DE19951181A1 - Burner-powered heater has combustion chamber and flame monitor containing thermoelement that protrudes with measurement point at least into edge region of flame in burner - Google Patents

Abstract

The heater has a burner (2) with a combustion chamber and a flame monitor, which outputs a signal to an associated control device on detecting a flame. The control device monitors the fuel supply and controls the combustion process. The flame monitor (8) contains a thermoelement that protrudes with its measurement point at least into the edge region of the flame in the burner

Description

The present invention relates to a burner-operated heating device, in particular a Motor vehicle auxiliary heater, the burner of a combustion chamber and one Flame detector has a signal to an assigned when a flame is detected Outputs control unit that monitors the fuel supply and controls the burning process.

Such a burner-operated heater is for example from DE 43 23 221 known. This known heater provides that the burner by means of a Combustion air blower and combustion air by means of a fuel delivery device Formation of a combustible mixture are supplied, wherein an annealing device for Fuel evaporation is used during a start phase of the burner, and being at Detection of flame formation by the flame monitor sends a signal to the assigned one Control unit is issued, which the speed of the combustion air fan and the Fuel delivery device, and controls the operation of the glow device. About the No information can be found in this document for training the flame guard.

Usually, the flame monitors include resistance thermometers, optical sensors, especially infrared sensors, but also sound measuring devices.  

Resistance thermocouples have the disadvantage that their operating temperature range is very high is small and is typically between 300 and 600 ° C. By using Platinum or tungsten and high-temperature ceramics are these resistance thermocouples relative expensive. Another disadvantage is the large tolerances of these resistance thermocouples, which lead to an inaccurate measurement or evaluation and thus, a relatively high Inertia in the response behavior of the flame monitoring system. A disadvantage of optical Flame detection sensors are sensitive to contamination, and low Temperature resistance typically below 125 ° C. Is critical with optical Sensors also the sensitivity of the flame signal to the influence of temperature on Sensor installation location and the influence of this sensor by glowing burner parts what typically leads to poor flameout detection.

From DE OS 18 15 295 is a safety device for a burner, especially an oil or heavy oil (masut) or gas burner known that an electromagnet comprises which is fed by a thermocouple which is the flame of the burner is exposed. For quick flame detection in conjunction with a This arrangement is not suitable for the control unit.

In view of this prior art, the invention is based on the object to create burner-operated heater of the type mentioned, which a Flame detection in a reliable manner using an inexpensive and robust Flame detector guaranteed.

This object is achieved by the characterizing features of claim 1. Advantageous developments of the invention are specified in the subclaims.

Accordingly, the invention provides a direct measurement of the flame temperature using a Thermocouple. The design of the flame detector in the form of a thermocouple brings a number of advantages. On the one hand, this component is concerned a tried and tested standard component with advantages in terms of procurement and price. Due to the low mass of this component, a quick response time is the  Flame on and off detection guaranteed. A precise evaluation results with With the help of a comparison measuring point compensation in the evaluation in the control unit. Such thermocouples are manufactured with small tolerances, so that a precise, reliable flame detection is guaranteed. When using a High temperature steel jacket is the thermocouple in question in its Embodiment as a jacket thermocouple very insensitive to flame and Pollution. Further advantages are given below in the explanation of a preferred one Exemplified embodiment.

The design as an open thermal wire element offers the advantage even faster Response times. This allows the thermocouple to go even further into the edge zone of the Flame positioned - the load on the components decreases and thus enables one even cheaper solution.

To direct measurement of the flame temperature and thus the detection of the flame too ensure, the thermocouple protrudes according to the invention at least with the measuring tip the edge area, but preferably into the central area of the flame.

To increase the response speed of the thermocouple, this shows advantageously a tapered measuring tip.

Particularly inexpensive embodiments of the considered Thermocouples and thermal wire elements are mentioned in claims 4 and 5.

The thermocouple can directly into the burner element in question, i. H. in a Breakthrough of the same be soldered, or the thermocouple has one Mounting flange for attachment to the burner element.

The thickness of the jacket of the jacket thermocouple is also advantageous a compromise between permanent service life and detection speed in the range of 0.05  optimized up to 0.5 mm. With the thermal wire element, the wire thickness is corresponding optimized. Wire thicknesses of approximately 0.5 mm have proven to be advantageous here.

In order to ensure high immunity to interference, the measuring tip of the Jacket thermocouple electrically isolated from the jacket of the same.

The invention is explained in more detail below using the drawing as an example; it demonstrate:

Fig. 1 shows a longitudinal section through a burner heating device operated with a used in this invention as a flame detector thermocouple,

Fig. 2 shows schematically an embodiment of the thermal element of Fig. 1 as a sheath thermocouple,

Fig. 3 shows schematically an embodiment of a thermal wire element, and

Fig. 4-7 Installation examples with different design of the combustion chamber in the lead-through area of the thermocouple.

In Fig. 1, a heater designed as an air heater is generally designated by the reference number 1 . It comprises a burner 2 , which as an evaporation burner has an absorbent body 3 for storing and evaporating liquid fuel. The thermocouple can also be used for any other combustion principle, e.g. B. used in atomization burners. The fuel is supplied to the absorbent body 3 by means of a fuel delivery device 5 via a fuel line 4 . The absorbent body 3 delimits a combustion chamber 7 at the end into which a glow device 6 for heating and evaporating fuel in the starting phase of the device and a flame monitor 8 for monitoring the flame formation and for continuously monitoring the flame protrude.

On the side facing away from the combustion chamber 7, a combustion air blower 9 is arranged behind the absorbent body 3 , by means of which combustion air is conveyed into the combustion chamber 7 . The combustion air fan 9 is driven by an electric motor 10 , the speed of which is variable. The speed or, in the case of a pump with reciprocating pistons, the frequency of the fuel delivery device 5 is also variable. The mixture of fuel and combustion air formed in the combustion chamber 7 burns and heats a heat exchanger 11 with its hot exhaust gas before it leaves the heater 1 via an exhaust pipe 12 . Over the outer walls of the heat exchanger 11 , a hot air blower 13 , which is driven by the same electric motor 10 , conveys hot air from an air inlet 14 arranged on the end face to an air outlet 15 arranged on the opposite end face. The air outlet 15 is connected to a room to be heated, for example a vehicle interior.

The speeds or frequencies of the fuel delivery device 5 as well as the speed of the electric motor 10 and the operation of the glow device 6 are controlled by means of a control device 16 , to which the signal of the flame monitor 8 is fed as an input signal and which is subjected to an evaluation in the control device 16 .

So far, the heater according to the invention corresponds to that in, for example State of the art described in DE 43 23 221 C1.

According to the invention, the flame monitor 8 is designed as a thermocouple 80 which, at least with its measuring tip, projects at least into the edge region and preferably into the central region of the flame. With this arrangement, a direct measurement of the flame temperature is achieved without the detour via a component of the heater that falsifies the measurement. Apart from these advantages obtained from the geometrical arrangement of the thermocouple 80 or the flame monitor 8 , this thermocouple is a standard component. Further advantages of such a thermocouple are both mentioned in the introduction and summarized below.

According to a particularly inexpensive variant, the thermocouple, which forms the flame monitor 8, is formed as a type K element, which is suitable for a permanent load ≦ 1,100 ° C. and consists of a pair of NiCr-Ni wires.

Alternatively, an element of type N can be used as a thermocouple for a permanent load ≦ 1,300 ° C. This element comprises a NiCrosil wire and a Nisil wire. This type N element is known to be more stable in the long term than the type K element and is assembled, for example, with a jacket. Since the thin high-temperature steel jacket limits the operating temperature, in particular the type N element in the version as an open thermal wire element 180 according to FIG. 3 is suitable.

The thermocouple 80 , which forms the flame monitor 8 and protrudes into the combustion chamber, is assembled, for example, with an additional jacket flange 81 A for attachment to the outside of the combustion chamber 7 D or to one of these adjacent components.

Alternatively, the jacket thermocouple is flange-free and is soldered directly into a combustion chamber component, preferably the combustion chamber 7 or 7 A, 7 B, 7 C. The compensating line of the jacket thermocouple extends continuously to the control unit 16 . With an appropriate arrangement of the control device, a compensating line could be dispensed with and the thermocouple could be led directly to the control device 16 .

A thermocouple or a jacket thermocouple 80 which is assembled with a jacket is shown in FIG. 2. This jacket thermocouple has a sleeve-shaped jacket 81, closed on one side, made of high-temperature steel, which is welded to an opening in the wall of the combustion chamber 7 , which comprises an annular deep drawing 82 in the opening area, which lies against the outer circumference of the jacket 81 and is welded to it. Parallel to the longitudinal center axis of the thermocouple 80 , two measuring wires 83 , 84 run in the sheath 81 , which are combined at the front end of the thermocouple 80 within the sheath 81 in a measuring point 85 and which are crimp-connected at the other end, inside the sheath 81, to compensating lines 86 , 87 are. In FIG. 2, the corresponding Crimpverbindungsstellen by the reference numerals 88 and 89, respectively. The compensation lines 86 and 87 are led out of the jacket 81 and connected to the control unit 16 . In addition, the inside of the shell 81 is filled with an insulating compound 90 .

The thickness of the sheathed thermocouple 80 is preferably chosen as a compromise between speed and permanent service life and is accordingly about 2 to 5 mm. One possible embodiment provides that the jacket thermocouple has a tapered measuring tip up to a diameter of approximately 1 mm. This measuring tip is preferably electrically insulated from the jacket in order to make the measurement by means of the jacket thermocouple as insensitive to interference as possible.

In the thermal wire element 180 shown in FIG. 3, the compensating lines 186 and 187 forming the feed lines are formed in a front region as stripped measuring wires 184 and 185 . The connection of both measuring wires 183 and 184 at the measuring point is designated with 185 . While in the area of the measuring point 185 a part of the stripped measuring wires 183 and 184 protrudes directly into the combustion chamber, the part behind it is surrounded by a sleeve 181 which is made of metal or ceramic and in which the measuring wires are embedded in an insulating compound 190 .

Figs. 4-7 show various embodiments for a recording or execution of a sheathed thermocouple element 80 and thermocouple wire element 180 through the burner-side end wall of the combustion chamber 7 A, 7 B, 7 C and 7 D

In FIG. 4, this end wall of the combustion chamber 7 A is provided asymmetrically to the burner axis X with a flange region parallel to the burner axis X, which provides a specific support length 1 for the thermal wire element 180 or the jacket thermocouple 80 .

In Fig. 5, this receptacle or implementation is designed as a passage leading from the combustion chamber 7 B to the outside with a slightly conically widened insertion slope.

In Fig. 6, the implementation in the combustion chamber 7 C is formed as an inward passage to the combustion chamber 7 , which also has a conical insertion bevel in the direction of insertion to the combustion chamber.

In the exemplary embodiment according to FIG. 7, the combustion chamber 7 has a simple bore or punching for the passage of the thermocouple 80 , into which the thermocouple is inserted with its front measuring area, a jacket flange 81 A coming to rest on the outside of the combustion chamber and there, for example is attached by soldering.

The support length 1 is preferably between 2 and 5 mm, so that an exact alignment and guidance of the thermocouple is made possible. In the variant according to FIG. 7, the jacket flange 81 A forms a stop with its end face facing the combustion chamber wall, which at the same time also ensures precise positioning of the thermocouple with respect to the flame.

The wire thickness of the thermocouples 80 or thermal wire elements 180 is preferably approximately 0.5 mm. The jacket thickness of a jacket thermocouple 80 is approximately 0.05 to 0.5 mm. A high-temperature steel such as Inconel 601 or Alloy 601 with the material number 2.4851 has proven to be particularly advantageous as the material for the casing 81 or the sleeve 181 .

The compensation lines of the thermocouple are preferably soldered to the circuit board of the control device 16 , which circuit board is enclosed by a housing, so that there is no risk of contamination, as in the case of flame monitors with plug contacts.

Strain reliefs are preferably provided for the compensation lines of the thermocouple, which are anchored to the housing of the control unit 16 in a manner known per se.

The evaluation of the measurement signal of the thermocouple can take place in the control unit 16 in different ways. The simplest solution is a simple YES / NO evaluation or flame available / flame not available, without compensation for the comparison measuring points of the thermocouple. As a somewhat more complex solution, a comparison measuring point compensation is provided by using an existing component in the evaluation or control device 16 , for example a transistor or a diode, whose base-emitter voltage or diode voltage forms the reference variable for the comparison measuring point compensation, since the component voltage is a function of Component temperature is. An even more complex and precise comparison measuring point compensation can be achieved by precise evaluation, ie correct determination of the board temperature with the aid of a component suitable for this purpose, for example an IC component.

To avoid EMC interference when evaluating the measurement signal from the thermocouple prevent, is preferably filtering this signal to remove such interference intended.

In summary, the following advantages result from using a thermocouple as a flame monitor 8 or 80 or 180 in the heater 1 :

• - Since the thermocouple is a tried and tested standard component, the procurement of this component is inexpensive;
• - Since the thermocouple has a low mass, it enables a very fast Evaluation;
• - Due to the low mass and the associated fast response time, can the thermocouple can be positioned in the cooler edge area of the flame;
• - When using a tapered thermocouple probe tip, an even faster evaluation in the control unit 16 is possible compared to a non-tapered probe tip;
• - A precise measurement is guaranteed by using a comparison measuring point compensation; this feature also contributes to the protection of the control device 16 , which can be switched off without any problems when a temperature threshold determined by the thermocouple is exceeded;
• - Due to small tolerances of the thermocouple, a more precise evaluation than with conventionally constructed flame monitors possible;
• - The thermocouple with a surrounding jacket (jacket thermocouple) insensitive to flame influences due to its coating; the Jacket of this sensor also helps to prevent contamination of the Sensor lines are not to be feared;
• - the installation of the thermocouple is easy to solder in, possibly very easily with the help of a flange;
• - The jacket thermocouple allows robust handling, and
• - through direct flame detection, without going through a component of the Heater, short response times are ensured;
• - The small dimensions and the small installation length required, as well as the aerodynamic cylindrical shape form a very small neglecting interference body for the flame (no negative effects on Combustion quality or deposits of combustion residues large dead water area).
• - The punctiform measuring source enables a more precise coordination than that of one larger volume integrating resistance thermometer.

Reference list

1

heater

2nd

burner

3rd

body

4th

Fuel line

5

Fuel conveyor

6

Annealing device

7

AD combustion chamber

8th

Flame guard

9

Combustion air blower

10th

Electric motor

11

Heat exchanger

12th

Exhaust pipe

13

Hot air blower

14

Air intake

15

Air outlet

16

Control unit

80

Thermocouple

81

coat

81

A jacket flange

82

Deep drawing

83

Measuring wire

84

Measuring wire

85

Measuring point

86

Compensation line

87

Compensation line

88

Crimp junction

89

Crimp junction

90

Insulating compound

180

Thermal wire element

181

Sleeve

183

Measuring wire

184

Measuring wire

185

Measuring point

186

Compensation line

187

Compensation line

190

Insulating compound

Claims (13)

1. Burner-operated heater, in particular a motor vehicle auxiliary heater, the burner ( 2 ) has a combustion chamber ( 7 ) and a flame monitor ( 8 ) which, when a flame is detected, emits a signal to an associated control unit ( 16 ) which monitors the fuel delivery and controls the burning process, characterized in that the flame monitor ( 8 ) comprises a thermocouple ( 80 , 180 ) which projects with its measuring point ( 85 , 185 ) at least into the edge region of the flame in the burner ( 2 ). 2. Heater according to claim 1, characterized in that the thermocouple ( 80 , 180 ) with its measuring point ( 85 ) protrudes into the central region of the flame. 3. Heater according to claim 1 or 2, characterized in that the thermocouple ( 80 , 180 ) has a tapered measuring tip. 4. Heater according to claim 1, 2 or 3, characterized in that the thermocouple ( 80 , 180 ) is a NiCr-Ni thermocouple or a type K thermocouple. 5. Heater according to claim 1, 2 or 3, characterized in that the thermocouple ( 80 ) is a NiCrosil-Nisil thermocouple or a thermocouple ( 80 , 180 ) of type N. 6. Heater according to one of claims 1 to 5, characterized in that the thermocouple ( 80 ) has a mounting flange. 7. Heater according to one of claims 1 to 5, characterized in that the thermocouple ( 80 ) is formed as a jacket thermocouple, and that the thickness of its jacket ( 81 ) is optimized with respect to a compromise between durability and speed of detection, the material thickness of the jacket ( 81 ) is preferably between 0.05 and 0.5 mm, and a high-temperature steel such as Inconel 601, ie 2.4851, is preferably selected as the material. 8. A heater according to claim 7, characterized in that the measuring tip or measuring point ( 85 ) of the thermocouple ( 80 ) is electrically insulated from its jacket. 9. Heater according to one of claims 1 to 5, characterized in that the thermocouple ( 180 ) is designed as a thermal wire element with an open measuring tip. 10. Heater according to one of claims 1 to 9, characterized in that the measuring tip of the thermocouple ( 80 , 180 ) extends so far into the combustion chamber of the combustion chamber ( 7 ) that a compromise between the continuous service life and the highest possible evaluation signal is achieved. 11. Heater according to one of claims 1 to 10, characterized in that the combustion chamber ( 7 ) has a deep drawing at the installation point of the thermocouple ( 80 ). 12. Heater according to one of claims 1 to 10, characterized in that the combustion chamber ( 7 ) has parallel walls of a certain length (preferably between 2 and 5 mm) at the installation site, which enable an exact alignment of the guide of the thermocouple. 13. Heater according to one of claims 1 to 10, characterized in that the Thermocouple has a stop on its outer shell, which at Mounting the combustion chamber limits the penetration depth.