CN113339841A

CN113339841A - Method and device for regulating a gas/air mixture in a heating device with variable output

Info

Publication number: CN113339841A
Application number: CN202110185197.0A
Authority: CN
Inventors: 克里斯蒂安·菲舍尔
Original assignee: Vaillant GmbH
Current assignee: Vaillant GmbH
Priority date: 2020-02-18
Filing date: 2021-02-10
Publication date: 2021-09-03
Also published as: EP3869099A1; EP3869099B1; DE102020104210A1; ES2934238T3

Abstract

The invention relates to a method for controlling the combustion in a heating device (1) by means of an ionization signal (I) measured in a flame region (2) of the heating device (1), said ionization signal being derived on the basis of an ion current flowing through the flame region (2) from an ionization electrode (8) to a counter electrode (9), said ion current being generated by an ionization alternating voltage (U) having a specific frequency (f), wherein, during the combustion process of the heating device (1), the ratio (lambda value) of combustion air to gas is determined on the basis of calibration data based on the ionization signal (I) and is controlled by adjusting the supply of gas and/or the supply of combustion air. This makes it possible to achieve reliable regulation at variable output, without any significant changes to the heating device, using only additional electronics, which also enables (subsequent) adjustment of existing regulation options for different outputs.

Description

Method and device for regulating a gas/air mixture in a heating device with variable output

Technical Field

The invention relates to the field of regulating a gas-air mixture for a combustion process in a heating device, in particular for hot water supply or heating of buildings. In order to measure the quality of combustion, which depends primarily on the ratio of combustion air to gas (lambda value, also referred to as air ratio or air-fuel ratio) during combustion, ionization measurements are carried out in the flame region, in particular in many heating devices. Such measurements are intended to achieve stable regulation over a long period of time. If the regulation fails, the heating device must be switched off in most cases, which of course should occur as little as possible.

Background

According to the prior art, regulation has hitherto been carried out during operation by means of separate ionization electrodes. Independent of the type of electrode, the respective actual value of the ionization in the flame region is determined, which is proportional to the current lambda value, so that the current lambda value can be derived from the ionization measurement. In this case, an alternating voltage is applied to the ionizing electrode, wherein, in the presence of a flame, the ionized flame region has a rectifying action, so that the ionization current flows predominantly in each case only in a half-cycle of the alternating current. The current or a proportional voltage signal derived therefrom (hereinafter referred to as an ionization signal) is measured and, if necessary, digitized in an analog/digital converter and further processed into an ionization signal. The lambda value can then be measured and set to a desired value by a control circuit. The supply of air and/or gas is modified by suitable regulators until the desired lambda setpoint is reached. Usually, for example, lambda values > 1(1 corresponds to the stoichiometric ratio), for example lambda 1.3, are sought to ensure that sufficient air is provided for clean combustion, substantially without generating carbon monoxide. However, λ must be kept small to ensure stable combustion. The regulation can be carried out in particular by a valve for supplying gas and/or a fan for supplying ambient air.

Combustion regulation is known, for example, from DE 19618573C 1 and DE 19502901C 1, which regulates the desired combustion quality (lambda value) by means of stored ionization current regulation curves.

The basic structure of such heating devices is also known, for example from EP 0770824B 1 and EP 2466204B 1, which relate to measuring systems for ionization measurements and their use for regulation. Wherein also introduced are: the adjustment accuracy can be changed over time due to various influences, in particular due to influences on the state or shape of the ionizing electrode. Various methods for subsequent tuning are presented herein as needed.

However, another parameter, namely the power at which the heating device operates, must be taken into account in the regulation. In practice, the measured ionization signal depends not only on the lambda value but also on the corresponding power of the heating device, so that this parameter must be known for precise regulation. In a first approximation, the power may be correlated to the speed of the fan for the combustion air (or the mixture of combustion air and gas), if it is assumed that there is a fixed relationship between the rotational speed and the power. However, precise adjustment may not necessarily be achieved, for example, if the operating and/or environmental conditions of the heating device change. In principle, an accurate measurement can be carried out if a flow meter is used to measure the flow of combustion air or combustion mixture, but this requires a certain additional measuring effort (self-test sensors, etc.).

Disclosure of Invention

The object of the invention is to provide an aid for the safe and reliable operation of a heating device and for stable and precise adjustment at different output levels with little effort.

The object is facilitated by a method, a device and a computer program product according to the independent claims. Advantageous embodiments and developments of the invention are specified in the respective dependent claims. This specification, particularly when read in conjunction with the appended drawings, illustrates the invention and provides other embodiments.

Heretofore, 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 systems used so far, in which the flame retardancy has a rectifying function superimposed with an electric resistance. In fact, another characteristic of the flame retardancy can be reproduced in an extended equivalent circuit diagram by using an additional resistor (so-called reverse resistor) connected in parallel with the diode. The diode effect (rectifying effect) of a flame (in any case in a typical flame or a carbon-containing flame in a gas burner) is not perfect (conducting only in the direction designated herein as positive), but a certain current flows in the opposite direction (designated herein as negative). However, in the conducting direction of the diode, the reverse resistance is several orders of magnitude greater than the so-called forward resistance, and therefore its influence is small. However, studies have shown that the forward resistance depends not only on the lambda value but also on the power of the heating device in such a way that it leads to excessively high lambda values with increasing power and without changing calibration data. The reverse resistance is qualitatively almost entirely dependent on the power of the heating device, but to a small extent. However, this fraction can be evaluated by sensitive measurements and used to determine the effect of power on the positive fraction of the ionization signal. Thus, deviations between the determination of the nominal power, for example from the rotational speed of the fan, and certain actual powers, for example from environmental variables, can be compensated.

The proposed method relates to the concept of regulating the combustion in the heating device with variable output by means of an ionization signal measured in the flame region of the heating device operated with combustion air and gas, said ionization signal being derived on the basis of the ion current flowing through the flame region from the ionizing electrode to the counter electrode. The ion current is generated by an ionizing alternating voltage having a predetermined frequency, and the ratio of combustion air to gas (lambda value) during combustion in the heating device is determined using calibration data from the ionization signal and is adjusted by adjusting the gas feed and/or the combustion air feed. Here, at least the following steps are performed:

1.1 the ionization signal contains a positive portion and a negative portion, which are observed separately.

1.2 the positive part depends on the ratio of combustion air to gas (lambda value) and is used to determine the ionization signal (I1).

1.3 the proportion of the negative portion and/or the quantity thereof to the positive portion depends on the current power of the heating device, which is determined by an evaluation unit (14) on the basis of empirical values or calibration data.

1.4 the information about the current power of the heating device is used to select the appropriate calibration data for this power in order to adjust the ratio of combustion air to gas (lambda value).

Here and in the following, the part of the ionization signal that is more dependent on the lambda value is defined as the positive part, the other part as the negative part. However, this is related to the type of signal evaluation and thus, in practice, the opposite may also be true depending on the evaluation electronics.

By analyzing the negative part, the actual value of the power of the heating device can be determined almost independently of the lambda value (at least in the region that is important for the regulation). In any case, the current power of the heating device can be determined from empirical values or calibration data without the use of additional sensors in the heating device.

For the method, in one embodiment, a frequency of the ionizing alternating voltage of between 10 and 10000Hz [ Hz ], preferably between 50 and 300Hz, in particular about 100Hz, is used. This means that known ionization measuring devices operating in these ranges can be used.

In a preferred embodiment, the maximum value of the amplitude of the positive part and the minimum value of the amplitude of the negative part of the ionization signal are determined and are processed further for different purposes. However, this embodiment is not the only feasible solution to the evaluation. The corrected average value of the respective half period can then also be used as a measure, for example.

In particular, the adjustment of the lambda value can be continuously corrected by means of information from the negative part of the ionization signal about the current power of the heating device.

In an alternative embodiment, the measurement of the current power of the heating device is used to correct the calibration data for the adjustment of the heating device by means of the speed of the fan, if necessary. In this way, known types of regulation can be used, but can be adapted repeatedly to changing operating conditions.

A heating device is also proposed, which has an air feed and a gas feed, which are regulated by a regulating unit using an ionization signal, comprising an ionization electrode, a counter electrode, an ionization alternating voltage source for a predetermined frequency and evaluation electronics for determining a positive part of the ionization signal, which can be fed to the regulating unit, wherein an analysis unit is present for evaluating the negative part of the ionization signal in order to determine the current power of the heating device.

The evaluation unit is preferably connected to or integrated into the evaluation electronics.

Furthermore, a computer program product is proposed, which comprises instructions for causing the heating device described herein to carry out the proposed method.

Drawings

The exemplary embodiments of the invention, which are not to be construed as limiting the invention, and the operating principle of the method according to the invention will now be explained in more detail with reference to the accompanying drawings. Wherein:

FIG. 1 shows an extended equivalent circuit diagram for flame retardancy in a combustion process, an

Fig. 2 shows a schematic view of a heating device according to the invention with a mechanism for regulation by an ionization signal.

Detailed Description

Fig. 1 schematically shows an equivalent circuit diagram 10 for the expansion of a flame in which an ionization current generated by an ionization voltage source 11 flows. On the one hand, the flame acts like a diode D, i.e. current can flow essentially only in one direction, and also has a certain resistance, i.e. a forward resistance RF, which can be represented by a resistance connected in series with the diode D. In addition, however, the diode D also allows a certain current to pass in its off-direction, which can be represented by a reverse resistance RR connected in parallel with the diode D. In the described application example, 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, it is important for the invention that the resistance varies with the power of the heating device to a large extent or as far as possible independently of the current lambda value, while the forward resistance varies with lambda value and power, so that the adjustment of the lambda value only at different powers is complicated. It is possible, however, to determine information about the power by measuring the reverse resistance, which is possible in measurement technology, and the influence of the power on the forward resistance can be eliminated, which is the subject of the present invention.

Fig. 2 schematically shows an embodiment of the device proposed herein. In a heating device 1 for burning gas with air in a combustion chamber, a flame region 2 is formed during operation. Air enters the heating device 1 through the air conveyance member 3 and the fan 5. The gas is mixed with the air through the gas delivery member 4 and the gas valve 6. The delivery of the gas and the speed of the fan 5 can be regulated by means of the control line 7. The ionization signal I in the flame region 2 is measured by means of an ionization electrode 8. For this purpose, a measuring system is used, by means of which the ionizing electrode 8 is supplied with an ionizing ac voltage U of a predetermined frequency f from an ionizing ac voltage source 11, the ionization signal I obtained is measured by a first evaluation electronics 13 and converted to a lambda value, i.e. the air-fuel mixture ratio, on the basis of calibration data (adjustment curve) stored in a calibration data memory 15. The setpoint value of the ionization signal can be defined or preset in a simplified manner. With this value as the actual value, the regulating unit 16 can regulate the fan 5 and/or the gas valve 6 such that the actual value of λ is set to the desired value.

In addition to the known regulation based essentially on what is referred to herein as the positive part of the ionization signal I, the negative part of the ionization signal I can also be evaluated. The ionization signal I is transmitted via the data line 12 to an evaluation unit 14, which obtains information about the power of the heating device 1 on the basis of the negative part or the ratio of the negative part to the positive part. This can preferably be done on the basis of empirical values or calibration data. The analysis unit 14 may of course be part of the evaluation electronics 13, which then evaluate the positive and negative part of the ionization signal I, respectively. Although the influence of the reverse resistance RR on the ion current in the flame is small, it can be measured without problems using today's measurement techniques. In practice, a conventional ionizing signal has a positive half-cycle and a negative half-cycle, the respective maximum or minimum of which can be determined and from which the required information for the adjustment is then obtained, respectively. Experiments have shown that the minimum value to be assigned to the reversal resistance RR is, in a large range, almost independent of the lambda value, but strongly dependent on the actually present power (actual value) of the heating device. This makes it possible to eliminate the effect of the power on the adjustment of the lambda value with the maximum value of the positive part of the ionization signal.

The invention makes it possible to reliably adjust at variable power without significant changes to the heating device itself, only by means of additional electronics, which also enables (subsequent) tuning of the existing adjustment for different powers.

List of reference numerals

1 heating device with combustion chamber

2 flame area

3 air conveyance

4 gas conveying part

5 Fan

6 gas valve

7 control pipeline

8 ionizing electrode

9 burner electrode/counter electrode

10 flame equivalent circuit diagram

11 electrode ac voltage source

12 signal line

13 evaluation electronics

14 analysis unit

15 adjusting data memory

16 regulating unit

U-ionized ac voltage

f frequency

I ionization signal

D diode

RF forward resistance

RR reverse resistance

Claims

1. Method for regulating the combustion in a heating device (1) at variable power by means of an ionization signal (I) measured in a flame region (2) of the heating device (1) operated with combustion air and gas, said ionization signal being derived on the basis of an ion current flowing through the flame region (2) from an ionizing electrode (8) to a counter electrode (9), said ion current being generated by an ionizing alternating voltage (U) having a specified frequency (f), wherein, during the combustion process in the heating device (1), the ratio (lambda value) of combustion air to gas is determined on the basis of calibration data on the basis of the ionization signal (I) and is regulated by adjusting the delivery of gas and/or the delivery of combustion air, comprising the following steps:

1.1 the ionization signal contains a positive part and a negative part, which are observed separately;

1.2 the positive part depends on the ratio of combustion air to gas (lambda value) and is used to determine the ionization signal (I);

1.3 the proportion of the amount of the negative portion and/or the positive portion thereof depends on the current power of the heating device (1), which is determined by an evaluation unit (14) on the basis of empirical values or calibration data;

1.4 the information about the current power of the heating device (1) is used to select suitable calibration data for this power in order to adjust the ratio of combustion air to gas (lambda value).

2. Method according to claim 1, wherein the frequency (f) of the ionizing alternating voltage (U) is between 10 and 10000Hz [ Hz ].

3. Method according to claim 1 or 2, determining a maximum value of the amplitude of the positive portion and a minimum value of the amplitude of the negative portion of the ionization signal (I).

4. Method according to any of the preceding claims, characterized in that the adjustment of the combustion air to gas ratio (λ -value) is corrected continuously by means of information about the current power of the heating device (1) based on the negative part of the ionization signal (I).

5. Method according to one of claims 1 to 3, wherein the adjusted calibration data of the heating device (1) are corrected, if necessary, by means of the rotational speed of the fan on the basis of the measurement of the current power of the heating device.

6. A heating device (1) having an air feed (3) and a gas feed (4) which are regulated by a regulating unit (16) using an ionization signal (I) comprises an ionization electrode (8), a counter electrode (9), an ionization alternating voltage source (11) for an ionization alternating voltage (U) having a frequency (f) and evaluation electronics (13) for determining a positive part of the ionization signal (I), which can be fed to the regulating unit (16), an analysis unit (14) being present for evaluating the negative part of the ionization signal (I) for determining a current power of the heating device (1).

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

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