DE102009054594B4 - Device and method for determining the particle size and particle concentration of a flowing, particle-carrying gas - Google Patents

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

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

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.

From the US 2009 / 0 079 981 A1 A laser-based device and a laser-based method for measuring agglomerate concentrations and mean agglomerate sizes are known. The device described therein includes a light source, a focusing lens to form a sample volume, a first light sensor arranged at a first angular position relative to the light beam, and a second light sensor arranged 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 the scattered light measured by the first and second sensors.

The JP 2003 - 114 192 A Disclosing 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 tailpipe at an oblique angle to the gas flow direction near the exhaust outlet. The instrument further comprises a light receiver positioned on one side of the tailpipe opposite the projector, with the light-receiving surface of the receiver oriented in the opposite direction to the gas flow direction. The instrument receives the scattered light generated when particles in the exhaust gas are irradiated with the visible light projected by the light projector onto the inside of the tailpipe. The particles are measured based on the intensity signal of the scattered light thus received.

The document WO 99 / 37 383 A1 This 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 proposed as an example of an optical sensor.

The document US 2005 / 0 178 675 A1 Disclosure reveals 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 adapt the engine's operating conditions.

The document WO 2007 / 100 785 A2 This describes a nanoparticle sensor for detecting individual particles through 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.

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

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.

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

An inventive device for determining the particle size and particle concentration of a flowing gas carrying particles, in particular exhaust gas from an exhaust system of a motor vehicle, comprises a gas guide 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 guide 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 thus positioned at a specific angle relative to the emission direction of the polychromatic light source. The unit is arranged so that scattered light components from the considered section of the gas duct strike it. The particle size and particle concentration can be determined from the wavelength range intensities of the scattered light components from the considered section of the gas duct, which are simultaneously recorded by the color sensor/spectral analyzer.

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.

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.

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.

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.

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.

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.

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.

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.

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°.

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.

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.

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 using a color sensor or a spectral analyzer arranged at a specific angle relative to the emission direction of the polychromatic light source unit; and determining the particle size and particle concentration from the wavelength range intensities simultaneously detected by the color sensor/spectral analyzer.

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

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.

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.

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

• 1 zeigt eine Messprinzipskizze für die Ermittlung der Partikelkonzentration eines Abgases aus einem Abgasstrang eines Kraftfahrzeugs, gemäß einem Ausführungsbeispiel der Erfindung; und
• 2 zeigt eine Berechnungsprinzipskizze für die Ermittlung der mittleren Partikelgröße d und der Partikel-Konzentration c aus den von dem Farbmess-Lichtsensor gemäß 1 bestimmten Wellenlängenbereichen des Rot-Farbanteils, des Gelb-Farbanteils und des Blau-Farbanteils, gemäß einem Ausführungsbeispiel der Erfindung.

The invention is explained in more detail below with reference to an exemplary embodiment and the accompanying figures:

• 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
• 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 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.

1 Figure 2 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.

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. 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.

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.

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.

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.

To allow the polychromatic light beam 12 to strike the area under consideration of the exhaust gas flow line and the scattering The proportion of light that can reach the color measurement light sensor 18 is either surrounded by a transparent wall, in particular a glass wall, or it has no wall at this point.

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.

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.

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.

2 Figure 26 shows a calculation principle diagram 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.

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

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.

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.

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)).

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.

1. 1. die Winkelabhängigkeit (Φ)
2. 2. das Verhältnis Partikel-Größe zu Laser-Wellenlänge;
3. 3. Brechungsindex der Partikel (n)
4. 4. Abstand Partikel zu Sensor (R)

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. 1. the angular dependence (Φ)
2. 2. the ratio of particle size to laser wavelength;
3. 3. Refractive index of the particles (n)
4. 4. Distance of particles to sensor (R)

The formula for intensity according to this Rayleigh scattering is as follows: $$\begin{array}{l}I=I_0\cdot \frac{1+{\text{cos}}^2\Phi }{2R^2}\cdot {\left(\frac{n^2-1}{n^2+2}\right)}^2\cdot {\left(\frac{2\pi }{\lambda }\right)}^4\cdot {\left(\frac{d}{2}\right)}^6\\ \\ \left(1\right)\left(3\right)\left(2\right)\end{array}$$

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.

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.

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

Claims (9)

Method for determining the particle size and particle concentration of a flowing, particle-carrying gas, in particular a gas from an exhaust system of a motor vehicle, comprising the following steps: continuous passage of the gas through a Gas duct; irradiation of a region of the gas duct 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 region of the gas duct by a color sensor (18) or a spectral analyzer (18) arranged at a specific angle to the emission direction of the polychromatic light source unit (4); and determination of the particle size and/or the particle concentration from the intensities of the wavelength ranges simultaneously detected 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. Procedure 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). Procedure according to one of the Claims 1 until 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. Procedure according to Claim 3 , where 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)). Procedure according to Claim 3 or 4 , where 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)). Procedure according to one of the Claims 1 until 5 , whereby the precision of the measured values of the particle concentration measurement is improved with the help of information about the mean particle size. 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 for carrying out a method according to one of the Claims 1 until 6 is configured, comprising: a gas flow line; a polychromatic light source unit (4) arranged such that it is directed substantially perpendicularly to the direction of gas flow onto a region of the gas flow line and irradiates the volume of gas flowing in that region; and a color sensor (18) configured to detect several wavelength ranges simultaneously, or a spectral analyzer (18); wherein the color sensor/spectral analyzer (18) is arranged at a specific angle to the direction of emission of the polychromatic light source unit (4) such that scattered light components from the region of the gas flow line under consideration strike it; and wherein the particle size and particle concentration are determined from the intensities of the wavelength ranges of the scattered light components from the region of the gas flow line simultaneously detected by the color sensor/spectral analyzer (18). device 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°. device according to one of the 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 considered area of the gas guide line and/or wherein a light sink (16) for the non-deflected light component of the polychromatic light source unit (4) is provided behind the considered area of the gas guide line.