Method for determining nitrogen oxide emissions during operation of an internal combustion engine

Abstract

A procedure for determining an emission (m NO ) of nitrogen oxides during operation of an internal combustion engine (10), wherein a volume (V(ϑ)) of the combustion chamber (14) is changed by a piston (18) guided in a cylinder as a function of a crank angle (ϑ), characterized in that a factor as a function of a product of the change ( | d V ( ϑ ) | d ϑ ) of the volume (V(ϑ)) with a reciprocal ( 1 V ( ϑ ) ) of the volume (V(ϑ)) is determined, and that the emission (m NO ) of nitrogen oxides is determined depending on the factor.

Description

State of the art

[0001] The invention relates to a method for determining an emission of nitrogen oxides during operation of an internal combustion engine according to the preamble of claim 1.

[0002] Methods designed to determine a nitrogen oxide value are known. For example, DE 10 2011 075 875 A1 relates to a method for calculating the raw NOx emissions of an internal combustion engine. Operating parameters of the internal combustion engine are used for this purpose. A correction function takes boost pressure into account.

[0003] DE 10 2010 041 907 A1 discloses a method for operating an internal combustion engine in which a modeled NOx value is determined using a NOx model. In particular, component tolerances of an injection system and component tolerances of an air system are taken into account. A determined value for nitrogen oxide emissions serves, for example, to correct fuel and / or urea injection quantities, to improve the function of catalytic converters, and thus ultimately to reduce overall nitrogen oxide emissions.

[0004] C. Guardiola, JJ Löpez, J. Martin, D. Garcia-Sarmiento: "Semiempirical incylinder pressure-based model for NOX prediction oriented to control applications" (Applied Thermal Engineering, Elsevier, 2011) discloses a baseline model for the rapid determination of nitrogen oxide emissions in diesel internal combustion engines. It also discloses how an adiabatic combustion temperature and a heat release rate of a fuel-air mixture in a combustion chamber can be determined. Disclosure of the invention

[0005] The problem underlying the invention is solved by a method according to claim 1. Advantageous further developments are specified in the subclaims and can also be found in the following description of exemplary embodiments.

[0006] A method is described for determining nitrogen oxide emissions during operation of an internal combustion engine. The volume of the combustion chamber is changed by a piston guided in a cylinder as a function of the crank angle. A factor is determined as a function of a product of the change in volume and an inverse of the volume. The nitrogen oxide emission is determined as a function of the factor. The determined factor advantageously takes into account that the movement of the charge in the cylinder due to the movement of the piston around top dead center significantly influences the nitrogen oxide reaction volume and thus the nitrogen oxide production during combustion. In this way, the determination of nitrogen oxide emissions can be carried out much more precisely using variables already available in the control unit.This more precise determination of nitrogen oxide emissions allows the engine's operating parameters to be better adapted to the current combustion conditions. Likewise, a nitrogen oxide sensor can be tested for functionality, or the sensor can be replaced using the aforementioned method.

[0007] In an advantageous embodiment, the factor is determined according to (1+|dV(ϑ)|dϑ⋅1V(ϑ))K4 where K4 is an applied quantity, ϑ the crank angle, and V(ϑ) the volume of the combustion chamber at the crank angle ϑ.

[0008] In an advantageous embodiment, the emission of nitrogen oxides is determined as a function of a crank angle range that includes top dead center. This allows the emission of nitrogen oxides to be determined more precisely.

[0009] In an advantageous embodiment, a heat release rate of a fuel-air mixture in the combustion chamber is determined as a function of the crank angle. An adiabatic combustion temperature of the fuel-air mixture in the combustion chamber is determined as a function of the crank angle. The emission of nitrogen oxides is determined as a function of the determined heat release rate, as a function of the adiabatic combustion temperature, as a function of the volume, and in particular as a function of the factor.

[0010] In an advantageous embodiment, the emission of nitrogen oxides is determined according to mNO=K1*⋅∫ϑHRR(ϑ)⋅(1+|dV(ϑ)|dϑ⋅1V(ϑ))K4⋅exp(K3Tad(ϑ))dϑ, where K1* represents a quantity determined from a characteristic map, where K4 represents an applied quantity, and where K3 represents an applied quantity.

[0011] Further features, possible applications, and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, which are illustrated in the figures of the drawing. All described or illustrated features, individually or in any combination, constitute the subject matter of the invention, regardless of their summary in the patent claims or their references, as well as regardless of their wording or representation in the description or in the drawing.

[0012] The sole figure of the drawing shows a schematic view of an internal combustion engine 10 of a motor vehicle. The internal combustion engine 10 operates according to a direct injection scheme, with fuel being injected directly into a combustion chamber 14 of the internal combustion engine 10 according to an autocycle, a diesel engine, or another method. According to the Otto cycle, a mixture of air and fuel is ignited by a spark plug 16. If the internal combustion engine 10 is a diesel engine, the spark plug 16 is not part of the internal combustion engine 10.

[0013] Each combustion chamber 14 is sealed by a movable piston 18 and is supplied with air by an intake system 50. After the combustion of an air-fuel mixture in the combustion chamber 14, the combusted charge of the combustion chamber 14 is expelled by the exhaust system 60. The exchange of charges is controlled by charge exchange valves 24, 26, which are operated by actuators 28, 30 synchronously with the movement of the piston 18. The actuators 28, 30 are cams of one or more camshafts, which are operated synchronously with the movement of the piston 18. By means of an exhaust gas recirculation system 70, exhaust gases can be recirculated to the combustion chamber 14 in order to reduce nitrogen oxide emissions, i.e., NOx emissions, or other pollutant emissions of the internal combustion engine 10.

[0014] The exhaust system 60 may include additional components for exhaust gas aftertreatment. Furthermore, the exhaust system 60 may include a NOX sensor 36 and a lambda sensor 37. The internal combustion engine 10 is operated by a control unit 38, which receives signals S from a corresponding sensor, for example, a signal S_36 from the NOX sensor 36, a signal S_37 from the lambda sensor 37, a signal S_40 from an engine speed sensor 40, a signal S_42 from an accelerator pedal sensor 42, a signal S_43 from a pressure sensor 43, and other signals such as an ambient temperature, a temperature of the internal combustion engine 10, an intake air temperature, etc. The pressure sensor 43 measures a pressure within the combustion chamber 14 and transmits this pressure as the signal S_43.Depending on these signals S or at least a portion of these signals S, the control unit 38 determines an operating parameter S_12 for the injector 12, if applicable, an operating parameter S_16 for the spark plugs 16, an operating parameter S_34 for an exhaust gas recirculation valve 34, and, if applicable, signals for other actuators that are part of the internal combustion engine 10. The control unit 38 has a digital processor unit on which a computer program can be executed.

[0015] The intake system 50 and the exhaust system 60, and other associated components such as the exhaust gas recirculation valve 34, may collectively be referred to as the air system. Other operating parameters related to the air system include, at least, a fluid flow rate through the exhaust gas recirculation valve 34, a boost pressure in an intake manifold, and a swirl number. The injectors 12 and associated components such as a fuel pump are referred to as the injection system.

[0016] Further operating parameters relating to the injection system include at least injection patterns, a timing of injections, a number of injections, a fuel mass, and a fuel pressure.

[0017] Turbulence of the fuel-air mixture in the sense of cylinder charge is influenced by the movement of the mass within the combustion chamber 14 and the atomization of the fuel. The turbulence induced by the atomization of the fuel does not, to a first approximation, change with the respective injection timing. Therefore, it is assumed that the movement of the mass within the combustion chamber 14 caused by the movement of the piston 18 around top dead center significantly influences the reaction volume for nitrogen oxides and thus the nitrogen oxide production during combustion.

[0018] Turbulence in the sense of squish turbulence that occurs at the top dead center can be caused, for example, by a squish speed v squish be simplified. This speed v squish is proportional to the speed of movement v piston of the piston 18 and is inversely proportional to the squared distance dp-ch between the upper crown of piston 18 and a cylinder head. The speed v squish of the piston 18 is proportional to the derivative of the instantaneous cylinder volume V(ϑ). The distance d p-ch is proportional to the instantaneous cylinder volume V(ϑ). Furthermore, an integration step of 1° of a crank angle ϑ is chosen. According to the following relationship equation 1, the above results in a product of a change |dV(ϑ)|dϑ of the instantaneous cylinder volume V(ϑ) with a reciprocal 1V(ϑ) of the cylinder volume V(ϑ) vsquish∝vpistondp−ch2∝vpistondp−ch∝dV(ϑ)dϑ⋅1V(ϑ)

[0019] An emission of nitrogen oxides for a combustion cycle during operation of the internal combustion engine 10 can thus be determined according to the following equation 2. The following term 3, which is included in equation 2, represents the proportion of the reaction volume in the nitrogen oxide generation process as well as the influence of the mass movement around the top dead center. The derivative of the instantaneous cylinder volume is given as an absolute value, since the corresponding sign is inherently important for the evaluation and consideration of turbulence when determining the emission m NO of nitrogen oxides plays a minor role. mNO=K1*⋅∫ϑHRR(ϑ)⋅(1+|dV(ϑ)|dϑ⋅1V(ϑ))K4⋅exp(K3Tad(ϑ))dϑ HRR(ϑ)⋅(1+|dV(ϑ)|dϑ⋅1V(ϑ))K4

[0020] The emission m NOof nitrogen oxides is determined according to Equation 2 by integrating over a crank angle range extending from a first crank angle to a second crank angle. The crank angle range may include the top dead center of ignition.

[0021] The emission m NO The mass of nitrogen oxides is also referred to as the mass of nitrogen oxides, where nitrogen oxides comprise a number of oxides of nitrogen. The quantity K1* is determined from a characteristic map as a function of engine speed and engine load.

Claims

[1] A method for determining an emission (m NO ) of nitrogen oxides during operation of an internal combustion engine (10), wherein a volume (V(ϑ)) of the combustion chamber (14) is changed by a piston (18) guided in a cylinder as a function of a crank angle (ϑ), characterized by that a factor depending on a product of change (|dV(ϑ)|dϑ) of the volume (V(ϑ)) with a reciprocal (1V(ϑ)) of the volume (V(ϑ)) is determined, and that the emission (m NO ) of nitrogen oxides is determined depending on the factor. [2] The method according to claim 1, wherein the factor is determined according to (1+|dV(ϑ)|dϑ⋅1V(ϑ))K4 where K4 is an applied quantity, ϑ the crank angle, and V(ϑ) the volume of the combustion chamber at the crank angle ϑ. [3] The method according to any one of the preceding claims, wherein the emission (m NO) of nitrogen oxides is determined as a function of a crank angle range that includes the top dead center. [4] The method according to one of the preceding claims, wherein a heat release rate (HRR(ϑ)) of a fuel-air mixture in the combustion chamber (14) is determined as a function of the crank angle (ϑ), wherein an adiabatic combustion temperature (T ad (ϑ)) of the fuel-air mixture in the combustion chamber (14) is determined as a function of the crank angle (ϑ), and wherein the emission (m NO ) of nitrogen oxides as a function of the determined heat release rate (HRR(ϑ)), as a function of the adiabatic combustion temperature (T ad (ϑ)), depending on the volume (V(ϑ)), in particular depending on the factor. [5] The method according to claim 4, wherein the emission (m NO ) of nitrogen oxides according to mNO=K1*⋅∫ϑHRR(ϑ)⋅(1+|dV(ϑ)|dϑ⋅1V(ϑ))K4⋅exp(K3Tad(ϑ))dϑ determined, where K1* represents a quantity determined from a characteristic map, where K4 represents an applied quantity, and where K3 represents an applied quantity. [6] The method according to any one of the preceding claims, wherein the emission (m NO ) of nitrogen oxides is a mass of nitrogen oxides. [7] A computer program for a digital computing device adapted to carry out the method according to any one of the preceding claims. [8] A control device (38) for operating an internal combustion engine (10), which is provided with a microprocessor on which a computer program according to claim 7 can run. [9] A storage medium for the control device (38) according to claim 8, on which the computer program according to claim 7 is stored.

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