DE102008002493A1 - Fuel mixture e.g. ethanol/petrol fuels mixture, composition determining method for e.g. petrol engine, involves determining composition of fuel mixture from signal differently based on components of exhaust gas - Google Patents

Abstract

The method involves determining a composition of a fuel mixture from a signal differently based on components of exhaust gas for pumping current (60) or a pumping current variation of a pumping cell of an exhaust gas probe (10) e.g. broadband lambda probe, of an internal combustion engine. The exhaust gas probe is installed in an exhaust gas channel of the engine. A defined mixture enriched fuel is provided periodically for known air mass. An independent claim is also included for a device for determining composition of a fuel mixture for operating an internal combustion engine.

Description

State of the art

The The invention relates to a method and a device for determination the composition of a fuel mixture of a first and at least a second fuel for operating an internal combustion engine, wherein the internal combustion engine, a fuel metering device and has at least one exhaust gas probe in an exhaust passage.

Internal combustion engines On the basis of gasoline engines are generally fueled Hydrocarbons derived from fossil fuels based on refined Operated oil. To this fuel is increasingly off renewable raw materials (plants) produced alcohol, for example Ethanol or methanol, in different mixing ratios added. In the US and Europe is often a mix of 75-85% Ethanol and 15-25% gasoline used under the brand name E85. The internal combustion engines are designed so that they are both pure Gasoline can also be operated with mixtures up to E85; this is called "flex-fuel operation". For economical operation with low pollutant emissions at the same time high engine power must be the operating parameters in flex-fuel operation be adapted to the respective present fuel mixture. By way of example, there is a stoichiometric air / fuel ratio at 14.7 parts by weight of air per part of gasoline before use ethanol, however, requires an air content of 9 parts by weight become.

about the interaction of sensors will dictate the instantaneous fuel composition the injection timing and the current exhaust gas composition, ie the oxygen partial pressure in the exhaust gas, determined and to the control electronics the internal combustion engine passed on. Based on this sensor data is the combustion of the internal combustion engine, in particular over the most favorable air / fuel ratio setting, optimized.

to Determining the composition of the fuel mixture will be different Fuel type sensors, also referred to as "fuel composition sensors", used. Fuel type sensors use the different ones Properties of alcohol and gasoline for determination of fuel composition. For example, ethanol is a protic solvent, which contains hydrogen ions and a large, however, dependent on the water content, dielectric constant having. Gasoline, on the other hand, is an aprotic solvent with a low dielectric constant. Based on that There are fuel type sensors which determine the fuel composition determine the dielectric properties of the fuel mixture. Other fuel type sensors use the different electrical Conductivity or the different optical properties the fuels such as the different refractive indices.

In the DE 41 12 574 a fuel supply system for an internal combustion engine is described in which the operating state of the internal combustion engine is detected and the amount of fuel to be supplied is controlled in accordance with the result of this detection. Here, it is provided that the fuel supply system includes fuel type detecting means for detecting the fuel type and calculating means for calculating a fuel type corresponding theoretical air-fuel ratio in accordance with the detection result of the fuel-type detection means and the amount of fuel to be supplied using the from Calculating means obtained theoretical air-fuel ratio is controlled as the target air-fuel ratio. In this case, it can be provided that the fuel-type detection means detects the fuel type by measuring at least one of the refractive index, the dielectric constant or the molar heat of the fuel in the liquid state.

A Accurate determination of the ethanol content is according to the prior art difficult, since in the fuel mixture and water can be included. One additional sensor with appropriate control is therefore required for ethanol detection. These ethanol sensors are expensive and error prone.

It is also known that the fat characteristic of planar broadband lambda probes strongly depends on the molecular mass m of the diffusing fat gases and that the diffusion constant D is proportional to the root of m ( Physics Journal No. 5-2006, pages 33 to 38 ). Such broadband lambda probes are for example from the DE 10 2005 061 890 A1 as well as from the DE 10 2005 043 414 A1 known, the DE 10 2005 061 890 A1 describes the structure of a broadband lambda probe, according to the invention, the use of certain chemical elements is provided in their construction.

From the DE 10 2005 043 414 A1 a method for determining the gas components in the exhaust gas of an internal combustion engine is known, in which from the signal of a arranged in the exhaust stream broadband probe and the signal of a arranged in the exhaust flow jumping probe on the concentration of individual gas components of the exhaust gas, in particular at least one gas other than oxygen, is closed. Likewise, a corresponding device is described in this document.

It The object of the invention is to provide a method and a device, which by using exhaust gas probe functions of an exhaust gas probe supports fuel analysis for flex-fuel mixtures and replace these additional ethanol sensors.

Advantages of the invention

The The object of the invention relating to the method is solved by that of one of the components of the exhaust gas differently dependent Signals for a pumping current or a pumping current change a pump cell of the exhaust gas probe determines the composition of the fuel mixture becomes. In particular unburned fuels or fuel components be on the outer electrode or the measuring electrode of the Flue gas probe oxidizes, which influences the output signal of the flue gas probe becomes. Different fuels differ, for example Alcohol and gasoline, in their oxidation behavior and in their oxidation kinetics and thus in their influence on the output signal of the exhaust gas probe. Based on the output signal of the exhaust gas probe can therefore on the composition of the fuel mixture are closed. This can be independent be exploited by the engine temperature or the engine condition. The advantage here is that the determination of the composition the fuel mixture with the help of in modern internal combustion engines anyway provided exhaust probes can be done and thus no additional Components and sensors are needed. This is in view to a simplification and associated cost reduction advantageous.

In A preferred method variant of the exhaust gas probe is at least at times a defined rich fuel mixture with known air mass supplied and from the pumping current at the known mass air flow, known amount of grease and known engine combustion temperature an ethanol content in the fuel determined. Such "fat trips" will be already in internal combustion engines for diagnostic purposes or, in diesel engines, applied for the regeneration of catalysts or particulate filters and can therefore be used, the fuel composition to determine. Depending on the components present in the exhaust gas In particular, at λ <1, a different pumping current occurs, which can be evaluated. The possibly contained water is here not involved as inert gas.

In a preferred variant of the method is a defined fat Fuel mixture at known air mass at periodic intervals, d. H. timed, fed.

In this case, in particular the control components CO and H ₂ in the exhaust gas are used to deduce the original relative composition of the burnt fuel. It can be provided that the ratio of CO and H _{2 is used} as a measure of the relative composition of the fuel. Their proportions differ depending on the composition of the fuel. Practically results in a sensitivity that moves between the leading components CO and H ₂ . From the actual size, taking into account the air mass flow and the injection quantity, the conclusion on the fuel composition.

A preferred variant of the method provides that the rich fuel mixture by means of the fuel metering device as a post-injection of Exhaust gas probe is supplied. In particular, the feeder of the rich fuel mixture during cold engine condition during the warm-up of the internal combustion engine advantageous. When the engine is cold or exhaust gas can unburned and not partially oxidized Fuel components reach the exhaust gas probe, so that the individual sensitivities the exhaust gas probe for gasoline and ethanol typical components are increased.

It can also be provided that in addition to the lead components CO and H ₂ in the exhaust gas and the conductive components of unburned gasoline and ethanol hydrocarbons are determined and compared. In this case, the Nacheinspritzmenge must be known and ensure that it fails large enough to decisively coining the gas composition in the field of installation position of the exhaust probe.

Of the Exhaust probe can be used without additional components and without a Influencing the operation of the internal combustion engine and unburned fuel be supplied by the fuel mixture of the Internal combustion engine by means of the fuel metering device in overrun mode is supplied. Especially with externally ignited internal combustion engines no ignition occurs during overrun, so that the fuel or the fuel mixture the Burning chamber can pass unburned. It is preferably during the fuel supply in overrun operation of the internal combustion engine a throttle open to a cold engine condition to create. Such test injections become, for example, too for shear calibration of the injectors in diesel internal combustion engines applied. Likewise, in the case of post-injection, the fuel can pass through unburned, as used in the regeneration of an oxidation catalyst becomes.

A variant of the method provides that the proportion of hydrogen by changing the pumping current at different exhaust gas pressures is determined. Here, one makes use of the effect that the mean free path of a gas depends on its mass and the ratio of gas-phase to Knudian diffusion is a function of the molecular mass ratios at a defined lambda value.

The response of the sensor flow to periodic pressure fluctuations in the exhaust gas depends on the flow characteristics of the gas molecules and thus on the molecular masses that vary, depending on the fuel composition or the exhaust gas composition. Therefore, it can be provided in a further variant of the method that the relative hydrogen content is determined during periodic pressure fluctuations with known lambda value and known pressure amplitudes from the amplitude of the pumping current or from its phase shift to the pressure fluctuations. Thus, in a high-carbon rich gas, more CO _{2 is} produced, so that the cross-section of the carrier gas is higher than that of a high hydrogen content. The curvature of the fat characteristic curve therefore increases. In addition, the gas influx decreases with pressure pulses at large molecules, because the viscosity increases. The additional outflow through the resulting inert gas in the fat area also reduces the dynamic pressure dependence.

A as slow as possible catalytic oxidation of the unburned Fuel at the outer electrode or the measuring electrode the exhaust probe leads to improved reliability and Measuring accuracy in determining the composition of the fuel mixture based on the output signal of the exhaust gas probe. Therefore it can be provided be that the pumping current change set at different Sensor temperatures is determined. A reduced temperature of Exhaust probe and thus the outer electrode or the measuring electrode leads for example to a reduced Oxidation rate of the fuel components. A comparison The measured values at different sensor temperatures can increase the accuracy increase the determination of the fuel composition. In Connection with one, at least temporary and / or periodic Lowering the temperature of the outer electrode can be connected with an additionally introduced platinum surface at the outer electrode for precatalysis the sensitivity the exhaust gas probe can be additionally increased.

A Another variant of the method provides that the exhaust gas probe with their Pump cell regulated to a lambda value λ ≈ 1 is controlled by the fuel metering so that the pump current at a positive pump voltage (about 600 mV) to zero goes back, and then, with the same Injection quantity, a Nernst voltage determined and with the Nernst voltage for a lambda value λ = 1 is compared. Of the exact value of the resulting lambda value is determined by the Diffusion properties of a diffusion barrier of the exhaust gas probe, the hydrogen and oxygen diffuse at different rates leaves. The measured Nernst voltage at this lambda value is determined by the diffusion constant of an outer Protective layer of the exhaust gas probe determined. Because the outer protective layer Hydrogen and oxygen differ from those Diffusion barrier of the exhaust probe separated turns a voltage a, which does not exactly correspond to a lambda value of λ = 1, but differs depending on the type of grease gas.

The the task concerning the device provides as a solution that the exhaust gas probe is a broadband lambda probe which close to the engine arranged in the direction of the exhaust stream upstream of a first catalyst is and that the exhaust gas probe at least temporarily a defined fat Fuel mixture can be fed. Broadband lambda probes are already widely used today in the exhaust duct of internal combustion engines used. Such an exhaust gas probe has one of the components the exhaust gas and their proportion in the exhaust gas differently dependent pumping current or a pumping current change and can therefore with appropriate Wiring and evaluation of the pumping current or the pumping current change in a control unit without the use of additional sensors used to determine the composition of the fuel mixture become.

The Method and / or the device can be inexpensively for determining the composition of a gasoline / ethanol fuel mixture and / or a gasoline / methanol fuel mixture and / or a Gasoline / ethanol / methanol fuel mixture in internal combustion engines Use for use with renewable fuels of the type mentioned above can be operated.

The accuracy of the determination of the composition of the fuel mixture by means of exhaust gas sensors is dependent on different factors, including the exhaust gas sensor used. Already an accuracy of better than 30% can be used as a supplement to the software algorithms, with which already today the composition of fuel mixtures is determined by different methods. With an accuracy better than 10%, a lower quality ethanol sensor can be completely replaced, with an accuracy better than 5%, a high quality, state-of-the-art ethanol sensor. Therefore, it may be provided that the determination of the composition of the fuel mixture exclusively from the Sig the flue gas probe or in combination with other methods of determining the composition of the fuel mixture.

Brief description of the drawings

The Invention will be described below with reference to the figures shown in the figures Embodiment explained in more detail. Show it:

1a and 1b in a schematic representation of a broadband lambda probe as an exhaust gas probe in different exhaust gas compositions and

2 in a diagram, the relationship between the oxygen content of the exhaust gas and a pumping current of the exhaust gas probe for various components of the exhaust gas.

embodiments the invention

1a and 1b show a schematic representation of an exhaust gas probe 10 , which is designed as a broadband lambda probe and with a rich exhaust 20 ( 1a ) on the one hand and a lean exhaust gas 30 ( 1b ) is acted on the other hand.

The exhaust gas probe 10 is arranged close to the engine in an exhaust passage of an internal combustion engine in the flow direction of the exhaust gas in front of a catalyst. The internal combustion engine has an intake duct with an air mass meter, with which the mass of the air supplied to the internal combustion engine is determined. Immediately before the internal combustion engine, a fuel metering device is provided. The fuel metering device makes it possible to supply defined quantities of a fuel mixture to the internal combustion engine. The internal combustion engine may be designed as a gasoline engine, which is operated in flex-fuel operation with fuel mixtures of gasoline and alcohol or methanol. In this case, the fuel mixture is injected into the intake passage immediately before the intake valves of the internal combustion engine and fed together with the intake air of the internal combustion engine.

The exhaust gas probe 10 , as in the example DE 10 2005 061 890 A1 includes a pump cell having an outer electrode 12 and an inner electrode 17 and a so-called Nernst cell (also referred to as a sensor cell) with a measuring electrode 18 and a reference electrode 19 , The exhaust gas probe 10 is usually in planar technology of several solid electrolyte layers 11 built up. Furthermore, a heater embedded in an insulation for heating the sensor element is provided (not shown in the figure). The exhaust 20 . 30 can have an opening 14 in the form of a hole and through a diffusion barrier 15 in a measuring room 16 be supplied. In the measuring room 16 is the inner electrode 17 the pump cell and the measuring electrode 18 the Nernst cell arranged. The outer electrode 12 at the exhaust 20 . 30 facing the outside of the exhaust probe 10 has a protective layer 13 on. The reference electrode 19 is arranged in a reference air channel which is filled with ambient air.

Via the Nernst cell there is a potential difference, the so-called Nernst voltage 70 , between the measuring electrode 18 and the reference electrode 19 measured. A voltage is applied to the pump cell from the outside. This generates one as pumping current 60 designated current with which - depending on polarity - oxygen ions are transported. An electronic control circuit causes the pump cell to the exhaust gas volume, which via the diffusion barrier 15 in contact with the measuring room 16 is, always just as much oxygen in the form of O ² ions on or off him, that in the measuring room 16 sets a lambda value of λ = 1, with lean exhaust gas 30 (with excess air), oxygen is pumped off and with rich exhaust gas 20 whereas oxygen is supplied. The pumping current set by the control circuit 60 depends on the air ratio lambda in the exhaust gas and forms the output signal of the broadband lambda probe. The pumping current 60 is in the case of lean exhaust 20 , in which O ₂ and also NO are the main components, positive and in the case of rich exhaust gas 30 with the lead components CO, H ₂ and HC (hydrocarbons) negative.

The pumping current 60 depends primarily on the air ratio λ of the exhaust gas, but this is also influenced by a different exhaust gas composition at the same λ. This influence is based on different diffusion coefficients at the diffusion barrier 15 for certain exhaust gas components. Thus, especially in the rich range, the ratio between CO and H ₂ affects, which in turn depends on the fuel composition.

2 shows in a diagram the relationship between the oxygen content of the exhaust gas and the pumping current 60 as an exhaust gas probe 10 used broadband lambda probe for various components of the exhaust gas. Shown is the pumping current 60 on the one hand as a function of a percentage oxygen content 40 with lean exhaust gas 30 as well as a percentage oxygen deficit 50 with rich exhaust 20 and second, from a resulting lambda value 80 , which lies in the diagram shown in the range between about λ ≈ 0.5 (extremely fat) to λ ≈ 20 (extremely lean).

In different characteristics 90 the progressions are shown for different leading components. In the area of lean exhaust gas 30 is only the O ₂ characteristic 91 represented in the first quadrant of the diagram, ie at a positive pumping current 60 and oxygen surplus shot or percent oxygen content 40 extends. In the range of rich exhaust 20 and negative pumping current 60 (ie in the 3rd quadrant of the diagram) are the characteristics for the leading components CO, H ₂ , CH ₄ and C ₃ H ₆ 92 . 93 . 94 . 95 shown, which differ significantly, so that they can be evaluated.

According to the invention it is provided that the exhaust gas probe 10 for the determination of the composition of the fuel mixture at times partially extremely rich exhaust gas in the form of unburned or at least partially unburned fuel mixture is supplied. The determination of the fuel composition takes place, for example, during separate diagnosis phases, for example during overrun operating phases of the internal combustion engine or during the warm-up phase of the internal combustion engine in the form of a post-injection, based on differences in the pumping current 60 when using fuel mixtures of different composition. In this case, the change in the pumping current 60 be evaluated against a known reference. For the determination of the fuel composition of the fuel mixture supplied, lower temperatures of the exhaust gas probe are also in broadband lambda probes 10 advantageous. Temperature ranges from 550 ° C to 700 ° C and 400 ° C to 550 ° C are suitable.

The Procedure supports the accurate and reliable Determination of the composition of a fuel mixture, in Flex-fuel operation powered internal combustion engines with existing components. In particular, when using a broadband lambda probe can thereby to be dispensed with additional sensors, resulting in cost advantages brings with it.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 4112574 [0005]
• DE 102005061890 A1 [0007, 0007, 0029]
• - DE 102005043414 A1 [0007, 0008]

Cited non-patent literature

• - Physics Journal No. 5-2006, pages 33 to 38 [0007]

Claims (17)

Method for determining the composition of a fuel mixture comprising a first and at least one second fuel for operating an internal combustion engine, wherein the internal combustion engine comprises a fuel metering device and at least one exhaust gas probe ( 10 ) in an exhaust passage of the internal combustion engine, characterized in that from a different of the components of the exhaust gas dependent signal for a pumping current ( 60 ) or a pump current change of a pump cell of the exhaust gas probe ( 10 ) the composition of the fuel mixture is determined. Method according to claim 1, characterized in that the exhaust gas probe ( 10 ) at least temporarily fed a defined rich fuel mixture at known air mass and from the pumping current ( 60 ) In the known air mass flow, known amount of fat gas and known engine combustion temperature, an ethanol content in the fuel is determined. Method according to claim 1 or 2, characterized that a defined rich fuel mixture with known air mass is supplied at periodic intervals. Method according to one of claims 1 to 3, characterized in that is closed via the guide components CO and H ₂ in the exhaust gas to the original relative composition of the burned fuel. A method according to claim 4, characterized in that the ratio of CO and H _{2 is used} as a measure of the relative composition of the fuel. Method according to one of claims 1 to 5, characterized in that the rich fuel mixture by means of the fuel metering device as a post-injection or during a coasting operation of the internal combustion engine of the exhaust gas probe ( 10 ) is supplied. Method according to Claim 6, characterized that the feeding of the rich fuel mixture in cold Engine condition during warm-up of the engine is carried out. A method according to claim 6 or 7, characterized in that in addition to the conductive components CO and H ₂ in the exhaust gas and the conductive components of unburned gasoline and ethanol hydrocarbons are determined and compared. Method according to one of claims 6 to 8, characterized in that during the fuel supply opened in overrun operation of the internal combustion engine, a throttle becomes. Method according to one of claims 1 to 9, characterized in that the proportion of hydrogen by changing the pumping current ( 60 ) is determined at different exhaust pressures. Method according to one of claims 1 to 10, characterized in that at periodic pressure fluctuations with known lambda value and known pressure amplitudes from the amplitude of the pump current ( 60 ) or from its phase shift to the pressure fluctuations, the relative hydrogen content is determined. Method according to one of claims 1 to 11, characterized in that the pumping current change at determined sensor temperatures is determined. Method according to one of claims 1 to 12, characterized in that the exhaust gas probe ( 10 ) with its pumping cell to a lambda value ( 80 ) λ ≈ 1 is controlled by the fuel metering is controlled such that the pumping current ( 60 ) goes back to zero at a positive pump voltage, and then, with the injection quantity remaining the same, a Nernst voltage ( 70 ) and with the Nernst voltage ( 70 ) for a lambda value ( 80 ) λ = 1 is compared. Method according to one of claims 1 to 13, characterized in that as exhaust gas probe ( 10 ) a broadband lambda probe is used. Device for determining the composition of a fuel mixture of a first and at least a second fuel for operating an internal combustion engine, wherein in the exhaust passage of the internal combustion engine at least one exhaust gas probe ( 10 ), characterized in that the exhaust gas probe ( 10 ) is a broadband lambda probe, which is arranged close to the engine in the direction of the exhaust gas flow in front of a first catalyst and that the exhaust gas probe ( 10 ) At least temporarily a defined rich fuel mixture can be fed. Apparatus according to claim 15, characterized in that the exhaust gas probe ( 10 ) one of the components of the exhaust gas and their proportion in the exhaust gas differently dependent pumping current ( 60 ) or a pumping current change. Use of the method according to one of claims 1 to 14 and / or use of the device according to one of claims 15 to 16 for determining the composition of a gasoline / ethanol fuel mixture and / or a gasoline / methanol fuel mixture and / or a Ben zin / ethanol / methanol fuel mixture in an internal combustion engine for regenerative fuels.