Method of regulating the combustion of a gas-air mixture in a heating device and heating device

Abstract

The invention relates to a method for regulating the combustion of a gas-air mixture in a heating device and to a heating device. The regulation is carried out at variable power by means of a measured ionization signal, comprising the following steps: the ionization signal is split into a positive part and a negative part, which are observed separately; the positive part is dependent on the ratio of combustion air to gas and is used to determine the ionization signal; the negative part and / or the ratio of its amount to the positive part is dependent on the current power of the heating device, which is determined by means of an evaluation unit on the basis of empirical values or calibration data; information about the current power of the heating device is used to select suitable calibration data for this power in order to regulate the ratio of combustion air to gas. This achieves reliable regulation at variable power by means of additional electronics without significant changes to the heating device.

Description

Technical Field

[0001] This invention relates to the field of regulating the combustion process of a gas-air mixture in a heating device, particularly for hot water supply or heating of buildings. To measure combustion quality, which depends primarily on the ratio of combustion air to gas during combustion (λ value, also known as the air-fuel ratio), especially in many heating devices, ionization measurements are performed in the flame zone. Such measurements aim to achieve stable regulation over long periods. If regulation fails, the heating device must, in most cases, be shut down, which should, of course, occur as infrequently as possible. Background Technology

[0002] According to existing technology, regulation during operation has so far been achieved using a separate ionization electrode. Regardless of the type of electrode, the corresponding actual value of ionization in the flame region is determined, which is proportional to the current λ value, so that the current λ value can be derived from the ionization measurement. Here, an AC voltage is applied to the ionization electrode, where, in the presence of a flame, the ionized flame region has a rectifying effect, so the ionization current flows primarily only within half a cycle of the AC current. This current, or the proportional voltage signal derived therefrom (hereinafter referred to as the ionization signal), is measured and, if necessary, digitized in an analog-to-digital converter, further processed into an ionization signal. The λ value can then be measured and regulated to its rated value via a regulating circuit. The supply of air and / or fuel gas is modified by a suitable regulator until the desired λ rating is achieved. Typically, an effort is made to achieve a λ value > 1 (1 is equivalent to a stoichiometric ratio), for example, λ = 1.3, to ensure sufficient air supply for clean combustion, with virtually no carbon monoxide production. However, λ must be kept small enough to ensure stable combustion. This adjustment can be made, in particular, through valves used to supply gas and / or fans used to supply ambient air.

[0003] For example, such combustion regulation is known from DE 196 18 573 C1 and DE 195 02 901 C1, which regulates the desired combustion quality (λ value) through a stored ionization current regulation curve.

[0004] For example, the basic structure of such heating devices is known from EP 0 770 824 B1 and EP 2 466 204 B1, which relate to a measurement system for ionization measurements and its adjustment scheme. They also describe how the adjustment accuracy can change over time due to various influences, particularly those affecting the state or shape of the ionization electrode. Various methods for subsequent calibration are provided here when necessary.

[0005] However, another parameter must be considered in the adjustment: the power of the heating device. In fact, the measured ionization signal depends not only on the value of λ but also on the corresponding power of the heating device; therefore, this parameter must be known for precise adjustment. In the first approximation, if a fixed relationship is assumed between rotational speed and power, this power can be correlated with the speed of the fan used for combustion air (or a mixture of combustion air and fuel gas). However, precise adjustment may not be achieved, for example, if the operation of the heating device and / or environmental conditions change. In principle, precise measurement can be achieved by using a flow meter to measure the flow rate of combustion air or the combustion mixture, but this requires certain additional measurement costs (self-testing sensors, etc.). Summary of the Invention

[0006] The purpose of this invention is to provide an auxiliary measure to achieve safe and reliable operation of the heating device and to enable stable and precise adjustment at different power levels with minimal cost.

[0007] The methods, apparatus, and computer program products according to the independent claims contribute to achieving this objective. Advantageous designs and modifications of the invention are given in the corresponding dependent claims. This specification, particularly in conjunction with the accompanying drawings, elucidates the invention and provides other embodiments.

[0008] So far, in the introduction of the ionization measurement principle for flame retardancy during combustion, a diode and a resistor connected in series have been used as a simplified equivalent circuit diagram. This can be used to introduce the system used so far, where flame retardancy has a rectifying function with superimposed resistance. In fact, another characteristic of flame retardancy can be reproduced in the extended equivalent circuit diagram by using an additional resistor connected in parallel with the diode (the so-called reverse resistor). (In any case, in a typical flame in a gas burner or a carbonaceous flame) the diode effect (rectification effect) of the flame is not perfect (conducting only in the direction specified here as positive), but a certain current flows in the opposite direction (the part specified here as negative). However, in the direction of diode conduction, the reverse resistance is several orders of magnitude larger than the so-called forward resistance, hence its small effect. However, studies have shown that the forward resistance depends not only on the value of λ, but also on the power of the heating device in such a way that the forward resistance leads to an excessively high value of λ when the power increases and the calibration data remains unchanged. The reverse resistance qualitatively depends almost entirely on the power of the heating device, but to a very small extent. However, this part can be evaluated through sensitive measurements and used to determine the effect of power on the positive portion of the ionization signal. Therefore, the deviation between the rated power determined, for example, by the fan speed, and some actual power determined, for example, by environmental variables, can be compensated for.

[0009] The proposed method relates to a scheme for regulating combustion in a heating device under variable power conditions by means of an ionization signal measured in the flame region of the heating device, which operates with combustion air and fuel gas. This ionization signal is derived based on an ion flow from the ionizing electrode to the counter electrode through the flame region. The ion flow is generated by an ionizing alternating voltage of a predetermined frequency. The ratio of combustion air to fuel gas (λ value) during combustion in the heating device is determined using calibration data from the ionization signal and regulated by adjusting the fuel gas supply and / or the combustion air supply. At least the following steps are performed:

[0010] 1.1 Ionization signals contain positive and negative parts; observe these two parts separately.

[0011] The positive part depends on the ratio of combustion air to fuel gas (λ value) and is used to determine the ionization signal (I1).

[0012] 1.3 The ratio of the negative portion and / or the positive portion depends on the current power of the heating device, which is determined by the analysis unit (14) based on empirical values ​​or calibration data.

[0013] 1.4 Information about the current power of the heating device is used to select appropriate calibration data for that power to adjust the ratio of combustion air to fuel gas (λ value).

[0014] In this context and below, the portion of the ionized signal that is more dependent on the λ value is defined as the positive portion, and the other portion as the negative portion. However, this depends on the type of signal being evaluated, and in practice, it may be the opposite, depending on the evaluation electronics.

[0015] By analyzing the negative portion, the actual power of the heating device can be determined almost independently of the λ value (at least in the region where regulation is important). In any case, the current power of the heating device can be determined based on empirical values ​​or calibration data without the need for additional sensors in the heating device.

[0016] In one embodiment of this method, the frequency of the ionizing alternating voltage is used, preferably between 50 and 300 Hz, and particularly around 100 Hz. This means that known ionization measuring devices operating within these ranges can be used.

[0017] In a preferred embodiment, the maximum value of the amplitude of the positive portion and the minimum value of the amplitude of the negative portion of the ionization signal are determined, and they are further processed separately for different purposes. However, this embodiment is not the only feasible approach for evaluation. Thus, for example, the corrected average value of the corresponding half-cycle can also be used as a measure.

[0018] In particular, the adjustment of the λ value can be continuously corrected using information about the current power of the heating device from the negative part of the ionization signal.

[0019] In an alternative implementation, if necessary, the calibration data for adjusting the heating device by means of the fan speed can be corrected using measurements of the current power of the heating device. In this way, known types of adjustments can be used, but adaptations can be made iteratively to varying operating conditions.

[0020] A heating device is also proposed, which has an air delivery component and a gas delivery component, which are regulated by an adjustment unit using an ionization signal. The device includes an ionization electrode, a counter electrode, an ionization AC voltage source for a predetermined frequency, and an evaluation electronics device for determining the positive portion of the ionization signal, which can be transmitted to the adjustment unit. An analysis unit is provided to evaluate the negative portion of the ionization signal in order to determine the current power of the heating device.

[0021] The analysis unit is preferably connected to or integrated into the evaluation electronics.

[0022] In addition, a computer program product is proposed, which includes instructions for causing the heating device described herein to perform the proposed method. Attached Figure Description

[0023] The illustrative embodiments of the invention, which are not intended to limit the invention, and the working principle of the method according to the invention will now be explained in more detail with reference to the accompanying drawings. Wherein:

[0024] Figure 1 An extended equivalent circuit diagram for flame retardancy during combustion is shown, and

[0025] Figure 2 A schematic diagram of a heating device according to the present invention is shown, which has a mechanism for adjustment via an ionization signal. Detailed Implementation

[0026] Figure 1An equivalent circuit diagram 10 for the extension of a flame is schematically shown, in which an ionized current generated by an ionization voltage source 11 flows. On one hand, the flame functions like a diode D, meaning the current can flow essentially only in one direction, and it also has a certain resistance, namely the forward resistance RF, which can be represented by a resistor connected in series with the diode D. However, the diode D also allows a certain amount of current to flow in its cutoff direction, which can be represented by a reverse resistance RR connected in parallel with the diode D. In the application example presented, the reverse resistance RR is several orders of magnitude larger than the forward resistance RF, and therefore the presence of the reverse resistance RR is ignored in many equivalent circuit diagrams and circuits. However, for the purposes of this invention, it is important that this resistance varies with the power of the heating device and, to a large extent or as much as possible, independently of the current value of λ, while the forward resistance varies with both λ and power; therefore, adjusting only the value of λ is complex at different power levels. However, it is feasible to determine information about the power by measuring the reverse resistance, which is technically possible, thus eliminating the influence of power on the forward resistance, which is the subject of this invention.

[0027] Figure 2 An embodiment of the apparatus presented herein is illustrated schematically. In a heating device 1 for burning fuel gas with air in a combustion chamber, a flame zone 2 is formed during operation. Air enters the heating device 1 through an air delivery member 3 and a fan 5. Fuel gas is mixed with air through a fuel delivery member 4 and a fuel valve 6. The fuel gas delivery and the speed of the fan 5 can be regulated by a control line 7. An ionization signal I in the flame zone 2 is measured by an ionization electrode 8. For this purpose, a measurement system is used in which an ionization AC voltage U of a predetermined frequency f from an ionization AC voltage source 11 is applied to the ionization electrode 8, the ionization signal I is measured by a first evaluation electronic device 13, and it is converted into a λ value, i.e., the air-fuel mixing ratio, according to calibration data (adjustment curve) stored in a calibration data memory 15. A rated value of the ionization signal can be specified or preset in a simplified manner. Using this value as the actual value, the adjustment unit 16 can adjust the fan 5 and / or the fuel valve 6 such that the actual value of λ is set to the desired value.

[0028] In addition to the known adjustment based primarily on the positive portion of the ionization signal I, the negative portion of the ionization signal I can also be evaluated. The ionization signal I is transmitted via data line 12 to analysis unit 14, which obtains information about the power of the heating device 1 based on the negative portion or the ratio of the negative to the positive portion. This can preferably be done based on empirical values ​​or calibration data. Analysis unit 14 can, of course, be part of evaluation electronics 13, which then evaluates the positive and negative portions of the ionization signal I separately. Although the reverse resistance RR has a small effect on the ion current in the flame, it can be measured without problems using current measurement techniques. In fact, a conventional ionization signal has a positive half-cycle and a negative half-cycle, and their corresponding maximum or minimum values ​​can be determined, from which the desired information for adjustment can be obtained separately. Experiments show that the minimum value corresponding to the reverse resistance RR is almost independent of the value of λ over a large range, but strongly depends on the actual power (actual value) of the heating device. This allows the influence of power on the adjustment of the value of λ, which has the maximum value of the positive portion of the ionization signal, to be eliminated.

[0029] This invention enables reliable regulation at variable power without significant changes to the heating device itself, using only additional electronics. It also allows for (subsequent) adjustments to existing regulation for different power levels.

[0030] List of reference numerals

[0031] 1. Heating device with combustion chamber

[0032] 2. Flame Zone

[0033] 3. Air delivery components

[0034] 4. Gas transmission components

[0035] 5 fans

[0036] 6. Gas valve

[0037] 7. Control piping

[0038] 8 Ionization Electrode

[0039] 9. Burner electrode / counter electrode

[0040] 10. Equivalent circuit diagram of a flame

[0041] 11-Electrode AC Voltage Source

[0042] 12 signal lines

[0043] 13. Evaluate electronic devices

[0044] 14 Analysis Units

[0045] 15. Adjust the data storage

[0046] 16 Adjustment Units

[0047] U Ionization AC voltage

[0048] f frequency

[0049] I ionization signal

[0050] D diode

[0051] RF forward resistor

[0052] RR reverse resistance

Claims

1. A method for regulating the combustion of a fuel-air mixture in a heating device (1), the regulation being performed at a variable power by means of a measured ionization signal I, the ionization signal I being derived based on an ion current flowing from an ionization electrode (8) to a counter electrode (9) through a flame region (2), the ion current being generated by an ionization AC voltage U having a specified frequency f, wherein, during the combustion process in the heating device (1), the ratio λ of combustion air to fuel gas is determined according to calibration data based on the ionization signal I and is regulated by adjusting the supply of fuel gas and / or the supply of combustion air, the method comprising the following steps: 1.1 The ionization signal I contains positive and negative parts; these two parts should be observed separately. 1.2 The positive part depends on the ratio λ of combustion air to fuel gas and is used to determine the ionization signal I; 1.3 The ratio of the negative portion or the positive portion depends on the current power of the heating device (1), which is determined by the analysis unit (14) based on empirical values ​​or calibration data; 1.4 Information about the current power of the heating device (1) is used to select appropriate calibration data for that power in order to adjust the ratio λ of combustion air to fuel gas.

2. The method according to claim 1, wherein, The frequency f of the ionization AC voltage U is between 10 Hz and 10000 Hz.

3. The method according to claim 1, determining the maximum value of the amplitude of the positive portion of the ionization signal I and the minimum value of the amplitude of the negative portion.

4. The method according to any one of the preceding claims, characterized in that, The ratio λ of combustion air to fuel gas is continuously adjusted by using information about the current power of the heating device (1) based on the negative part of the ionization signal I.

5. The method according to any one of claims 1 to 3, wherein, Based on the measurement results of the current power of the heating device (1), the adjustment data of the heating device is corrected by means of the fan speed when necessary.

6. A heating device (1) for regulating the combustion of a gas-air mixture, comprising an air delivery element (3) and a gas delivery element (4), the air delivery element and the gas delivery element being regulated by an regulating unit (16) using an ionization signal I, comprising an ionization electrode (8), a counter electrode (9), an ionization AC voltage source (11) for an ionization AC voltage U having a frequency f, and an evaluation electronics (13) for determining the positive portion of the ionization signal I, the ionization signal being capable of being transmitted to the regulating unit (16), and an existence analysis unit (14) for evaluating the negative portion of the ionization signal I to determine the current power of the heating device (1) based on empirical values ​​or calibration data; the heating device (1) regulating the combustion of the gas-air mixture in the heating device (1) according to the method of claim 1.

7. The heating device (1) according to claim 6, wherein, The analysis unit (14) is connected to the evaluation electronics (13).

8. A computer program product comprising instructions for causing a heating device according to any one of claims 6 or 7 to perform the method according to any one of claims 1 to 5.

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