WO2018185007A1

WO2018185007A1 - Method for ascertaining a property of a fluid

Info

Publication number: WO2018185007A1
Application number: PCT/EP2018/058179
Authority: WO
Inventors: Rupert SCHREINER; Christoph Langer; Stephan Heinrich; Torsten Reitmeier
Original assignee: Continental Automotive Gmbh
Priority date: 2017-04-07
Filing date: 2018-03-29
Publication date: 2018-10-11

Abstract

The invention relates to a method for ascertaining the composition of a fluid (F1, F2), preferably a gas mixture, such as a natural gas mixture for example. A sensor device (100) is provided which can come into contact with the fluid (F1, F2) and which has a heating element (130) that can be supplied with electric heating power and has a temperature-dependent electric resistance (R). The method has the steps of supplying the heating element (130) with a specified electric heating power for a specified first duration (Δt1) at a first temperature (T1) of the fluid (F1, F2), detecting a first time curve of the electric resistance (R) of the heating element (130) during the specified first duration (Δt1), ascertaining a first temperature conductivity (a1) of the fluid (F1, F2) at least partly on the basis of the detected first time curve of the electric resistance (R) of the heating element (130), and determining the composition of the fluid (F1, F2) at least partly on the basis of the ascertained first temperature conductivity (a1).

Description

description

Method for determining a property of a fluid The present invention relates to a method for determining at least one property of a fluid, in particular a method for determining the calorific value of the fluid, preferably a gas mixture, such as a natural gas mixture. To determine the properties of a gas mixture, example ^¬, for measuring the quality of natural gas, it is crucial selectively as possible to capture the main components of the gas mixture quantitatively. Natural gas is this example ^¬ as to the components methane, ethane, propane, butane, carbon dioxide and nitrogen. In particular, the non-flammable gases carbon dioxide and nitrogen play an important role in the combustion in terms of knock resistance. Since this selective measurement is very difficult and with a considerable measurement effort is possible, often correlative techniques are applied, with which from individual independent physical quantities, such. As density, speed of sound, thermal conductivity, specific heat capacity or viscosity, the composition or properties of the corresponding mixture is determined.

For binary gas mixtures, which consist of at least two specific gas components, it is possible to conclude by measuring a physical quantity on the composition or concentration of these gas components. For gas mixtures with more than two components, however, such a relationship is no longer unambiguous, which is why it helps to the above-mentioned correlation calculations. An attempt is made to mathematically connect two or more physical quantities in such a way that one approximates a functional connection as far as possible can reach small deviations. This principle of correlation can be applied not only to the composition or concentration or property of the gas mixture, but also to other physical quantities, such as the calorific value of the gas mixture, which is important for setting the Ver ^¬ combustion parameters in an internal combustion engine.

In particular, the calorific value is that physical quantity of a gas mixture which is relevant for setting the combustion parameters in an internal combustion engine of a vehicle. Another combustion-relevant variable is the amount of oxygen required for a stoichiometric combustion. To ^¬ before described correlation allows, for example, the quality of natural gas to be specified, in which one uses the physical properties kaiischen relating to calorific value, methane number or air required for combustion.

However, determining these physical quantities of fluids, especially gases, as described above, can be very difficult to sometimes impossible. For example, the thermal conductivity or Thermal conductivity ^¬ ness can be determined relatively easily by temperature sensitive probes, so the specific heat capacity can be achieved only by expensive equipment and conditions in combination with defined set measurement. In this context, that is

Generating a defined gas flow via a critical nozzle call or measuring the gas flow with hot wire anemometer and retroactive accounting for the heat capacity of the gas. In physics, the so-called thermal conductivity (also called temperature code) is known. The thermal diffusivity is a material property that is used to describe the temporal change in the spatial distribution of the temperature due to heat conduction as a result of a temperature gradient. she is often specific to the material and is made up of the quotient of thermal conductivity and the product of density and specific heat capacity ^¬ fish. By measuring the individual quantities mentioned in this formula, the temperature conductivity can be calculated from this. Consequently, the two physi ^¬ cal variables thermal conductivity and thermal conductivity are different physical quantities.

Thus, the thermal diffusivity as material property is also suitable for the characterization of fluids, in particular gas mixtures, such as natural gas mixtures, and can be used as an input for correlation calculations to determine fluid properties. The convection and radiation are negligible.

For example, from DE 10 2013 012 434 AI an improved Pirani sensor is known, in which the measuring element is arranged in the fluid between a base plate and a heat sink. The measuring element is held by suspensions in the correct position. The suspensions are connected to the base plate and a separate heating element is in turn thermally conductive with the suspensions. The Pirani sensor detects the heat losses through the fluid to the heat sink while balancing the heat losses to the suspensions with the separate heating elements. This compensates for the parasitic heat losses from the Pirani sensor to the suspension.

Furthermore, EP 1 409 963 B1 discloses a sensor for generating a signal which indicates a predetermined physical parameter. The sensor includes a sensor element, to which a drive signal can be applied and dependent on the vorbe ^¬ voted physical parameter and the control signal generates an output signal. In addition, a drive device is provided, which controls the drive signal with a predetermined "

Waveform applied to the sensor element such that the output signal ^¬ from the sensor element reaches a predetermined Schwel ^¬ lenwert. A time measuring circuit of the sensor detects the time duration until which the output signal reaches the aforementioned threshold value from a predetermined starting value of the output signal and generates from the time duration the signal indicating the physical parameter.

DE 10 2013 220 908 AI relates to a sensor element with a measuring element and a measuring ^{¬ the} housing at least partially um ^¬ giving, designed as Kunststoffmoldgehäuse functional ^¬ housing. The measuring element is in this case designed as a hotplate, which is largely thermally decoupled by means of narrow arms mounted on a carrier substrate.

It is an object of the present invention to provide a method with which, as simply as possible, at least one property of a fluid, in particular of a gas mixture, such as a natural gas mixture, can be determined. This object is achieved by a method according to independent claim 1. Preferred embodiments are specified in the subclaims.

The invention is based, at least in part, on the idea of determining the thermal conductivity of the fluid by means of a suitable measurement setup and of determining the at least one property of the fluid by means of suitable mathematical correlation calculations. The physical effect of a temperature-dependent resistor is used. Namely, the temperature-dependent resistance is differently sensitive with suitable control with electrical power to the present fluid, in particular gas mixture, such as natural gas mixture. In particular, with the aid of the temperature-dependent resistor, the heat-conducting keit and the thermal diffusivity are determined to turn, as described above, on the at least one property such. As the calorific value of the fluid to be able to conclude by means of the correlation calculations.

This can be particularly advantageous in internal combustion engines, which are operated exclusively with natural gas, whereby the need for a liquid fuel, such as Ben ^¬ zin, for starting the internal combustion engine can be omitted. By knowing at least one property of the natural gas, as in ^¬ example, the calorific value of the natural gas, the operating ^¬ parameters of the engine can be optimally adjusted so that the engine can be started with natural gas.

According to a first aspect of the invention there is thus disclosed a method for determining at least one property of a fluid, preferably a gas mixture, such as a natural gas mixture. For this purpose, a sensor device (100) is provided, which can come into contact with the fluid and having a heating capacity can be acted upon with electrical heating element with a ^¬ em temperature-dependent electrical resistance. The inventive method comprises applying the heating element with a predetermined first electrical heating power for a predetermined first period of time at a first temperature of the fluid, detecting a first time course of an electrical variable characterizing the electrical resistance of the heating element during the predetermined first period of time Determining a first temperature conductivity of the fluid based at least in part on the detected first time history of the electrical quantity and determining the at least one property of the fluid based at least in part on the determined first temperature conductivity of the fluid. _r

In an advantageous embodiment, the inventive method further comprises determining a first time profile of the electrical resistance of the heating element at least partially based on the detected first time profile of the electrical variable and the first electrical heating power. In this case, the at least one property of the fluid is determined at least partially based on the determined first time profile of the electrical resistance of the heating element. In particular, on the Ohm 'law see from the temporal course of the electrical quantity, that is via the electrical clamping ^¬ voltage or the electric current, the time profile of the electrical resistance of the heating element are determined in consideration of the predetermined heat output.

In an advantageous embodiment, the determination of the first thermal conductivity is also based at least in part on the determined profile of the electrical resistance of the heating element.

Thus, a method is provided which can be performed by means of a relatively simple sensor device and a specific operating strategy. Preferably, the sensor device used has a structure similar to a Pirani vacuum gauge. In a preferred embodiment, which will be described in more detail below, the sensor device compared to a Pirani vacuum gauge only one used as a heat source and heat sink Heiz ^¬ element, which is characterized by a temperature-dependent resistance.

In an advantageous embodiment, the method according to the invention further comprises subjecting the heating element to a predetermined second electrical heating power for a given period of time. ^

certain second time duration at a second temperature of the fluid, which is different from the first temperature, detecting a second time course of an electrical resistance of the heating element characterizing the fresh fresh variable during the predetermined second period of time and determining the at least one property of the fluid ^{¬ at} least partially based on the detected time course of the electrical quantity.

In an advantageous embodiment, a determination of a second time profile of the electrical resistance of the heating element is also provided based at least partially on the detected second time profile of the electrical variable and the second electrical heating power. In this case, the at least one property of the fluid is determined based at least partially on the determined second time profile of the electrical resistance of the heating element. In particular, the time characteristic of the electrical resistance of the heating element, taking into account the predetermined heating power, can be determined via the ohmic law from the time profile of the electrical variable, that is to say via the electrical voltage or the electric current.

In a further advantageous embodiment, the inven tion proper method further comprises determining a second thermal conductivity of the fluid based at least partially on the detected second time course of the electrical quantity and / or at least partially based on the detected second time profile of the electrical resistance of the heating element. In this case, the at least one property of the fluid is determined at least partially based on the second determined thermal conductivity. ₀

O

The electrical quantity is preferably the voltage drop across the heating element during the respective predetermined periods of time, during which the heating element is supplied with an electric current for supplying the respective predetermined electrical heating powers. Alternatively, the electrical quantity of the electrical current flowing through the heating element during the respective predetermined periods, during which the electrical voltage for supplying the vorbe ^¬ votes electrical heating power is applied to the heating element.

In a preferred embodiment, the inventive method further comprises applying the heating element with a predetermined heating power for a predetermined heating period for heating the fluid from the predetermined first temperature to the predetermined second temperature. The heating element can therefore simultaneously assume a heating function in addition to its actual main function as a sensor element.

Preferably, the method according to the invention further comprises determining a first time constant which indicates the time duration that the electrical resistance of the heating element ^goes from a first electrical resistance at the beginning of the predetermined first time period to a predetermined proportion of a second electrical resistance at the end of the first predetermined first time duration, and determining a second time constant, which indicates the time duration, the electrical resistance of the heating element from a first electrical resistance at the beginning of the predetermined second time period to increase to a predetermined proportion of a second electrical resistance at the end of the predetermined second time period needed. In this case, the determination of the composition of the fluid is based at least partially on the determined first time constant and the determined second time constant. "

Alternatively, it may be advantageous if the time constants are respectively determined based on the detected time profiles of the electrical quantity. From the time constants determined in this way, it is then possible to deduce directly the at least one property of the fluid, or additionally or alternatively the temperature conductivities of the fluid.

Advantageously, the method fer ^¬ ner according to the invention comprises determining a first electrical resistance difference between a first electric resistance of the heating element at the beginning of said predetermined first period and a second electrical resistance of the heating element at the end of vorbe ^¬ approved first time period and determining a second electrical resistance difference between a first electrical resistance of the heating element at the beginning of the predetermined second time period and a second electrical resistance of the heating element at the end of the predetermined second time period. In this case, the determination of the at least one property of the fluid is based at least in part on the determined first electrical resistance difference and the determined second electrical resistance difference.

Again, it may alternatively be preferable to respectively determine a voltage and / or Stromdif ^¬ conference instead of resistance reading differences, resulting in one characteristic of the fluid can be closed at least turn.

Preferably, the method further comprises thereby to determining a first thermal conductivity of the fluid at least partially ba ^¬ sierend on the detected first electrical resistance difference and determining a second thermal conductivity of the fluid at least partially based on the detected second electrical resistance difference (AR). It is based on that Determining the composition of the fluid at least partially on the determined first thermal conductivity and the determined second thermal conductivity. In a further advantageous embodiment of the method according to the invention, the application of a predetermined electrical current pulse to the heating element with the respective electrical heating power in each case for the predetermined periods of time. It may be preferred if the predetermined current pulses have a rising, falling, sudden, triangular and / or sinusoidal time course.

Furthermore, it may be preferred that the application of the heating element with electrical heating power comprises applying a predetermined electric current pulse to the heating element for the predetermined period of time. Alternatively, the Beauf ^¬ beat of the heating element with electrical heating power can apply a predetermined electrical voltage to the heating element for the predetermined period of time.

According to the present method, the time constants, which preferably corresponds to the respective rise time to the predetermined proportion of the determined second electrical resistance at the end of the respective predetermined time period, can be proportional to the respective thermal conductivity. In addition, the resistance difference determined can be proportional to the thermal conductivity ^¬ ability of the present fluid. The respective plurality of such parameters determined thermal diffusivity and thermal conductivity can be as input variables of mathematical correlations for the characterization of the fluid, in particular of the gas mixture, such as natural gas mixture zoom are drawn ^¬. From the characterization of the fluid can then be relevant for setting the combustion parameters of the internal combustion engine for the vehicle operating parameters, such as calorific value, methane number, Wobbe index, oxygen or. Air requirements for the stoichiometric combustion, etc., to be determined.

In the context of the present invention, by suitable mathematical correlation of the detected parameters, such as thermal conductivity, which can be determined based on the time constant, thermal conductivity, which can be determined based on the resistance difference, and density, the at least one property of the fluid are determined. The mathematical correlation can be, for example, a polynomial function or an exponential function of the detected parameters. For example, the detected parameters thermal diffusivity, thermal conductivity and density can each be provided with an exponent and multiplied together to determine a value from which one can derive the at least one property of the fluid, such as the calorific value of the fluid.

Alternatively or additionally, the detected or determined electrical quantities and / or the time constants and / or the differences formed can also be used in the mathematical correlation.

Further features and aspects of the present invention will become apparent to those skilled in the art from the practice of the present teachings and from the accompanying drawings, in which:

1 shows a plan view of an exemplary Sensorvor ^¬ direction, FIG. 2 shows a sectional view of the sensor device of FIG. 1 along the line II - II, in which the sensor device is at a first production step, FIG.

FIG. 3 shows the sensor device shown in FIG. 2 at a later production time, FIG.

4 shows the sensor device shown in FIG. 3 at an even later time of manufacture,

5 is a diagram showing the time course of a temperature-dependent resistance of a heating element for two different fluids,

FIG. 6 is a flowchart of an example method; FIG.

7 shows a flow diagram of an exemplary method according to the invention,

FIG. 8 is a graph showing the time courses of the electric current, the electric voltage and the temperature, which result according to the method according to the invention of FIG. 7, FIG.

9 shows the different temperature-dependent specific heat capacities for different fluids,

FIG. 10 shows the temperature-dependent course of the thermal conductivity for the fluids shown in FIG. 9, and FIG Fig. 11 shows the temperature-dependent profile of the thermal conductivity for the in Figs. 9 and 10 Darge ^¬ presented fluids.

Those skilled in the art will recognize that the features and aspects of the present invention, which are more particularly specified in the present specification, are in any way combinably and loosely disclosed. This particularly concerns the order of the disclosed methods.

In the context of the present invention, the at least one property of the fluid, which is determined by means of the method according to the invention and the sensor device according to the invention, describes a combustion-relevant size of the fluid, such as the calorific value of the fluid, the amount of oxygen required for stoichiometric combustion of the fluid, etc. It should be emphasized that that does not include at least one ^self-¬ shaft of the fluid, the temperature of the fluid. Fig. 1 shows a plan view of an exemplary sensor ^¬ device 100 is adapted to determine the composition and a property of a fluid mixture fluid, especially a gas mixture, such as a natural gas mixture. In this case, the sensor device 100 has an essentially planar micromechanical structure (MEMS).

The sensor device 100 includes an applied on a support substrate 110. Sensor substrate 120, in and / or on which in turn a heating element is seen 130 in the form of a meander in front ^¬. In the carrier substrate 110, which preferably consists of silicon, a recess 112 is provided (see also FIG. 4), wherein the sensor substrate 120 extends at least partially over the recess 112. The sensor substrate 120, which preferably consists of silicon nitride, has a sensor region 122 and two connection ^regions 124, 126. The connection regions 124, 126 are connected to the sensor region 122 via narrow arms 123A, 123B, 123C, 123D such that the sensor region 122 is substantially thermally decoupled from the connection regions 124, 126.

The heating element 130 is electrically connected via connecting lines which run on and / or in the narrow arms 123A, 123B, 123C, 123D, to connecting elements 142, 144 respectively arranged in and / or on the connecting regions 124, 126 of the sensor substrate 120, and can be of a control device (not explicitly shown in the drawings) are driven. The connecting elements 142, 144 are preferably made of gold. The heating element 130 has a temperature-dependent electrical resistance.

The heating element 130 provided in and / or on the sensor region 122 of the sensor substrate 120, which is preferably made of nickel or a nickel alloy, together with the sensor region 122 forms a self-supporting structure, which essentially decouples from the connection regions 124, 126 and the carrier substrate 110 is. The sensor device 100 of FIG. 1 is a micromechanical structure, i. H. the sensor device 100 is produced in a so-called MEMS construction.

With reference to FIGS. 2 to 4, a manufacturing process of the micromechanical sensor device 100 is described by way of example. 2 to 4 each show a section through the sensor device 100 shown in FIG. 1 along the line II-II of FIG. 1 at different times during the manufacturing process of the MEMS structure. As already explained above, the sensor device 100, the carrier substrate 110, on which the sensor substrate 120 is set ^¬ introduced, in which the heating element 130 and the connection ^¬ elements 142, 144 are at least partially introduced (see FIG. 2). At this time, the sensor substrate 120, the heating element 130, and the connecting elements 142, 144 from ^¬ are already separated.

In a further step, the sensor substrate 120 is dry-etched in such a way that at least the structure of the heating element 130, in particular in the sensor area 122 of the sensor substrate 120, is placed freely ^¬ (see Fig. 3).

In a last step, by anisotropic undercutting, the sensor region 122 of the sensor substrate 120, in and / or on which the heating element 130 is arranged, is exposed such that the four narrow arms 123A, 123B, 123C, 123D are formed, which are designed to carry the sensor area 122 together with the heating element 130. By creating the depression 112 extending below the heating element 130, it can be ensured that the fluid approaches the heating element 130 in almost all spatial directions and thus makes contact with the contact surface between the heating element 130 and the fluid whose properties are to be determined can. Consequently, substantially all of the heating element may reach 130 with the fluid in thermal exchange ^¬ effective. For example, the recess 112 has a length of about 1 mm to about 2 mm, with the support substrate 110 having dimensions of about 5 mm in length, about 6 mm in width, and about 1 mm in height.

In this case, it is preferred that the four arms 123A, 123B, 123C, 123D are as narrow and thin as possible in order to ensure that the thermal conductivity of the solids (ie the heating element 130, the sensor region 122 of the sensor substrate 120 and the four arms 123A, 123B, 123C, 123D) are as small as possible and consequently only the thermal diffusivity of the fluid to be measured is detected. The parasitic influence of the aforementioned interference temperature conductivities can thus be minimized.

The sensor device 100 is preferably arranged in the fuel delivery system of an internal combustion engine (not shown). The natural gas-powered internal combustion engine may for this purpose have a natural gas tank, in which usually the natural gas is kept under a pressure between about 200 and 250 bar. The natural gas tank may be connected to the combustion chambers of the internal combustion engine via a filter, which is also connected to the ambient air for sucking in the ambient air, and a pressure regulator. At a point downstream of the pressure regulator there is a pressure of, for example, a maximum of 20 bar. The sensor device is preferably mounted at a position downstream of the pressure regulator and upstream of the combustion chambers. Consequently, with the sensor device 100, the thermal conductivity of that natural gas mixture which is immediately before combustion can be detected. Thus, the internal combustion engine can be optimized operating parameters with knowledge of the thermal diffusivity determined, the fuel ^¬ value, the methane number, etc., are operated in an effective and efficient manner.

The sensor device 100 shown in FIGS. 1 to 4 can be used to detect the thermal diffusivity of the fluid to be measured according to the method shown in FIG. 6 or according to the method shown in FIG. 7, in each case that shown in FIG. 5 shown context is at least partially taken advantage of.

FIG. 5 shows time profiles of the temperature-dependent resistance R of the heating element 130, which vary with different Fluids Fl, F2 has come into contact and was applied with a predetermined heating power for a predetermined period of time At. For example, the heating element 130 for the certain period of time before ^¬ At with a predetermined current pulse was aufschlagt loading.

The predetermined period of time At is about 60 ms, for example. For example, the greater the pressure of the fluid, the greater the predetermined time period Δt. That is, the heating element 130 is supplied with the predetermined current pulse for the predetermined period of time Δt, for example, a constant current pulse of about 2 mA to about 4 mA. During this predetermined period of time Δt, the electrical resistance R of the heating element 130 is detected. For example, 130 detected with the particular front ^¬ current pulse which berthing at the heating element 130 by means of the voltage and see Ohm 'law of ent ^¬ speaking electric resistance R during the application of the heating element are determined. Alternatively, for detecting the temporal course of the electrical resistance R of the time course of the voltage drop across the heating element 130 electric voltage can be detected and for determining the at least one characteristic of the fluid Fl, F2 are attracted ^¬ forth. This is particularly advantageous in applying a con- stant current pulse, since this results in a proportional to the elec trical resistance profile ^¬ electrical voltage curve.

FIG. 5 essentially shows two characteristic curves for two different fluids F1 and F2. The solid line shows the time profile of the temperature-dependent resistance R for the heating element 130, which is in contact with a first fluid Fl, wherein the dashed line in FIG. 1 shows the time profile of the resistance R of the heating element 130th represents, in which the heating element 130 is in contact with a second fluid F2, which is different from the first fluid Fl. For example, the first fluid Fl is a gas mixture consisting of 100% methane. The second fluid F2, on the other hand, is a gas mixture consisting of approximately 70% methane and approximately 30% nitrogen. It can thus be seen from FIG. 5 that the time profile of the electrical resistance of the heating element 130 during the predetermined period of time Δt may depend on the composition of the gas mixture.

The heating element 130 is acted upon at a first time ti with the predetermined current pulse, which is switched off again at a later second time t ₂ . The predetermined current pulse is preferably a constant current pulse. Alternatively, the predetermined current pulse may have a rising shape, a falling shape, a sine shape, or any other known current pulse shape.

The time interval between ti and t ₂ describes the predetermined time t. In the diagram in Fig. 5, it is assumed that the temperature of the two fluids Fl and F2 are at the same level at the beginning of the application of the heating element 130 with the predetermined heating power, for example at ambient temperature. In particular, the fluid temperature is a relevant parameter, since the time course of the electrical resistance of the fluid temperature depends significantly. Consequently, the detection of the temperature of the fluid is advantageous, for example by means of a separate temperature sensor.

Alternatively, the fluid temperature can be detected by means of a further current pulse following the current pulse.

At the beginning of the current pulse at time ti, the first fluid Fl has the predetermined temperature and the electrical resistance R of the heating element 130 has a first electrical resistance RFH on. At the end of the current pulse at time t _2, the first fluid Fl a higher temperature and the electric resisting ^¬ stand the heating element 130 has a second electrical resistance R _F i2.

Similarly, at the beginning of the current pulse, the second fluid F2 has the predetermined temperature and the electrical resistance R of the heating element 130 has a first electrical resistance R _F 2i. At the end of the current pulse at time t _2, the second fluid F2 is higher in temperature and the electric resistance R of the heating element 130 has a second electrically ^¬ en resistor R _F 22.

FIG. 6 shows a flowchart of an exemplary method for determining the composition of the fluid F1 (see FIG. 5). In this case, reference is made to the time profile of the electrical resistance R of the heating element 130 of FIG. 5 reference. The process of FIG. 6 starts at a step 200 and then goes to step 201 where a predetermined heating power is applied to the heating element 130 in the form of a predetermined constant current pulse for the predetermined period of time Δt. Alternatively, the predetermined heating power may also be provided in the form of a predetermined constant voltage applied to the heating element 130.

In a subsequent step 202, which also begins predominantly simultaneously with step 201, the time profile of the electrical resistance R of the heating element 130 is recorded or determined during the predetermined period of time Δt. As shown in Fig. 5, thereby resulting in different fluids Fl, F2 different temporal profiles of the elec tric ^¬ resistance. This is particularly important for the attributable to different thermal conductivities and thermal diffusivities of the different fluids.

The time profile of the electrical resistance R of the heating element 130 can be determined, for example, by detecting the electrical voltage resulting from the application of the current pulse and the conversion of the current pulse together with the electrical voltage by means of the ohmic law. As already mentioned, alternatively, the time profile of the electrical voltage drop across the heating element 130 can be evaluated directly with regard to the at least one property of the fluid.

In a subsequent step 203, a first electrical resistance R _F n at the time ti and a second electrical resistance R _F i2 at the time t ₂ are determined from the determined temporal profile of the electrical resistance R of the heating elements ^¬ 130th From the first electrical resistance R _F n and the second electrical resistance R _F i2, a resistance difference AR, which is proportional to the thermal conductivity λ of the fluid F1, is also formed at step 203. Thus, from the electrical resistance difference AR, the thermal conductivity λ of the fluid F1 can be determined or at least partially estimated.

In addition, the time constant ^¬ ii ₆₃ is determined at step 203 from the time variation of the electric resistance R of the heating element 130 with which the composition of the first fluid Fl is detected. The time constant ii ₆₃ is thus a rise time, which indicates that length of time that the elekt ^¬ generic resistance R of the heating element 130, starting from the first electrical resistance R _F n to rise to a vorbe ^¬ agreed proportion of the second electrical resistance R _F i2 be ^¬ compels , The predetermined proportion is preferably in one Range between about 30% and about 90%, more preferably in a range between about 55% to about 70%. In the most preferred embodiment of the method, the predetermined proportion is approximately 63.2%. The value of about 63, 2% results from 1 / e. In a dynamic system, the time constant ii 63 is a characteristic quantity.

The determination of the time constant ii 63 is carried out with knowledge of the first and second electrical resistance R _F H, R _F I2 and with the predetermined proportion, from which the electrical resistance value R _F I 63 is determined. Of the electric resistance value R i _F 63 via the time course associated value is the time constant Ti ^¬ · 63

The time constant 63 determined ii is proportional to the Tem ^¬ peraturleitfähigkeit a (or the thermal diffusivity) of the fluid Fl. This means that with a measuring cycle, namely the single application of the heating element 130 with temperature-dependent resistance with a predetermined heating power, the thermal diffusivity a of the present fluid Fl by determining the time constant ii 63 and the thermal conductivity λ of the ^¬ lying fluid Fl by determining the resistance difference AR can be determined.

The determined from the time constant ii 63 Temperaturleitfähig ^¬ a ness according to the formula known from the literature be calculated as follows: λ

a =

p- c _P with: a thermal conductivity of the fluid Fl, λ thermal conductivity of the fluid Fl,

p density of the fluid Fl, and

c _P specific heat capacity of the fluid Fl. Thus, by determining the time constant ii 63 at step 204, the temperature conductivity a of the fluid Fl can be determined. More specifically, to determine the thermal diffusivity a, the specific heat capacity c _P and / or the density p of the fluid Fl need not be determined, since by determining the time constant ii 63, the thermal diffusivity a (ie the quotient given above) is determined directly or at least partially can be estimated.

From the temperature conductivity a determined via the time constant ii 63 and the thermal conductivity λ determined via the resistance difference AR, the composition of the fluid F1 can be determined by means of a suitable mathematical correlation.

For even more accurate determination of the composition of the fluid F1, the density p of the fluid F1 can be determined in accordance with the method of FIG. 6 in addition to the thermal conductivity a and the thermal conductivity λ. To this end, at step 205, the pitch coupled with ^¬ means of an ultrasonic transmitter and ultrasonic ^¬ lempfängers, ultrasonic waves in the fluid Fl, and the reflections thereof detected. Here, preferably, a reflector within the fluid is provided, to which the out ^¬ emitted ultrasounds can reflect. The reflector has to the ultrasonic transmitter / receiver on a predetermined distance. By recording the transit time of the ultrasound over the predetermined distance (way and return), the sound velocity ^¬ speed can be determined in the fluid Fl.

At a subsequent step 206, the speed of sound determined at step 205 is taken into account (adiabatic) compression modulus determines the density p of the fluid Fl. The density p of the fluid Fl can then, together with the previously determined sizes, thermal diffusivity a and heat conductivity λ ^¬ operates comparable means of a mathematical correlation (see step 207).

The mathematical correlation can be, for example, a polynomial function or an exponential function of the detected parameters. For example, the parameters recorded thermal conductivity, thermal conductivity and

Density are each provided with an exponent and multiplied together to determine a value from which one can derive the at least one property of the fluid, as in ^¬ example, the calorific value of the fluid. For example, a mathematical correlation might look like this:

H = λ ^{2 ■} eP ^'a where H indicates the calorific value of the fluid.

At a further step 208, the composition of the fluid F1 is finally determined from the mathematical correlation of the variables density p, thermal conductivity λ and thermal conductivity a before the method of FIG. 6 ends at a step 209. From the determined composition of the fluid Fl then further relevant for the operating parameters of an exclusively natural gas-powered internal combustion engine such. As the calorific value of the fluid Fl, the methane number of the fluid, and the oxygen demand for a stoichiometric combustion of the fluid Fl, are determined.

According to the method described above, however, an even more precise determination of the composition of the fluid F1 in addition to the sensor device 100 is an additional ultrasonic sensor for detecting the speed of sound in the fluid Fl required. borrowed. Alternatively, to determine the density of the fluid Fl also the viscosity can be ^¬ it averages, which in turn can be considered in the mathematical correlation by means of a viscosity sensor.

With reference to FIG. 7, a method according to the invention for operating the sensor device 100 of FIGS. 1 to 4 for determining the composition of a fluid F1 is shown. The following description of the method according to the invention of FIG. 7 is given in conjunction with the diagram of FIG. 8, which shows the time profiles of the electrical current I applied to the heating element 130, the electrical voltage U applied to the heating element 130 and the temperature T of the fluid F. FIG shows.

The inventive method of FIG. 7 makes use of the knowledgeable ^¬ It utilizes the fact that the thermal conductivity λ, the Tempe ^¬ raturleitfähigkeit A and the specific heat capacity c _p of fluids is temperature-dependent (see in particular Figs. 9 to 11). This means that the thermal ^diffusivity a and the thermal conductivity λ can be determined at different temperatures of the fluid to be measured, in which case the temperature conductivities and the thermal conductivities determined at different temperatures serve as input variables for the mathematical correlations already mentioned above.

In particular, determining the temperature conductivities and the thermal conductivities at different temperatures eliminates the determination of the density of the fluid by means of ultra-sound waves, whereby an additional ultrasonic sensor is no longer needed, which can lead to a reduction in the cost of the sensor. In addition, the mechanical structure of the sensor device is simplified and requires less space. The method of FIG. 7 begins at step 300 and then moves to step 301, at which the heating element is applied with a predetermined first electrical heating power for a predetermined first time period Atl in a vorbe ^¬ voted first temperature T _Pi 130th The first time period Atl extends between a first time ti and a second time t ₂ . For example, the charging of the heating element with the first electric heating power is effected by applying the heating element 130 with a predetermined first current pulse I _P i (see FIG. 8). Alternatively, the heating element 130 can be subjected to the predetermined first electrical heating power by applying a predetermined first voltage U to the heating element 130.

At a further step 302, which starts simultaneously with step 301, the time profile of the resistance R of the heating element 130 is detected. For example, ^¬ beat of the heating element 130 with the predetermined first current pulse I which pi-applying to the heating element 130 detects voltage U and see using the Ohm 'law the time characteristic of the resistance R after Beauf be determined as follows:

II PI

R _P1

'PI with: electrical resistance R at the heating element 130 during the first electric current pulse I _P i, electrical voltage U at the heating element 130 during the first electric current pulse I _P i, and first electric current pulse. An exemplary time profile of the electrical voltage U applied to the heating element 130 upon application of the heating element 130 with the predetermined first electrical current pulse I pi for the first predetermined period of time Atl at the first temperature Tl is shown in FIG. It is also apparent from FIG. 8 that the first electrical current pulse I pi is a constant electric current pulse. Alternatively, the first electric current pulse I _P i, a rising ^¬ to form a sloping shape, a sinusoidal shape or jeg- Liehe comprise other known current pulse shape.

In a subsequent step 303, from the detected time profile of the electrical voltage U, in a manner similar to that already described with respect to the method according to FIG. 6 on the basis of the time characteristic of the electrical resistance R at the heating element 130, a first one is determined clamping ^¬ voltage difference AUpi and a first time constant _τ Ρ ι _63, indicating the that time period that the voltage at the heating element 130 from a first voltage Uo at the beginning of the predetermined first time period Atl to rise to a predetermined portion of a second electrical voltage Upi determined at the end of the predetermined first time Atl needed. The predetermined first time period Atl extends from a first time t1 to a second time t2.

Since, as described above, the electrical voltage U and the electrical resistance R are linked to each other via the above-mentioned Ohm's law, in a subsequent step 304, a first thermal conductivity λΐ of the first voltage difference AU _P i and a first thermal conductivity can al be determined from the first time constant τ _Ρ ι ₆₃ at the first temperature T _Pi . Rather than the first thermal conductivity λΐ and the first Tempe ^¬ raturleitfähigkeit al via the electrical voltage U to he ^¬ forward, it is alternatively possible, these two physical quantities, as already described with reference to the example shown in FIG. 6 method in detail, from the time course of the electrical resistance R, namely, a first resistance difference and a first time constant determined from a first resistor at the beginning of the first time period Atl and a second resistance at the end of the first time period Atl. In addition, it is possible to determine the first thermal conductivity λΐ over the time profile of the voltage drop across the electrical resistance.

At time t ₂ , the fluid Fl has the first temperature Tl. In a further step 305, the heating element 130 is subjected to a predetermined heating power for heating the fluid near the sensor to a predetermined second temperature T2. The heating of the fluid near the sensor takes place during a heating ^¬ duration At _He i _z , which extends between the second time t2 and a third time t3. For example, the heating element ^¬ 130 is subjected to a predetermined heating current I _H, which for example is constant and about 15 mA is (see Fig. 8). In this case, the electrical voltage at the heating element 130 rises from the second electrical voltage U _P i to an electrical heating voltage U _H. The temperature increase from T1 to T2, for example, is about 25 ° C, and any increase in temperature can be implemented.

The first current pulse I _P i can be approximately 2 mA, for example. The heating current I _H is z. For example, about 15 mA. The second current pulse I _P2 is approximately 17 mA, wherein therein the heating current I _{H is} taken into account and thus the absolute value of the second current pulse I _P2 relative to the heating current is equal to the absolute value of the first current pulse I _P i. ^ ₀

In a subsequent step 306, the heating element 130 at time t3, at which the fluid has the second temperature T2, with a second heating power, preferably a second current pulse I _P 2, applied. It should be mentioned that the second current pulse I _{P2 is} preferably selected such that it represents a sum of the first current pulse I _P i and the heating current I _H. This means that even during the second time period At2, the heating current I _H is present, so that the fluid Fl continues to be heated.

The subsequent steps 307-309 are essentially the same be ^¬ registered already in relation to the first current pulse I _P i steps 302 to 304, wherein a second thermal conductivity of a second Temperaturleit ^¬ ability is determined a2 at the second temperature T2 at step 309, X2 and , In this case, the heating element 130 is acted upon by the second electrical current pulse I _P2 for a second time period At2, which extends between the third time point t3 and a fourth time point t4.

Preferably, the first time period Atl and the second time duration At2 are the same length. In addition, it is preferable if the first electric current pulse IPI is equal to the second electric current pulse IP2.

In particular, 'can again following Ohm shear connection between the second electric current pulse I _P2, the electric Heizstrompuls I _H, which provide the resultant second voltage difference U 2 _P and the resultant electrical resistance R _P 2 fixed ^¬:

AU P, 2

AR P2

AI P2 With :

AR _P2 electrical resistance R (relative to the starting resistance at time t3) at the heating element 130 during the second electric current pulse I _P2 ,

Δυ _Ρ2 electrical voltage difference between a

Voltage U _H at the beginning of the second time period At2 and a voltage U _P 2 at the end of the second time period At2 during the second electric current pulse I p ₂ , and

ΔΙρ2 second electric current pulse (based on the heating current I _H ).

Thus were up to the step 309 at two different temperatures Tl, T2 different physical variables, it averages ^¬, namely λΐ a first thermal conductivity of the first fluid temperature Tl and a first thermal conductivity and at a2 of the second fluid temperature T2, a second thermal conductivity X2 and a second temperature conductivity a2 ,

In alternative method, the steps can be repeated 305 to 309 after the step 309 again, so that further heat conductivities _λ η ^¬ and further temperature conductivities a _n of the fluid at another different temperatures T _n can be determined. It can be said that the accuracy of the determined composition of the gas temperature increases with the increase of the determined thermal conductivities and thermal conductivities. In a subsequent step 310, the composition of the fluid can be determined with reference to FIGS. 9 to 11 from the plurality of detected thermal conductivities λ and the plurality of detected thermal conductivities a using a mathematical correlation. With reference to FIGS. 9 to 11, the temperature-dependent curves of the specific heat capacity (see FIG. 9), the thermal conductivity λ (see FIG. 10) and the temperature conductivity a (see FIG. 11) are for predetermined fluids, in particular natural gases , namely, for methane, ethane, propane, n-butanes, nitrogen dioxide and nitrogen. In FIGS. 9 to 11, the solid lines describe the progressions for methane, the dashed-dotted lines the progressions for ethane, the dash-dotted lines the progressions for propane, the long-dashed short-dashed lines the progressions for N Butane, the dotted lines the gradients for nitrogen and the dotted lines the gradients for carbon dioxide. It should be noted that the natural gas, methane, ethane, propane, and N-butanes are combustible hydrocarbons such, whereas the nitrogen and carbon dioxide, inert gases ^¬ and thus are not combustible.

Knowing the respective courses for the different fluids, by operating the sensor device 100 according to the method described in FIG. 7, the present fluid can be specified. Thus, it is possible to deduce the composition of the fluid and thus the calorific value (or other properties of the fluid) so that the operating parameters of an internal combustion engine operated exclusively with natural gas can be set such that the internal combustion engine can also be started with natural gas and operated optimally.

The project leading to the present application received funding from the European Union's Horizon 2020 research and development program under grant agreement number 652816.

Claims

claims

1. A method for determining at least one property of a fluid (Fl, F2), preferably a gas mixture, such as a natural gas mixture, wherein a sensor device (100) is provided, which can come into contact with the fluid (Fl, F2) and a heating output can be acted upon with electrical heating element (130) having a temperaturab ^¬ dependent electrical resistance (R), said method comprising:

Applying a predetermined first electrical heating power to the heating element (130) for a predetermined first period of time (Atl) at a first temperature (Tl) of the fluid (Fl, F2),

- detecting a first time course of the electrical resistance (R) of the heating element (130) cha ^¬ rakterisierenden electrical quantity during the predetermined first time period (Atl)

Determining a first thermal conductivity (al) of the fluid (Fl, F2) based at least partially on the detected first time profile of the electrical variable, and

Determining the at least one property of the fluid (Fl, F2) based at least in part on the determined first thermal conductivity (al)

2. The method of claim 1, further comprising:

Determining a first time history of the electrical resistance (R) of the heating element (130) based at least in part on the detected first time history of the electrical quantity and the first electrical heating power, wherein the at least one property of the fluid (Fl, F2) is based at least in part on the determined first time course of the electrical resistance (R) of the

Heating element (130) is determined.

3. The method according to any one of the preceding claims, wherein the determination of the first thermal conductivity (al) of the fluid (Fl, F2) further based at least partially on the determined first time profile of the electrical resistance (R) of the heating element (130).

4. The method according to claim one of the preceding

Claims, further comprising:

Supplying the heating element (130) with a predetermined second electric heating power for a predetermined second period (At2) at a second temperature (T2) of the fluid (Fl, F2) different from the first temperature (T1),

Detecting a second time course of the electrical resistance (R) of the heating element (130) cha ^¬ rakterisierenden electrical quantity during the predetermined second time period (AT2), and

Determining the at least one property of the fluid (Fl, F2) based at least in part on the detected second time history of the electrical quantity.

5. The method of claim 4, further comprising:

Determining a second time profile of the electrical resistance (R) of the heating element (130) based at least partially on the detected second time profile of the electrical variable and the first electrical heating power, wherein the at least one property of the fluid (Fl, F2) based at least partially the determined second time profile of the electrical resistance (R) of the

Heating element (130) is determined.

6. The method according to any one of claims 4 and 5, further comprising: Determining a second thermal conductivity (a2) of the fluid (Fl, F2) based at least in part on the detected second time profile of the electrical quantity and / or based at least in part on the determined second time profile of the electrical resistance (R) of the heating element (130),

wherein the at least one property of the fluid (Fl, F2) is determined based at least in part on the determined second thermal conductivity (a2).

7. The method according to any one of the preceding claims, wherein the electrical quantity is a voltage drop across the heating element (130) or an electric current flowing through the heating element (130).

8. The method according to any one of claims 4 to 7, further comprising:

Energizing the heating element (130) with a third predetermined electric heating power for a predetermined heating period (At _He iz) for heating the fluid (Fl, F2) from the predetermined first temperature (Tl) to the predetermined second temperature (T2).

9. The method according to any one of claims 4 to 8, further comprising:

Determining a first time constant (ii ₆₃ ), which indicates the time duration, the electrical resistance (R) of the heating element (130) starting from a first electrical resistance (R _FH , R _F 2 _I ) AT the beginning of the predetermined first time period (Atl) for increasing to a predetermined proportion of a second electrical resistance (R _FI 2, R _F 2 _I ) at the end of the predetermined first time period (Atl), and

Determining a second time constant (i2 ₆₃ ), which indicates the duration of the electrical resistance (R) of the heating element (130) from a first electrical resistance (RFH, RF2I) at the beginning of the predetermined second time period (At2) to increase to a predetermined level of a second electrical resistance (RFI2, RF2I) at the end of the predetermined second time period (At2) .

wherein determining the at least one property of the fluid (Fl, F2) is based at least in part on the determined first time constant (ii 63) and the determined second time constant (τ ₂ _63).

10. The method according to any one of claims 4 to 9, further comprising:

Determining a first electrical resistance difference between a first electrical resistance (RFH _/ RF2I) of the heating element (130) at the beginning of the predetermined first time period (Atl) and a second electrical resistance (R _F i2, RF22) of the heating element (130) at the end of the predetermined first period of time (Atl), and

Determining a second electrical resistance difference between a first electrical resistance (RFH, RF2I) of the heating element (130) at the beginning of the predetermined second time period (At2) and a second electrical resistance (RFI2 _/ RF22) of the heating element (130) at the end of FIG ^¬ certain second time period (At2),

wherein determining the at least one property of

Fluids (Fl, F2) based at least partially on the determined first electrical resistance difference and the determined second electrical resistance difference.

11. The method of claim 10, further comprising:

Determining a first thermal conductivity (λΐ) of the fluid (Fl, F2) based at least partially on the determined first electrical resistance difference, and Determining a second thermal conductivity (λ2) of the fluid (Fl, F2) based at least partially on the determined second electrical resistance difference (AR).

wherein the determination of the composition of the fluid (Fl, F2) based at least partially on the determined first heat ^¬ conductivity (λΐ) and the determined second Wärmeleitfä ^¬ ability (λ2).

12. The method of claim 10, wherein the predetermined heating powers, with which the heating element (130) for the predetermined periods of time (Atl, At2) is applied, an ascending, falling, jumping, triangular and / or sinusoidal time course.