Device and method for determining the particle size and particle concentration of a flowing, particle-carrying gas

Abstract

Method for determining the particle size and particle concentration of a flowing gas carrying particles, in particular a gas from an exhaust system of a motor vehicle, comprising the following steps: Continuous passage of the gas through a gas guide line; irradiation of a region of the gas guide line by a polychromatic light source unit (4) arranged substantially perpendicular to the direction of gas flow; Simultaneous detection of intensities of several wavelength ranges of the scattered light components of the considered area of ​​the gas flow line by a color sensor (18) or a spectral analyzer (18) arranged at a specific angle relative to the emission direction of the polychromatic light source unit (4); and Determining the particle size and / or particle concentration from the wavelength range intensities simultaneously recorded by the color sensor / spectral analyzer (18), characterized in that the particle concentration is determined from the absolute intensity of the detected wavelength ranges and the particle size is determined from the ratio of the detected intensities of the wavelength ranges.

Description

[0001] The invention relates to a device and a method for determining the particle size and particle concentration of a flowing gas carrying particles, in particular an exhaust gas from an exhaust stream of a motor vehicle. State of the art

[0002] Periodic emissions testing of diesel vehicles currently requires a check of soot and particulate emissions. The opacimeters currently in use are not sensitive enough to detect the low concentrations of particulate matter and small particles produced by vehicles with diesel particulate filters.

[0003] US Patent 2009 / 0079981A1 discloses a laser-based device and a laser-based method for measuring agglomerate concentrations and mean agglomerate sizes. The device described therein includes a light source, a focusing lens to form a sample volume, a first light sensor positioned at a first angular position relative to the light beam, and a second light sensor positioned at a second angular position relative to the first direction of the light beam. The mean particle size and concentration are determined by using nearly invariant functions of a ratio of scattered light measured by the first and second sensors.

[0004] JP 2003-114192A discloses an instrument and a method for measuring granular material. The compact instrument is equipped with a light projector that projects visible light onto the exhaust gas flowing through the vehicle's exhaust pipe at an oblique angle to the gas flow direction near the exhaust outlet. This instrument further comprises a light receiver positioned on one side of the exhaust pipe opposite the projector, in a state where the light-receiving surface of the light receiver is oriented in the opposite direction to the gas flow direction. The instrument receives the scattered light generated when the particles contained in the exhaust gas are irradiated with the visible light projected by the light projector onto the inside of the exhaust pipe, by means of the light receiver.The particles are measured based on the intensity signal of the scattered light contained therein.

[0005] Document WO 99 / 37383A1 describes a system for monitoring airborne particles, consisting of an optical sensor for size determination and a humidity sensor for determining relative humidity, whereby a corrected value for the particle concentration is calculated from both measurements. A multi-wavelength nephelometer is suggested as an example of an optical sensor.

[0006] Document US 2005 / 0178675A1 discloses a sensor for the continuous measurement of the particle mass concentration in the exhaust gas of an internal combustion engine, comprising a signal electrode and a detector electrode. The sensor can also be coupled with a control system to adjust the engine's operating conditions.

[0007] Document WO 2007 / 100785A2 describes a nanoparticle sensor for detecting individual particles by interferometric detection of scattered, multicolored light. By analyzing the frequency dependence of the polarizability, it is possible to deduce the composition of the particle material.

[0008] The devices and methods described there are complex. Low particle concentrations and small particles in the exhaust gas are difficult to detect with them. Disclosure of the invention

[0009] It is therefore an object of the present invention to provide a cost-effective device and an associated method with which even small particle concentrations and even small particles contained in the exhaust gas can be reliably detected.

[0010] This problem is solved by the subject matter of the independent patent claims; advantageous developments result from the dependent claims.

[0011] An inventive device for determining the particle size and particle concentration of a flowing gas carrying particles, in particular exhaust gas from the exhaust system of a motor vehicle, comprises a gas line, a polychromatic light source unit arranged such that it is directed substantially perpendicularly to the direction of gas flow onto a region of the gas line and irradiates the gas volume flowing in that region, and a color sensor configured to simultaneously detect several wavelength ranges, or a spectral analyzer. The color sensor / spectral analyzer is arranged at a specific angle relative to the emission direction of the polychromatic light source unit such that scattered light components from the region of the gas line under consideration strike it.The particle size and particle concentration can be determined from the intensities of the wavelength ranges of the scattered light components of the considered area of ​​the gas flow line, which are simultaneously recorded by the color sensor / spectral analyzer.

[0012] The polychromatic light source unit can either be designed as a single polychromatic light source that emits polychromatic light, or it can be designed as a unit of several light sources that emit light with different wavelengths, e.g. 4-color LEDs.

[0013] According to one of the inventors' findings underlying the invention, the scattered light intensity at a given angle depends on the ratio of the wavelength to the particle size.

[0014] According to a fundamental principle of the invention, only a single color sensor or spectral analyzer is used, and this sensor is capable of simultaneously detecting at least two wavelengths. The particle size and particle concentration are then inferred from the intensity of the detected at least two wavelengths.

[0015] The device according to the invention is structurally simpler and less expensive to manufacture than conventional devices that require two light sensors. By separately analyzing several wavelength ranges of the scattered light components, even low particle concentrations and small particles contained in the exhaust gas can be reliably detected. The results obtained by the device according to the invention for particle concentration and particle size are highly informative.

[0016] According to the invention, the particle concentration can be determined from the absolute intensity of the detected wavelength ranges, and the particle size can be determined from the ratio of the detected intensities of the wavelength ranges.

[0017] Advantageously, when determining the particle size and particle concentration from the simultaneously recorded intensities of the wavelength ranges, the theory of Mie or Rayleigh scattering, known to those skilled in the art, can be used as a basis, which describes the intensity of the scattered light as a function of the intensity of the incoming polychromatic light beam, the number of particles, the ratio of wavelength to particle size and the observation angle of the color sensor / spectral analyzer.

[0018] According to a further embodiment of the invention, the wavelength ranges emitted by the polychromatic light source unit and detected by the color sensor / spectral analyzer can be the red, yellow, and blue ranges of visible light. The wavelength ranges emitted by the polychromatic light source unit and detected by the color sensor / spectral analyzer can also be the UV and IR ranges.

[0019] The mean particle size d can be determined according to a function that includes the intensities of the red, yellow, and blue regions of visible light. The particle concentration c can be determined according to a function that considers only the intensity of one wavelength range of visible light.

[0020] The fixed angle at which the color sensor / spectral analyzer is arranged in relation to the emission direction of the polychromatic light source unit can be in a range of 15 to 165°, in particular in a range of 30 to 75°.

[0021] According to a further embodiment of the invention, at least one focusing unit, in particular a focusing lens, is arranged in the light path between the polychromatic light source unit and the area of ​​the gas duct under consideration. This allows the polychromatic light beam to be directed precisely onto the area of ​​the gas duct under consideration.

[0022] According to a further embodiment of the invention, a light sink for the undeflected light component of the polychromatic light source unit is arranged behind the considered section of the gas duct. Such a light sink reliably prevents undesired reflection, interference, and scattering effects.

[0023] The invention also relates to a method for determining the particle size and particle concentration of a flowing gas carrying particles, in particular a gas from an exhaust system of a motor vehicle, comprising the following steps: Continuously passing the gas through a gas guide line; irradiating a region of the gas guide line with a polychromatic light source unit arranged substantially perpendicular to the direction of gas flow; simultaneously detecting intensities of several wavelength ranges of the scattered light components of the considered region of the gas guide line by a color sensor or a spectral analyzer arranged at a specific angle to the emission direction of the polychromatic light source unit; and determining the particle size and particle concentration from the intensities of the wavelength ranges simultaneously detected by the color sensor / spectral analyzer.

[0024] The particles in the gas under consideration may in particular be soot particles that were produced during combustion in the internal combustion engine.

[0025] This method is easy to perform and provides meaningful values ​​for particle size and particle concentration in the gas. Since only a color sensor or spectral analyzer is required, the measurement setup for this method is also simpler and more cost-effective.

[0026] The embodiments listed above with reference to the device according to the invention, and the advantages arising from each, are identical, in each case in a procedural configuration, in the method according to the invention for determining the particle size and particle concentration of a flowing gas carrying particles. To avoid repetition, these embodiments are not listed again with reference to the method.

[0027] The invention can also be described as scattered light measurement with polychromatic light for the detection of particle sizes in aerosols.

[0028] The invention is explained in more detail below with reference to an exemplary embodiment and the accompanying figures: Fig. Figure 1 shows a measurement principle diagram for determining the particle concentration of an exhaust gas from an exhaust stream of a motor vehicle, according to an embodiment of the invention; and Fig. Figure 2 shows a calculation principle sketch for determining the mean particle size d and the particle concentration c from the measurements taken by the color measurement light sensor according to Fig. 1 specific wavelength ranges of the red color component, the yellow color component and the blue color component, according to an embodiment of the invention.

[0029] Fig. Figure 1 shows a measurement principle diagram 2 for determining the particle concentration of an exhaust gas from an exhaust stream of a motor vehicle, according to an embodiment of the invention.

[0030] A polychromatic light source 4 is provided, which emits a polychromatic light beam 12 with a wavelength range of a red color component 6, a wavelength range of a yellow color component 8, and a wavelength range of a blue color component 10. The polychromatic light beam 12 strikes an exhaust gas particle sample 14 perpendicularly in a measuring chamber. The measuring chamber is an open arrangement through which exhaust gas flows continuously. The exhaust gas flows continuously in a direction perpendicular to the plane of the drawing. Fig. 1 through the measuring chamber, so that different particle samples are irradiated over time. The undeflected portion of the polychromatic light beam 12 then enters a light sink 16. Thus, the non-scattered portion of the polychromatic light beam 12 passes into the light sink 16, and unwanted reflection or interference effects due to backscattering can therefore be avoided.

[0031] Furthermore, a color measurement sensor 18 is provided, which is arranged relative to the measuring chamber 14 at a defined angle to the emission direction of the polychromatic light beam 12 from the polychromatic light source 4, which in this example is 60°. The color measurement sensor 18 is designed to simultaneously detect several wavelength ranges, in this case, in particular, the wavelength range of the red color component 20, the wavelength range of the yellow color component 22, and the wavelength range of the blue color component 24. The color measurement sensor 18 is arranged relative to the exhaust gas flow line such that it receives a scattered light component of the light scattered by the exhaust gas sample in the exhaust gas flow line and simultaneously detects several wavelength ranges of this scattered light.

[0032] The polychromatic light source 4 can, in particular, be a polychromatic white light source. Generally, the color measurement light sensor 18 used can be of the type commonly used for color measurement. In particular, such a color measurement light sensor can be designed to simultaneously determine the intensity of the spectral components for three or four color components separately.

[0033] As an alternative to providing a color measurement light sensor 18, a spectral analyzer can also be used, which could provide the entire color spectrum of the scattered light simultaneously at all wavelength ranges considered.

[0034] In order to allow the polychromatic light beam 12 to strike the area of ​​the exhaust gas flow pipe under consideration and for the scattered light component to reach the color measurement light sensor 18, the exhaust gas flow pipe in this area is either surrounded by a transparent wall, in particular a glass wall, or it has no wall at this point.

[0035] According to one of the inventors' findings underlying the invention, the scattered light intensity at a given angle depends not only on the intensity of the polychromatic light beam 12 and the particle concentration 14, but also on the ratio of the wavelength to the particle size.

[0036] Since the intensities of the color components of the red color component 6, the yellow color component 8 and the blue color component 10 are determined simultaneously in the present measurement principle diagram 2, the particle size can be determined from this information.

[0037] Furthermore, an evaluation and control unit can be provided, which is connected to the polychromatic light source 4 and the color measurement light sensor 18.

[0038] Fig. Figure 2 shows a calculation principle sketch 26 for determining the mean particle size d and the particle concentration c from the wavelength ranges of the red color component 20, the yellow color component 22 and the blue color component 24 determined by the color measurement light sensor 18.

[0039] This calculation is preferably performed in an evaluation unit not shown in the figures.

[0040] According to the invention, for a fixed observation angle and a given particle size distribution, the dependence of the signals at different wavelengths is observed.

[0041] The signals of the red color component 20, the yellow color component 22 and the blue color component 24 received by the color measurement light sensor 18 are different with respect to the particle distribution of the exhaust gas particle sample 14 in the measuring chamber, because the ratio of the wavelength to the mean particle size is different for these three color components.

[0042] From the ratio of the three intensity signals I(S1) for the red color component 20, I(S2) for the yellow color component 22 and I(S3) for the blue color component 24, the mean particle size d can be determined according to the calculation function d = f(I(S1), I(S2), I(S3)).

[0043] The particle concentration c [mg / m³], i.e., the number of particles per volume, can be determined from the absolute intensity of the individual output signals of the color measurement light sensor 18. This is illustrated using the calculation function c = g(I(S3)) as an example for the intensity signal I(S3) of the blue color component 24, as generated by the color measurement light sensor 18.

[0044] For this purpose, the theories of Rayleigh and Mie are used. Rayleigh scattering describes the behavior for very small particles (d << λ) and it obtains terms for: 1. the angular dependence (Φ) 2. the ratio of particle size to laser wavelength; 3. Refractive index of the particles (n) 4. Distance of particles to sensor (R)

[0045] The formula for intensity according to this Rayleigh scattering is as follows: I=I0⋅1+cos2Φ2R2⋅(n2−1n2+2)2⋅(2πλ)4⋅(d2)6 (1) (3) (2)

[0046] Before carrying out the method according to the invention, the gas guide line of the measuring chamber (not shown) is connected to an exhaust system, in particular to an exhaust tailpipe of a motor vehicle, and the internal combustion engine of the motor vehicle, in particular a diesel engine, is then operated so that exhaust gas from the exhaust system of the motor vehicle flows through the gas guide line. This is known to those skilled in the art and need not be described further here.

[0047] The particle concentration can now be determined from the absolute intensity of the detected wavelength ranges recorded by the color measurement sensor 18, and the particle size can now be determined from the ratio of the intensities of the wavelength ranges recorded by the color measurement sensor 18.

[0048] Information about particle size can optionally be used to improve the accuracy of particle concentration measurement.

Claims

[1] Method for determining the particle size and particle concentration of a flowing gas carrying particles, in particular a gas from an exhaust system of a motor vehicle, comprising the following steps: Continuous passage of the gas through a gas guide line; irradiation of a region of the gas guide line by a polychromatic light source unit (4) arranged substantially perpendicular to the direction of gas flow; Simultaneous detection of intensities of several wavelength ranges of the scattered light components of the considered area of ​​the gas flow line by a color sensor (18) or a spectral analyzer (18) arranged at a specific angle relative to the emission direction of the polychromatic light source unit (4); and Determining the particle size and / or particle concentration from the wavelength range intensities simultaneously recorded by the color sensor / spectral analyzer (18), characterized by , that the particle concentration is determined from the absolute intensity of the detected wavelength ranges and the particle size is determined from the ratio of the detected intensities of the wavelength ranges. [2] Method according to claim 1, wherein the determination of the particle size and / or the particle concentration from the simultaneously recorded intensities of the wavelength ranges is based on the theory of Mie or Rayleigh scattering, which describes the intensity of the scattered light as a function of the intensity of the incoming polychromatic light beam, the number of particles, the ratio of wavelength to particle size and the observation angle of the color sensor / spectral analyzer (18). [3] Method according to one of claims 1 to 2, wherein the wavelength ranges emitted by the polychromatic light source unit (4) and detected by the color sensor / spectral analyzer (18) are the red range, the yellow range and the blue range of visible light. [4] Method according to claim 3, wherein the mean particle size d is determined according to a function which includes the intensities of the red, yellow and blue ranges of visible light (d = f(I(S1), I(S2), I(S3)). [5] Method according to claim 3 or 4, wherein the particle concentration c is determined according to a function which considers only the intensity of one wavelength range of visible light (c = g(I(S3)). [6] Method according to any one of claims 1 to 5, wherein the precision of the measured values ​​of the particle concentration measurement is improved by means of information about the mean particle size. [7] Device for determining the particle size and particle concentration of a flowing gas carrying particles, in particular an exhaust gas from an exhaust stream of a motor vehicle, wherein the device is configured to carry out a method according to one of claims 1 to 6, comprising: a gas pipeline; a polychromatic light source unit (4) arranged such that it is substantially perpendicular to the direction of gas flow, is directed at a section of the gas pipeline and irradiates the volume of gas flowing in that section; and a color sensor (18) designed to detect several wavelength ranges simultaneously, or a spectral analyzer (18); wherein the color sensor / spectral analyzer (18) is arranged at a specific angle relative to the emission direction of the polychromatic light source unit (4) such that scattered light components from the area under consideration in the gas flow line strike it; and wherein the particle size and particle concentration are determined from the intensities of the wavelength ranges of the scattered light components of the considered area of ​​the gas supply line, which are simultaneously recorded by the color sensor / spectral analyzer (18). [8] Device of claim 7, wherein the angle at which the color sensor / spectral analyzer (18) is arranged in relation to the emission direction of the polychromatic light source unit (4) is in a range of 15 to 165°, in particular in a range of 30 to 75°. [9] Device according to one of claims 7 or 8, wherein at least one focusing unit is arranged in the light path between the polychromatic light source unit (4) and the area of ​​the gas guide line under consideration and / or wherein a light sink (16) for the non-deflected light component of the polychromatic light source unit (4) is provided behind the area of ​​the gas guide line under consideration.

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