JPH06259675A - Fire measuring method - Google Patents

Abstract

PURPOSE:To accurately measure the burning scale of fire from a position separated from the fire by calculating the exoergic scale of the fire by using a value in which a radioactive component proper to flame is subtracted from the intensity of a detected infrared ray. CONSTITUTION:Infrared intensity in plural infrared radiation zones including a resonance radiation zone for CO2 are detected. For example, the intensity of wavebands (1) 2.8-3.2mum, (2) 4.2-4.6mum, and (3) 4.6-5.5mum when the magnitude of flame is changed by using normal heptane and methanol are measured. In such a case, the radioactive component proper to the flame is located on a line connecting an FR point to the line segment of black body radiation in spite of the kind of fuel. In other words, the radioactive component proper to the flame is provided with the intensity of the waveband (2) and the waveband (3) of the component ratio of a PR point. Therefore, the intensity is concentrated on one point on the line of black body radiation by subtracting the radioactive component proper to the flame in spite of the magnitude of the flame, and output added on the waveband (3) is corrected, and temperature can be accurately measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the scale of a flame by detecting infrared rays emitted from the flame, and more particularly to a method for accurately measuring the scale of combustion regardless of the state of the flame such as fuel. .

[0002]

2. Description of the Related Art Conventionally, a flame measuring method has been put into practical use, in which only a specific wavelength of infrared rays emitted from a flame is detected to measure the combustion scale of the flame. In these flame measurement methods, the characteristic spectral lines (4.4 μm band;
The mainstream is to detect the resonance radiation band of CO ₂ . In addition, a flame measurement method for measuring the combustion state of a flame such as incomplete combustion by detecting the resonance radiation band (4.7 μm band) of CO has been put into practical use.

[0003]

However, the conventional flame measuring method is to measure only the combustion of a specific fuel under specific conditions. For example, a flame (a fire, etc.) generated in a part of a wide range of space. It was not possible to measure the combustion scale of).

[0004]

In order to solve the above problems, (1) the infrared intensity in a plurality of infrared radiation bands including the resonance radiation band of CO ₂ is detected, and the intensity of the detected infrared light is characteristic of a flame. A flame measurement method characterized by calculating a heat generation scale of a flame using a value obtained by subtracting the radiation component of. (2) In (1) above, the infrared radiation band to be detected is
2.8 μm to 3.2 μm, 4.2 μm to 4.6 μm, 4.6 μm to 5.5 μm
A flame measurement method characterized in that Invented

[0005]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be specifically described below. Detecting wavelength band is λ ₁ , λ ₂ , ... λn (n = integer of 2 or more)
, And the detection outputs of the respective wavelength bands detected by the infrared sensor are V ₁ , V ₂ , ... Vn. It is assumed that these detection outputs accurately reflect the infrared intensity of each wavelength band incident on the infrared sensor. by the way,
According to Planck's radiation law, the radiant intensity per unit area of infrared rays radiated by a body at a certain temperature T into a half space at a wavelength λ is expressed by the following equation.

[Equation 1] Here, C ₁ and C ₂ are constants determined by C ₁ = 2πhc ² and C ₂ = hc / k. However, h is Planck's constant, c is light velocity, and k is Boltzmann's constant.

Substituting the two detection wavelength bands λ ₁ and λ ₂ and the infrared radiation intensities P ₁ and P ₂ in the wavelength bands into the above formula 1 to derive an approximate formula for obtaining the temperature T,

[Equation 2] Here, P _1, P ₂ in the formula 2 when the infrared source S ₁ absorption lambda between to the infrared detection unit D, lambda ₂ are both not V
₁ , V ₂ can be substituted. That is,

[Equation 3] Becomes From equation 3, the temperature of the infrared source can be obtained by detecting infrared rays of two different wavelengths.

Next, from the temperature T obtained by the equation 3, λ ₁
Alternatively, the blackbody radiation intensity per unit area at λ ₂ (this is referred to as P ₁ 'or P ₂ ') is obtained from Planck's radiation law, that is, Equation 1. On the other hand, the intensity of the infrared rays incident on the infrared detector D depends on the distance L from the infrared source S to 1 / 2πL ²
become. Therefore, the infrared intensity P ₁ ″ or P ₂ ″ that should be incident on the infrared sensor from the infrared source having the area having the temperature T obtained above (s times the unit area) becomes P ₁ ′ or P ₂ ′. It is a value obtained by multiplying 2πL ² by s. That is,

[Equation 4] Becomes Since it is assumed here that the output of the infrared detector accurately reflects the intensity of the incident infrared light, P ₁ or P ₂ can be found from V ₁ or V ₂ by using the above equations 3 and ₂ . Therefore,
If the distance L is known, the actually detected incident infrared ray intensity P ₁ or P ₂ and the calculated incident infrared ray intensity P ₁ ″
Alternatively, the ratio with P ₂ ″ represents the area s of the infrared source S as can be seen from the equation 4.

Furthermore, by using the wavelength band for detecting the resonance radiation band of CO _2, an infrared intensity of black body radiation in resonance radiation band of CO ₂ by the equation 1 from the temperature and heating area of the infrared source obtained above means Pco calculating a ₂ ', infrared intensity Pco ₂ to be incident on the infrared sensor in the same manner as such the P ₁ "
And calculate the ratio of this to the actually observed Pco ₂ . Here, if Pco ₂ ″ << Pco ₂ , the infrared source is accompanied by a flame.

By the way, the radiation of a flame is divided into a radiation portion of a black body in the flame and a radiation portion peculiar to the flame, and becomes the sum of the radiation of the black body portion and the radiation peculiar to the flame. There is. Further, the amount of the radiation component peculiar to the flame changes depending on the size of the flame. Here, the wavelength band in which the radiation peculiar to flame appears is mainly CO ₂
In the resonance radiation band of 4.2μm ~ 4.6μm wavelength band,
Radiation peculiar to flame appears in the wavelength band of 4.6 μm to 5.5 μm.
Radiation appearing in the wavelength band is considered to be water generated by combustion.

Therefore, the inventor of the present invention measured the intensity of the above-mentioned wavelength band when the size of the flame was variously changed by using normal heptane and methanol. The result is shown in FIG. It can be seen from FIG. 1 that the radiation component peculiar to the flame is on the line connecting the FR point and the black body radiation line segment in FIG. 1 regardless of the type of fuel. That is, it can be seen that the radiation component peculiar to the flame has the wavelength band and the intensity of the wavelength band of the component ratio at the FR point. Therefore, if you subtract the radiation component peculiar to the flame, it will gather at a certain point on the line of blackbody radiation regardless of the size of the flame,
The output added to the wavelength band is corrected and the accurate temperature can be measured. The present invention is based on this finding.

Radiation of flame means CO generated by combustion.
₂ , resonance radiation due to molecular vibration such as H ₂ O and thermal radiation due to solid particles such as graphite generated by combustion are superposed. The radiation of solid particles is mostly distributed over the flame and is the radiation of particles that are dispersed in a gas, and is therefore translucent. Even if this part is a translucent body, the emissivity can be considered to be approximately 1 if the flame is large to some extent. Also, the radiation peculiar to the flame due to CO ₂ , H ₂ O, etc. has a very high radiation efficiency, and is emitted from the surface of the flame. Therefore,
For example, the radiation accompanying the combustion of normal heptane is a straight line drawn between the point a, which is the heat radiation by solid particles such as graphite generated by the combustion, and the FR point, which is the radiation peculiar to the flame due to CO ₂ , H ₂ O, etc. Has the radiant component above. Similarly, the radiation accompanying the combustion of methanol becomes the radiation component on the straight line between the point b and the FR point.

The temperature of the flame is highest in the gas body in the outer layer of the flame. Therefore, the temperature that causes thermal radiation is often not the maximum temperature of the flame, but when considering the scale of the flame as a whole, the radiation of the flame as a whole, that is, solid particles such as graphite generated by combustion, should be followed according to the above idea. It is better to consider the heat radiation by.

The calculation method for obtaining this temperature will be examined below. In the example of FIG. 1, the FR point, which is the origin of the straight line showing the characteristic of each flame of normal heptane and methanol, has a component ratio of wavelength band: wavelength band = 74: 26. Therefore, a phase diagram with this point as the apex may be considered.

Considering in this way, the component of thermal radiation in the flame can be separated by subtracting the radiation peculiar to the flame represented by the FR point from the radiation component of the flame actually detected. You will ride on the curve of the black body radiation inside. If such a process is performed, the temperature can be obtained by the calculation of the equation 3 from the ratio of the wavelength band and the wavelength band as in the case of the temperature calculation of the normal black body radiation. Therefore, the radiation component of the flame may be subtracted from the wavelength band.

A concrete calculation example will be shown below. In this calculation example, an approximate calculation is performed in order to simplify the calculation. It can be seen from the examination of FIG. 1 and the like that the characteristic of the curve of the black body radiation is that the ratio of the wavelength band is small with respect to temperature and is about 20% of the total of the three wavelengths. Therefore, by subtracting the flame-specific component so that the ratio of the wavelength band is about 20% of the total of the three wavelengths of wavelength band-wavelength band-wavelength band, it is possible to leave almost a blackbody radiation component. here,
The standard of the ratio of the wavelength band after subtraction is 700 ℃ ~ 1000 ℃
The error can be reduced by adjusting to the blackbody radiation of.
In this case, the error given to the temperature calculation result is at most 20.
It is about ℃. If this is adjusted to blackbody radiation below 500 ° C, the error at high temperature becomes large.

The calculation procedure will be described below. First, the radiation component peculiar to the flame is subtracted before obtaining the relative ratio of the intensities of a plurality of infrared radiation bands including the infrared radiation intensity in at least the CO ₂ resonance radiation region to the temperature of the object to be detected. For example, let V ₁ , V ₂ , and V ₃ be the output values of the infrared sensors that detect the components 3 to 3 of the three wavelength bands, and Vx be the values that are subtracted as the flame-specific components. Vx is the sum of the wavelength band and the components peculiar to the flame in the wavelength band, and the respective ratios are Vf ₂ and Vf ₃ . At point c in Fig. 2, Vx is the distance from point c on the extension of the straight line from FR point to point c to the curve of black body radiation, of which the component of the wavelength band is Vf ₂ and the component of the wavelength band. Is Vf ₃ . In addition, the ratio of the wavelength band in the reference black body radiation is R ₂
given that,

[Equation 5] Becomes Therefore,

[Equation 6] Becomes It is sufficient to subtract the radiation component of the flame from the wavelength band and the wavelength band using Vx obtained here.

By the above procedure, the blackbody radiation component and the flame-specific radiation component can be separated from the flame radiation component. The blackbody radiation component obtained here is used to measure the scale of flame combustion. By applying the value of the wavelength band and the value of the wavelength band corrected here to Equation 3, the temperature of the flame can be obtained. The area, Pco ₂ ″, is calculated from the temperature obtained here by applying the equation 4 to the area for the wavelength band and the Pco ₂ ″ ratio for the wavelength band.

The radiant energy W of the heat source having the temperature T and the area s obtained here is calculated from the Stefan-Boltzmann law as follows.

[Equation 7] Is expressed as Here, σ is a Stefan-Boltzmann constant, and σ = 5.673 × 10 ⁻¹² (W / cm ² · deg ⁴ ). However, in the actual flame, most of the generated thermal energy is diffused by the convection of the combustion product gas. The inventor has found that the amount of heat diffused by convection of the produced gas and the amount of radiant heat always have a constant ratio. The radiant heat amount is 1/30 to 1/10 of the calorific value as shown in FIG. 3, and the radiant heat amount is 1/20 of the calorific value on average. In addition, this value is almost the same regardless of whether the fuel is methanol or normal heptane, and is not affected by the type of fuel.

That is, when the combustion scale of the flame is represented by the calorific value, a value 20 times the radiant heat quantity obtained by the equation 7 is obtained. Therefore, when the calorific value of the flame is calculated from the temperature area calculated by the above formulas 1 to 6,

[Equation 8] Becomes

[0017]

EXAMPLE An example of application to fire detection will be shown as an example of the present invention. FIG. 4 shows an example of the configuration of a fire detector to which the present invention is applied. In this example, infrared rays emitted from a fire source or a similar heat source are periodically divided by a chopper, and four pyroelectric infrared sensors detect different four wavelength bands. These sensors have a built-in bandpass filter that transmits a predetermined wavelength band. However, even with four or less pyroelectric infrared sensors, a method of detecting the wavelength divided into four using the switching means may be used. Further, even with four or less pyroelectric infrared sensors, a method of detecting four kinds of wavelength bands by using the switching means may be used. The signal detected by each sensor is amplified by an amplifier circuit and then converted into a digital signal by an A / D converter. The microprocessor performs synchronous detection and filtering on the digital signal according to the division cycle of the chopper, and returns the signal divided by the chopper to a continuous signal sequence. Furthermore, the signal sequence obtained here is converted into a signal sequence for communication and digitally transmitted to the host computer.

The infrared wavelength band detected in the example of FIG. 4 is a wavelength band for efficiently detecting the radiation of the heating element from the low temperature region to the high temperature region as shown in FIG. That is,
Center wavelength 3 μm half width 0.4 μm, center wavelength 4.4 μm half width
0.4 μm, center wavelength 5.5 μm, half width 0.8 μm, center wavelength 8.
The half-value width of 5 μm is 1.0 μm. Regarding the above wavelength band, the radiation of the heating element in the high temperature region is mainly detected, and the heating element in the high temperature region of 400 ° C. or higher is monitored in combination with the infrared intensity detected in the wavelength band. The presence or absence of flame is monitored for the wavelength band. The wavelength band is a wavelength band that efficiently detects from low temperature to high temperature.In combination with the wavelength band, the heating element in the high temperature area is monitored, and in combination with the wavelength band, the heating element in the low temperature area is monitored and In combination, flame burning scale measurements are made. As for the wavelength band, the radiation of the low-temperature heating element below 400 ° C is efficiently detected, and the heating element in the low-temperature region below 400 ° C is monitored in combination with the wavelength band. In the process from a smoldering state to a fire, a low temperature heating element gradually increases in temperature and expands. Therefore, it is necessary to monitor the temperature of the heat source in a wide temperature range from low temperature to high temperature.

In this embodiment, the detection wavelength bands of the respective sensors of the detection section shown in FIG. 4 are 3.0 ± 0.2 μm, 4.4 ± 0.2 μm, 5.0.
± 0.4μm and 8.5 ± 0.5μm. Calculation formulas 1 to 8 are stored in the host computer, and the temperature, area, presence / absence of flame, and radiant heat amount of the heating element are calculated. Also, in the host computer, the output of the sensor is
If it is 100 times or less, noise reduction filtering is performed. The time constant of the filtering process is 100 when the sensor output is the noise level.
If it is less than double, it is 8 seconds, if the output of the sensor is small, the time constant is increased, and if it is less than 10 times, it is 64 seconds. Fires are judged in 6 stages based on the amount of radiant heat. Furthermore, the increase rate of radiant heat is obtained by the method of least squares, and if this is 1 W / sec or more, it is assumed that the heating element is expanding,
If it is 10 W / sec or more, it is said to be expanding rapidly. If the fire is being expanded, the classification of fire determination is advanced to the one-stage risk side, and if it is being expanded rapidly, it is advanced to the two-stage risk side. The storage time when performing the least squares method is 20 seconds when the sensor output is 100 times the noise level or more, but when the sensor output is small, the storage time is lengthened and the sensor output Is less than 10 times the noise level, 3
I'm going for a minute. In this embodiment, the FR point in FIG. 1 is set as wavelength band: wavelength band = 74: 26. Also, R ₂ in Equation 6
Is set to 0.21 based on 700 ° C blackbody radiation.

The scale of the flame measured according to the present invention is used for judging a fire. Simply, for example, a flame having a calorific value of 20 KW or more is judged to be a fire, but in this embodiment installed at a position of the floor surface of 10 m, this judgment is made into 6 stages, normal is less than 600 W, and heating element is 600 W or more. Alarm to notify the presence of 1.5KW
With the above, an alarm to notify the presence of a large-scale heating element, 3KW
The above alerts for the presence of dangerous heating elements, 6KW and above alerts that the possibility of fire cannot be denied, 12KW
With the above, a fire alarm is sent. Of course, this value is a value that needs to be set as needed depending on the state of the space in which it is installed. In the embodiment, R ₂ is set to 0.
Although it is set to 21, a more accurate value can be obtained by recalculating according to the calculated temperature.

[0021]

According to the flame measuring method of the present invention, the combustion scale of a flame can be accurately measured from a position away from the flame. The flame measurement method of the present invention can measure the calorific value of combustion irrespective of the type of the combusted material, and is particularly effective for detecting a fire, and accurately detects the combustion scale of the initial fire to take an appropriate response. It becomes possible. Furthermore, since the scale of combustion can be measured regardless of the type of combusted material, it is effective for combustion control using an unspecified fuel.

[Brief description of drawings]

FIG. 1 shows relative ratios of sensor outputs in respective wavelength bands when an experiment for detecting various heating elements was performed.

FIG. 2 is a reference diagram of a processing procedure formula in the present invention.

FIG. 3 is a diagram showing a relationship between a calorific value of a flame and a radiant heat value.

FIG. 4 is a configuration diagram of a fire detector that is an embodiment of the present invention.

FIG. 5 shows a detection wavelength band of a fire detector which is an embodiment.

Claims (2)

[Claims] 1. A flame exothermic scale is calculated by detecting infrared intensities in a plurality of infrared emission bands including a CO ₂ resonance emission band and using a value obtained by subtracting a radiation component peculiar to a flame from the detected infrared intensity. A flame measuring method characterized by: 2. The infrared radiation band to be detected according to claim 1, which is 2.8 μm to 3.2 μm, 4.2 μm to 4.6 μm, 4.6 μm
A flame measuring method characterized by being 5.5 μm.