DE102018222619A1 - Method for operating an incinerator or internal combustion engine, and device for determining an exhaust gas speed - Google Patents

Abstract

A device (10) is used to determine a first variable that characterizes an exhaust gas velocity or is related to it. It is proposed that it comprises: a device (27) for generating a laser light spot (22) in an area (40) carrying exhaust gas, a detector (32) for detecting temperature radiation emanating from the laser light spot (22) ( 26), which provides an output signal (34) dependent on the detected temperature radiation (26), and an evaluation device (53) which is designed and set up to determine the first variable from the output signal (34) at least indirectly.

Description

State of the art

The invention relates to methods for operating an incinerator or internal combustion engine and a device for determining an exhaust gas velocity according to the preambles of the independent claims.

It is known from the market to determine an exhaust gas mass flow and an exhaust gas speed that can be calculated therefrom in engine control units of internal combustion engines, inter alia, from the signals of an air mass meter, an injection quantity, an exhaust gas recirculation rate (if present) and combustion equations. The exhaust gas mass flow is used, among other things, to calculate a loading condition of a particle filter or to determine the dosage of a urea injection for NOx reduction. Furthermore, from the DE 10 2017 207 402 A1 a particle sensor is known that works on the principle of laser-induced incandescence. Particles present in an exhaust gas area, for example soot particles, are heated to several thousand degrees Celsius with a laser focused on a laser light spot, so that they emit significant heat or temperature radiation. This thermally induced light emission of the particles is measured with a light detector.

Disclosure of the invention

The problem underlying the invention is solved by a method with the features of claim 1 and a device with the features of the independent claims. Advantageous further developments are specified in the subclaims.

The method and the device according to the invention are based on the detection of particles in an exhaust gas using the principle of laser-induced incandescence ( LII ). First of all, a particle is heated to several thousand degrees by partial absorption of the laser light using laser light, which emanates from a laser and is preferably bundled with sufficient intensity in a laser light spot, that is to say a volume region with the smallest dimensions in the μm range. According to the Planck law of radiation, this hot particle emits a characteristic temperature radiation (incandescence or glow emission), which serves as a measurement signal and is received with a detector.

For this purpose, for example, an optical element arranged in the beam path of the laser is used, which is designed and set up to bundle the laser light emanating from the laser in the very small laser light spot. With a focus diameter of 10 µm, for example, it can be assumed that only one particle flies through the laser light spot at a given time (intrinsic single particle detectability) if a particle concentration of 10 ¹³ / m ^{3 is used} as a basis. The detector is set up and arranged in such a way that it detects the temperature radiation emanating from the laser light spot. Inexpensive semiconductor laser diodes can be used as lasers. The temperature radiation can be detected, for example, by means of a multi-pixel photon counter (MPPC) or a silicon photon multiplier (SiPM).

1. a. Erzeugen eines Laserlicht-Spots in einem Abgas führenden Bereich;
2. b. Erfassen einer von dem Laserlicht-Spot ausgehenden Temperaturstrahlung mittels eines Detektors,
3. c. Bereitstellen eines von der erfassten Temperaturstrahlung abhängigen Ausgangssignals,
4. d. Ermitteln einer eine Abgasgeschwindigkeit charakterisierenden oder mit dieser zusammenhängenden ersten Größe mindestens mittelbar aus dem Ausgangssignal.

The following steps belong to the method according to the invention:

1. a. Generating a laser light spot in an area carrying exhaust gas;
2. b. Detecting a temperature radiation emanating from the laser light spot by means of a detector,
3. c. Providing an output signal dependent on the detected temperature radiation,
4. d. Determining a first variable that characterizes an exhaust gas velocity or is associated therewith at least indirectly from the output signal.

1. a. eine Einrichtung zum Erzeugen eines Laserlicht-Spots in einem Abgas führenden Bereich,
2. b. ein Detektor zum Erfassen einer von dem Laserlicht-Spot ausgehenden Temperaturstrahlung, der ein von der erfassten Temperaturstrahlung abhängiges Ausgangssignal bereitstellt, und
3. c. eine Auswerteeinrichtung, welche dazu ausgebildet und eingerichtet ist, aus dem Ausgangssignal mindestens mittelbar eine eine Abgasgeschwindigkeit charakterisierende oder mit dieser zusammenhängende erste Größe zu ermitteln.

Belong to the device according to the invention

1. a. a device for generating a laser light spot in an area carrying exhaust gas,
2. b. a detector for detecting a temperature radiation emanating from the laser light spot, which provides an output signal dependent on the detected temperature radiation, and
3. c. an evaluation device which is designed and set up to determine, at least indirectly, a first variable characterizing an exhaust gas velocity or related to it from the output signal.

According to the invention, it was found that the temperature radiation detected by means of the detector or the output signal of the detector dependent thereon is an indicator of the speed of the fluid in and with which the particles which emit the temperature radiation are transported. This temperature radiation is namely dependent on the length of time the soot particles in the exhaust gas remain in laser light sport, and this length of time in turn depends on the speed of the exhaust gas. The inventive method and the inventive device are thus simple and reliable working means are provided with which the actual speed of an exhaust gas in an exhaust gas-carrying area can be recorded. The knowledge of the actual speed of the exhaust gas can be used for numerous tasks of monitoring and controlling an incineration plant or internal combustion engine.

No additional device is required, since both the method according to the invention and the device according to the invention can use a device, namely a particle sensor, with which the concentration and / or size of particles (soot particles) present in the exhaust gas is determined. This particle sensor therefore has a dual function: on the one hand, the detection of soot particles present in the exhaust gas, which allows, for example, information about the loading of a particle filter, and on the other hand, the determination of the speed of the exhaust gas. Additional costs are thus avoided by the invention. It goes without saying that the output signal of the detector can be both an analog output signal and a digital output signal.

In a further development it is provided that the first variable is determined from the time during which temperature radiation is detected and a dimension of the laser light spot. As a result, the physical relationships between the temperature radiation or the output signal provided by the detector and the exhaust gas velocity are correctly mapped, and this can be implemented or programmed very easily. The dimensions of the laser light spot are known at all times, and the time during which a temperature radiation is detected or during which the output signal indicates a detected temperature radiation can be determined very easily.

In a further development, it is provided that a correction factor is used when determining the first variable. In this way it can be taken into account that the laser light sport is not necessarily arranged in the actual exhaust pipe, but for example in a measuring space arranged transversely to the actual exhaust pipe. However, the speed of the exhaust gas in this measuring space is in a known dependence on the speed of the exhaust gas in the actual exhaust pipe, this dependence being dependent, for example, on the geometry of the measuring space.

In a further development it is provided that the first variable related to the exhaust gas velocity is a second variable that characterizes an exhaust gas mass flow. The exhaust gas mass flow is an important variable in the control of an incineration plant and in particular in the control of an internal combustion engine. The exact knowledge of the exhaust gas mass flow permits an even more precise control of the combustion system or internal combustion engine, as a result of which the consumption of fuel is reduced and the emission of exhaust gas can also be optimized. To determine the exhaust gas mass flow from the exhaust gas velocity, the signals of further sensors, for example of pressure and temperature sensors, which are arranged in the area carrying the exhaust gas and / or at another point in the combustion system or the internal combustion engine, can be used.

In a further development, it is provided that a current state variable of a particle filter is determined from the second variable. Such a state variable can be the loading of the particle filter, for example. Their particularly precise knowledge makes it possible to postpone a point in time at which the particle filter has to be regenerated as far as possible, which reduces the load on the particle filter and saves both fuel and CO2.

In a further development it is provided that the dosage of an exhaust gas aftertreatment agent depends on the second variable. Such an exhaust gas aftertreatment agent can be, for example, urea, such as is used in the selective catalytic reduction in SCR catalysts of diesel internal combustion engines. Such a metering can take place more precisely due to the more precise knowledge of the exhaust gas mass flow, which leads to a more economical use of the exhaust gas aftertreatment by means of and thus to lower operating costs and longer periods of time between required after fillings.

In a further development, it is provided that an exhaust gas recirculation rate depends on the second variable. This known principle of exhaust gas recirculation has a favorable influence on the emissions of an incineration plant or internal combustion engine. Due to the more precise knowledge of the exhaust gas mass flow thanks to the method according to the invention, the exhaust gas recirculation rate can be controlled or regulated more precisely, as a result of which pollutant emissions and / or the consumption of fuel can be reduced. In addition, pressure sensors that were previously required can be saved, which in turn can reduce costs.

In a further development it is provided that a third variable characterizing the exhaust gas mass flow is additionally determined in a different way, and that if the second variable and the third variable differ from one another by at least one limit value, a malfunction of one Air mass meter, an injection nozzle, an exhaust gas recirculation and / or a spark plug, or a leak in the exhaust gas leading area is concluded. In this way, a previously non-existent possibility of diagnosis or plausibility check of the function of important components of combustion systems or internal combustion engines is created. The safety and reliability in the operation of an incineration plant or internal combustion engine is thus improved.

In a further development it is provided that an average value from a plurality of detected values of the temperature radiation is used to determine the first variable. This reduces measurement errors.

• 1 ein Blockschaltbild zur Erläuterung des Aufbaus eines Partikelsensors, der nach dem Prinzip der laserinduzierten Inkandeszenz arbeitet;
• 2 eine detailliertere Darstellung des Aufbaus des Partikelsensors von 1, einschließlich der Darstellung eines strömenden Fluids, in dem Partikel vorhanden sind;
• 3 ein Diagramm, in dem ein Ausgangssignal eines Detektors des Partikelsensors der 1 und 2 über der Zeit aufgetragen ist;
• 4 eine schematische Darstellung von Komponenten einer Benzin-Brennkraftmaschine mit dem Partikelsensor der 1 und 2;
• 5 eine schematische Darstellung von Komponenten einer Diesel-Brennkraftmaschine mit dem Partikelsensoren der 1 und 2; und
• 6 ein Flussdiagramm eines Verfahrens zum Betreiben der Brennkraftmaschinen der 3 und 4.

Embodiments of the invention are explained below with reference to the accompanying drawing. The drawing shows:

• 1 a block diagram for explaining the structure of a particle sensor, which works on the principle of laser-induced incandescence;
• 2nd a more detailed representation of the structure of the particle sensor of 1 , including the representation of a flowing fluid in which particles are present;
• 3rd a diagram in which an output signal of a detector of the particle sensor of 1 and 2nd is plotted over time;
• 4th is a schematic representation of components of a gasoline engine with the particle sensor of 1 and 2nd ;
• 5 is a schematic representation of components of a diesel engine with the particle sensors of 1 and 2nd ; and
• 6 a flowchart of a method for operating the internal combustion engine of the 3rd and 4th .

Functionally equivalent elements and areas have the same reference symbols in the following description.

1 shows a block diagram of a possible embodiment of a particle sensor 10 . First of all, one recognizes a laser12, in the present case, for example, a CW laser (CW = continuous wave, ie “continuous wave”), the laser light 14 emitted. The laser 12th can in particular have a laser diode, which is very inexpensive. The laser light 14 is through a lens 16 first formed into a parallel beam by a beam splitter 18th for example in the form of a beam splitter or a dichroic mirror. From there he gets to a lens 20 and continue in focused form to a laser light spot 22 . As a laser light spot 22 is understood here as a volume element with very small dimensions in the µm range or even in the nm range, in which the laser light 14 is extremely focused and therefore extremely energy-tight or intensive.

Laser light 14 high intensity can in the laser light spot 22 to a particle present there 24th meet, for example, a soot particle in the exhaust gas stream of an internal combustion engine, as will be shown below. The intensity of the laser light 24th is in the laser light spot 22 so high that from the particle 24th absorbed energy of laser light 14 the particle 24th heated to several thousand degrees Celsius (only in the volume of the laser light spot 22 reaches the intensity of the laser light 14 for laser-induced incandescence ( LII ) necessary high values). As a result of the heating, the particle emits 24th spontaneously and essentially without preferred direction significant temperature radiation 26 (dashed arrows), also referred to as LII light. Part of the thermal radiation 26 is therefore also opposite to the direction of the incident laser light 14 emitted. The temperature radiation 26 is, for example, in the near infrared and visible spectral range, but is not limited to this spectral range. The laser 12th , the Lens 16 , the beam splitter 18th and the lens 20 to this extent form a facility 27 to generate the laser light spot 22 .

The temperature radiation 26 one in the laser light spot 22 through the laser light 14 excited particle 24th again passes through the lens 20 back to the beam splitter 18th where it is deflected by 90 ° through a focusing lens 28 passes and through a filter 30th (this is not mandatory) to a detector 32 reached. The filter 30th is designed to match the wavelengths of the laser light 14 filtered out, which is also radiated back to a small extent (dash-dotted arrows 31 ). Through the filter 30th the annoying background is reduced. It is also conceivable to use a simple edge filter. This improves the signal-to-noise ratio.

In one embodiment, not shown, the laser light is guided from the laser to the focusing lens with the aid of an optical waveguide and corresponding optical elements that couple in and out. The same applies to the LI I light to be detected. It is also not absolutely necessary for the laser light and the LII light to be focused and collected appropriately via the same lens.

The dimensions of the laser light spot 22 are in the range of a few µm, in particular in the range of at most 200 µm, so that the laser light spot 22 passing particles 24th be stimulated to emit evaluable radiation powers, be it by laser-induced incandescence or through chemical reactions (especially oxidation). As a result, it can be assumed that there is always at most one particle 24th in the laser light spot 22 located and that a current output signal 34 of the particle sensor 10 only of this at most one particle 24th comes from.

The output signal 34 is from the detector 32 generated in the particle sensor 10 is arranged so that it is away from the laser light spot 22 flying particles 24th outgoing radiation 26 , in particular temperature radiation is detected. In this respect it is from the detector 32 provided output signal 34 one from the detector 32 Detected temperature radiation characterizing variable or depends on this. The detector 32 preferably comprises a multi-pixel photon counter (MPPC) or a silicon photon multiplier (SiPM) or a SPAD diode (single-photon avalanche diode), which (r) the temperature radiation 26 detected and the present example digital output signal 34 generated in the form of pulses with a certain voltage or with a certain current. The stronger the temperature radiation 26 is, the more pulses per unit of time are output. This enables a single particle measurement, which is the extraction of information about the particle 24th how size and speed allows.

An example of such an output signal 34 is in 3rd applied. Through the vertical lines entered there, a single pulse 35 symbolizes the pulse-like increase in a signal value S , for example a voltage U or a current. In fact, these pulses also have a certain temporal latitude, which can be characterized, for example, by the so-called "half-width" or FWHM ("Full Width at Half Maximum"). Due to background radiation or signal noise, pulses are continuously generated 35 generated ("dark counts"). But then when the detector 32 a thermal radiation 26 detected, these pulses occur 35 at significantly shorter intervals. Such a period during which the detector 32 a thermal radiation 26 is detected is in 3rd denoted by t.

With the above types of detectors 32 can already be one of a particularly small particle 24th generated and therefore extremely small light signal, which is formed, for example, by a few photons. This reduces the dimensions of particles 24th that are just still detectable, down to a lower detection limit of up to 10 nm.

It is quite possible that the laser 12th is modulated or switched on and off (duty cycle <100%). However, it remains preferred that the laser 12th is a CW laser. This enables the use of inexpensive semiconductor laser elements (laser diodes), which is the complete particle sensor 10 cheaper and the control of the laser module 12th and the evaluation of the output signal 34 greatly simplified. However, the use of pulsed lasers is not excluded.

2nd shows in more detail an advantageous embodiment of a particle sensor 10 , which is suitable for use as a soot particle sensor in an exhaust gas 36 a combustion process, for example in the exhaust system of an internal combustion engine (diesel or gasoline) of a motor vehicle. The exhaust gas 36 In this respect, an example of a fluid flowing at a certain speed is the particle 24th contains. How out 2nd can be seen, the exhaust gas 36 in an exhaust pipe 37 guided.

The particle sensor 10 has an arrangement of an outer protective tube 38 and an inner protective tube 40 on. The two protective tubes 38 , 40 preferably have a general cylindrical shape or prism shape. The base areas of the cylindrical shapes are preferably circular, elliptical or polygonal. The protection tubes 38 , 40 are preferably arranged coaxially, with the axes of the protective tubes 38 , 40 across the flow of the exhaust gas 36 or the exhaust pipe 37 are aligned. The inner protective tube 40 protrudes in the direction of the axes over the outer protective tube 38 out and into the exhaust pipe 37 and that in the exhaust pipe 37 flowing exhaust gas 36 inside. On the flowing exhaust gas 36 opposite end of the two protective tubes 38 , 40 protrudes the outer protective tube 38 over the inner protective tube 40 out. The clear width of the outer protective tube 38 is preferably so much larger than the outer diameter of the inner protective tube 40 that between the two protective tubes 38 , 40 a first and in the present case approximately circular flow cross section results. The clear width of the inner protective tube 40 forms a second and in the present case circular flow cross section.

This geometry results in exhaust gas 36 over the first flow cross-section into the arrangement of the two protective tubes 38 , 40 occurs, then at the exhaust gas 36 opposite end of the protective tubes 38 , 40 changes its direction in the inner protective tube 40 enters and from this in the exhaust pipe 37 exhaust gas flowing past 36 is sucked out (arrows with the reference symbol 42 ). This results in the inner protective tube 40 a laminar flow. This arrangement of protective tubes 38 , 40 becomes transverse to the flow direction of the exhaust gas 36 attached to or in an exhaust pipe (not shown). The laser light spot 22 is located inside the inner protective tube 40 . This structure has the particularly important advantage that only one optical access to the exhaust gas 36 is needed because the same optics, especially the same lens 20 either for the generation of the laser light spot 22 as well as for the detection of the particle 24th outgoing temperature radiation 26 is used.

The particle sensor 10 preferably has one of the exhaust gas 36 exposed first part 44 (Protection tubes 38 and 40 ) and the exhaust gas 36 unexposed second part 46 on the the optical components of the particle sensor 10 contains. Both parts 44 , 46 are by a partition 48 separated that between the protective tubes 38 , 40 and the optical elements of the particle sensor 10 he runs. The wall 48 serves to isolate the sensitive optical elements from the hot, chemically aggressive and "dirty" exhaust gas 36 . In the partition 48 is in the beam path of the laser light 14 a protective window 50 attached, through which the laser light 14 into the exhaust 36 between the flow 42 occurs and about that from the laser light spot 22 outgoing temperature radiation 26 on the lens 20 and from there via the beam splitter 18th and the filter 30th on the detector 32 can come up with.

The particle sensor 10 also has an arrangement 52 for processing the output signal 34 of the detector 32 which is designed and set up on the basis of the output signal 34 of the detector 32 an evaluation of that from the detector 32 provided and the detected temperature radiation 26 characterizing size. The arrangement can be, for example, an amplifier and an evaluation device 53 include, in particular the latter can also be implemented as software that is stored on a memory and runs on a microprocessor. The memory and the microprocessor can, for example, be part of a control device, for example an engine control device of an internal combustion engine. The evaluation device 53 serves in the present case, as will be explained in the following, a speed of the exhaust gas 36 and to determine an exhaust gas mass flow from this.

Two highly schematic examples of such internal combustion engines are now described with reference to the 4th and 5 explained. 4th shows a gasoline engine 54 . Intake air passes through an intake pipe 56 into one of the combustion chambers of the internal combustion engine 54 , one of which is drawn as an example and the reference symbol 58 wearing. Fuel gets into the combustion chamber 58 directly via an injector 60 , the fuel is ignited by an ignition device 62 , for example a spark plug. From the combustion chamber 58 the exhaust gas enters the exhaust pipe 37 passed in which a particle filter 64 is available. Upstream of the particulate filter 64 branches an exhaust gas recirculation line 66 in which an exhaust gas recirculation valve 68 is arranged. The exhaust gas recirculation line 66 opens into the intake pipe 56 .

In the intake pipe 56 is an air mass sensor 70 arranged, which can be designed for example as an HFM sensor. In or on the exhaust pipe 37 is downstream of the particulate filter 64 the already in connection with the 1 and 2nd described particle sensor 10 arranged.

In the 5 The internal combustion engine shown is a diesel internal combustion engine. In their exhaust pipe 37 are also an oxidation catalyst 72 and an SCR catalyst 74 arranged, being upstream of the SCR catalyst 74 an injector 76 is arranged with a reducing agent, for example a urea solution, in the exhaust pipe 37 can be injected.

Now referring to 6 a method for operating an internal combustion engine 54 according to the 4th or 5 described. After a starting block 78 is in a block 80 by means of the facility 27 the laser light sport 22 generated, in the inner protective tube 40 which of the flow 42 of the exhaust gas 36 is flowed through. In this respect, the laser light spots 22 generated in an exhaust gas leading area. In one block 82 is from the detector 32 the temperature radiation 26 captured by in the laser light spot 22 soot particles 24th is emitted. It is expected that even after the particulate filter 64 still numerous particles 24th the particle sensor 10 and thus the laser light spots 22 , which can have a dimension of the order of 10 µm, for example. The said dimension of the laser light spot 22 lies significantly above the diameter of the expected particles 24th . In most cases this should be less than 0.1 µm. In the case of the gasoline engine from 4th diameters in the range between 10 nm and 300 nm can even be expected.

In one block 84 is that from the detected temperature radiation 26 dependent output signal 34 of the detector 32 provided. In one block 86 the time period t (see above 3rd ) determined during which the output signal 34 the detection of one of a soot particle 24th outgoing temperature radiation 26 signals. This is done either over a certain period of time or over a certain number of soot particle acquisitions 24th repeated so that in one block 88 then an average of the determined time periods can be formed. However, this averaging is not absolutely necessary.

In one block 90 is made using the known dimension of the laser light spot 22 and the one in the block 88 determined mean value of the time period t a speed of the exhaust gas 36 determined. However, this speed is the speed of the flow 42 of the exhaust gas 36 internally Protective tube 40 . The speed of the exhaust gas 36 in the exhaust pipe 37 is in the block 90 obtained by using a correction factor. In the present case, this speed is also referred to as the “first” variable. Since the distance is very short, there are deviations due to jumps in the exhaust gas velocity due to the very short measuring time per particle 24th be negligibly small.

In one block 92 becomes from the speed of the exhaust gas 36 in the exhaust pipe 37 an exhaust gas mass flow in the exhaust pipe, for example using temperature and pressure values detected by means of sensors 37 determined, which in the present case is also referred to as the “second” quantity. In one block 94 the determined exhaust gas mass flow together with other information, for example that from the particle sensor 10 determined concentration and / or size of soot particles 24th in the exhaust gas 36 , used for this, a current loading of the particle filter 64 with soot particles 24th to determine what in turn can be used to regenerate the particulate filter at the right time 64 initiate. The internal combustion engine, for example, becomes such for a short time 54 operated so that the temperature of the exhaust gas 36 to a value that leads to a burning of the in the particle filter 64 soot particles 24th leads.

In one block 96 is using the in block 92 Exhaust gas mass flow determined influence on the metering of by means of the injector 76 into the exhaust pipe 37 injected reducing agent and on the control of the exhaust gas recirculation valve 68 and thus taken to the exhaust gas recirculation rate. Finally, in a block 98 the exhaust gas mass flow or a characteristic characterizing it additionally in a different way than via the particle sensor 10 determined, for example on the basis of the signal from the air mass sensor 70 , the exhaust gas recirculation rate and the amount of fuel injected. In the same block, this exhaust gas mass flow, which is a “third” quantity, is based on the output signal 34 of the particle sensor 10 determined exhaust gas mass flow, ie the "second" size, compared.

A difference is then formed between the exhaust gas mass flows determined in these different ways, and this difference is compared with a limit value. If the difference reaches or exceeds the limit value, the air mass sensor is malfunctioning 70 , an injector injector 60 , generally the exhaust gas recirculation or specifically the exhaust gas recirculation valve 68 and / or the spark plug 62 closed. It is also possible to detect a leak in the area leading to the exhaust gas, in particular in the exhaust pipe 37 , getting closed. In practice, however, such a leakage would possibly only be detected in the event of a major leak, such as, for example, as a result of an accident damage or after a motor vehicle has been put into the internal combustion engine 54 installed, on a rocky surface, occurs. If such a malfunction is detected, an entry can be made in a fault memory and / or an indication to the operator of the internal combustion engine 54 , for example to the driver of the motor vehicle in which the internal combustion engine 54 installed, are output.

The process ends in a block 100 .

QUOTES INCLUDE IN THE DESCRIPTION

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Patent literature cited

• DE 102017207402 A1 [0002]

Claims (10)

Method for operating an incinerator or internal combustion engine (54), in which a first variable characterizing an exhaust gas velocity or associated therewith is determined, characterized in that it comprises the following steps: a. Generating a laser light spot in an area (40) carrying exhaust gas; b. Detecting a temperature radiation (26) emanating from the laser light spot (22) by means of a detector (32), c. Providing an output signal (34) dependent on the detected temperature radiation (26), i. Determining the first variable at least indirectly from the output signal (34). Procedure according to Claim 1 , characterized in that the first variable is determined from a duration (t) of the output signal (34) and a dimension of the laser light spot (22). Method according to at least one of the preceding claims, characterized in that a correction factor is used when determining the first variable. Method according to at least one of the preceding claims, characterized in that the first variable related to the exhaust gas velocity is a second variable which characterizes an exhaust gas mass flow. Procedure according to Claim 4 , characterized in that a current state variable of a particle filter (10) is determined from the second variable. Method according to at least one of the Claims 4 or 5 , characterized in that the dosage of an exhaust gas aftertreatment agent depends on the second size. Method according to at least one of the Claims 4 - 6 , characterized in that an exhaust gas recirculation rate depends on the second variable. Method according to at least one of the Claims 4 - 7 , characterized in that a third variable characterizing the exhaust gas mass flow is additionally determined in another way, and that if the second variable and the third variable differ from one another by at least one limit value, a malfunction of an air mass sensor (70), an injection nozzle (60), an exhaust gas recirculation and / or a spark plug (62), or a leak in the exhaust gas leading area (40) is concluded. Method according to at least one of the preceding claims, characterized in that an average value from a plurality of detected output signals is used to determine the first variable. Apparatus (10) for determining a characterizing an exhaust gas speed or with this continuous first size, characterized in that it comprises: a. a device (27) for generating a laser light spot (22) in an area (40) carrying exhaust gas, b. a detector (32) for detecting a temperature radiation (26) emanating from the laser light spot (22), which provides an output signal (34) dependent on the detected temperature radiation (26), and c. an evaluation device (53) which is designed and set up to determine the first variable at least indirectly from the output signal (34).

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