value 122 is an empirically determined constant stored in the control unit.

In the exemplary embodiment, the nominal combustion parameter 130 is determined in step 116 by forming the product of the signal maximum 82 with the calibration factor 132. In alternative embodiments, the set combustion parameter 130 is determined by the control unit 18 with the aid of a functional rule, in particular a rational functional rule, from the signal maximum 82. It is conceivable that this functional rule depends on further operating parameters.

In the exemplary embodiment, the calibration factor 132 is a constant stored in the control unit 18. In alternative embodiments, the calibration factor 132 is determined as a function of the first burner output parameter 104 and / or on the second burner output parameter 95. In this way, it can be taken into account that, in general, the ionization flow 86 corresponding to a desired fuel-air ratio 56 differs from the signal maximum 82 of the ionization flow 86 by a power-dependent factor. This fact is taken into account in the exemplary embodiment by taking the correction value 122 into account. In special variants of these alternative embodiments, the correction value 122 is a constant, in particular with the value zero.

In the exemplary embodiment, the fluid supply change 60 largely has the shape of a ramp. In alternative embodiments, the fluid supply change 60 is largely triangular in shape. This has the advantage that the second peak 92 of the double peak structure 94 is formed particularly clearly. In further embodiments, the fluid supply change 60 has a largely rectangular shape and / or largely the shape of a sine and / or largely the shape of a Gaussian curve. These fluid supply changes 60 are particularly suitable for short pulses.

In alternative embodiments, an additional fluid supply change is generated in an additional step. The additional fluid supply change is largely opposite to the fluid supply change 60. In this way, the mean fluid supply parameter 62 over a period of time corresponds to which the Fluid supply change 60 and the additional fluid supply change largely include the normal value 70. In preferred embodiments, the graph of the time course of the fluid supply parameter 62 of the fluid supply change 126 largely resembles the graph of the time course of the fluid supply parameter 62 of the fluid supply change 60 mirrored and time-shifted at the normal value 70 If the fluid supply change 60 is realized by a largely ramp-shaped pulse with a certain positive pulse height 76 and a certain pulse width 78, the additional fluid supply change is selected by a largely ramp-shaped pulse with a largely identical pulse width 78 and an additional pulse height, which depends on the amount of the pulse height 76 of the first largely corresponds to the ramp-shaped pulse of the fluid supply change 60 and is negative. This additional step can be carried out at any point in the method 54. In preferred embodiments, the additional step is positioned such that the additional fluid supply change does not influence the change in the combustion parameter 84 that is correlated with the fluid supply change 60. The additional step is preferably carried out after step 58, particularly preferably after step 80.

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 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 consists of 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 blower 32. In alternative embodiments, a metering value of the metering device 34 is measured and used as the fluid supply parameter 62. "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 84 is an ionization current 86. The ionization current 86 is determined by an ionization current measurement on a flame 40 of the heating system 46 is determined. The ionization current 86 is determined by the ionization probe 42 and transmitted to the control unit 18. In further embodiments, the combustion parameter 84 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 emission is 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 first burner output parameter 104 is determined from the first time difference 108 between the first point in time 72 and the second point in time 106. In alternative embodiments, the first burner output parameter 104 is determined from a second time difference 136 between the second time 106 and the third time 118 and / or from a third time difference 138 between the second time 106 and the fourth time 120 (see FIG Figure 3 ). The second time difference 136 and the third time difference 138 are a measure of a time width of the double peak structure 94. The time width of the double peak structure 94 is a measure of a flow rate of a fuel-air mixture flowing to the burner 28. The second time difference 136 and the third time difference 138, like the first time difference 108, thus describe the output of the heating system 46. The first time difference 108, the second time difference 136 or the third time difference 138 can be used in any combination to determine the first burner output parameter 104 . In this way, measurement inaccuracies in particular can be taken into account when determining the first time difference 108 and / or the second time difference 136 and / or the third time difference 138.

In the exemplary embodiment, the second burner output parameter 95 is a fan speed 96. In alternative embodiments, the second burner output parameter 95 and / or the first burner output parameter 104 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 and / or a performance of the fan. 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. These parameters can also be used in combination. The temperature can be determined in the exhaust system 38 and / or by the flame 40. The first burner output parameter 104 and the second burner output parameter 95 are each determined using different methods.

In the exemplary embodiment, the fluid supply change 60 is selected as a function of the second burner output parameter 95. The pulse height 76 and pulse width 78 each depend linearly on the fan speed 96. 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 second burner output parameter 95. The functional relationship is selected such that a good detection of the signal maximum 82 is possible, taking into account the technical properties of the heating system 46. If, for example, resonances occur at certain fan speeds 96, which increase the signal noise of the ionization stream 86, then at these fan speeds 96 the fluid supply change 60 is increased. In further embodiments, the change in fluid supply is selected as a function of the second burner output parameter 95 and / or the first burner output parameter 104. In this way, the fluid supply change 60 is more precisely adapted to an actual output of the heating system 46. Optionally, for example if step 102 has not yet been carried out, a first burner output parameter 104 from a previous iteration of method 54 can be used.

Claims (15)

Method (54) for setting and regulating a fuel-air ratio (56) in a heating system (46) with a sensor for detecting a combustion parameter (84), in particular an ionization current (86), which comprises the following steps: • Generating (58) a temporary, temporal fluid supply change (60) of a fluid supply parameter (62) which is provided to generate a temporal change in the combustion parameter (84), the fluid supply change (60) being selected so that the temporal change in the combustion parameter (84) has a double peak structure (94) which has at least a first peak (88), a first depression (90) and a second peak (92), • Determining (80) the first peak (88) and the second peak (92) of the temporal change in the combustion parameter (84) correlated with the temporal change in the fluid supply (60), • Determination (101) of an oxygen concentration (103) as a function of a quotient of the first peak (88) and the second peak (92), • determining (102) a first burner output parameter (104), • Determination (116) of a target combustion parameter (130) based on the oxygen concentration (103) and the first burner output parameter (104), • Regulation of the heating system (46) on the basis of the target combustion parameter (130). Method (54) according to Claim 1, characterized in that the heating system (46) is calibrated when the determined oxygen concentration (103) exceeds a stored critical maximum value or falls below a stored critical minimum value. Method according to Claim 1 or 2, characterized in that a signal maximum (82) is determined from the first peak (88) and / or the second peak (92) and is taken into account when determining (116) the target combustion parameter. Method (54) according to Claim 3, characterized in that the target combustion parameter (130) is determined by forming the product of the signal maximum (82) with a calibration factor (132). Method (54) according to Claim 4, characterized in that, when determining (116) the setpoint combustion parameter (130), a compensation factor is taken into account which depends on the determined oxygen concentration (103). Method (54) according to Claim 4 or 5, characterized in that the calibration factor (132) is determined as a function of the first burner output parameter (104) and / or of the or a second burner output parameter (95). Method (54) according to one of the preceding claims, characterized in that the change in fluid supply over time (60) largely has the shape of a ramp and / or largely a triangular shape. Method (54) according to one of the preceding claims, characterized in that in an additional step a temporary additional fluid supply change is generated, this additional fluid supply change being largely opposite to the fluid supply change (60). Method (54) according to one of the preceding claims, characterized in that the fluid supply parameter (62) corresponds to a control signal (64) for metering a fuel and / or the combustion air and / or a mixture of a fuel and combustion air. Method (54) according to one of the preceding claims, characterized in that the combustion parameter (84) is determined by measuring the ionization current on a flame (40) of the heating system (46). The method (54) according to any one of the preceding claims, characterized in that the first burner output parameter (104) from a first time difference (108) between the generation of the fluid supply change (60) and the determination of the time change correlated with the fluid supply change (60) from the Combustion parameter (84) is determined. Method (54) according to one of the preceding claims, characterized in that the first burner output parameter (104) is determined from the double peak structure (94), in particular from a second time difference (136) between the first peak (88) and the first sink (90) ) and / or from a third time difference (138) between the first peak (88) and the second peak (92). Method (54) according to one of the preceding claims, characterized in that the fluid supply change (60) is selected as a function of the first burner output parameter (104) and / or the or a second burner output parameter (95). Control unit (18) for a heating system (46), wherein the control unit (18) is set up to carry out a method (54) according to one of the preceding claims. Heating system (46) with a control unit (18) according to Claim 11, with a metering device (34) for a fuel and / or combustion air and / or for a mixture of a fuel and combustion air, and with an ionization probe (42) on a flame ( 40) and with a fan (32) with a variable fan speed (96).

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