Method for operating an internal combustion engine

Abstract

Method for operating an internal combustion engine (10) of a vehicle with a fuel mixture (12) of a fossil fuel (12a) and a synthetic fuel (12b), the method comprising: - defining (S1) a pure substance emission profile of the internal combustion engine (10) when the internal combustion engine (10) is operated with the pure fossil fuel (12a) under defined operating parameters of the internal combustion engine (10); - determining a first proportion of the fossil fuel (12a) and a second proportion of the synthetic fuel (12b) in the fuel mixture (12) to determine (S2) a composition of the fuel mixture (12); - determining (S3) a mixture emission profile of the internal combustion engine (10) during operation of the internal combustion engine (10) with the determined composition of the fuel mixture (12) under the defined operating parameters of the internal combustion engine (10); and - adjusting (S4) at least one of the operating parameters of the internal combustion engine (10) such that the mixture emission profile corresponds to the pure substance emission profile, characterized in that - the exhaust gas temperature is increased by an increase in the fuel mass (m) during the post-injection and / or a retarding of the post-injection and / or a reduction in the boost pressure and / or an adjustment of the exhaust gas recirculation rate (rA), and Injection timing (t gemisch ) relative to an injection time (t fossil ) of the pure fossil fuel (12a) is shifted by Δt > 0. - as an operating parameter of the internal combustion engine (10), an injection time (t_gemisch) of the fuel mixture (12) is adapted when injecting the fuel mixture (12) into combustion chambers (18) of the internal combustion engine (10), wherein - the

Description

[0001] The invention relates to a method for operating an internal combustion engine of a vehicle with a fuel mixture of a fossil fuel and a synthetic fuel.

[0002] Due to CO2 reduction targets required for climate protection, fuel blends for internal combustion engines will be offered in the future. These blends consist of the currently known petroleum-based or fossil fuels, such as gasoline and / or diesel, plus synthetically produced fuels. Two, three, or even more different fuels may be present in the fuel blend. Fossil fuels are understood to mean all fuels obtained by refining crude oil, i.e., petroleum. This includes both diesel fuels and gasoline fuels, as well as all other known, standard crude oil-based fuels.

[0003] Synthetic fuels are fuels that have been synthetically produced through a controlled chemical reaction. In particular, this refers to fuels that have been produced using carbon dioxide (CO2) that is already freely available in the environment and electrical energy from renewable energy sources. One example of such a synthetic fuel is oxymethylene ether, known as "OME," which is particularly suitable as a fuel for diesel engines because, like diesel, it burns spontaneously.

[0004] The physical and chemical properties of the two fuel types (fossil, i.e., mineral oil-based, and synthetic, i.e., produced from renewable sources) can differ significantly. Therefore, the physical and chemical properties of the blends of the two fuel types also differ. This also depends on the blending ratio.

[0005] However, vehicles or their internal combustion engines are not sensitive to significant changes in fuel properties.

[0006] From DE 10 2005 001 882 A1 a method for operating an internal combustion engine is known, comprising at least one step in which the content of at least one fuel component is detected by means of a fuel sensor and then, depending on this, parameters relevant for the operation of the internal combustion engine are influenced.

[0007] From DE 10 2007 050 122 A1 a method for classifying fuels in direct-injection internal combustion engines, in particular diesel combustion engines, is known, comprising at least one oxygen sensor element for determining the air characteristic lambda, which is used in the exhaust gas of the internal combustion engine.

[0008] EP 1 775 584 A2 discloses a method and a device for assessing the quality of fuel combusted in an internal combustion engine. It is proposed to determine a fuel-specific factor k using a sensor that records, for example, the combustion chamber pressure profile and / or a lambda value, and an algorithm. In a further embodiment, the operating parameters (injection quantity, start of injection, end of injection, injection pattern, exhaust gas recirculation rate, etc.) are corrected using the factor k.

[0009] Engine tests, particularly on EU6d diesel engines, have shown that different blends of synthetic fuel and fossil fuel lead to different emissions due to changes in fuel properties. This is undesirable, especially if the emissions of the fuel blend deteriorate compared to emissions from combustion of pure fossil fuel.

[0010] The object of the invention is therefore to propose a method for operating an internal combustion engine with which this can be avoided.

[0011] This object is achieved by a method for operating an internal combustion engine with the combination of features of claim 1.

[0012] Advantageous embodiments of the invention are the subject of the dependent claims.

[0013] A method for operating an internal combustion engine of a vehicle with a fuel mixture of a fossil fuel and a synthetic fuel comprises the following steps: - Defining a pure substance emission profile of the internal combustion engine when operating the internal combustion engine with the pure fossil fuel under defined operating parameters of the internal combustion engine; - determining a first proportion of the fossil fuel and a second proportion of the synthetic fuel in the fuel mixture to determine a composition of the fuel mixture; - determining a mixture emission profile of the internal combustion engine when the internal combustion engine is operated with the determined composition of the fuel mixture under the defined operating parameters of the internal combustion engine; and - Adjusting at least one of the operating parameters of the internal combustion engine such that the mixture emission profile corresponds to the pure-fuel emission profile. The exhaust gas temperature is increased by increasing the fuel mass during the post-injection and / or retarding the post-injection and / or reducing the boost pressure and / or adjusting the exhaust gas recirculation rate.

[0014] Essentially, the invention is therefore based on the idea that, if different properties of the fuel mixture are known compared to pure fossil fuel, an engine calibration, i.e. a calibration of the internal combustion engine, reacts to these differences in order to be able to ensure optimal engine operation for the existing fuel mixture.

[0015] The fuel mixture may contain not only a fossil fuel and a synthetic fuel. Multiple fuels may also be present in the fuel mixture.

[0016] The definition of the pure substance emission profile of the internal combustion engine is carried out before the internal combustion engine is operated with the fuel mixture.

[0017] The pure fuel emission profile is defined in particular by the NOx content in the exhaust gas of an internal combustion engine. The main emissions in the exhaust gas of an internal combustion engine include CO2, CO, and NOx. Since the blending of synthetic fuel with a fossil fuel leads to the binding of CO2 available in the environment, a vehicle can be operated in an essentially CO2-neutral manner by burning synthetic fuel, despite local CO2 emissions. Therefore, the key factor determining the emission profile of the internal combustion engine, both for the pure fossil fuel and for the fuel blend, is the NOx content in the exhaust gas of the internal combustion engine that is produced during combustion.

[0018] By adjusting at least one operating parameter of the internal combustion engine after the mixture ratio of fossil fuel and synthetic fuel in the fuel mixture has been determined, a NOx emission of the internal combustion engine during combustion of the fuel mixture can be achieved which is the same for any fuel mixture of fossil fuel and synthetic fuel.

[0019] In the best case, by adjusting at least one operating parameter of the internal combustion engine, the mixture emission profile can even be influenced to such an extent that the proportion of NOx in the mixture emission profile is lower than in the pure substance emission profile.

[0020] Advantageously, diesel is used as the fossil fuel and oxymethylene ether as the synthetic fuel in the fuel mixture. Oxymethylene ether can be understood as either polyoxymethylene ether or dimethyl ether. Oxymethylene ether can be used as the synthetic fuel and diesel fuel in various specifications in the fuel mixture.

[0021] In one possible embodiment, an injection mass m is used as an operating parameter of the internal combustion engine. gemisch of the fuel mixture when injecting the fuel mixture into the combustion chambers of the internal combustion engine, whereby the injection mass m gemisch especially for torque-generating injections.

[0022] By determining the proportion of fossil fuel and synthetic fuel in the fuel mixture, it is known how the fuel mixture in a tank, for example, consists of synthetic fuel and fossil fuel. Since the composition of the fuel mixture is known, the actual calorific value H u of the fuel mixture. Because the calorific values ​​H u The calorific values ​​of the two base fuels, namely the synthetic fuel and the fossil fuel, differ by a known factor. This factor is approximately 2 when using oxymethylene ether as the synthetic fuel and diesel as the fossil fuel. Each fuel mixture of both fuels therefore has a specific calorific value H U,gemischAs the proportion of synthetic fuel in the fuel mixture increases, this results in a shift within the active characteristic maps of the engine's air and fuel path. This, in turn, leads to unpredictable engine conditions, altered fuel consumption, and, in particular, increased NOx emissions.

[0023] If the calorific value H u for the pure fossil fuel to that of the fuel mixture, the gain factor F v for the fuel mixture used. The gain factor F v refers to the ratio of the calorific value H U,gemisch of the currently available fuel mixture based on the calorific value H U,fossil of the pure fossil fuel. This amplification factor F vis now applied as a gain to the characteristic maps for the fuel mass m known for pure fossil fuel. This can be multiple maps. There are maps for different boundary conditions, such as different temperatures, and also different operating states. In addition, there are maps for the torque-generating pilot, main, and post-injections for the previously mentioned different boundary conditions and operating states. The determined gain factor F v is now applied to all torque-generating injections. This allows the shift within the maps for the active air and fuel path to be corrected. This ensures that the torque setpoint once again matches the delivered torque, resulting in a reduction in both fuel consumption and NOx emissions.

[0024] The injection mass m gemischcan also be adjusted for non-torque-generating injections. An example of this is a post-injection used for the regeneration of a particulate filter in an exhaust system. Combustion of the fuel in this post-injection can increase the temperature of the exhaust gas. Evaporation of the fuel in the hot exhaust gas is also used, introducing hydrocarbons into the exhaust gas. These hydrocarbons can then be made available to a DOC catalyst in the exhaust system for an exothermic reaction, which also increases the exhaust gas temperature. The injection mass m gemisch The post-injection is increased according to the same regulation so that the temperature required for particulate filter regeneration is reached.

[0025] The adjusted injection mass m gemisch is therefore advantageous according to the context mmixture=Fv⋅mfossil adjusted, where F vis the amplification factor resulting from the calorific value ratio of the calorific value HU, fossil of the pure fossil fuel and the calorific value HU, gemisch of the determined fuel mixture. This is calculated according to: Fv=Hu,fossilHu,mixture Advantageously, an injection mass m is used as an operating parameter of the internal combustion engine. gemisch of the fuel mixture during a post-injection of the fuel mixture in combustion chambers of the internal combustion engine compared to an injection mass m fossilof pure fossil fuel. Because a larger fuel mass m is injected during post-injection, the temperature in the resulting exhaust gas during combustion can be increased. The higher the exhaust gas temperature, the greater the efficiency of an exhaust gas purification system downstream of the internal combustion engine. Therefore, improved exhaust gas purification can be achieved by increasing the fuel mass m during post-injection, so that the NOx content in the mixture emission profile can be significantly reduced.

[0026] According to the invention, an injection time t gemisch of the fuel mixture when injecting the fuel mixture into the combustion chambers of the internal combustion engine.

[0027] According to the invention, the injection time t gemisch relative to an injection time t fossilof pure fossil fuel shifted by Δt > 0.

[0028] This measure results in a late shift in the combustion of the fuel mixture in the working cycle, which also leads to a higher exhaust gas temperature and therefore to an improvement in the efficiency of the exhaust gas purification system.

[0029] In a further possible embodiment, an exhaust gas recirculation rate r is used as an operating parameter of the internal combustion engine. A of an exhaust gas of the internal combustion engine to combustion chambers of the internal combustion engine compared to an exhaust gas recirculation rate r A when pure fossil fuel is burned in the combustion chambers of the internal combustion engine.

[0030] The oxygen content in synthetic fuels is significantly higher than that of fossil fuels. For example, diesel fuel contains essentially no oxygen, whereas oxymethylene ether has an oxygen content of around 40%. During fuel combustion, fresh air is supplied, which has an oxygen content of around 20%. When synthetic fuels are used, oxygen is introduced via the synthetic fuel itself in addition to the oxygen supply via the fresh air. This results in an oxygen excess, which prevents stoichiometric combustion of the fuel in the combustion chamber. The lambda value is therefore above 1, and the internal combustion engine runs "lean," i.e., with an oxygen excess. A large proportion of oxygen remains in the exhaust gas. This oxygen concentration is largely responsible for the formation of NOx emissions.The proportion of oxygen present in the fuel mixture is a function of the mixture ratio between the fossil fuel and the synthetic fuel in the fuel mixture. If the mixture ratio is known from determining the proportions of fossil fuel and synthetic fuel in the fuel mixture, the air path parameters, such as the exhaust gas recirculation rate r, can be adjusted. A of the exhaust gas to the combustion. This means that proportionally less oxygen is supplied to the combustion, and NOx emissions are reduced. Lambda can then be brought closer to a value of 1, so that there is just enough oxygen in the combustion chamber of the internal combustion engine to fully oxidize all of the injected fuel. Thus, no oxygen remains in the exhaust gas, and less NOx can form.

[0031] In a further embodiment, as an operating parameter of the internal combustion engine, the mass of clean air supplied to the combustion chambers of the internal combustion engine can be reduced compared to the mass of clean air supplied during combustion of pure fossil fuel in the combustion chambers of the internal combustion engine. This can also significantly reduce the oxygen content during combustion and thus reduce NOx emissions. In order to reduce the mass of clean air during combustion, it is possible, for example, to reduce the boost pressure of the clean air. An alternative embodiment would be to increase the temperature of the clean air, which is accompanied by a reduced density of the clean air and thus a lower concentration of oxygen per unit volume of the clean air.

[0032] The exhaust gas temperature, which, as mentioned above, is crucial for the efficiency of the emission control system, can be increased, as already described, by increasing the fuel mass m during, for example, post-injection and possibly retarding it. This results in an extension of the combustion duration in the combustion chambers and thus an increase in the exhaust gas temperature. Reducing the boost pressure also results in higher combustion temperatures and thus a higher exhaust gas temperature. By adjusting the exhaust gas recirculation rate r A The combustion time in the combustion chambers is also extended, resulting in a higher exhaust gas temperature. In addition to reducing the oxygen content in the fuel-air mixture to be burned, the exhaust gas temperature is also increased, thus ensuring a consistent effect of the exhaust gas purification system.

[0033] Advantageous embodiments of the invention are explained in more detail below with reference to the accompanying drawings.

[0034] It shows: Fig. 1 is a schematic flow diagram illustrating individual steps in a method for operating an internal combustion engine with a fuel mixture of fossil fuel and synthetic fuel; Fig. 2 a schematic overview of an internal combustion engine with a fuel injection system and an exhaust system; and Fig. 3 a schematic diagram showing an injection mass m as a function of an injection time t.

[0035] Fig. 1 shows a schematic flow diagram of a method for operating an internal combustion engine 10, which in Fig. 2 is shown in a schematic overview. The internal combustion engine 10 is operated with a fuel mixture 12 comprising a fossil fuel 12a and a synthetic fuel 12b. In the method, in a first step S1, a pure substance emission profile of the internal combustion engine 10 is first defined during operation of the internal combustion engine 10 with the pure fossil fuel 12a under defined operating parameters of the internal combustion engine 10. The pure substance emission profile is essentially determined by a NOx content in an exhaust gas 14 that arises during the combustion of fuel in the internal combustion engine 10.

[0036] In a second step S2, a composition of the fuel mixture 12 is determined by determining a first proportion of the fossil fuel 12a and a second proportion of the synthetic fuel 12b in the fuel mixture 12.

[0037] In a third step S3, once the composition of the fuel mixture 12 is known, a mixture emission profile of the internal combustion engine 10 is determined, which is expected to be present when the internal combustion engine 10 is operated with the determined composition of the fuel mixture 12 under the predefined operating parameters of the internal combustion engine 10. In particular, an expected NOx content in the exhaust gas 14 during the combustion of the fuel mixture 12 is determined here.

[0038] Finally, in a fourth step S4, at least one operating parameter of the internal combustion engine 10 is adjusted so that the mixture emission profile corresponds to the pure substance emission profile.

[0039] Operating parameters that can be adjusted for this purpose are, on the one hand, an injection mass m gemisch of the fuel mixture 12, an injection time t gemisch of the fuel mixture 12, an exhaust gas recirculation rate r Aof exhaust gas 14 from an exhaust line 16 of the internal combustion engine 10 back into a combustion chamber 18 of the internal combustion engine 10 and a supplied air mass m L of clean air 30 to the combustion chamber 18.

[0040] Fig. 2 shows a schematic overview of the internal combustion engine 10 with the exhaust system 16.

[0041] The internal combustion engine 10 is supplied with fuel, for example pure fossil fuel 12a such as diesel, or the fuel mixture 12 of fossil fuel 12a and synthetic fuel 12b such as oxymethylene ether - OME - via a fuel injection system 20.

[0042] The fuel injection system 20 has a tank 22 into which both pure fossil fuel 12a and a fuel mixture 12 of synthetic fuel 12b and fossil fuel 12a can be filled. Consequently, different fuel mixtures 12 can be present in the tank 22 and in the entire fuel injection system 20 at different times, depending on which fuel—synthetic fuel 12b, fossil fuel 12a, or a mixture thereof—has been filled into the fuel tank 22.

[0043] From the tank 22, the fuel mixture 12 is pumped by a high-pressure fuel pump 24 into a fuel storage line 26, from where the fuel mixture 12 is injected via fuel injectors 28 into combustion chambers 18 (only one shown) of the internal combustion engine 10. Clean air 30 is also supplied to the combustion chambers 18, providing the oxygen necessary for the combustion of the fuel mixture 12. The fuel mixture 12 burns in the combustion chambers 18, producing the exhaust gas 14, which is discharged from the internal combustion engine 10 via the exhaust system 16.

[0044] The exhaust system 16 comprises an exhaust manifold 32 and a particle filter which is designed to at least partially capture any particles present in the exhaust gas 14 before the exhaust gas 14 is released to the environment.

[0045] Starting from the exhaust line 16, an exhaust gas recirculation line 34 leads back into the combustion chambers 18 of the internal combustion engine 10, via which at least a portion of the exhaust gas 14 is recirculated in accordance with a predetermined exhaust gas recirculation rate r A can be fed into the combustion chambers 18. There, the recirculated exhaust gas 14 mixes with the supplied clean air 30 and the fuel mixture 12, whereby the combustion properties of the fuel mixture 12 can be optimized.

[0046] The exhaust gas 14 of each combusted fuel has a specific emission profile. A pure substance emission profile of the pure fossil fuel 12a differs from a mixture emission profile during the combustion of the fuel mixture 12. The emission profiles are essentially determined by the NOx content in the exhaust gas 14. Once the composition of the fuel mixture 12 is known, the mixture emission profile can be at least adapted to the pure substance emission profile with regard to the NOx content by readjusting individual operating parameters of the internal combustion engine 10, and possibly even improved. To determine the composition of the fuel mixture 12, as corresponds to the second step S2 of the method described above, various sensors 36 already present in the fuel injection system 20 or the exhaust system 16 and their measurement results can be evaluated.For example, a fuel sensor can be provided in the tank 22 to directly determine the fuel composition. However, it is also possible, for example, to use a pressure sensor in the fuel storage line 26 to detect the fuel properties, such as the composition of the fuel mixture 12, over a temporal pressure profile. Conclusions about the fuel composition of the fuel mixture 12 can also be drawn from signals from a particle sensor or a temperature sensor in the exhaust system 16.

[0047] One possibility to change operating parameters of the internal combustion engine 10 such that the mixture emission profile at least corresponds to the pure substance emission profile is to change injection parameters at the fuel injectors 28.

[0048] For example, an injection mass m gemisch be changed, but it is also possible to set an injection time t gemischBoth options are shown in the diagram in Fig. 3, where an injection mass m of the fuel is plotted against an injection time t. Schematically shown are injections for both the pure fossil fuel 12a (suffix "fossil") and for the fuel mixture 12 (suffix "mixture"), as well as for a pilot injection 1, a main injection 2, and a post-injection 3.

[0049] The calorific value H u of a fuel or fuel mixture 12 has a direct influence on the proportion of NOx in the resulting exhaust gas 14. Since the calorific value H u of a synthetic fuel 12b, for example OME, of the calorific value HU, fossil of the fossil fuel 12a, and is usually significantly lower, an amplification factor results from the formula Fv=Hu,fossilHu,mixture F v = Gain factor, H U,gemisch= Calorific value of the fuel mixture 12, H U,fossil = Calorific value of pure fossil fuel 12a.

[0050] To achieve this gain factor F v The injection mass m must be increased to achieve a similar NOx emission in the exhaust gas 14 and thus an alignment of the mixture emission profile with the pure fuel emission profile. This is particularly important for fuel injections that have a direct influence on the torque of the internal combustion engine 10. The gain factor F v is now applied to all maps that define the injections, i.e. both the pilot injection 1, the main injection 2, and the post-injection 3, so that a higher injection mass m gemisch of the fuel mixture 12 compared to an injection mass m fossil of the pure fuel 12a.

[0051] Alternatively or additionally, it is also possible to delay the respective injection time t, so that both the pilot injection 1 and the main injection 2, as well as the post-injection 3, occur later by Δt during the injection of the fuel mixture 12 than if the pure fossil fuel 12a were injected. This results in later combustion of the fuel mixture 12 and thus a higher exhaust gas temperature, particularly if the post-injection 3 is delayed by Δt. A higher exhaust gas temperature leads to a lower density in the exhaust gas 14 and thus to a lower volume concentration of oxygen present in the exhaust gas 14.This allows the ratio between the fuel mixture 12 and the recirculated exhaust gas 14 to be adjusted so that stoichiometric combustion of the fuel mixture 12 is possible and there is no excess oxygen, which would lead to a higher NOx concentration in the exhaust gas 14.

[0052] The same effect can be achieved by increasing the exhaust gas recirculation rate r A is reduced, or by adding an air mass m L of clean air 30 is reduced. This can be done, for example, by reducing a boost pressure of the clean air 30 and / or by increasing a temperature of the clean air 30, which is also accompanied by a reduction in density and thus a lower volume concentration of oxygen in the clean air 30.

[0053] At the same time, the adjustment of the exhaust gas recirculation rate r Aand the reduction of the boost pressure of the clean air 30 also results in a higher exhaust gas temperature, which has a positive effect on the oxygen content in the recirculated exhaust gas 14.

[0054] Overall, various operating parameters of the internal combustion engine 10 such as injection mass m gemisch , injection timing t gemischr , exhaust gas recirculation rate r A and air mass m L to clean air 30 in order to adjust the NOx concentration in the exhaust gas 14 during the combustion of the fuel mixture 12 at least to the NOx concentration in the exhaust gas 14 during the combustion of a purely fossil fuel 12a.

Claims

[1] Method for operating an internal combustion engine (10) of a vehicle with a fuel mixture (12) of a fossil fuel (12a) and a synthetic fuel (12b), the method comprising: - defining (S1) a pure substance emission profile of the internal combustion engine (10) when the internal combustion engine (10) is operated with the pure fossil fuel (12a) under defined operating parameters of the internal combustion engine (10); - determining a first proportion of the fossil fuel (12a) and a second proportion of the synthetic fuel (12b) in the fuel mixture (12) to determine (S2) a composition of the fuel mixture (12); - determining (S3) a mixture emission profile of the internal combustion engine (10) during operation of the internal combustion engine (10) with the determined composition of the fuel mixture (12) under the defined operating parameters of the internal combustion engine (10); and - adjusting (S4) at least one of the operating parameters of the internal combustion engine (10) such that the mixture emission profile corresponds to the pure substance emission profile, characterized by , that - the exhaust gas temperature is increased by an increase in the fuel mass (m) during the post-injection and / or a retarding of the post-injection and / or a reduction in the boost pressure and / or an adjustment of the exhaust gas recirculation rate (rA), and Injection timing (t gemisch ) relative to an injection time (t fossil ) of the pure fossil fuel (12a) is shifted by Δt > 0. - as an operating parameter of the internal combustion engine (10), an injection time (t_gemisch) of the fuel mixture (12) is adapted when injecting the fuel mixture (12) into combustion chambers (18) of the internal combustion engine (10), wherein - the [2] Method according to claim 1, characterized bythat as an operating parameter of the internal combustion engine (10) an injection mass (m gemisch ) of the fuel mixture (12) during a post-injection of the fuel mixture (12) into combustion chambers (18) of the internal combustion engine (10) in comparison to an injection mass (m fossil ) of the pure fossil fuel (12a). [3] Method according to one of claims 1 or 2, characterized by that as an operating parameter of the internal combustion engine (10) an air mass (m L ) of clean air (30) compared to an air mass (m L ) of clean air (30) is reduced, wherein in particular a boost pressure of the clean air (30) is reduced and / or a temperature of the clean air (30) is increased. [4] Method according to one of claims 1 to 3, characterized bythat as an operating parameter of the internal combustion engine (10) an exhaust gas recirculation rate (r A ) of an exhaust gas (14) of the internal combustion engine (10) to combustion chambers (18) of the internal combustion engine (10) in comparison to an exhaust gas recirculation rate (r A ) is increased during combustion of the pure fossil fuel (12a) in the combustion chambers (18) of the internal combustion engine (10). [5] Method according to one of the preceding claims, characterized by that the pure substance emission profile is defined by a proportion of NOx in an exhaust gas (14) of the internal combustion engine (10). [6] Method according to one of claims 1 to 5, characterized by that in the fuel mixture (12) diesel is used as fossil fuel (12a) and oxymethylene ether (OME) is used as synthetic fuel (12b). [7] Method according to one of claims 1 to 6, characterized by that as an operating parameter of the internal combustion engine (10) an injection mass m gemischof the fuel mixture (12) when injecting the fuel mixture (12) into combustion chambers (18) of the internal combustion engine (10), wherein the injection mass (m gemisch ) is adjusted particularly for torque-generating injections. [8] Method according to claim 7, characterized by that the adjusted injection mass (m gemisch ) according to the context mmixture=Fv⋅mfossil is adjusted, where F v is a gain factor resulting from a calorific value ratio of the calorific value (H u,fossil ) of the pure fossil fuel (12a) and the calorific value (H u,gemisch ) of the determined fuel mixture (12) according to Fv=Hu,fossilHu,mixture results.

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