DEVICE AND METHOD FOR DETERMINING THE CONCENTRATION OF A SUBSTANCE IN A MEASURING VOLUME

Description

[0001] The present invention relates to a device for determining the concentration of at least one gaseous or solid substance in at least one measuring volume at a stationary measuring point, wherein at least one measuring unit is provided to emit a light beam with a predetermined light intensity through the measuring volume, and at least one detector is provided to detect the light beam after it has passed through the measuring volume, wherein the at least one detector is designed to determine a decrease in the light intensity due to the at least one gaseous or solid substance in the measuring volume.

[0002] The invention further relates to a corresponding method for determining the concentration of at least one gaseous or solid substance in an exhaust gas cloud in at least one measuring volume.

[0003] Emissions of substances in exhaust gases, especially from private transport, are a much-discussed topic due to the increasing number of vehicles, not only as a result of global warming, but also due to the health risks posed to humans by nitrogen oxides, partially combusted fuel components, and particulate matter. Developments in recent decades have aimed, on the one hand, to prevent the emission of partially combusted compounds through the mandatory installation of catalytic converters in gasoline engines, and, on the other hand, to prevent the emission of nitrogen oxides through catalytic converters in diesel engines. The permissible levels of emitted substances are often determined by national and supranational standards.

[0004] Nevertheless, there are still vehicles in public use today that, although they met the legal standards for emissions reduction at the time of their registration, are considered high emitters when used over an extended period. The reasons for this can be, for example, the failure to retrofit a catalytic converter or a lack of maintenance, such as when a diesel catalyst is neglected to refill the urea, which prevents the proper functioning of an SCR (selective catalytic reduction) catalyst. Among other things, this can also be due to a lack of knowledge regarding the (non-)functionality of these components while driving.

[0005] Exhaust gas measurements are largely limited to systems that measure substances in the exhaust gases, such as gaseous substances or particles, within the vehicle itself, for example, in or after the exhaust. However, these systems are limited to a small number of test vehicles and therefore cannot provide a representative picture of a large number of different vehicles in real-life operation. Exhaust gas measurements during regular vehicle inspections in a workshop are equally unrepresentative, because such inspections are only performed at long intervals. Therefore, attempts are being made to enable exhaust gas measurements of vehicles in real-life operation in public spaces. This so-called "remote sensing," also in the sense of "real driving emissions" (RDE) measurements, is carried out at a stationary measuring point and can, for example, be installed on advantageously pre-installed infrastructure, such as toll booths, streetlights, bridges, or even building facades in the city, etc.This could, for example, be used to notify owners of vehicles with high emissions and / or to stipulate mandatory maintenance. However, the device must be set up at a suitable measuring point to obtain representative results. In general, intersections with traffic lights, which could potentially cause vehicles to come to a standstill, should be avoided. Furthermore, it has been shown that a slight incline in the road at the measuring point is suitable for generating a positive engine load.

[0006] Remote sensing often involves using a light source that emits a characteristic wavelength or wavelength range(s) to detect a gaseous substance, such as carbon monoxide or nitrogen oxides. A detector enables, for example, a measurement of the attenuation of the light emitted by the exhaust plume. Such a concentration determination using absorption spectroscopy is known from US 4,924,095 A. US 4,924,095 A describes an analytical device for monitoring exhaust emissions from motor vehicles at a stationary measuring point. A planar arrangement of gas analyzers with corresponding radiation sources and detectors measure the change in intensity of rays of specific wavelengths as they pass through a cross-section of an exhaust plume in order to determine the concentration of pollutants in the exhaust gas. A three-dimensional matrix of rays is positioned so that the exhaust plume passes through the matrix.The arrangement can determine a relative change in the quantity of pollutants per unit volume emitted by a motor vehicle passing the arrangement.

[0007] However, it may also be intended to measure particles, such as soot particles, as a substance. This can be achieved, for example, using light scattering or by measuring the attenuation of the reflected beam in relation to the incident light. However, the reliable measurement of such substances in exhaust clouds can lead to various difficulties. On the one hand, the emissions of substances from different engines or other energy systems, such as fuel cells, are always different and must be measurable with the same system. Furthermore, the concentration range to be measured varies greatly and depends on the vehicle class being measured (e.g. truck vs. motorcycle). Low concentrations in particular cause problems during evaluation. Differences in the operating temperature of an engine can also lead to differences in the substances to be measured.

[0008] Although this method can be used to determine absorption values, these are difficult or even impossible to compare due to the aforementioned differences. In particular, it cannot be used to determine the concentration of a gaseous or solid substance in the exhaust plume.

[0009] State-of-the-art systems available today detect gaseous or solid substances as optical mass (OM), which can usually be related to a constant reference concentration of a second substance in the exhaust cloud, for example carbon dioxide

[0010] (CO2). Such a reference value can provide representative values for some exhaust clouds. For example, such a reference value can be used for exhaust clouds from gasoline internal combustion engines to reliably determine different OMs of different substances in the exhaust clouds. If, for example, the absorption of a substance differs in different exhaust clouds, the absorption of the reference value is proportional and can be put into relation. Consequently, the concentration of the substance can be calculated back using the known concentration of the reference value and the absorption of the reference value. This type of calculation can work relatively reliably for gasoline internal combustion engines because the concentration value is relatively constant due to stoichiometric combustion.However, this type of concentration calculation cannot be used for diesel-powered vehicles, as the non-stoichiometric combustion process can result in significant fluctuations in the reference concentration, such as CO2 concentration. This approach is therefore unreliable.

[0011] CN 103712929 A1 describes a system for locating and measuring an exhaust cloud using an optical camera, an infrared camera, and a spectroscopic unit. The optical camera measures the vehicle speed and determines the license plate number. The infrared camera locates the position of the exhaust cloud, and the spectroscopic measuring unit is aligned to measure the exhaust cloud. While the disclosure improves the localization of the exhaust cloud, it does not allow for the determination of the concentration value of an exhaust gas component.

[0012] EP 3 789 755 discloses a method for measuring exhaust clouds using multispectral analysis with a plurality of infrared cameras. The IR cameras are arranged above or next to the road and, using suitable filters, can measure, for example, carbon monoxide and / or carbon dioxide. This arrangement has the disadvantage that no spectroscopic analysis is used, thus limiting the ability to measure exhaust components. Furthermore, such methods have very low sensitivities and are also unable to directly measure absolute concentrations.

[0013] The present invention is defined in claims 1 and 14.

[0014] It is an object of the present invention to enable reliable concentration measurements of a gaseous or solid substance in a measuring volume during a remote sensing measurement.

[0015] This object is achieved according to the invention by a device mentioned at the outset in that an image unit is provided in the device in order to record at least a part of the exhaust gas cloud in the measuring volume when an exhaust gas cloud is partially or completely present, that an evaluation unit is provided in the device in order to determine a total passage distance of the light beam through the exhaust gas cloud in the measuring volume from at least one recorded image of at least a part of the exhaust gas cloud, and that the evaluation unit is provided to determine a concentration of the gaseous or solid substance in the measuring volume from the determined decrease in light intensity and the total passage distance.

[0016] The inventive concentration determination based on the total distance the light beam travels through an exhaust cloud in the measurement volume and on a determined decrease in the light beam's light intensity due to the presence of at least one gaseous or solid substance allows the concentration of the substance to be determined directly, reliably, and accurately. This determination of the concentration is also independent of the size or composition of the exhaust cloud.

[0017] In an advantageous embodiment, the at least one measuring unit is arranged at a distance from at least one first reflecting unit, wherein the measuring volume is formed between the at least one measuring unit and the at least one first reflecting unit and the at least one measuring unit is provided to emit a light beam in the direction of the at least one reflecting unit, and wherein the at least one first reflecting unit is provided to reflect the light beam after passing through the measuring volume and send it to at least one detector. Such a configuration can simplify the arrangement of the detector in the device because the detector no longer necessarily has to be arranged opposite the measuring unit. This makes the use of the device more flexible. It is particularly advantageous if the light beam reflected by the reflecting unit penetrates the measuring volume at least once more before reaching the detector.Due to the two-fold passage of the light beam through the measuring volume, the sensitivity of the concentration measurement can be increased and lower concentrations of the gaseous or solid substance can be measured.

[0018] Advantageously, the total passage distance is the sum of the partial passage distances of all passages of the light beam through the exhaust cloud.

[0019] In one variant of the invention, a multiplexer unit is provided in the measuring unit, which generates a plurality of light beams. The measuring unit emits the plurality of light beams at different locations throughout the measuring volume, and at least one detector detects each of the plurality of light beams, preferably after reflection by a reflecting unit. This allows a spatially resolved concentration measurement in the measuring volume to be achieved in a simple manner. This allows the concentration of the gaseous or solid substance to be determined at various locations within an exhaust cloud within the measuring volume.

[0020] If at least two of the plurality of light beams in the measuring unit are each guided via an optical path, wherein preferably the optical paths have at least partially different optical path lengths, the detection of these light beams at a detector can be simplified because the light beams arrive at the detector with a time delay due to the resulting different travel times.

[0021] To achieve a two-dimensional resolution of the measurement volume, in one variant of the invention, the measuring unit emits at least a first light beam of the plurality of light beams in a first direction through the measurement volume, and the measuring unit emits a second light beam of the plurality of light beams in a second direction through the measurement volume, wherein the first direction differs from the second direction. This allows the concentration of the gaseous or solid substance to be measured in different dimensions. When combined with a spatially resolved concentration measurement, a very precise reconstruction of a concentration distribution in the exhaust cloud is possible.

[0022] The number of times the light beam passes through the measuring volume can be further increased if the device is provided with a second reflection unit which is arranged at a distance from and opposite the at least one first reflection unit and the measuring unit emits the light beam at an angle deviating from a normal to a first reflection plane of the first reflection unit, wherein the first reflection unit reflects the light beam emitted by the measuring unit to the opposite second reflection unit and the opposite second reflection unit reflects the light beam back to the first reflection unit, wherein the at least one detector is provided to detect the light beam after a plurality of such reflections. The angle of the light beam can be adjustable particularly advantageously in order to be able to select and adjust the number of reflections depending on the application.In such a variant, a positioning optical unit is provided in the measuring unit with which the angle of the light beam can be adjusted.

[0023] The device can also contain multiple measuring units, with at least two of the measuring units emitting a light beam through different measuring volumes. In another variant, the device can contain multiple measuring units, with at least two of the measuring units emitting a light beam in different directions through the same measuring volume. This allows the device to be very flexibly and easily adapted to different applications.

[0024] Preferably, the imaging unit comprises at least one camera and / or at least one lidar unit.

[0025] To protect sensitive mirror units from dirt or damage, a replaceable protective film is advantageously applied over the mirror unit. This can reduce the necessary maintenance intervals.

[0026] The object of the invention is also achieved by a method mentioned at the outset, in which the at least one measuring unit emits a light beam with a predetermined light intensity through the exhaust gas cloud in the measuring volume, the light beam is detected by a detector after passing through the exhaust gas cloud and the detector determines a decrease in the light intensity of the light beam due to the at least one gaseous or solid substance, wherein according to the invention at least part of the exhaust gas cloud in the measuring volume is recorded by an image unit and a total passage distance of the light beam through the exhaust gas cloud in the measuring volume is determined from the recorded image of the at least part of the exhaust gas cloud, and that a concentration of the gaseous or solid substance in the measuring volume is determined from the determined decrease in light intensity and the total passage distance.

[0027] The present invention is described below with reference to the Figuren 1 bis 6 which show exemplary, schematic and non-limiting advantageous embodiments of the invention. Fig.1 the principle of remote exhaust gas measurement (remote sensing), Fig.2 an embodiment of the concentration determination in an exhaust gas cloud according to the invention, Fig.3 an advantageous embodiment of a measuring unit, Fig.4 an embodiment of the device with a lidar unit as an image unit, Fig.5 an embodiment of the device with a multiple passage of the light beam through the exhaust cloud, and Fig.6 an embodiment for the protection of a mirroring unit.

[0028] Fig. 1 shows a device 1 according to the prior art for measuring a gaseous or solid substance in an exhaust cloud 9 emitted by an emission source, such as a vehicle in a public space. A wide variety of gaseous and solid (e.g. particle) components can occur in the exhaust cloud 9. The substances in the exhaust cloud 9 can originate from any type of emission source, for example on a surface 7, for example from a vehicle such as a passenger car (PC), a truck (HGV), but also a single-track vehicle such as a motorcycle, moped and the like, which have an internal combustion engine. Emissions from another emission source, such as fuel cells, which generally only emit water vapor and no pollutants, can also be measured using such a device 1.The detection of such emission sources can be helpful, for example, in determining the proportion of vehicles with low or high emission values in road traffic. The measurement can be taken on a surface 7, for example, a road, advantageously at a certain distance above a surface 7. However, it is also conceivable for the device 1 to be arranged to the side of an exhaust cloud 9 and the measurement to be taken parallel to a surface 7, or the device 1 can be built into the surface 7 itself. Combinations of measurements from multiple sides are also conceivable.

[0029] The device 1 can also measure an exhaust cloud 9, for example, at other locations away from a surface 7. It is conceivable that the device 1 measures an exhaust cloud 9 from an aircraft during takeoff or landing on a runway at an airport. It is also conceivable that an exhaust cloud 9 from a ship is measured, for example, in a harbor basin or in a lock.

[0030] In addition to the automotive industry, other applications involving exhaust clouds 9 containing gaseous or solid substances are also conceivable, for example, in the process industry. For example, emissions can be measured in chimneys that can have diameters of several meters. The measurement volume VM would be located within the chimney.

[0031] The invention is not limited to the above-mentioned applications; rather, all possible uses that are apparent to a person skilled in the art are conceivable. However, the exhaust cloud 9 does not necessarily have to originate from a vehicle; in principle, it can originate from any emission source. One example is an exhaust cloud from an industrial process, for example, emitted from a chimney.

[0032] The substances in an exhaust cloud 9 can be gaseous substances such as carbon dioxide (CO 2 ), carbon monoxide (CO), nitrogen oxides (NO X ), sulfur dioxide (SO 2 ), gaseous polycyclic aromatic hydrocarbons (PAHs) and the like. However, it is also conceivable to measure solid substances in an exhaust cloud 9, such as soot particles. The substances and their concentrations in the exhaust cloud 9 of a vehicle usually depend on the type of fuel, the combustion engine, the operating state of the combustion engine, and the status of a catalytic converter or exhaust gas aftertreatment system (if present). For example, an internal combustion engine that has not yet reached operating temperature often emits a higher concentration of partially burned substances, such as polycyclic aromatic hydrocarbons, than at normal operating temperature. Likewise, different substances are emitted under different operating conditions (e.g. given by the current speed and current torque).

[0033] According to the invention, the concentration of such a gaseous or solid substance in the exhaust cloud 9 is to be measured.

[0034] Depending on the arrangement of the measuring unit 4 of the device 1, a light beam 6 can penetrate the exhaust cloud 9 over different distances x. The light beam 6 is detected and evaluated in a detector 3 after passing through the exhaust cloud 9. For example, with different arrangements, as in Fig. 1 Given, the passage distance x of the light beam 6, which is normal to the surface 7, may be different from the other passage distance x' of another light beam 6, which runs parallel to the surface 7, and may therefore depend on the arrangement of the measuring units 4, 4' relative to the exhaust cloud 9. This may lead to different measurement results for the substance in the exhaust cloud 9 for a nominally identical concentration of a substance, because absorption is generally higher for a longer passage distance x, x'.

[0035] Fig. 2 shows an embodiment of the device 1 according to the invention, with which a concentration of a gaseous or solid substance in an exhaust cloud 9 can be reliably measured. In this embodiment, the device 1 is provided with at least one light source 2 that generates light with a predetermined light intensity. The light source 2 can, for example, emit monochromatic light, for example a laser light that has a defined wavelength with a predetermined light intensity. In particular, quantum cascade lasers (QCL) can be used, but other types and combinations of light sources and lasers are also conceivable in order to cover different wavelength ranges. It is also conceivable for the light source 2 to have a polychromatically emitting lamp, such as a lamp in the ultraviolet (UV) or infrared (IR) range. A monochromator in the light source 2 is also conceivable in order to specifically select wavelengths.The light source 2 generates a primary light beam 17 with a specific light intensity and at least one wavelength. The primary light beam 17 can be guided to at least one measuring unit 4, for example, via a light guide, such as a fiber optic cable, a mirror system, or another suitable optical system. However, the light source 2 can also be integrated into the measuring unit 4 and generate the primary light beam 17 in the measuring unit 4.

[0036] The measuring unit 4 generates a light beam 6 with at least one defined wavelength and a defined light intensity I from the primary light beam 17 of the light source 2, which light beam is emitted by the measuring unit 4. Preferably, the wavelength and the light intensity I of the light beam 6 correspond to the wavelength and the light intensity of the primary light beam 17. However, the measuring unit can also change the light properties of the primary light beam 17 (e.g., wavelength or light intensity), for example, by means of a monochromator or a beam splitter, in order to generate the light beam 6. The light beam 6 can also be generated in a pulsed manner, e.g., in the form of individual light packets.

[0037] To perform the concentration measurement, the measuring unit 4 emits the light beam 6 directly or indirectly toward the measuring volume VM, so that the light beam 6 penetrates the measuring volume VM and a partially or completely contained exhaust gas cloud 9. After passing through the exhaust gas cloud 9 in the measuring volume VM, the light beam 6 is detected by a detector 3.

[0038] In the embodiment of the invention according to Fig.2 The measuring unit 4 is arranged at a distance L from a reflection unit 8 having a reflection plane 8.1, for example on the surface 7. The reflection plane 8.1 of the reflection unit 8 is arranged facing the measuring unit 4. The measuring volume VM is formed between the measuring unit 4 and the reflection unit 8, in which volume an exhaust gas cloud 9 to be measured can be partially or completely located when the device 1 is used as intended. An incident light beam is reflected at the reflection unit 8, or at the reflection plane 8.1.

[0039] The distance L can depend on the application, for example, on the number of passing vehicles, but also on the direction of the measurement. For example, the distance L can be shorter if a measurement is taken parallel to surface 7 and longer if the measurement is taken perpendicular to surface 7. In any case, the distance L can be selected to suit the application.

[0040] The orientation and alignment of the reflecting unit 8 can be chosen arbitrarily and application-specifically. For example, the reflecting unit 8 can be mounted parallel to the plane of the surface 7, perpendicular to the plane of the surface 7, or at any angle to the plane of the surface 7. Advantageously, the reflecting unit 8 can also be integrated into a surface 7 and protected from damage and contamination, for example, by vehicles driving over the surface 7, by means of a suitable coating or a structure.

[0041] The arrangement of the reflection unit 8 and the orientation of the light beam 6 emitted by the measuring unit 4 are in any case selected such that the light beam 6 penetrates the measuring volume VM and impinges on the reflection unit 8. However, the light beam 6 does not have to be directed directly at the reflection unit 8, but can also be directed toward the reflection unit 8 via an optical system, for example, a mirror arrangement.

[0042] The exact dimensions of the measuring volume VM can be specified or selected by a user and, for example, depend on the expected extent of an exhaust cloud 9. The measuring volume VM can, for example, also be selected to be smaller than an expected exhaust cloud 9 in order to prevent the measurement of mixtures of different exhaust clouds 9 from different emission sources in a measuring volume VM.

[0043] To carry out the concentration measurement with a device 1 in the embodiment according to Fig.2 the measuring unit 4 emits the light beam 6 directly or indirectly in the direction of the reflecting unit 8. The emitted light beam 6 penetrates the measuring volume VM and is reflected by the reflecting unit 8. The reflected light beam 6 is guided to at least one detector 3, which detects the reflected light beam 6. The reflected light beam 6 can penetrate the measuring volume VM a second time, depending on the design of the reflection. The light beam 6 thus penetrates the measuring volume VM and an exhaust gas cloud 9 partially or completely located therein at least once. Preferably, the reflected light beam 6 is reflected by the reflecting unit 8 in such a way that the reflected light beam 6 also penetrates the measuring volume VM and an exhaust gas cloud 9 located therein.By repeatedly penetrating the exhaust gas cloud 9 with the light beam 6, the sensitivity of the concentration measurement can be increased because the light is influenced several times along the beam path by the gaseous or solid substances in the measuring volume VM and thus clearer measurement signals are possible.

[0044] The detector 3 can be arranged in close proximity to the light source 2, for example in a common housing with the light source 2, but it can also be arranged, for example, in the measuring unit 4 or at any other location of the device 1. In the device 1 according to Fig.2 the detector 3 is installed with the light source 2 in a housing and the reflected light beam 6 is guided along the same optical path as the primary light beam 17.

[0045] According to the invention, the detector 3 measures an attenuation of the light intensity I of the detected light beam 6 due to a gaseous or solid substance in the measuring volume VM . This attenuation of the light intensity I can be related to a reference measurement which is carried out in the absence of substances in the measuring volume VM and leads to a reference light intensity I 0 . This can be used to calculate, for example, an absorption 1-(I / I 0 ), referred to as A for short, or transmission I / I 0 of a specific wavelength, or even several different wavelengths. The transmission and absorption A can be converted into one another and can be considered equivalent.

[0046] For solid substances in the measurement volume VM, a loss of light intensity can be caused by light scattering, such as forward or side scattering. Detector 3 can, for example, also detect light scattering from solid particles in the measurement volume VM and thus measure a decrease in light intensity due to scattering. This also allows the size of solid particles in detector 3 to be estimated. It is also possible to record a spectrum across different wavelengths and perform a spectroscopic evaluation, for example, in the form of multivariate analyses or fingerprinting of a substance. This allows several different substances to be measured simultaneously. This can also be achieved using suitable optical filters or monochromators.

[0047] The decrease in light intensity I of the light beam 6 detected by the detector 3 depends on the total distance x of the light beam 6 passing through an exhaust cloud 9 in the measuring volume VM and can also vary depending on the arrangement of the measuring unit 4 and / or the reflection unit 8. Different sizes of the exhaust cloud 9, depending on the vehicle, can also lead to different measured values at the detector 3.

[0048] The measurement of the absorption of a gaseous or solid substance is known to be frequency-dependent and should therefore take place at or near the absorption maximum to obtain a reliable result. For example, CO2 has characteristic vibrational oscillations at a wavenumber (inverse of the wavelength) of 1388 cm -1 (asymmetric stretching vibration) and at 667 cm -1 (bending vibration). According to Lambert-Beer's law, the absorption A depends on the total distance x, the concentration c, and an absorption coefficient k (as a known material parameter). This relationship can be expressed using the formula ln I I 0 = k * x * c be specified. In order to determine a reliable concentration c of a substance, knowledge of the total passage distance x and the absorption A is required. Absorption A (or equivalently a decrease in light intensity) can be determined via detector 3. However, the total passage distance x depends on the extent of the exhaust cloud 9 in the measuring volume VM and the beam path of the light through the exhaust cloud 9 and is usually not known.

[0049] For reliable concentration measurement of a wide variety of exhaust clouds 9, it is therefore advantageous to have knowledge of the total distance x of the light passing through the exhaust cloud 9, as this eliminates the need to resort to the calculation using an optical mass mentioned above with the limitations mentioned above. The total distance x depends on the beam path of the light beam 6 and thus on how often and at which point the light beam 6 penetrates the exhaust cloud 9.

[0050] To record the total passage distance x, an imaging unit 29 is provided in the device 1 according to the invention in order to record at least a portion of the measuring volume VM, preferably from different directions (e.g. angles ω, β). The imaging unit 29 generates at least one image of a portion of an exhaust gas cloud 9 in the measuring volume VM, preferably a plurality of images from different directions, which is processed in an evaluation unit 11. The evaluation unit 11 can then determine the total passage distance x of the light beam 6 through the exhaust gas cloud 9 from the at least one image obtained. For this purpose, the evaluation unit 11 can reconstruct at least a portion of an image of an exhaust gas cloud 9 in the measuring volume VM.From the image of the part of the exhaust cloud 9, the total passage distance x through the exhaust cloud 9 can be determined using the known beam path of the light (which is determined by the arrangement of the reflection unit 8 and the orientation of the light beam 6) through the measuring volume VM.

[0051] The total passage distance x includes at least the partial passage distance x1 of the light beam 6 through the exhaust cloud 9. If the light beam 6 is reflected and directed again through the exhaust cloud 9, then the partial passage distance x2 of the reflected light beam 6 is added. The total passage distance x is thus the sum of the individual partial passage distances of the light beam 6 through the exhaust cloud 9.

[0052] For example, based on the known dimensions of the measuring volume VM, the dimensions of at least one reconstructed part of the exhaust gas cloud 9 in the measuring volume VM and thus a partial passage distance x1, x2 can be calculated back.

[0053] In an arrangement as in Fig.2 , in which the light beam 6 is directed essentially perpendicular to the reflection plane 8.1 of the reflection unit 8, the partial passage distances x1, x2 of the emitted light beam 6 and the reflected light beam 6 are equal because the light beam 6 is reflected in the opposite direction. It may therefore be sufficient to determine only the partial passage distance x1 of the emitted light beam 6 or the partial passage distance x2 of the reflected light beam 6 and to double this to obtain the total passage distance x.

[0054] To determine the partial passage distances x1, x2, or the total passage distance x derived therefrom, a 2D projection of the exhaust cloud 9 in the plane of the light beam 6 and / or the reflected light beam 6 can be generated from the images recorded with the imaging unit 29, and the partial passage distances x1, x2 can thus be determined directly. Advantageously, the evaluation unit 11 creates a spatial reconstruction of the exhaust cloud 9, which requires images of the exhaust cloud 9 from different directions. This reconstruction can, for example, also be dependent on a control variable, such as time. For example, a time-dependent expansion of an exhaust cloud 9 can be determined.

[0055] In an advantageous embodiment, the evaluation unit 11 can receive data on outside temperature and humidity. Depending on the outside temperature and humidity, differences may occur in the evaluation and reconstruction of an exhaust gas cloud 9. For example, temperature differences between the environment and the exhaust gas cloud 9 are less pronounced in summer than in winter. This can lead to a determined partial passage distance x1, x2 exhibiting seasonal differences. To avoid or at least limit this source of error, a correction factor can be provided for calculating the reconstruction depending on the outside temperature and humidity. This allows the evaluation unit 11 to perform a more reliable calculation of the total passage distance x, regardless of the ambient conditions.

[0056] The evaluation unit 11, typically a computer with appropriate evaluation software, can also receive data on the absorption A (or the light intensity of the detected light beam 6) from at least one detector 3. A reference light intensity I0 can be stored in the evaluation unit 11 and can be assumed to be known. The evaluation unit 11 uses the total passage distance x and the decrease in light intensity, or an absorption A, to determine the concentration c of a gaseous or solid substance, for example, according to the Lambert-Beer law mentioned above. In an advantageous embodiment, different absorptions A at different wavelengths of the light beam 6 can also be used to determine concentrations c of different gaseous or solid substances. This can be done sequentially at one wavelength each or in the form of a spectroscopic evaluation at several wavelengths simultaneously.

[0057] The image unit 29 can be in the form of at least one camera 5, preferably several cameras 5 (as in Fig.2 shown). A design of the imaging unit 29 with one or more lidar units, one or more radar units, or combinations of such units or with cameras is also conceivable. In addition, other designs of an imaging unit 29 are possible.

[0058] The imaging unit 29, for example, the at least one camera 5, can be arranged, for example, on the measuring unit 4. In one variant, the imaging unit 29 is installed on a separate device, or existing infrastructure in the area of the device 1, such as bridges, houses, streetlights, or the like, is used for the arrangement. With a plurality of measurement volumes VM, the imaging unit 29 can also be arranged such that it can, for example, capture several measurement volumes VM simultaneously. This allows the number of required imaging units 29 to be kept to a minimum.

[0059] In one embodiment of the imaging unit 29 with multiple cameras 5, these are installed at different locations to capture the measurement volume VM from different directions ω, β. By capturing the measurement volume VM from different directions, the reconstruction of the exhaust cloud 9 can be facilitated or improved.

[0060] The at least one camera 5 can capture images of the measurement volume VM and thus also capture an exhaust cloud 9 present in the measurement volume VM. However, it is also possible for the camera 5 to additionally record metadata of a vehicle, such as size, type, or license plate number. When using a camera 5 as the imaging unit 29, available image processing software can be used, for example, to reconstruct the exhaust cloud 9 or a portion thereof from the images.

[0061] The at least one camera 5 can, for example, be an infrared camera that captures thermal images of the existing exhaust cloud in the measurement volume VM. This also allows the heat distribution in the exhaust cloud 9 to be recorded, which can influence the gaseous or solid substances or the absorption coefficient k. Temperature differences can lead to convection and diffusion phenomena that cause substances to be distributed over time. Individual concentrations c of substances can also be temperature-dependent, since some reactions only occur at higher temperatures or are temperature-dependent.

[0062] However, the at least one camera 5 can also operate, for example, in the ultraviolet (UV) or visible (VIS) range, or even in both ranges (UV / VIS cameras). UV or VIS is higher-energy radiation than IR and excites electron transitions in molecules, which can be more advantageous for measurement.

[0063] In one embodiment, the at least one camera 5 can be designed as a multi- and hyperspectral camera. Instead of the classic simple recording in a single spectral range, a large number of spectral bands are used. This can be advantageous for detecting significantly higher color quality and color differences, since each pixel already contains a complete color spectrum. In such a camera 5, for example, the snapshot mosaic technique is used.

[0064] The measuring point, in particular the measuring volume VM, is stationary during the measurement with the device 1, thus a stationary measurement is realized with the device 1 at a specific stationary measuring point. The exhaust gas cloud 9 can therefore move or change relative to the measuring volume VM during the measurement, but the device 1, specifically the individual units of the device 1, remain stationary at the measuring point. In particular, the at least one light source 2, a measuring unit 4, a detector 3, a reflection unit 8, and an imaging unit 29 remain stationary during the measurement. If further units are present in the device 1, such as a multiplexer unit 10, these are also stationary during the measurement.

[0065] The device 1 according to the invention is therefore in particular not a measuring unit that is installed in a moving vehicle for exhaust gas measurement and moves with the vehicle during the measurement.

[0066] However, the device 1 is only necessarily stationary during the measurement. Between two measurements, the device 1 or parts thereof can also be moved. In the course of remote sensing measurements, for example, it may be necessary for the device 1 to switch between different measuring points, for example in order to record a larger proportion of vehicles driving in a larger area (e.g. a city). In this context, it can also be provided to mount the device 1 partially or completely on a trailer in order to be able to move the device 1 between the measuring points in a mobile manner. The main part of the device 1, in particular a light source 2, a measuring unit 4, a detector 3 and an imaging unit 29, can be pre-mounted on an extendable frame on the trailer. Parts of the device 1 that can be attached to the measuring point, such as the mirroring unit 8, are then arranged at the measuring point in a suitable manner.However, during the measurement all units are stationary again.

[0067] It may happen that different exhaust clouds 9 from emission sources located behind or next to each other, such as vehicles, mix in the measurement volume VM. The measurement can then be adjusted accordingly, for example, by positioning or aligning the imaging unit 29, in particular the at least one camera 5.

[0068] In one variant, a plurality of measuring units 4 are provided in the device 1 according to the invention, also at different distances L from a respectively assigned reflecting unit 8. Several reflecting units 8 can also be provided, for example a separate one for each measuring unit 4 or one for different groups of measuring units. Several measuring units 4 are advantageous in order to realize spatially resolved measurements of an exhaust gas cloud 9 in a measuring volume VM, or also to measure several exhaust gas clouds 9 in different measuring volumes VM simultaneously. For this purpose, a primary light beam 17 of a light source 2 can, if necessary, also be split accordingly using optical systems, for example by means of beam splitters, deflection units, mirrors, multiplexers, etc., in order to supply each of the measuring units 4 with light.However, a light source 2 for generating a primary light beam 17 can also be provided in each measuring unit 4, or in some of them.

[0069] By taking multiple measurements of an exhaust cloud 9, an average value of the concentration of a gaseous or solid substance in the exhaust cloud 9 can be determined. However, it is also possible to determine a spatially resolved measurement of the concentration in the exhaust cloud 9. With an appropriate arrangement of the measuring units 4 and mirroring units 8, a two-dimensional spatial resolution of the concentration of a gaseous or solid substance in the exhaust cloud 9 can also be determined. For this purpose, for example, a first group of light rays 6 could penetrate the exhaust cloud in a first direction and a second group of light rays 6 could penetrate the exhaust cloud in a second direction different from the first, for example normal to the first direction.

[0070] Fig. 3 shows an advantageous embodiment of the measuring unit 4 with multiple measurements of an exhaust gas cloud 9. In this embodiment, the light source 2 and detector 3 are arranged in the measuring unit 4. In a variant, the light source 2 and / or the detector 3 can also be arranged externally of the measuring unit 4 at any suitable location. The imaging unit 29 is in Fig.3 only hinted at and can be seen above in connection with Fig.2 explained or how in connection with Fig.4 explained below. The image unit 29 generates the images of the measurement volume VM, which are processed in the evaluation unit 11. In the measuring unit 4, a multiplexer unit 10 is provided, which generates a plurality of light beams 6 (wherein Fig.3 For reasons of clarity, only some are designated by reference numerals. The multiplexer unit 10 generates from the primary light beam 17 (in Fig. 3 not shown) of the light source 2 the plurality of light rays 6.

[0071] The multiplexer unit 10 can be implemented, for example, as an optical fiber multiplexer, optical coupler, or optical splitter. Implementation of the multiplexer unit 10 as a fiber optic switching network is also conceivable. Various designs of a multiplexer unit 10 are well known, and one skilled in the art can select one suitable for the respective application.

[0072] The individual emitted light beams 6 are guided through different locations or areas of the measuring volume VM, whereby the light beams 6 also penetrate an exhaust cloud 9 located in the measuring volume VM at different locations. This allows the exhaust cloud 9 to be detected with spatial resolution. The individual light beams 6 can be detected by at least one detector 3 or reflected by at least one reflection unit 8 (as in Fig.3 ) as described above and directed as reflected light beams 6 to at least one detector 3 (which in the embodiment of the Fig.3 arranged in the measuring unit 4) and thus recorded.

[0073] Of course, a reflection unit 8 can be provided for each light beam 6 or a group of light beams 6. Likewise, a detector 3 can be provided for each reflected light beam 6 or for a group of reflected light beams 6.

[0074] The at least one detector 3 can now, as described, determine a decrease in light intensity, or an absorption A, for each detected light beam 6 and transmit it to the evaluation unit 11. Likewise, the evaluation unit 11 can determine a total passage distance x from the at least one image of the measurement volume VM recorded by the imaging unit 29 for each light beam 6, and any associated reflected light beam 6 (provided it penetrates the exhaust cloud 9), as described. This allows a concentration c of a gaseous or solid substance to be determined at various locations in the exhaust cloud 9.

[0075] It is obvious that a two-dimensional spatial resolution of the exhaust cloud 9 is also possible here if the device 1 is designed such that at least two groups of light beams 6 penetrate the exhaust cloud 9 in different directions (preferably perpendicular to each other). If such a two-dimensional resolution is performed several times in succession, a three-dimensional concentration distribution (in the case of a moving exhaust cloud 9) or a temporal progression of the concentration distribution in an exhaust cloud 9 can also be determined.

[0076] The individual light beams 6 are in the embodiment according to Fig. 3 in the measuring unit 4 via optical paths 13, for example, optical fibers, at the ends of which the light beams 6 are emitted via an output coupling unit 12. If at least two of these optical paths 13 are designed with different optical path lengths, this causes the return beams 6 associated with the optical paths with different path lengths to arrive at a detector 3 at different times due to the different light travel times. This can simplify or facilitate the detection of different light beams 6 with a single detector 3.

[0077] Of course, the device 1 can also comprise a plurality of measuring units 4 with multiplexer units 10, as described with reference to the Fig.3 described. This again enables multiple measurements in a measurement volume VM, preferably to achieve a two-dimensional resolution of the measurement volume VM, or also the measurement of different measurement volumes VM.

[0078] A spatially resolved determination of the concentration c in an exhaust gas cloud 9 (for example with a measuring unit according to Fig.3 or with multiple measuring units 4 as in Fig.2 The system (or a combination of such arrangements) can then be used, for example, to simulate a continuous distribution of a gaseous or solid substance in the exhaust cloud 9, for example, data-driven or using hybrid modeling. Hybrid modeling is understood to be a combination of discrete terms, such as the measured concentration values, and continuous terms, such as "fluid / gas dynamics" in an exhaust cloud 9.

[0079] Fig. 4 shows a further embodiment of the device 1 according to the invention. In this embodiment, several measuring units 4 (in Fig.4 For reasons of clarity, two of them are indicated), which can be designed as described above and for which a detector 3 is provided each. The multiple measuring units 4 are used to carry out concentration measurements of a gaseous or solid substance in an exhaust gas cloud 9 in the respective measuring volume VM in different measuring volumes VM. The measuring volumes VM can have different volumes, whereby the volumes depend on the measuring arrangement of the measuring units 4. The beam paths for the concentration measurement are in Fig. 4 For reasons of clarity, the figures are not fully drawn or only partially indicated. Fig.4 An imaging unit 29 is provided, which takes images of all exhaust clouds 9 in the various measuring volumes VM and sends them to an evaluation unit 11. The evaluation unit 11 also receives values of the absorptions A determined by detectors 3.

[0080] In this embodiment of the device 1, the imaging unit 29 is designed as a lidar unit 14. The lidar unit 14 can be arranged locally near the measuring units 4, but can also be arranged, for example, at a certain height above the measuring units 4, or can be controlled by a mobile drone to carry out a measurement campaign.

[0081] A lidar unit 14 can be used to carry out a very precise measurement of an exhaust cloud 9, wherein the lidar unit 14 takes images of at least a part of the exhaust cloud 9 in order to determine the total passage distance x as described above.

[0082] The lidar unit 14 is based on a laser, for example, a YAG laser with a wavelength of 1064 nm or 532 nm, or similar designs deemed suitable by those skilled in the art. IR lasers can also be used, although adequate shielding may be necessary to avoid eye damage.

[0083] A lidar unit 14 in the UV or NIR range can also be used, for example, to directly measure gaseous or solid substances. Lidar is used, among other things, to detect carbon dioxide (CO2), sulfur dioxide (SO2), and methane (CH4) in atmospheric measurements. This can be used, for example, to make rough estimates of gaseous or solid substances in the measured exhaust plume 9 or to obtain a concentration measurement that is redundant to the concentration measurement according to the invention.

[0084] The lidar unit 14 can move along at least one axis or can be pivoted about at least one axis in order to emit the laser light in different directions, so that an image of the surroundings and any exhaust cloud 9 that may be present can be recorded. In the embodiment according to Fig.4 The lidar unit 14 is used to image different exhaust clouds 9 in different measuring volumes VM. For this purpose, the lidar unit 14 scans the environment 15 (in Fig.4 represented by a circle around the lidar unit 14) and depending on the reflection time of the emitted laser pulse, images of the environment 15 are taken. Fig. 4 The operation of the lidar unit 14 is shown in two dimensions as an example. The lidar unit 14 rotates about an angle defined by the lidar unit 14 normal to the drawing plane of Fig. 4 , and scans the environment 15 at an angular frequency ω. Sections 16 of the exhaust clouds 9 are detected, combined to form images of the exhaust cloud 9 and can thus be reconstructed by the evaluation unit 11 to form part of an image of the exhaust cloud 9.

[0085] Such a lidar unit 14 can of course also be used only for a single measuring volume VM , for example as in Fig.2 or 3 , can be used. Likewise, a plurality of lidar units 14 can be present in the device 1, which enable a more precise and possibly larger image of the exhaust cloud 9.

[0086] Combinations of lidar units 14 and cameras 5 are also conceivable. This allows, for example, the concentrations of gaseous substances to be measured via the lidar unit 14, while the concentration of a solid substance in the exhaust cloud 9 can be detected via a measuring unit 4 according to the invention. This allows a representative concentration measurement of several critical gaseous and solid substances in the exhaust cloud 9 to be performed.

[0087] Fig. 5 shows a further advantageous embodiment of the invention. In this embodiment, two reflection units 8, 8' are provided, arranged at a distance from one another. The respective reflection planes 8.1, 8.1' of the two reflection units 8, 8' are arranged facing one another. The light beam 6 is now emitted by the measuring unit 4 at an angle α that deviates from a normal to the first reflection plane 8.1 of the first reflection unit 8. The light beam 6 is reflected at the first reflection plane 8.1 and directed to the second reflection plane 8.1' of the second reflection unit 8'. At this, the light beam 6 is further reflected back to the first reflection unit 8. The light beam 6 thus travels back and forth between the first reflection unit 8 and the second reflection unit 8' in a plurality of reflections and moves along a longitudinal extent of the reflection planes 8.1, 8.1'.Depending on the angle α, a plurality of reflections can thus be achieved. After the last reflection at the end of the reflection units 8, 8', the light beam 6 is reflected in the embodiment according to . Fig.5 directed to a detector 3, which detects the light beam 6.

[0088] After the last reflection at the end of the reflection units 8, 8', the light beam 6 can also be deflected in an embodiment not shown, for example by a deflection mirror, and return in a number of further reflections between the first reflection unit 8 and the second reflection unit 8' along a longitudinal extension of the reflection planes 8.1, 8.1'. In this case, the detector 3 can be arranged in the measuring unit 4. However, the detector 3 can in principle be arranged at any suitable location on the device 1 that allows the light beam 6 to be detected after a plurality of reflections of the light between the first reflection unit 8 and the second reflection unit 8'.

[0089] Due to the multiple reflections, a plurality n of light beams 6 pass through an exhaust cloud 9 in the measurement volume VM. The resulting partial passage distances xn of the light through the exhaust cloud 9 can be determined as described above using the imaging unit 29, from which the total passage distance x is derived as the sum of the partial passage distances xn (here, n=1, 2, 3). This, in turn, allows the concentration of at least one gaseous or solid substance in the exhaust cloud 9 to be determined.

[0090] By the plurality n of passages of the light beam 6 through the exhaust cloud 9, the sensitivity of the concentration measurement can be further increased and even very low concentrations of a gaseous or solid substance in the exhaust cloud 9 can be determined.

[0091] In order to be able to adjust the plurality n of passages of the light beam 6 through the exhaust cloud 9 selectively and as needed, a positioning optical unit 18 can also be provided in the measuring unit 4, which allows the angle α of the emitted light beam 6 to be adjusted. Such a positioning optical unit 18 can be, for example, an xy galvanometer or an adjustable mirror.

[0092] A further advantageous embodiment for protecting a mirror unit 8 is a protective film unit 24, which is Fig.6 This serves to arrange a protective film 23 replaceably over a mirror unit 8 in order to protect it from soiling or damage (e.g., scratches). The protective film 23 is designed to be sufficiently transparent. A soiled protective film 23 can be replaced by a clean protective film 23 if necessary. One possible embodiment of a protective film unit 24 is shown in Fig.6from a first roll 20, onto which clean protective film 23 is wound. Clean protective film 23 can be unwound from this first roll 20 and arranged over a mirroring unit 8. A second roll 21 can be provided, onto which the contaminated protective film 23 can be wound. When used as intended, clean protective film 23 is unwound from the first roll 20 as needed, and contaminated protective film 23 is simultaneously wound from the second roll 21. In this advantageous embodiment, the mirroring unit 8 is arranged below the surface 7.

[0093] The unwound protective film 23 is arranged over the reflection unit 8 to protect the reflection unit 8 from contamination or damage. For stability reasons, a mechanical protection 22 can also be provided between the reflection unit 8 and the protective film 23, which, however, should have sufficient optical transparency. One of the two rollers 20, 21 can be driven to cause the protective film 23 to move further over the reflection unit 8 as needed. An automation unit can also be provided for this purpose, which controls the drive of the driven roller 20, 21. Advantageously, the rollers 20, 21 can be driven when a limit value is undershot, for example a loss of light intensity of a light beam 6 detected by a detector 3. The automation unit can then automatically control the driven roller 20, 21 to move the protective film 23 further.This allows the contaminated protective film 23 above the reflecting unit 8 to be easily replaced with a clean one as needed. This can be advantageous if the reflecting unit 8 is generally exposed to high levels of contamination.

[0094] A heating device, for example an electric heater, can also be integrated in the protective film unit 24, preferably in the mechanical protection 22. The heating device can prevent the optical system of the device 1 from being impaired by the formation of ice or puddles on the surface of the protective film 23 in wet conditions, such as rain, fog or snow.

Claims

1. A device for determining the concentration of at least one gaseous or solid material in at least one measurement volume (VM) at a stationary measurement point, wherein at least one measurement unit (4) is provided to emit a light beam (6) with a predetermined light intensity (I) through the measurement volume (VM), and at least one detector (3) is provided to detect the light beam (6) after it has passed through the measurement volume (VM), wherein the at least one detector (3) is configured to determine a decrease in the light intensity due to the at least one gaseous or solid material in the measurement volume (VM), whereas an image unit (29) is provided in the device (1), in order to capture at least a part of an exhaust plume (9) in the case of partial or complete presence of an exhaust plume (9) in the measurement volume (VM), whereas an evaluation unit (11) is provided in the device (1) which is configured to determine a total passage path (x) of the light beam (6) through the exhaust plume (9) in the measurement volume (VM) from at least one captured image of the at least one part of the exhaust plume (9), whereas the evaluation unit (11) is further configured to determine a concentration of the gaseous or solid material in the measurement volume (VM) from the determined decrease in the light intensity and the total passage path (x).

2. The device according to claim 1, characterized in that the at least one measurement unit (4) is arranged at a distance from at least one first reflection unit (8), the measuring volume (VM) being formed between the at least one measurement unit (4) and the at least one first reflection unit (8), and the at least one measurement unit (4) is configured to emit a light beam (6) in the direction of the at least one reflection unit (8), and in that the at least one first reflection unit (8) is provided to reflect the light beam (6) after it has passed through the measurement volume (VM) and to transmit it to at least one detector (3).

3. The device according to claim 2, characterized in that the light beam (6) reflected at the reflection unit (8) passes through the measurement volume (VM) at least once more before reaching the at least one detector (3).

4. The device according to claim 3, characterized in that the total passage path (x) is the sum of the partial passage paths of all passages of the light beam (6) through the exhaust plume (9).

5. The device according to any of claims 1 to 4, characterized in that a multiplexer unit (10) is provided in the measurement unit (4), which multiplexer unit generates a plurality of light beams (6), and the measurement unit (4) emits the plurality of light beams (6) at different locations through the measurement volume (VM) and at least one detector (3) detects each of the plurality of light beams (6), preferably after a reflection at a reflection unit (8).

6. The device according to claim 5, characterized in that at least two of the plurality of light beams (6) are guided in the measurement unit (4) via an optical path (13) in each case, wherein the optical paths (13) preferably have different optical path lengths at least in part.

7. The device according to claim 5 or 6, characterized in that the measuring unit (4) emits at least one first light beam (6) of the plurality of light beams (6) in a first direction through the measuring volume (VM) and the measuring unit (4) emits a second light beam (6) of the plurality of light beams (6) in a second direction through the measuring volume (VM), the first direction being different from the second direction.

8. The device according to any of claims 2 to 7, characterized in that a second reflection unit (8') is provided in the device, which is arranged at a distance from and opposite the at least one first reflection unit (8) and the measurement unit (4) emits the light beam (6) at an angle deviating from a normal to a first reflection plane (8.1) of the first reflection unit (8), wherein the first reflection unit (8) reflects the light beam (6) emitted by the measurement unit (4) to the opposite second reflection unit (8') and the opposite second reflection unit (8') reflects the light beam (6) back to the first reflection unit (8), wherein the at least one detector (5) is set up to detect the light beam (6) after a plurality of such reflections.

9. The device according to claim 8, characterized in that a positioning optical unit (18) is provided in the measurement unit (4), with which the angle of the light beam (6) is adjustable.

10. The device according to any of claims 1 to 9, characterized in that in the device (1), a plurality of measurement units (4) is provided, wherein at least two of the measurement units (4) emit a light beam (6) through different measurement volumes (VM).

11. The device according to any of claims 1 to 10, characterized in that a plurality of measurement units (4) are provided in the device (1), wherein at least two of the measurement units (4) emit a light beam (6) with different directions through the same measurement volume (VM).

12. The device according to any of claims 1 to 11, characterized in that the image unit (29) comprises at least one camera (5) and / or at least one lidar unit (14).

13. The device according to any of claims 2 to 12, characterized in that a protective foil (23) is arranged replaceably above the at least one reflection unit (8).

14. A method for determining the concentration (1) of at least one gaseous or solid material in an exhaust plume (9) in at least one measuring volume (VM) at a stationary measuring point, wherein at least one measuring unit (4) emits a light beam (6) with a predetermined light intensity (I) through the exhaust plume (9) in the measuring volume (VM), the light beam (6) is detected by a detector (3) after passing through the exhaust plume (9) and the detector (3) determines a decrease in the light intensity of the light beam (6) due to the at least one gaseous or solid material, whereas at least a part of the exhaust plume (9) in the measuring volume (VM) is captured by an imaging unit (29) and a total passage path (x) of the light beam (6) through the exhaust plume (9) in the measuring volume (VM) is determined from the captured image of the at least one part of the exhaust plume (9), and whereas a concentration of the gaseous or solid material in the measuring volume (VM) is determined from the determined decrease in light intensity and the total passage path (x).