GB2275109A

GB2275109A - Flame monitoring device and method

Info

Publication number: GB2275109A
Application number: GB9400435A
Authority: GB
Inventors: Josef Poeppel
Original assignee: Temic Telefunken Microelectronic GmbH
Current assignee: Conti Temic Microelectronic GmbH
Priority date: 1993-01-29
Filing date: 1994-01-12
Publication date: 1994-08-17
Also published as: DE4302531A1; GB9400435D0; FR2701088A1

Description

2275109 Flame monitoring device and method The invention relates to a

flame monitoring device with a burner and a combustion chamberassigned thereto.

As a rule the monitoring of flames, such as are present for example in heater burners, is carried out with an - IR camera or a ?, probe for 02 measurement in the exhaust gas of the flame. Such monitoring means are expensive, both as regards the cost of manufacture and as regards the licensing procedure on the part of the official licensing authorities. In addition the known IR cameras exhibit poor selectivity with respect to extraneous light. Finally, flame sensors working on the optical principle can easily become dirty in the combustion chamber, and the recording of the combustion quality can therefore still be unsatisfactory.

The present invention seeks to provide a flame monitoring device of the kind described above which allows simple construction and moderately priced manufacture.

According to a first aspect of the present invention there is provided a flame monitoring device with a burner and an associated combustion chamber, wherein there are provided a transmitter and a receiver assigned thereto, the transmitter being so arranged that a signal path formed in the combustion chamber passes through the region of the flame of the burner, and wherein the receiver converts the transmission signals received into electric signals and electronic 3s analysis means are connected at the output side of the receiver for carrying out propagation time 2 measurements of the transmission signal and/or of velocity measurements on the flame for different operating states of the burner.

According to a second aspect of the present invention there is provided a f lame monitoring device with a burner and an associated combustion chamber, wherein there is provided a transmission and reception unit as a reversible transducer, which is so arranged that the signal transmitted by it into the combustion chamber passes through the region of the flame of the burner and after reflection off the combustion chamber wall impinges on the unit now operating as a receiver and electronic analysis means are provided for the carrying out of propagation time measurements of the transmission signal and/or velocity measurements on the flame for different operating states of the burner.

The invention also provided methods employing the above devices.

In apparatus according to the invention, the propagation time of the signal depends on the sound velocity and the latter on the density of the medium through which the signal passes. The hot gases of the burner f lame reduce the sound velocity compared with the cold state of the burner and hence prolong the propagation time of the signal. For example, if the propagation time with the burner in the cold state is taken as a reference value, it may be determined subsequently by means of a further propagation time measurement whether the burner has ignited and if so, what temperature or density and modulation or variations thereof the f lame exhibits, if calibration measurements have been made beforehand.

JA 3 Since the flame consists of mobile gases, the Doppler effect based on this mobility may also be analysed by means of the electronics in order to determine the velocity of the flame. According to one embodiment the receiver may be arranged opposite the transmitter, but on the other side of the flame. Furthermore the receiver may be so arranged according to the known echo-sounding method that the signal impinges on the receiver only after reflection off the combustion chamber wall.

In another advantageous embodiment a further transmitter is envisaged which is so arranged in the combustion chamber that its transmission signal is also received by the receiver assigned to the first transmitter. In this way scanning of the flame is possible, in order to determine for example its temperature distribution or its spatial extent. This takes place according to a further embodiment of the invention by means of an analysis and control circuit, which supplies the transmitters with mutually out-ofphase transmission signals. Such an arrangement may likewise be constructed with a plurality of transmission and reception units.

In addition, ultrasonic transmitters may be used as transmitters in advantageous embodiments of the invention. Finally, the device according to the invention may be used for the monitoring of hot gases enclosed in suitable receptacles.

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, of which:

4 Figure 1 shows a diagrammatic view of a first embodiment of the invention; Figure 2 shows a diagrammatic view of a second embodiment of the invention; and Figure 3 shows a diagrammatic view of a third embodiment of the invention.

Figure 1 shows a burner 1 and a combustion chamber 2 assigned thereto. The burner 1 generates a flame 5 through which passes a transmission signal of an ultrasonic transmitter 3. The ultrasonic transmitter 3 and the associated receiver 4 are arranged adjacent on the same side of the flame 6. The transmission signal is reflected off the opposite combustion chamber wall and impinges on the receiver 4 only after a further passage through the flame 6. The corresponding signal path is designated in Figure 1 with the reference symbol 5. It would however also be possible to arrange the receiver 4 on the opposite side, so that the transmission signal of the ultrasonic transmitter impinges directly on the receiver 4. Both the generation of the transmission signals for the ultrasonic transmitter 3 and the analysis of the received signals of the receiver 4 are carried out by means of an analysis circuit 7.

First of all the analysis electronic device 7 undertakes with the burner in the cold state a propagation time measurement, which forms from this a reference value for the subsequent control measurement during the operation of the burner. The propagation time of the signal is derived from the velocity in the medium through which the signal passes. The sound velocity for its part varies with the temperature according to the following formula:

C co/(1 + T/273.2)1/2 J1 where co is the sound velocity at OOC and T the temperature in degrees Kelvin. For a flame of 19000C a reduction in the sound velocity to 1/3 of the standard value is obtained.

It may therefore be determined with the control measurement whether on the one hand the burner has come into operation and on the other what the flame temperature is.

In the embodiment according to Figure 2 there is arranged on the same side of the flame 6 as the ultrasonic transmitter 3 a further ultrasonic transmitter 3a. The transmission signals of both transmitters are received by the receiver 4 after reflection at the other side of the flame 6. The corresponding transmission paths are marked with the reference numerals Sa and 5b.

This arrangement with two ultrasonic transmitters 3 2s and 3a allows scanning of the flame in order for example to record the temperature distribution in the flame. To this end out-of-phase transmission signals are generated by analysis and control electronic device 7a and analysed after reception by the receiver 4. This also allows conclusions to be drawn on the spatial extent of the flame.

The device shown in Figure 3 is distinguished from that of Figure 1 in that instead of a transmitter 3 and a receiver 4 a transmission and reception unit 8 is used as a reversible transducer, where transmission 6 and reception functions can be mutually substituted. The transmission signal passes through the flame 6 on the signal path 5 and is reflected back off a reflector again on the same path into the transmission and reception unit. Monitoring of the flame may also be carried out with a plurality of such reversible transducers according to the embodiment according to Figure 2 with a suitable analysis and control electronic device 7a, whereby the monitoring becomes more effective if the individual elements are operated alternately as transmitter and as receiver. Piezo elements may for example be used as reversible transducers.

Finally, the analysis electronic device 7 according to Figure 1 or 3 and the analysis and control electronic device 7a according to Figure 2 may be constructed in such a way that the velocity of the f lame 6 may be determined with the use of the Doppler effect. In this way it is possible to evaluate the quality of the combustion process, and in particular to monitor the uniformity of the combustion.

The above f lame monitoring devices are self -cleaning which provides robust and sensitive arrangements.

The invention is not limited to the monitoring of flames, but may also be used for the monitoring of hot gases which are located in a suitable receptacle.

7 claims A f lame monitoring device with a burner and an associated combustion chamber, wherein there are provided a transmitter and a receiver assigned thereto, the transmitter being so arranged that a signal path f ormed in the combustion chamber passes through the region of the f lame of the burner, and wherein the receiver converts the transmission signals received into electric signals and electronic analysis means are connected at the output side of the receiver for carrying out propagation time measurements of the transmission signal and/or of velocity measurements on the flame for different operating states of the burner.

2. A device according to claim 1, wherein the receiver is so arranged that the transmission signal of the transmitter impinges directly on the receiver.

3. A device according to claim 1, wherein the receiver is so arranged that the transmission signal of the transmitter impinges on the receiver after reflection off the combustion chamber wall.

4. A device according to any preceding claims wherein a further transmitter is provided and is so arranged that its transmission signal is also received by the receiver assigned to the first transmitter.

1 8 5. A f lane monitoring device with a burner and an associated combustion chamber, wherein there is provided a transmission and reception unit as a reversible transducer, which is so arranged that the signal transmitted by it into the combustion chamber passes through the region of the flame of the burner and after reflection off the combustion chamber wall impinges on the unit now operating as a receiver and electronic anaylis means are provided for the carrying out of propagation time measurements of the transmission signal and/or velocity measurements on the flame for different operating states of the burner.

6. A device according to claim 5, wherein a plurality of transmission and reception units are provided.

7. A device according to claim 5 or 6, wherein an analysis and control circuit is provided, which supplies the transmitters or the transmission and reception units with mutually out-of-phase transmission signals and carries out a propagation time analysis with respect to the respective transmission signal.

8. A device according to any preceding claim, wherein the electronic analysis means or the analysis and control circuit is formed in such a way that the frequency shift occurring by virtue of the Doppler effect is analysed in order to determine the velocity of the flame.

g. A device according to any preceding claim, wherein ultrasonic transmitters are provided.

A 9 10. A flame monitoring device substantially as herein described with reference to Fig. 1, Fig. 2 or Fig. 3 of the accompanying drawings.

11. A method of monitoring a flame employing a device according to any preceding claim.

12. A method of monitoring hot gases employing a device according to any preceding claim.