Method and arrangement for the acoustic observation of flames in a combustion chamber of a heating device

Description

[0001] The invention relates to a method and a system for observing flames in a heating device, in particular one that can be operated with hydrogen and / or a hydrogen-containing fuel gas. Hydrogen as a fuel gas or as an additive to fuel gases is becoming increasingly important, and great efforts are being made to upgrade new or existing heating devices for operation with it. This applies not only to large systems, but also to wall-mounted water heating devices and, in general, to heating devices for heating buildings and / or providing hot water.

[0002] Hydrogen combustion differs in several respects from previously used fuel gases. In particular, a hydrogen flame is almost invisible to the human eye, radiates less heat than flames generated with carbon-containing fuels, and requires different measurement systems than those used in heaters using hydrocarbon fuels. The present invention is therefore particularly, but not exclusively, suitable for heaters operated with pure hydrogen or with fuel gas that consists of more than 50%, in particular more than 97%, hydrogen.

[0003] To date, simple and robust sensors have generally been used in heating systems to control the systems and ensure their safe operation. However, with conventional sensor technology, some measurements cannot be performed reliably when hydrogen is used as the fuel gas. One important task is to determine the presence of a stable flame (a so-called flame monitor), another is to set a suitable ratio of combustion air to fuel gas (lambda value) for stable and environmentally friendly combustion. To date, ionization measurement systems have generally been used for these tasks with conventional fuel gases. These systems measure the ionization in the combustion chamber, particularly in the area of flames, and their measured values can be used to monitor combustion (as flame monitors and to control combustion). Optical systems are also used.However, for the reasons mentioned above, these applications reach their limits when burning pure hydrogen and even fuels with high hydrogen content, so alternatives must be found.

[0004] DE 43 02 531 A1 discloses a device for flame monitoring, wherein an ultrasonic transmitting and receiving unit is provided, with the signal path passing through the spatial region of the flame. The transmitted, reflected, and received signals are converted into electrical signals and evaluated to perform runtime measurements and velocity measurements under different operating conditions of the burner. This makes it possible to determine whether the burner has ignited and, if so, the flame's temperature or density and its modulation.

[0005] EP 2194 325 A1 relates to the measurement of interface properties between a flame to be examined and a surrounding medium of the flame using an acoustic sensor device. The sensor device comprises an acoustic transmitter for transmitting an acoustic wave to a flame location of the flame to be examined, an acoustic receiver suitable for receiving a modified acoustic wave from the flame location and for outputting a receiver signal based on the modified acoustic wave, and a processing unit configured to process the output receiver signal and to derive the at least one interface property of the interface between the flame medium of the flame and a surrounding medium of the flame based on the processed receiver signal.

[0006] EP 2 887 027 A1 relates to an active measurement of gas flow velocity or the simultaneous measurement of velocity and temperature in combustion gas flow in combustion chambers of gas turbine engines. In particular, a circumferentially and axially spaced array of acoustic sensors, acoustic transmitters, and / or transceivers is proposed for one or more real-time measurements of the active combustion gas flow velocity or the simultaneous velocity / temperature measurement.

[0007] The object of the present invention is to at least partially solve the problems described with reference to the prior art. In particular, methods and arrangements for the acoustic observation of flames or combustion processes in a combustion chamber of a heating device are to be created, which are suitable for use as flame monitors and / or for controlling combustion, wherein the arrangement is to be simple and suitable for everyday operation of a heating device.

[0008] To achieve this object, a method and an arrangement, as well as a computer program product, are provided according to the independent claims. Advantageous embodiments and refinements of the invention are specified in the respective dependent claims. The description, particularly in conjunction with the drawings, illustrates the invention and provides further exemplary embodiments.

[0009] Methods for observing or monitoring flames in a combustion chamber of a heating device contribute to this. Sound signals transmitted from a source point to at least one microphone are determined or analyzed, with the sound signal passing at least partially through a hot area heated by the flames on its path from the source point to the microphone. The type of sound signal analysis can include propagation time and / or noise pattern recognition, as explained in detail below.

[0010] In particular, a method for observing or monitoring flames in a combustion chamber of a heating device contributes to this, wherein a propagation time of a sound signal from a starting point to at least one microphone is determined and wherein the sound signal on its way from the starting point to the microphone passes at least partially through a hot area that can be heated by the flames.

[0011] The principle of the method exploits the dependence of the speed of sound in a gas on its temperature. The higher the temperature, the greater the speed of sound. Changes in the chemical composition can be neglected or compensated for in this case. Put simply, a sound signal takes less time to travel from a given starting point to the microphone if combustion occurs in an area (hot area) along its path, which (significantly) increases the temperature there, than if no combustion occurs, i.e. no flames are present. This effect can be used to reliably detect the presence of flames (similar to a flame detector). Many types of sound can be used for this method.Periodic sound waves are the easiest to process because they exhibit a phase shift when flames ignite or extinguish, which is a very simple and quick way to measure time of flight. Such periodic noises can also be generated by a fan or other components of the heater and used for measurement.

[0012] The sound signal is generated upstream of the combustion chamber in a cold zone through which air and / or fuel gas can flow. In particular, the sound signal can be transmitted from the cold zone to the hot zone. This allows non-heat-resistant materials to be used for the sound generator, and any maintenance of this sound generator is easier than in the hot zone.

[0013] The at least one microphone is also arranged in and / or downstream of the combustion chamber so that at least part of the sound signal's path runs through a hot area. In particular, the sound signal is thus detected or received in an area in and / or downstream of the combustion chamber.

[0014] Preferably, the sound signal is generated by at least one (separate) sound generator (e.g., a loudspeaker). This enables the sound signal to be emitted with a predefined signal shape, signal strength, and / or frequency that can be easily compared with the signals measured by the microphone, allowing the propagation time and / or phase shift to be measured or determined.

[0015] It is possible that a value for the runtime is determined during the process. This value can be compared with at least one reference value, for example, a stored or (previously) determined reference value. Based on this comparison, an assessment can be made as to whether a (significant) shortening and / or (significant) lengthening of the runtime has occurred. This allows a conclusion to be drawn from a shortening of the runtime that the flames have ignited, and / or from an extended runtime that the flames have extinguished.

[0016] In particular, the (determined) propagation time of a sound signal can even be used to determine a temperature in the hot zone, which not only provides a qualitative statement about the presence of flames, but also a quantitative statement about the temperature and thus about the heater's performance and / or the air-to-fuel ratio. The measurement can therefore also be used to control a combustion process, at least if the temperature or the air-to-fuel ratio is known from other measurements.

[0017] In addition or alternatively to the measurements described above, the microphone can be used to record sounds and / or noise patterns, which are compared with known sounds or noise patterns, thereby obtaining information about the ignition and / or extinguishing of flames and / or the state of the heater and / or properties of a combustion process in the combustion chamber. A method for observing or monitoring flames in a combustion chamber of a heater, wherein sound signals (noises and / or noise patterns) from the combustion chamber are recorded with at least one microphone, and wherein these sounds and / or noise patterns are used for an (automatic) evaluation of the flame state, the operating state of the heater and / or the combustion process.

[0018] Heaters produce very typical noises when ignited and during operation in different operating states, so that with advanced pattern recognition processes (similar to those used in speech recognition), a great deal of information can be extracted from the sound signals picked up by the microphone. If other sensors or information sources for detecting operating states are available, such a system can be designed to be self-learning, so that recorded patterns can be assigned with increasing precision to specific events or operating states and can be used, for example, for a plausibility check. A runtime measurement then takes a back seat or can even be omitted altogether (at least temporarily). This makes it possible, for example, to recognize very specific noise patterns that arise in the heater during an ignition sequence leading to correct ignition and to use these to determine the presence of flames.A similar approach can be applied to other events and states. Ambient noise and other external disturbances can be filtered out.

[0019] An arrangement for observing or monitoring flames in a combustion chamber of a heating device also contributes to the solution of the problem, wherein in or downstream of the combustion chamber at least one microphone is arranged, which can receive sound signals from an output point and is connected to an evaluation unit which is set up to determine and further process the propagation time of the sound signals between the output point and the microphone, and wherein between the output point and the microphone there is a hot area which can be heated by the flames and which the sound signals must pass through.

[0020] The starting point is located upstream of the combustion chamber in or near a cold zone through which air and / or fuel gas can flow. A sound signal fed into this zone propagates through the air and / or fuel gas, reaches the burner, and from there into the combustion chamber and through the hot zone to the microphone.

[0021] For this, it is not absolutely necessary that a sound signal be generated at the source point itself. Sound signals from other sources (e.g., fans) can also be used, but in this case, the time at which the sound signal passes the source point should be determined (e.g., using another microphone).

[0022] Preferably, at least one sound generator (separate, possibly configured for this method) is present at the starting point as a sound source. This generator is controlled by an evaluation unit, so that the evaluation unit already has information about the time of emission of a sound signal and / or about the frequency and phase of a periodic signal.

[0023] The evaluation unit is preferably configured to conclude that flames have ignited from a shortening of the running time and / or that flames have extinguished from an extension of the running time.

[0024] Additionally or alternatively, the evaluation unit is configured to process sounds or sound patterns picked up by the microphone and compare them with stored sounds or sound patterns for further processing. The stored data can be predefined or generated through a learning process.

[0025] A further aspect also relates to a computer program product comprising instructions that cause the described arrangement to execute the described method. The evaluation of the measured data and their further use in the heater require a program and data for controlling the heater, both of which must be updated occasionally.

[0026] The explanations of the procedure can be used to further characterize the arrangement, and vice versa. The arrangement can also be designed to carry out the procedure.

[0027] Another aspect concerns the use of sound signals generated in the heater to provide information about the heater's condition and / or the characteristics of a combustion process in the combustion chamber. In particular, the sound signals can be used as flame detectors.

[0028] A schematic embodiment of the invention, to which it is not limited, and the functioning of the method will now be explained in more detail with reference to the drawing. It shows: Fig. 1: a heater with a microphone for acoustic monitoring.

[0029] Fig. 1shows a schematic of a heater 1 with an air supply 2, which is equipped with a fan 4 and transports air to a burner 6. Fuel gas is mixed with the air L via a fuel gas supply 3 with a fuel gas valve 5. The resulting fuel gas-air mixture is ignited and burned in a combustion chamber 7 by means of an ignition device 10. The resulting exhaust gases give off most of their heat to a heat exchanger 9 and are then discharged into the environment through an exhaust system 8. A control and regulating unit 11 controls each start-up of the heater 1 and the actual ignition process that takes place during this. The control and regulating unit 11 controls the fan 4 and the fuel gas valve 5 via data lines 13. An ignition line 14 connects the control and regulating unit 11 to the ignition device 10, in most cases an ignition electrode for generating ignition sparks.

[0030] For acoustic monitoring of the combustion process, in particular for detecting flames 22, a microphone 16 is arranged in or downstream of the combustion chamber 7 and is connected to an evaluation unit 12 via a measuring line 15. The evaluation unit 12 also controls a sound generator 17, e.g., a loudspeaker, via a signal line 18. This sound generator generates a sound signal, preferably a periodic one. This signal is fed into a cold area 20 at an inlet 19, where it generates sound waves that propagate at a first speed of sound in the air and / or fuel gas present in this cold area 20. They thus reach the burner 6 and from there into the combustion chamber 7. If no combustion is taking place, this speed of sound does not change, and the sound waves reach the microphone 16 after a baseline travel time. The baseline travel time is determined in the evaluation unit.The phase of the waves can also be determined for periodic sound waves. If flames 22 ignite in the combustion chamber 7, a hot zone 21 is created by the heat released. In this hot zone 21, a second, higher speed of sound prevails, since the speed of sound in a gas increases with temperature. The signal's propagation time is therefore shorter than the base propagation time, which can be measured and allows a reliable conclusion to be drawn about the presence of flames 22. If the phases of a periodic signal are observed, a phase shift results when the flames 22 ignite, which can also (or alternatively) be measured. When the flames 22 extinguish, the process is reversed, which also allows a reliable conclusion to be drawn about the extinguishment. The realization of an acoustic flame detector is therefore possible. A quantitative determination of the temperature in the hot zone 21 can also be carried out in this way.

[0031] In principle, the sound generator 17 can be omitted if there are other (periodic) sound waves (e.g., caused by the fan 4 and / or the burner 6) whose propagation time or phase can be measured. In particular, for observing the phase of such sound waves, a microphone 16 is sufficient as instrumentation. However, an additional microphone (not shown) can also be used instead of the sound generator 17, for example, so that the propagation time of particularly distinguishable sound signals can be determined between two microphones.

[0032] Finally, it is also possible, either additionally or alternatively, to use the microphone 16 to generally record noises generated by the heater 1 in different operating situations. During ignition, switching between load states, different speeds of the fan 4, and / or different settings of the fuel gas valve 5, characteristic noises or noise patterns are generated that can be detected and assigned by the evaluation unit 12. In particular, the ignition of flames 22 or their extinguishing generate characteristic patterns that can be detected. A flame detector can also be implemented in this way.If, as is common with modern heaters, extensive sensor technology is present (at least during commissioning), noise pattern recognition can also be designed to be self-learning (similar to speech recognition) so that, over the course of operation, noise patterns can be increasingly better assigned to specific states or events (of an individual heater at its location) until the noise recognition can be used as a flame monitor and / or for control or at least for the plausibility check of other measured data.

[0033] In particular, an ignition process can be acoustically monitored particularly well, as it generates many characteristic sounds. From the start-up of the fan 4 through the opening of the fuel gas valve 5 to the crackling of ignition sparks, the ignition process can be precisely acoustically monitored. Ignition should then occur within a specific time interval after the ignition sparks are detected, so attention must be paid to a characteristic sound (pattern) for the ignition of flames 22 during this time interval. If the evaluation unit 12 does not detect this sound within the time interval, the ignition process is aborted. With modern electronics, this can be accomplished within the short time required for (safety-relevant) flame detectors.

[0034] The present invention makes it possible to implement an acoustic flame detector and the measurement of other variables important for control using simple and robust instrumentation on a heating device, in particular one operated with hydrogen or hydrogen-containing fuel gas. List of reference symbols

[0035] 1 Heater 2 Air supply 3 Fuel gas supply 4 Blower 5 Fuel gas valve 6 (Premix) burner 7 Combustion chamber 8 Exhaust system 9 Heat exchanger 10 Ignition device 11 Control and regulation unit 12 Evaluation unit 13 Control lines 14 Ignition line 15 Measuring line 16 Microphone 17 Sound generator (loudspeaker) 18 Signal line 19 Feed 20 Cold area 21 Hot area 22 Flames

Claims

1. Method for observing or monitoring flames (22) in a combustion chamber (7) of a heating appliance (1), wherein a propagation time of a sound signal is determined from a starting point to at least one microphone (16) and wherein the sound signal on its path from the starting point to the microphone (16) passes at least partially through a hot region (21) which can be heated by the flames (22), wherein the sound signal is generated upstream of the combustion chamber (7) in a cold region (21) filled with air and / or combustion gas, propagates in the air and / or the combustion gas, reaches a burner (6) of the heating appliance (1) and from there into the combustion chamber (7) and through the hot region to the at least one microphone (16), which is arranged in and / or downstream of the combustion chamber (7).

2. Method according to claim 1, wherein the sound signal is generated by at least one sound generator (17).

3. Method according to claim 1, wherein sound signals from a fan (4) are utilised at different speeds of the fan (4) of the heating appliance (1).

4. The method according to claim 3, wherein a further microphone is used to determine when the sound signal passes the starting point.

5. Method according to one of the preceding claims, wherein the ignition of flames (22) is inferred from a shortening of the running time and / or the extinction of flames (22) is inferred from an extension of the running time.

6. Method according to one of the preceding claims, wherein a temperature in the hot region (21) is inferred from the running time.

7. The method according to any one of the preceding claims, wherein the microphone (16) is used to record sounds or sound patterns which are compared with known sounds or sound patterns, thereby obtaining information about the state of the heating appliance (1) and / or characteristics of a combustion process in the combustion chamber (7).

8. Heating appliance with an arrangement for observing or monitoring flames (1) in a combustion chamber (7) of the heating appliance (1), wherein the heating appliance comprises a cold area (2) through which air and / or combustion gas can flow and a combustion chamber (7), wherein the arrangement comprises at least one microphone (16) and an evaluation unit (12), wherein a starting point of sound signals is arranged upstream of the combustion chamber (7) in or at the cold area (2), wherein the at least one microphone is arranged in and / or downstream of the combustion chamber (7), wherein the microphone (16) can receive sound signals from the starting point and is connected to the evaluation unit (12), which is set up to determine and further process the transit time of the sound signals between the starting point and the microphone (16), and wherein a hot area (21), which can be heated by the flames (22) and through which the sound signals must pass, lies between the starting point and the microphone (16).

9. Arrangement according to claim 8, wherein at least one sound generator (17) is present at the starting point as a sound source.

10. Arrangement according to claim 8, wherein a fan (4) of the heating appliance (1) is present as a sound source for generating sound signals at different speeds , wherein an additional microphone is preferably present, which is set up to determine the time when the sound signal passes the starting point.

11. A computer program product comprising instructions which, when executed by a control and regulation unit of a heating appliance according to any one of claims 8 to 10, cause the heating appliance to perform the method according to any one of claims 1 to 7.