JPH0355780B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method and apparatus for simultaneously measuring the concentration and particle size of sprayed suspended particles.

[Prior Art] In general, the spray combustion method, in which liquid fuel is injected into a room and burned as fine particles, is widely used in diesel engines, gas turbines, industrial furnaces, etc.
The particle size distribution of this atomized fuel plays an important role in the ignition performance of various combustors, flame stability, combustion efficiency, and control of emissions of air pollutants such as nitrogen oxides (NOx) and soot. It is a well-known place. However, the reality is that the above-mentioned relationship between spray and combustion is only understood in terms of circumstances, and we have developed a highly accurate measurement of particle size distribution that will be fully useful for combustor design and the development of combustion models for this purpose. It is hoped that this will establish a quantitative and universal relationship between spray and combustion.

Therefore, methods for measuring the particle size and spatial distribution of substances that have been atomized using various methods have been considered.
The first method is called the immersion method, which has been used for a long time. This method involves placing particles in a suitable liquid and measuring their size using a microscope.If you can collect the correct sample, the measurement accuracy, resolution, and reliability are excellent, but if you are willing to put in the effort, expensive equipment is required. It is characterized by the ability to measure particle diameters without requiring a high degree of skill.
However, there are inherent problems common to direct methods, such as sampling being affected by droplet coalescence and splitting, and measurement in a high-pressure, high-temperature atmosphere being extremely difficult. Therefore, an optical measurement method was considered that has the potential to alleviate the limitations and drawbacks of such direct measurement methods. This optical measurement method includes a method of measuring the size of the droplet image and a method of determining the particle size from physical quantities related to the size of the droplet. TV imaging methods, or holography, belong to the former category, while most of the latter utilize the light scattering properties of particles.

Research in this field has been active since monochromatic, coherent laser light sources became readily available. Traditionally, scattering methods that utilize the light scattering properties of fine particles mainly target particles that are not very large compared to the wavelength, but recently they have been used to measure particles that are more than 100 times the wavelength, such as particles in atomized spray. An attempt was made.

One method for measuring the particle size distribution of a particle group consisting of particles that are sufficiently large compared to the wavelength is to determine the particle size distribution from changes in the intensity of forward scattered light. This calculates the distribution function using an inverse transformation formula within the range of diffraction approximation. However, this method has a problem in that it is extremely difficult to accurately evaluate the differential coefficient of the light intensity with respect to the angle, which is necessary for this conversion. Another method is to determine the shape parameters of a particle size distribution function from the intensity distribution of scattered light and measure the particle size distribution of the sprayed granules, instead of using an inverse transformation formula. Although this method cannot determine the parameters themselves, it can relatively easily determine the Sauter mean particle diameter (hereinafter referred to as SMD) from the attenuation of the scattered light intensity. However, when analyzing the formula I〓(θ) of Mie's scattering theory, which expresses the intensity of scattered light, the influence of the central region, which is susceptible to direct light interference, becomes large. Furthermore, an effective method for obtaining the weight particle size distribution from the scattered light intensity distribution has not been established.

[Object of the invention] This invention was made in view of the above circumstances, and when measuring the particle size distribution of sprayed particles using the light scattering characteristics from the particles, the intensity of the scattered light is
Instead of analyzing the diffraction pattern of Mie's scattering theory formula I〓(θ), let's measure it by analyzing the diffraction pattern of I〓(θ)・θ, which is the integrand with respect to the angle θ of the scattered light energy. To provide a method and apparatus for easily and accurately measuring the concentration and particle size distribution of sprayed granules by solving all the problems of conventional spray particle size measurement methods. The purpose is to

[Structure of the invention] The present invention has been made to achieve the above object,
The forward small angle scattered light obtained by irradiating a laser beam onto a group of particles to be measured is focused by a lens, and is received by an annular optical detector consisting of at least three channels of concentric photoelectric conversion elements arranged above the focal point position. , after amplifying and sample-and-holding the minute current signal photoelectrically converted by the photodetector, the signal from each channel proportional to the pattern of scattered light received by the photodetector is expressed as I〓(θ)・
A method for measuring the concentration and particle size of suspended particles, characterized by analysis based on the formula θ [where I = (θ) is the intensity of scattered light from a group of particles, and θ is the scattering angle]. By analyzing the diffraction pattern of the integrand of the scattered light energy by the scattering angle of the scattered light intensity of the particle group, the concentration of particles and the particle size distribution can be measured.

Furthermore, the apparatus for carrying out the above method includes a laser oscillator, an optical lens for condensing forward small angle scattered light from a group of measured microparticles irradiated with a laser beam, and a focal position of the optical lens. an annular optical detector consisting of at least three channels of photoelectric conversion elements such as concentric silicon photodetectors disposed in the photodetector; and a number of channels of the optical detector that simultaneously amplifies minute current signals of each channel photoelectrically converted by the optical detector. the same number of amplifiers, and a circuit that samples and holds the current signal amplified by the amplifiers for each channel;
The A/D converter converts the current signal of each channel into a digital signal, and the optical detector converts the current signal into a digital signal.The amount of light energy received by each channel is calculated.
Concentration of suspended particles consisting of a microcomputer that stores an analysis procedure based on the formula I〓(θ)・θ [where I〓(θ) is the intensity of scattered light from the particle group, and θ is the scattering value] This method specifies a particle size measuring device and can accurately measure the particle size by simply analyzing and calculating the light energy converted by the A/D converter based on a computer program.

[Example] The present invention will be described in detail below based on the measurement principle and illustrated examples.

When a single isotropic spherical particle with a diameter D is irradiated with an unpolarized laser beam of wavelength λ, the intensity distribution of the light scattered by the spherical particle is determined by the refractive index m and the particle size parameter α (= πD /λ). As the value of the grain size parameter α increases, the amount of light scattered toward a small forward angle relative to the total amount of scattered light increases rapidly, and the shape of the scattered light intensity distribution with respect to angle in this region changes sensitively depending on the grain shape parameter α. I come to do it. The forward small-angle scattering method in a broad sense uses this property to determine the particle size or particle size distribution of a particle group consisting of particles larger than the wavelength λ of light. The key point of this invention is to measure the particle size distribution.

As shown in Figure 1, when a laser beam (monochromatic parallel beam) 1' is irradiated onto a particle group 2 and a lens 3 is placed in front of it to collect the scattered light, the scattered light from each particle is The component in the angle θ direction is γ at the focal plane 4 of the light receiving lens, regardless of the position and velocity of the particle.
It is collected on the circumference of a circle whose radius is =f・sinθf・θ. The distribution of the scattered light intensity I (θ) at the focal plane 4 can be considered to be a superposition of the scattered light intensities I (θ, α) from individual single particles if the influence of multiple scattering can be ignored. In other words, the number particle size distribution is N(α)
Then, the following relationship holds, I〓(θ)＝c∫ ^∞ ₀ I(θ,α)N(α)dα...(1) I(θ・α) is the series solution of the scattering equation given by Mie. It is calculated as Measuring I〓(θ) and determining the particle size distribution is nothing but solving the integral equation of equation (1).

In addition, if the function I〓(θ)・θ formula is used instead of the I〓(θ) formula for analysis to obtain the weight particle size distribution from the scattered light intensity distribution, the scattering angle with the value of I〓(θ)・θ Since there will always be a peak value at , it is very convenient for understanding the characteristics of the distribution. Here I〓(θ)・θ
The expression is an integrand with respect to the scattering angle θ of the scattered light energy. There is also the advantage that the influence of the central area, which is susceptible to direct light interference, can be reduced in analysis. When the diffraction approximation holds, equation (1) becomes I〓(θ)・θ= c∫ ^∞ ₀ [2J ₁ (αθ)] ² /αθα ³ N(α)dα……(2), and the weight When the distribution function W(α) is introduced, I(θ)·θ=c= c∫ ^∞ ₀ [2J ₁ (αθ)] ² /αθW(α)dα (3). Obtaining W(α) from equation (3) corresponds to solving a Fredholm integral equation of the first kind with a symmetric kernel [2J ₁ (α, θ)] ² /αθ. From this relationship, the concentration of particles can be obtained.

The present invention will be explained in more detail below based on the apparatus of the embodiment. Figure 2 shows the basic concept of an apparatus for carrying out the method of the present invention, in which a helium-neon laser oscillator (hereinafter simply referred to as a He-Ne laser) 1
When the laser beam 1' is expanded by the beam expander or collimator lens 5 and the laser beam is irradiated onto the particle group 2 to be measured, the scattering angle θ of the scattered light of the laser beam colliding with the particle group 2 is
The direction component is γ=f・sinθf・θ at the focal plane of the light receiving lens 3, regardless of the position and velocity of the particle.
are collected on the circumference of a circle with radius. By positioning an annular optical detector 6 such as a concentric silicon photodetector having at least three channels of light receiving sections on this focal plane, the intensity of light that can be considered to be a superposition of the scattered light intensities of individual particles as described above can be obtained. The distribution I〓(θ) can be directly received. The intensity distribution of the scattered light received by the annular optical detector 6 is photoelectrically converted and becomes an input to the optical energy measuring device 7 as a minute current signal. As shown in the block diagram in FIG. 3, the optical energy measuring device 7 includes amplifiers 71 ₁ to 71 _i and sample-and-hold circuits 72 ₁ to 72 _i corresponding to each channel (channel number i) of the annular optical detector.
It is composed of an A/D converter 73, a computer interface 74, and a microcomputer 75.

The analysis procedure in the microcomputer 75 is as follows. First, in order to analyze the above equation (3), Rosim-Rammler's distribution function W(D)=C(D/X ₃ ) ^X 2-1 EXP[-(D/X ₃ ) ^X 2] ...(4 ) It was adopted. The reason is that parameters X ₂ and X ₃ are
X ₂ : Distribution spread, X ₃ : Representative particle size (the weight of particles smaller than this particle size is 1/1/2 of the total weight)
This is because it is easy to understand. In equation (4), ∫ ^∞ ₀
When W(D)dD=1, C=X ₂ /X ₃ (C: constant) and the weight proportionality constant X ₁
Introducing equation (4) becomes W(D)=X ₁ X ₂ /X ₃ (D/X ₃ ) ^X2-1 ·EXP [−(D/ ^X ₃ ) By changing the parameters X _{2 and} X ₃ , the above I〓
Find the pattern of (θ)/θ equation using equation (5). Find X ₁ , X ₂ , and X ₃ from the pattern of the measured I〓(θ)・θ equation. The average particle diameter SMD=∫ ^∞ ₀ N(D)D ³ dD/∫ ^∞ ₀ N(D)D ² dD is calculated from the following equation using X ₂ and X ₃ .

SMD=X ₃ /Γ(1-1/X ₂ ) Γ: Gamma function (6) In the case of an annular optical detector, the particle size distribution is determined based on the amount of optical energy Ei to the i-th channel. Ei is given by the following equation.

Ei＝C∫〓 ⁱ⁺ 〓 _i- I〓(θ)・θdθ……(7) θ _i+ and θ _i- are the outer shape of the annular optical detector.
ROUT, the inner diameter is _Rio , and the focal length of the receiving lens is f
Then, θ _i+ = R _put /f and θ _i- = R _io /f, which are the scattering angles. When the particle size parameter α=πD/λ is sufficiently large and the diffraction approximation holds true, using the approximation of equation (3), E _i =C∫〓 ⁱ⁺ 〓 _i- ∫ ^∞ ₀ [2J ₁ (αθ)] ² /αθ W(α)dαdθ ……(8) E _i =∫ ^∞ ₀ W(α) {∫〓 ⁱ⁺ 〓 _i- [2J ₁ (αθ)] ² /dθdθ｝dα……(9), and integrating this , E _i = C∫ ^∞ ₀ W(D) {J ₀ ² (αθ _i- ) +J ₁ ² (αθ _i- )−J ₂ ² (αθ _i+ ) −J ¹ ₂ (αθ _i+ )}/Ddα …… (10), and the required value based on the amount of light energy E _i can be found from equation (10). That is, data based on the width of each channel of the annular optical detector 6 and the angle from the center and the calculation procedure of equation (10) are input to the microcomputer 7.
By storing the information in the memory No. 5, it is possible to simultaneously measure the particle concentration and particle size from the scattered light pattern received by the annular light detector.

Furthermore, the meanings of the symbols used in each of the above formulas are as follows.

α: particle size parameter, c: constant, D: particle size,
E _i : amount of light energy, I(θ), I(α, θ): intensity of scattered light from a single particle, I(θ): intensity of scattered light from a group of particles, J ₀ (α, θ): first Zero-order seed, Bessel function, J ₁
(α, θ): linear Bessel function of the first kind, N(D), N
(α): Number particle size distribution function, SMD: Sauter average particle size, W(D), W(α): Weight particle size distribution function, X ₁ :
Parameter of weight proportionality constant, X ₂ : Parameter of distribution spread, X ₃ : Parameter of representative particle size, f: Focal length of lens, θ: Scattering angle, θ _i- :
Scattering angle with respect to the inner diameter of the i-channel of the annular optical detector, θ _i+ : Scattering angle corresponding to the outer diameter of the i-channel of the annular optical detector, λ: wavelength of the laser beam,
Γ: Gamma function.

[Effects of the Invention] As explained above, the method for measuring suspended particle concentration and particle size according to the present invention irradiates a group of particles to be measured sprayed into the air with a laser beam, and collects the scattered light emitted through the group of particles. The light is collected by a lens, received by an annular light detector with at least three channels arranged above the focal point of the lens, and a signal from each channel proportional to the scattered light pattern received by the light detector is expressed as I〓(θ)・Analysis using the equation θ has the excellent effect of allowing the concentration and particle size of suspended particles to be easily measured, something that has been considered extremely difficult in the past.

Further, as a device for carrying out the measurement method, a laser oscillator, a laser beam expander, and an optical lens that condenses the scattered light passing through the microparticles,
At least a three-channel annular optical detector placed at the focal point, an amplifier, a signal hold circuit, and an A/D converter are organically coupled, and the A/D converted light energy is converted into scattered light. The device consists of a computer that analyzes and calculates the integrand function based on intensity and scattering angle, and is able to accurately measure particles and concentration despite its simple configuration.

Furthermore, the effects of the above measurements will improve the combustion efficiency of various combustors that employ the spray combustion method, contributing to energy conservation and greatly contributing to the reduction of air pollutant emissions. It is also effective.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram for explaining the principle of this invention, Fig. 2 is a schematic configuration diagram of an apparatus for carrying out the method of this invention, and Fig. 3 is a block diagram of a light energy measuring device in the same apparatus. It is a diagram. 1... Oscillator, 2... Particle group, 3... Light receiving lens, 4... Focal plane, 5... Collimator lens,
6... Annular optical detector, 7... Optical energy measuring device, 71 ₁ to 71 _i ... Amplifier, 72 ₁ to 72 _i ...
...Sample and hold circuit, 73...A/D
Converter, 74...interface, 75...microcomputer.

Claims (1)

[Scope of Claims] 1. Forward small-angle scattered light obtained by irradiating a laser beam onto a group of particles to be measured is focused by a lens, and from at least three channels of concentric photoelectric conversion elements arranged on the focal point position. After amplifying, sampling and holding the minute current signal that was received by the annular optical detector and photoelectrically converted by the optical detector, the signal from each channel proportional to the pattern of scattered light received by the optical detector is
A method for measuring the concentration and particle size of suspended particles, characterized by analysis based on the formula (θ)·θ [where I = (θ) is the intensity of scattered light from a particle group, and θ is the scattering angle]. 2. A laser oscillator, an optical lens that condenses forward small angle scattered light from a group of microparticles to be measured irradiated with a laser beam, and a concentric silicon photodiode with at least three channels arranged at the focal point of the optical lens. An annular optical detector consisting of a photoelectric conversion element such as a photodetector, an amplifier of the same number as the number of channels of the optical detector that simultaneously amplifies minute current signals of each channel photoelectrically converted by the optical detector, and a current signal amplified by the amplifier. The amount of light energy received by each channel of the circuit that samples and holds each channel, the A/D converter that converts the current signal of each channel into a digital signal, and the optical detector that has been converted into a digital signal is expressed as I〓
(θ)・θ [In the formula I, (θ) is the intensity of scattered light from the particle group, and θ is the scattering angle]. Diameter measuring device. 3. The device for measuring the concentration and particle size of suspended particles according to item 2 above, further comprising a collimator lens for collimating the laser beam of the laser oscillator.