EP4650660A1

EP4650660A1 - Combustion appliance

Info

Publication number: EP4650660A1
Application number: EP24176616.1A
Authority: EP
Inventors: Sander KLEIN NIJENHUIS; Evert Gerhard TEN HAAKEN; Mark Heimgartner; Dirk Jan WESTHOF; Teunis Keizer; Leander Martinus Baak
Original assignee: BDR Thermea Group BV
Current assignee: BDR Thermea Group BV
Priority date: 2024-05-17
Filing date: 2024-05-17
Publication date: 2025-11-19

Abstract

The invention relates to a combustion appliance (1) comprising a housing (2) delimiting a combustion chamber (3), a burner (4) which is arranged in the combustion chamber (3), an oxygen sensor (5) for measuring an oxygen value in the combustion chamber (3), in particular a flue gas resulted from combusting an air to fuel gas mixture by the burner (4), and at least one heat exchanger (6) comprising at least one heat exchange region (8a, 8b) of the heat exchanger (6, 6a), the heat exchange region (8) projects from the combustion chamber (3). The combustion appliance is characterized in that the oxygen sensor (5) is arranged between the burner (4) and an inlet (9) of the at least one heat exchange region (8a, 8b) through which the flue gas flows into the at least one heat exchange region (8).

Description

The invention relates to a combustion appliance, in particular to a gas adaptive combustion appliance.
Gas adaptive combustion appliances, in particular gas adaptive boilers are known from the prior art. Such kind of gas adaptive combustion appliances can be adapted to different fuel gas types. Said combustion appliances, in particular boilers, comprise a housing delimiting a combustion chamber in which the gas and fuel mixture is combusted by a burner of the combustion appliance. Additionally, the combustion appliance comprises a burner door for closing the combustion chamber wherein the burner door is mechanically connected to the housing and/or supports the burner. A control unit of the combustion appliance controls the air flow and fuel gas flow to the combustion chamber to achieve a predetermined air to fuel gas ratio. Combustion appliances are known in which an oxygen value is used for controlling the air to fuel gas ration.
The known combustion appliances have the disadvantage that the oxygen sensor has a long response time on a change in the air to fuel gas ratio on which the burner is operating. This results in high CO emissions, flame loss, flash back and overheating. Additionally, as a result of the long response time of the oxygen sensor a smooth transition between two gas families within 1 min is not possible without a manual intervention.
The object of the application is to provide a combustion appliance in which high CO emissions, flame loss, flash back and overheating can be avoided or reduced. Additionally, another object of the invention is to enable a transition between two gas families within 1 min without manual intervention.
The object is solved by a combustion appliance comprising

a housing delimiting a combustion chamber,
a burner which is arranged in the combustion chamber,
an oxygen sensor for measuring an oxygen value in the combustion chamber, in particular a flue gas resulted from combusting an air to fuel gas mixture by the burner, and
at least one heat exchanger comprising at least one heat exchange region, the heat exchange region (8) projects from the combustion chamber, characterized in that
the oxygen sensor is arranged between the burner and an inlet of the at least one heat exchange region through which the flue gas flows into the at least one heat exchange region.

Such a combustion chamber has the advantage that high CO emissions, flame loss, flash back and overheating can be avoided or reduced. Additionally, a transition between two gas families within 1 min without manual intervention can be realized. Said advantages are possible due to the arrangement of the oxygen sensor between the burner and the inlet of the heat exchange region.
In the invention it was realized that the oxygen sensor has to be placed in a high velocity region of the combustion appliance. This is advantageous because the reaction time of the oxygen sensor has a correlation with the flue gas velocity perpendicular to the axis of the sensor. The flue gas has a high velocity in the region between the burner and the heat exchange region so that by arranging the oxygen sensor in said region a fast reaction time is achieved. Additionally, it was realized that in the combustion chamber before the heat exchanger in the flue gas path, all water vapor is still present in the flue gasses. If the sensor would be placed after the heat exchanger the water vapor concentration is depending on the central heating water temperature. In the heat exchanger water vapor can condensate if the temperature is low. Varying water vapor concentration leads also to a varying oxygen concentration.
The oxygen sensor can measure the oxygen value of the flue gas. In this case a burner of the combustion appliance combusted an air and fuel gas mixture being in the combustion chamber. Additionally or alternatively, the oxygen value of a non-combusted gas, for example of the air and fuel gas mixture can be measured. In this case the oxygen value can be measured in the combustion chamber before the burner combusts the air and fuel gas mixture. The oxygen sensor can measure the partial oxygen pressure and uses this to determine the oxygen concentration in the gas to be measured, wherein the measured concentration can be outputted. Specifically, the oxygen sensor can measure the oxygen volume percentage of oxygen in the gas being analyzed.
The oxygen sensor can be an unheated or a heated oxygen sensor, or a paramagnetic sensor. Alternatively, the oxygen sensor can be a fast light off oxygen sensor or planar sensor, which uses layers of zirconia and alumina bonded together to allow a much faster warm up. The oxygen sensor can also be air fuel ratio and wideband sensors.
A combustion appliance is a device designed to burn a fuel source in a controlled manner for the purpose of producing heat. The combustion reaction occurs in the combustion chamber and the combustion appliance comprises means for conveying air and fuel gas into the combustion chamber. The air and fuel, in particular fuel gas, can mix before the combustion chamber or inside the combustion chamber. The combustion appliance may be designed to burn various types of fuels, including but not limited to, natural gas, propane, oil, hydrogen, biogas, or solid fuels such as wood or pellets. A combustion appliance can be a boiler, space heater, oven, or a gas water heater.
The at least one heat exchanger is used for transferring the heat generated during combustion to a fluid, in particular liquid or air, flowing within at least one channel of the heat exchanger, thereby converting the energy from the combustion process into usable heat. The heat exchanger projects from the combustion chamber in radial direction referring to a central axis of the combustion chamber. Specifically, a length axis of the heat exchanger projects from the combustion chamber in a radial direction referring to the central axis of the combustion chamber and/or of the burner. A heat exchanger housing is mechanically coupled with the housing of the combustion appliance that delimits the combustion chamber.
As is discussed below more in detail such a heat exchanger supports the velocity increase of the flue gas due to the radial extension of the heat exchanger from the housing and/or combustion chamber of the combustion appliance. In a heat exchanger, which is arranged concentric to the central axis of the combustion chamber, the flue gas velocity can be slower in regions that are easy to access than in the present embodiment. An arrangement of the oxygen sensor between for example the tubes of the heat exchanger is not easy as said region is hard to access.
The arrangement of the oxygen sensor between the burner and the inlet of the heat exchanger means that the oxygen sensor is arranged in a region of the combustion chamber that is placed between the burner, in particular burner surface, and the inlet of the heat exchanger. in radial direction referring to the central axis of the combustion chamber. "Between" can also comprise the inlet of the heat exchanger so that the oxygen sensor can be arranged in the inlet of the heat exchanger. Placing the oxygen sensor in front of the inlet or in the inlet has the advantage that a fast reaction time can be realized due to high velocity of the flue gas in this area. Additionally, the flue gas is forced to pass said area due to the design combustion appliance so that it is ensured that the oxygen sensor is arranged in the flow path of the flue gas.
On the other hand, placing the sensor close to the burner reduces the time to detect a change in air to gas ratio. To notice a change in the air to gas ratio the changed flue gas needs to travel to the oxygen sensor. Therefore placing the oxygen sensor close to the burner a change is detected faster than when placing the oxygen sensor in a fluid path after the heat exchanger.
The heat exchange region is the region of the heat exchanger in which the flue gas flows within the heat exchanger and in which a heat transfer occurs between the flue gas and a fluid, in particular air or a liquid, flowing in at least one channel of the heat exchanger. The heat exchanger can comprise heat exchange elements that are arranged inside the heat exchange region. The heat exchange elements are elements that increase the heat exchange area of the heat exchanger. Specifically, the flue gas comes into contact with the heat exchange elements in the heat exchange region.
The terms "radial", "tangential" and "axial" used in the application refer to a central axis of the burner of the combustion appliance.
According to an embodiment the heat exchange region can comprise an outlet through which the flue gas leaves the heat exchange region. The outlet of the heat exchange region can be arranged further away from the burner, in particular further away from a central axis of the burner, than the inlet. Specifically, the outlet can be arranged in the radial direction further away from the burner central axis than the inlet of the heat exchange region. In the end a heat exchanger can be realized that has an extension in radial direction from the combustion chamber.
The heat exchanger can be configured such that the flue gas flows along a length axis of the heat exchanger and/or in radial direction inside the heat exchange region. The heat exchanger, i.e. the complete heat exchanger, can be arranged geodetically below the burner and/or the combustion chamber. The heat exchanger, in particular a housing of the heat exchanger can be mechanically connected to the housing of the combustion appliance that delimits the combustion chamber. Thus, a heat exchanger can be provided that extends from the combustion chamber in a radial direction.
Such a heat exchanger has the advantage that a higher and/or more efficient heat transfer between the flue gas and the fluid flowing in the heat exchanger can be realized in comparison to heat exchangers which surround the burner and/or the combustion chamber. In said heat exchangers the length axis of the heat exchanger is concentrical or parallel to the central axis of the burner. In comparison thereto the present heat exchanger is arranged such that the length axis of the heat exchanger runs perpendicular or transverse to the central axis of the burner.
The heat exchanger can be a pin fin heat exchanger. In said heat exchanger design pin fins are used to increase the surface area for heat transfer. In said embodiment pin fins correspond to the heat exchanging elements.
According to an embodiment the oxygen sensor can be arranged outside a reaction zone of the burner. "Reaction zone" is the region of the combustion chamber in which the combustion reaction takes place. Said region can be characterized among others as region in which the temperature exceeds the ignition temperature
The oxygen sensor can be arranged such that a distance between a burner surface and the oxygen sensor is between 40 to 100 mm, in particular between 60 to 70mm. The distance can be measured in radial direction referring to the central axis of the burner and/or combustion chamber. Additionally or alternatively, the oxygen sensor can be arranged such that a further distance between the inlet of the heat exchanger and the oxygen sensor is between 5 to 100 mm, in particular 5 to 30mm. The distance is measured in radial direction referring to the central axis of the burner and/or combustion chamber. Placing the oxygen sensor in said area has the advantage that it is arranged outside the reaction zone but close to the burner and close to the inlet of the heat exchange region.
The oxygen sensor can be arranged such that a distance between a central axis of the burner and the oxygen sensor, in particular a central axis of the oxygen sensor, can be between 50% to 98%, in particular 65% to 90%, of a distance between the central axis of the burner and the inlet of the heat exchange region. The distance is measured in radial direction referring to the central axis of the burner and/or combustion chamber.
The oxygen sensor can be arranged relative to the heat exchanger such that a plane exists that extends along the length axis of the heat exchanger and comprises a part of the oxygen sensor and a part of the inlet. Such a placing of the oxygen sensor has the advantage that flue gas will always contact the oxygen sensor before it enters the heat exchanger, in particular the heat exchange region. Additionally or alternatively, the oxygen sensor can be arranged in a region of the combustion chamber in which a flue gas velocity is higher than in another combustion chamber region in which the burner is arranged. This has the advantage that changes in the air to fuel gas ratio can be easily and fast detected by the oxygen sensor. Additionally, a fast reaction time of the oxygen sensor is achieved.
The combustion appliance can comprise a burner door for closing the combustion chamber. The burner door can support the oxygen sensor. In particular, the oxygen sensor can be arranged in a hole of the burner door.
According to an embodiment the combustion appliance can comprise several heat exchange regions, wherein the heat exchange regions protrude from the combustion chamber. The heat exchange regions can protrude in the same direction, namely in radial direction. The provision of several heat exchange regions has the advantage that the a high heat transfer from the flue gas to the fluid flowing in the heat exchanger can be realized. The oxygen sensor can be arranged between the burner and an inlet of a heat exchange region of one of the plurality of heat exchange regions. Thus, it is not necessary to arrange several oxygen sensors.
The heat exchange regions can protrude such from the combustion chamber that a length axis of a heat exchange region is parallel to a further length axis of a further heat exchange region. Thus, both heat exchange regions protrude in the same direction and/or manner from the combustion chamber. The heat exchanger regions can be arranged geodetically below the burner and/or the combustions chamber. Both heat exchange regions are fluidically connected to the combustion chamber.
According to an embodiment the combustion appliance can comprise a data processing device that receives the measured oxygen values from the oxygen sensor and controls the combustion appliance dependent on the received oxygen value. The data processing device can comprise at least one processor or be a processor. The data processing device can be part of a, printed circuit board, in particular a printed circuit board assembly, and have different portions executing different functions. The processor can have an internal memory.
The combustion appliance can comprise a fan for controlling an air flow and a fuel valve, in particular a fuel gas valve, for controlling a fuel flow, wherein the data processing device is data connected with the fan and/or the fuel valve. The burner can burn a mixtures of air and fuel gas. The air and fuel gas can be mixed inside the burner and thus inside the combustion chamber or outside the combustion chamber, e.g. in a manifold of the combustion appliance. Furthermore, the combustion appliance can comprise a throttle unit for controlling the fuel flow, wherein the data processing device is data connected with the throttle unit, in particular a throttle motor of the throttle unit.
Specifically, the throttle unit can be used for controlling a fuel gas flow from the fuel gas valve of the combustion appliance. The throttle unit is used for adapting the combustion appliance to the gas adaptive appliance by controlling the fuel gas flow that passes the fuel gas valve as it is described more in detail. The throttle unit and the oxygen sensor are separated components and/or can be separately connected to the data processing device of the combustion appliance.
The throttle unit comprises a throttle element for controlling a throttle opening cross section through which the fuel gas flows. The throttle unit has the advantage that the fuel gas flow coming from the fuel gas valve can be controlled independent of the fan speed. The data processing device can control the throttle unit and/or the fan and/or the fuel gas valve dependent on the measured at least one oxygen value.
An adjustment of the throttle element results in a change in fuel gas flow resulting in a different air to fuel gas mixture. The position of the throttle element can be adjusted several times. Specifically, the position of the throttle element can be adjusted such that the measured oxygen value, in particular fuel gas oxygen value, is between the lower and the upper threshold. The adjustment of the position of the throttle element is necessary to adapt the combustion appliance to changes in a fuel gas type quality. Likewise, to the adjustment of the throttle unit, the fuel valve can be adjusted such that the measured oxygen value, in particular fuel gas oxygen value, is between the lower and the upper threshold.
The throttle unit can at least partly be arranged fluidically downstream the fuel gas valve. Fluidically downstream means that the throttle unit as a hole component is arranged outside the fuel gas valve and adjacent to the fuel gas valve. Alternatively, fluidically downstream means that at least a part of the throttle unit, in particular the throttle element, can be arranged inside the fuel gas valve. However, said throttle element is arranged inside the fuel gas valve such that it receives the fuel gas that passed a valve element of the fuel gas valve.
The fuel valve, in particular the fuel gas valve, can be a pneumatic valve, in particular a pneumatic gas valve. The fuel valve, in particular the fuel gas valve, can also be a controllable pneumatic valve, or a stepper valve, or a modulator valve. In said fuel valve the fuel flow automatically changes when an air flow changes due to e.g. a different fan speed. The fuel gas valve can be arranged downstream a fuel gas source and upstream the throttle unit, in particular the throttle element. The data processing device can be data connected with the throttle unit. Additionally or alternatively the throttle unit can be attached on the fuel gas valve. Thus, a compact unit comprising the fuel gas valve and the throttle unit is provided.
The throttle unit can be fully open, fully closed, or in-between open and closed allowing a partial flow. The throttle unit comprises an electrical actuator, in particular throttle motor, in combination with the throttle element. The electrical actuator is configured to carry out modulating control, often referred to as a digital positioning system. The electrical actuator is thus able to accurately position the throttle element. The throttle unit can be anywhere between the fully open and the fully closed position or in-between open and closed allowing a partial flow. Typically, modulation is achieved using a control loop system and a positioning circuit board placed in the actuator.
The actuator can use a feedback system to give feedback on the fuel valve's position to an operator. The modulation is achieved by comparing the input position (desired position) to the physical position of the output shaft (actual position). The output shaft's location is fed back to the positioning circuit board by a potentiometer that is driven by the output shaft. The positioning circuit board then compares the two positions, and if there is a difference it considers this an 'error'. To correct the error, the control unit will operate the modulator valve until it reaches the desired position. The control signals are typically either 0-10 V DC or 4-20 mA. A 0 V DC or 4 mA signal completely closes the fuel valve while a 10 Vdc or 20 mA completely open the fuel valve. Any signal between these would cause a corresponding partially opened or closed position. An example would be a 6mA signal that would result in a 12° turn.
The stepper valve comprises a stepper motor, also known as step motor or stepping motor, which is an electrical motor that rotates in a series of small angular steps. The stepper motor thus divides a full revolution into a number of equidistant steps. The stepper motor consists of several "toothed" electromagnets arranged as a stator around a central rotor. These electromagnets are activated by an external driver circuit or a microcontroller. Each step rotates the shaft through a fixed angle. The circular arrangement of electromagnets is divided into groups referred to as phases. A stepper motor can be precisely rotated through a specific angle by activating the electromagnets one after the other.
The controllable pneumatic valve is a valve wherein a fluid flow rate is controlled by varying the size of the flow passage via a restrictor. In an automatic control valve, the restrictor is directed by a signal from an actuator.
Typical examples of controllable pneumatic valves are solenoid valves, in particular proportional solenoid valves. The proportional control solenoid valve utilizes a solenoid as an actuator for variable valve positioning. In a normally closed solenoid control valve, with zero current fed to the coil, the spring pushes the plunger downwards to a fully closed position. Applying current to the coil generates a magnetic field to move the plunger upward against the return spring. At 100% duty cycle, power is fully fed to the solenoid and the solenoid valve is open. The term duty cycle describes the proportion of on time to the cycle duration interval in a pulse-width modulation for controlling a load. Pulse-width modulation in other words is a method of controlling the average power or amplitude delivered by an electrical signal. A low duty cycle corresponds to low power, because the power is off for most of the time. Duty cycle is expressed in percent, with 100% being fully on. Duty cycles between 0 to 100 percent range proportionally change the flow of the valve. For example, a duty cycle of 50% fed to the solenoid moves the spring and the plunger to 50% of the operating range.
According to an embodiment the data processing device can control the throttle unit and/or the fan and/or the fuel gas valve dependent on the at least one oxygen value received from the oxygen sensor. Specifically, the data processing device can comprise a throttle unit control portion for controlling the position of a throttle element of the throttle unit. Providing the throttle control portion has the advantage that the throttle unit has only to be connected in regard to data to the data processing device. In other words, the installer does not have to perform any other actions for configuring the throttle unit to the data processing device.
In an operation of the combustion appliance, the data processing device can use the measured oxygen value for monitoring purposes and guarding predetermined oxygen limits and/or trigger a locking or blocking of the combustion appliance dependent on the measured oxygen value. In said operation, the position of the throttle element is not changed.
In the figures, the subject-matter of the invention is schematically shown, wherein identical or similarly acting elements are usually provided with the same reference signs.

Figure 1: a cross section view of a part of a combustion appliance according to the invention.
Figure 2: an enlarged view of an upper portion of the combustion appliance shown in figure 1.
Figure 3: an overview of the combustion appliance.

A cross section view of a part of an inventive combustion appliance 1 is shown in figure 1. Figure 2 an enlarged view of an upper portion of the combustion appliance shown in figure 1.
The combustion appliance 1 comprises a housing 2 delimiting a combustion chamber 3 and a burner 4. The burner 4 is arranged in the combustion chamber 3 and comprises a cylindrical burner deck. Additionally, the combustion appliance 1 comprises an oxygen sensor 5 for measuring an oxygen value in the combustion chamber 3. The oxygen sensor 5 is used to measure the oxygen value in a flue gas resulted from combusting an air to fuel gas mixture by the burner 4.
The combustion appliance 1 comprises also a heat exchangers 6 that extends in a radial direction from the combustion chamber 3. Specifically, the heat exchanger 6 is geodetically arranged below the burner 4 and the combustion chamber 3. The heat exchanger 6 comprises two heat exchange regions 8a, 8b, namely a first heat exchange region 8a and a second heat exchange region 8b. Both heat exchange regions 8a, 8b extend in the same direction from the combustion chamber 3 and are identically structured.
The heat exchanger 6 comprises a plurality of heat exchange elements 7. A part of the heat exchange elements 7 are arranged in the first heat exchange region 8a and another part of the heat exchange elements are arranged in the second heat exchange region. Additionally, the heat exchanger 6 comprises a plurality of channels through which a liquid flows. A part of the channels is arranged in a housing portion of the heat exchanger that is arranged between the two heat exchange regions 8a, 8b in tangential direction. Another channels are arranged in an outer housing portion of the heat exchanger 6 that extends from the housing 2 of the combustion appliance 1 that delimits the combustion chamber. The heat exchanger 6 is a pin finheat exchanger so that the pin fins correspond to the heat exchanging elements The pin fins are used to increase the heat transfer area and transfer the heat to the fluid flowing in the channels 19 of the heat exchanger 6.
The heat exchange regions 8a, 8b comprise at an upper end the inlet 9 through which the flue gas enters the respective heat exchange region 8a, 8b. Additionally, the heat exchange regions 8a, 8b comprise an outlet 10 through which the flue gas leaves the respective heat exchange region 8a, 8b. The outlet 10 is arranged further away from the central axis of burner 4 than the inlet 9. Specifically, the inlet 9 is arranged at one end of the heat exchange region 8a, 8b and the outlet 10 is arranged at another end of the heat exchange region 8a, 8b along the length axis 11 of the heat exchanger 6.
The oxygen sensor 5 is arranged between the burner 4 and an inlet 9 of the heat exchange region 8 through which the flue gas flows into the heat exchange region 8a, 8b. Specifically, the oxygen sensor 5 is arranged near the inlet of the first heat exchange region 8a. The oxygen sensor 5 is arranged such that a plane 13 exists that extends along the length axis 13 of the heat exchanger 6 and comprises a part of the oxygen sensor 5 and a part of the inlet 9. A distance d1 between a burner surface 12 and oxygen sensor 5 can be between 40 to 100 mm, in particular 60 to 80 mm in radial direction referring to the central axis 20 of the burner 4. A further distance d2 between the inlet 9 of the heat exchanger 6 and the oxygen sensor 5 is between 5 to 100 mm, in particular 5 to 30mm, in radial direction referring to the central axis 20 of the burner 4.
Figure 3 shows an overview of the combustion appliance 1. The combustion appliance 1 comprises a fan 15, a fuel gas source 21 for providing fuel gas and a fuel valve 16, in particular a fuel gas valve, for controlling the fuel gas flow. The fuel valve 16 is a pneumatic valve so that the fuel flow depends on the fan speed. The combustion appliance 1 also comprises a throttle unit 17 that is located downstream the fuel valve 16.
The throttle unit 17 controls the fuel flow, in particular the fuel gas flow, coming from the fuel valve 16. The throttle unit 17 comprises a non-shown throttle motor and a throttle element. The throttle motor changes the position of the throttle element to control the fuel flow through the throttle unit 17. The throttle element delimits a throttle opening cross section through which the fuel, in particular fuel gas, can flow. Thus, the fuel flow that passes through the throttle unit 17 depends on the position of the throttle element. The throttle unit 17 is electrically connected with a data processing unit14 of the combustion appliance 1 as is indicated with dotted line in figure 3.
The throttle element position depends on the instruction that is received from the data processing unit 14. For setting a throttle element position the data processing unit 14 transmits a throttle position signal P to the throttle unit 17, in particular the throttle motor. The throttle motor changes the position of the throttle element according to the received throttle position signal P.
The data processing device 14 comprises a processor and/or can be used to set the power state of the combustion appliance 1. Thereto, the data processing device 14 sends at least one operation signal S to the fan 15 to set the fan speed. In particular, the data processing device 15 can set the combustion appliance 1 to operate in a minimum power state, a maximum power state or a power state that is between the maximum and minimum power state.
The combustion appliance 1 also comprises a manifold 22. The manifold 22 is arranged upstream of the burner 4 of the combustion appliance 1 and is used to mix the fuel, in particular the fuel gas, passing the throttle unit 17 with air provided by the fan 15. The combustible mixed gas is burned in the combustion chamber 3 of the combustion appliance 1 by the burner 4. The combustion chamber 3 is delimited by the housing 2 of the combustion appliance 1. Additionally, the combustion appliance 1 comprises a burner door 18 that closes the combustion chamber 3 on one side. The burner door 18 is used to support the burner 4 and the oxygen sensor 5. The oxygen sensor 5 transmits the measured oxygen value O to the data processing device 14.
The heat exchanger 6 is used to transfer the heat from the flue gas to a liquid, in particular water. Said heated liquid can be is used for a central heating and/or for domestic hot water. The flue gas leaves the heat exchanger 6, in particular the heat exchange region 8a, 8b via an outlet 10 and leaves the combustion appliance via a flue gas path 23.
As discussed above, the oxygen sensor 5 measures the oxygen concentration in the flue gas when a combustion occurred in the combustion chamber 3. The data processing device 14 is electrically connected to the oxygen sensor 5 and receives the measured flue gas oxygen values. An air to fuel gas ratio can be determined on the basis of the received flue gas oxygen value. The data processing device 14 can control the combustion appliance 1 on the basis of the determined air to fuel gas ratio in an operation mode of the combustion appliance.

Reference Signs

1: Combustion appliance
2: Housing
3: Combustion Chamber
4: Burner
5: Oxygen sensor
6: Heat exchanger
7: Heat exchange elements
8a: First heat exchange region
8b: Second heat exchange region
9: Inlet
10: Outlet
11: Length axis of heat exchanger
12: Burner surface
13: Plane
14: Data processing device
15: Fan
16: Fuel valve
17: Throttle unit
18: Burner Door
19: Channel
20: Central axis of burner
21: Fuel gas source
22: Manifold
23: Flue gas outlet

O: Oxygen value
P: Throttle position signal
S: Operation signal

d1: distance between burner surface and oxygen sensor
d2: distance between inlet of heat exchanger and oxygen sensor

Claims

Combustion appliance (1) comprising
a housing (2) delimiting a combustion chamber (3),

a burner (4) which is arranged in the combustion chamber (3),

an oxygen sensor (5) for measuring an oxygen value in the combustion chamber (3), in particular a flue gas resulted from combusting an air to fuel gas mixture by the burner (4), and

at least one heat exchanger (6) comprising at least one heat exchange region (8a, 8b), the heat exchange region (8) projects from the combustion chamber (3), characterized in that

the oxygen sensor (5) is arranged between the burner (4) and an inlet (9) of the at least one heat exchange region (8a, 8b) through which the flue gas flows into the at least one heat exchange region (8).
Combustion appliance (1) according to claim 1, characterized in that the heat exchange region (8a, 8b) comprises an outlet (10) through which the flue gas leaves the heat exchange region (8a, 8b), wherein the outlet (10) is arranged further away from the burner (4) than the inlet (9).
Combustion appliance (1) according to claim 1 or 2, characterized in that
a. the heat exchanger (6) is configured such that the flue gas flows along a length axis (11) of the heat exchanger (6, 6a) and/or in that

b. the heat exchanger (6) is arranged geodetically below the burner (4) and/or the combustion chamber (3).
Combustion appliance (1) according to at least one of the claims 1 to 3, characterized in that the heat exchanger (6) is a pin fin heat exchanger.
Combustion appliance (1) according to at least one of the claims 1 to 4, characterized in that the oxygen sensor (5) is arranged outside a reaction zone of the burner (4).
Combustion appliance (1) to at least one of the claims 1 to 5, characterized in that
a. a distance (d1) between a burner surface (12) and the oxygen sensor (5) is between 40 to 100 mm, in particular between 60 to 70mm, and/or

b. a further distance (d2) between the inlet (9) of the heat exchanger (6) and the oxygen sensor (5) is between 5 to 100 mm, in particular 5 to 30mm and/or

c. a distance (d1) between a central axis of the burner and the oxygen sensor, in particular a central axis of the oxygen sensor, can be between 50% to 98%, in particular 65% to 90%, of a distance between the central axis of the burner and the inlet (9) of the heat exchange region (8a, 8b).
Combustion appliance (1) according to at least one of the claims 1 to 6, characterized in that the oxygen sensor (5) is arranged relative to the heat exchanger (6, 6a) such that a plane (13) exists that extends along to the length axis (11) of the heat exchanger (6) and comprises a part of the oxygen sensor (5) and a part of the inlet (9).
Combustion appliance (1) according to at least one of the claims 1 to 7, characterized in that
a. the oxygen sensor (5) is arranged in a region of the combustion chamber (3) in which a flue gas velocity is higher than in another combustion chamber region in which the burner (4) is arranged and/or in that

b. a burner door (18) of the combustion appliance supports the oxygen sensor (5).
Combustion appliance (1) according to at least one of the claims 1 to 8, characterized in that the heat exchanger (6) comprises several heat exchange regions (8a, 8b), wherein the heat exchanger regions (8a, 8ba) protrude from the combustion chamber (3).
Combustion appliance (1) according to claim 9, characterized in that the oxygen sensor (5) is arranged between the burner (4) and an inlet (9) of one of the heat exchange regions (8a, 8b).
Combustion appliance (1) according to claim 9 or 10, characterized in that
a. the heat exchange regions (8a, 8b) protrude from the combustion chamber (3) in the same direction and/or in that

b. the heat exchanger regions (8a, 8b) are arranged geodetically below the burner (4) and/or the combustion chamber (3).
Combustion appliance (1) according to at least one of the claims 1 to 11, characterized in that the combustion appliance (1) comprises a data processing device (14) that receives the measured oxygen value and controls the combustion appliance (1) dependent on the received oxygen value.
Combustion appliance (1) according to claim 12, characterized in that the combustion appliance (1) comprises a fan (15) for controlling an air flow and a fuel valve (16), in particular a fuel gas valve, for controlling a fuel flow, wherein the burner (4) burns a mixture of the air and fuel gas, wherein the data processing device (14) is data connected with the fan (15) and/or the fuel valve (16).
Combustion appliance (1) according to claim 12 or 13, characterized in that the combustion appliance (1) comprises a throttle unit (17) for controlling the fuel flow, wherein the data processing device (14) is data connected with the throttle unit (17), in particular a throttle motor (18) of the throttle unit (17).
Combustion appliance (1) according to at least one of the claims 12 to 14, characterized in that the data processing device (14) controls the throttle unit (17) and/or the fan (15) and/or the fuel valve (16) dependent on the received at least one oxygen value.