GB2239090A

GB2239090A - Flame detection

Info

Publication number: GB2239090A
Application number: GB9023820A
Authority: GB
Inventors: Peter Donald Baker
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1989-11-10
Filing date: 1990-11-02
Publication date: 1991-06-19
Also published as: GB9023820D0; FR2654509A1; CA2029317A1; JPH03170821A; GB8925460D0; DE4035324A1

Abstract

The presence or absence of a flame in an engine combustion chamber 4 is detected by monitoring the level of radiation at two different wavelengths. One wavelength is between 470nm and 530nm whereas the other wavelength is about 670nm. The ratio of the level of radiation at one wavelength to that at the longer wavelength is measured. When the ratio is between about 0.1 and 1.0, this indicates the presence of a flame. When the ratio is outside this range this indicates absence of a flame and causes a signal to be supplied to an igniter control unit 13. <IMAGE>

Description

1 ;2 Z2 C3 a 0 'D (2) FLAME DETECTION This invention relates to flame

detection.

In gas-turbine engines it is desirable to know whether or not a flame is present in the combustion chamber or afterburner. The presence of a flame can be detected by monitoring when optical radiation of a particular wavelength is greater than a predetermined background level. The problem with this, is that hot parts of the engine casing will also emit optical radiation a part of which will be at the wavelength being monitored. Stray radiation from the sun can also, in some cases, enter the engine and give rise to a spurious indication of the presence of a flame.

It is an object of the present invention to provide a method and apparatus for flame detection which is less susceptible to false indication.

According to one aspect of the present invention there is provided a method of flame detection including the steps of comparing the level of radiation at one wavelength with the level of radiation at a longer wavelength,'' nd ptoviding an indication of the presence of a flame when the' ratio of the level of radiation at the one wavelength td. that at the longer wavelength is greater than a first value and less than a second, higher value.

According to another aspect of the present invention there is provided a method of flame detection including the steps of comparing the level of radiation at one wavelength with the level of radiation at a longer wavelength, and providing an indication of the absence of a flame when the ratio of the level of radiation at the one wavelength to that at the longer wavelength is less than a first value or greater than a second, higher value.

The method may include the step of supplying an output to an ignition unit in response to the indication of the absence of a flame.

The one wavelength may be between about 470= and about 530nm, the longer wavelength being about 670nm. The first value may be about 0.1 and the second value about 1.0.

According to another aspect of the present invention there is provided apparatus for carrying out a method according to the above one or other aspect of the present invention.

According to a further aspect of the present invention there is provided apparatus for detecting the presence of a flame including means for comparing the level of radiation at one wavelength with the level of radiation at a longer wavelength, and means for providing an indication of the presence of a flame when the ratio of the level of radiation at the one wavelength to that at the longer wavelength is greater than a first value and less than a second, higher value.

According to yet another aspect of the present inventon there is provided apparatus for detecting the absence of a flame including means for comparing the level of radiation at one wavelength with the level of radiation at a longer wavelength, and means for providing an indication of the absence of a flame when the ratio of the level of radiation at the one wavelength to that at the longer wavelength is less than a first value or greater than a second, higher value.

The indication may be provided on a display The apparatus may include an optical probe arranged to view a combustion zone, a fibre-optic cable arranged to supply radiation from the probe to a dichroic bean splitter, and the beam splitter being arranged to split the radiation from the probe into wavelengths including the one wavelength and into wavelengths including the longer wavelength. The apparatus may include a first photodiode arranged to provide an electrical output representative of the level of radiation at the one wavelength and a second photodiode arranged to provide an electrical output representative of the level of radiation at the longer wavelength.

Flame detector apparatus for a gas-turbine engine and its method of operation will now be described, by way of example, with reference to the accompanying drawing, in which:

Figure 1 shows the apparatus schematically; and Figure 2 is a graph illustrating spectral intensity of a radiant source at three different temperatures.

1 - With reference first to Figure 1, the apparatus includes an optical probe 1 mounted on the casing 2 of a gas-turbine engine 3 to view optical radiation within the combustion chamber or zone 4. The probe 1 supplies the received radiation via a fibre-optic cable 5 to a dichroic bean splitter 6. The beam splitter 6 divides the radiation passed via the cable 5 into two component wavelengths. Radiation within a wavelength band located between about 470nm and 530nm, that is with a colour between blue and green is passed to a first photodiode 7. The wavelength band may be of any width and may be located anywhere within this blue to green part of the spectrum according to the availability of the dichroic beam splitter and the response of the photodiode 7. The other output of the dichroic beam splitter 6 comprises radiation in a band of substantially the same width as that passed to the photodiode 7 but is of longer wavelength being centred around 670nm, that is. it is of red colour. radiation is supplied to a second photodiode 8.

The outputs of the two photodiodes 7 and 8 are supplied to a comparator 10 which produces an output indicative of the ratio of the levels of radiation at the two different wavelengths bands. The output of the comparator,16 i's t'upplied to a unit 11 which detects when the ratio is greater than a first value of 0.1 and less than a second value of 1.0.

When the ratio lies between the two values, the unit 11 provides an output to a display 12 which gives an indication of the presence of a flame. An output could be provided to other utilization means 13, such as an igniter control unit which causes energization of an igniter when the absence of flame is detected.

The average flame colour temperature Tc in a gas-turbine combustion chamber is around 1800K, whereas the engine casing may be at about 1000K and that of the sun about 6000K. The wavelength at which the maxima of emitted radiation occurs is given by Wien's Displacement Law:)max = 2897. 9/Tc micron.

With reference now to Figure 2, it can be seen that, at any temperature, some radiation is emitted at all wavelengths but that the proportion emitted at any selected wavelength will depend on how close that wavelength is to the maxima. More particularly, for the three different colours: blue (470nn), green (527nm) and red (670nn), the radiation emitted by the sun will be at 99% that of the maxima, 99% of maxima and of 83% of maxima respectively. For a flame at 1800K these values for the three colours will be 1.3t, 4% and 20% respectively. For a body, such as the engine casing at 1000K the values will be 2 X 10 1.5 X 10 and 4 X 10 If the level in the blue-green range 'is compared with that of red radiation, this gives, approximately, for the sun, a value greater than 1; for a flame, a value less than 1 but greater than 0.1; and for the casing, a value of less than 0.1.

Thus, by determining whether the 'relative values of the radiant intensity at the different wavelengths are greater or less than 1 and greater or less than 0.1, it is possible to determine whether the radiation is from a flame, the sun or the engine casing.

It will be appreciated that the invention is not confined to engine applications but could be useful in other applications, especially where the flame probe can receive sunlight, such as in flame stacks.

1

Claims

A method of flame detection including the steps of comparing the level of radiation at one wavelength with the level of radiation at a longer wavelength, and providing an indication of the presence of a flame when the ratio of the level of radiation at the one wavelength to that at the longer wavelength is greater than a first value and less than a second, higher value.

A method of flame detection including the steps of comparing the level of radiation at one wavelength with the level of radiation at a longer wavelength, and providing an indication of the absence of a flame when the ratio of the level of radiation at the one wavelength to that at the longer wavelength is less than a first value or greater than a second, higher value.

A method according to Claim 2, including the step of supplying an output to an ignition unit in response to the indication of the absence of a flame.

1 i A method according to any one of the preceding claims, wherein said one wavelength is between about 470nm and 530nm.

A method according to any one of the preceding claims, wherein the said longer wavelength is about 670nm.

A method according to any one of the preceding claims, wherein the said first value is about 0.1.

A method according to any one of the preceding claims, wherein the said second value is about 1.0.

A method substantially as hereinbefore described with reference to the accompanying drawings.

Apparatus for carrying out a method according to any one of the preceding claims.

- 10 10.

12.

Apparatus for detecting the presence of a flame including means for comparing the level of radiation at one wavelength with the level of radiation at a longer wavelength, and means for providing an indication of the presence of a flame when the ratio of the level of radiation at the one wavelength to that at the longer wavelength is greater than a first value and less than a second, higher value.

Apparatus for detecting the absence of a flame including means for comparing the level of radiation at one wavelength with the level of radiation at a longer wavelength, and means for providing an indication of the absence of a flame when the ratio of the level of radiation at the one wavelength to that at the longer wavelength is less than a first value or greater than a second, higher value.

Apparatus according to Claim 11, wherein the means for providing an indication of the absence of a flame is arranged to provide an output signal to an igniter control unit.

13. Apparatus according to any one of claims 10 to 12, wherein the said indication is provided on a display.

14.

15.

16.

Apparatus according to any one of Claims 10 to 13. including an optical probe arranged to view a combustion zone, a fibre-optic cable arranged to supply radiation from the probe to a dichroic beam splitter, and wherein the beam splitter is arranged to split the radiation from the probe into wavelengths including said one wavelength and into wavelengths including said longer wavelength.

Apparatus according to any one of Claims 10 to 14, including a first photodiode arranged to provide an electrical output representative of the level of radiation at said one wavelength and a second photodiode arranged to provide an electrical output representative of the level of radiation at said longer wavelength.

Apparatus according to any one of Claims 10 to 15, wherein the said one wavelength is between about 470= and 530nm.

17.

Apparatus according to any one of Claims 10 to 16, wherein the said longer wavelength is about 670nm.

1 18. Apparatus according to any one of Claims 10 to 17, wherein the said first value is about 0.1.

19.

Apparatus according to any one of Claims 10 to 18, wherein the said second value is about 1.0.

20.

Apparatus substantially as hereinbefore described with reference to the accompanying drawings.

21.

Any novel feature or combination of features substantially as hereinbefore described.

t c Published 1991 at llie Patent 0111ce. State House. 66171 High Holborn. London WC1R4TP. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point, Cwmrclinfach. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques lid, St Mary Cray, Kent.