| Method for operating a compression-ignition internal combustion engine -> Monitor Keywords |
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Method for operating a compression-ignition internal combustion engineRelated Patent Categories: Power Plants, Internal Combustion Engine With Treatment Or Handling Of Exhaust Gas, Methods, Anti-pollutionMethod for operating a compression-ignition internal combustion engine description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070157599, Method for operating a compression-ignition internal combustion engine. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND AND SUMMARY OF THE INVENTION [0001] This application claims the priority of German patent document 103 16 112.0, filed Apr. 9, 2003 (PCT International Application No. PCT/EP2004/001518, filed Feb. 18, 2004), the disclosure of which is expressly incorporated by reference herein. [0002] The invention relates to a method for operating a compression-ignition internal combustion engine. [0003] One objective in the development of new diesel internal combustion engines is to minimize the formation of exhaust gas emissions, in particular the emissions of nitrogen oxides. Exhaust gas recirculation is often used as a means for reducing the emission levels, with an exhaust gas recirculation rate being set as a function of the load point. A further drop in the nitrogen oxide emissions can be achieved by means of an SCR catalytic converter, in which the addition or metering of a reducing agent (e.g., ammonia) is implemented proportionally to the formation of nitrogen oxide in the internal combustion engine. The required safety devices permit only limited conversion rates in an SCR catalytic converter of this type, since the untreated nitrogen oxide emissions from the internal combustion engine can be determined only from known engine map data. Sensors for the direct measurement of the concentrations of nitrogen oxides or ammonia in the exhaust gas are still in the research stage, and the sensors which are currently available are still unreliable. [0004] German patent document DE 197 34 494 C1 discloses a method for operating an internal combustion engine, in which a recirculation rate of the exhaust gas is calculated on the basis of a two-fold measurement of the oxygen concentration in the exhaust gas and in the charge air. In addition to its high cost, in this method, only the recirculation rate of the exhaust gas is determined. [0005] German patent document EP 554 766 B1 discloses a method in which a metering device for an SCR catalytic converter is controlled. The knowledge of the untreated nitrogen oxide emission levels which is required for this purpose is obtained by using engine map data, which provide a relatively inaccurate description of the engine emission as a function of engine parameters. On account of the fact that the untreated nitrogen oxide emission level is known only approximately, considerable safety margins have to be built in to avoid a breakthrough of ammonia downstream of the catalytic converter. Consequently, the conversion rate in the catalytic converter achieved is low, at up to approximately 70%. [0006] German patent document DE 100 43 383 C2 also discloses a method for determining the nitrogen oxide content in exhaust gases from internal combustion engines, in which the air mass fed to the internal combustion engine is recorded, with the combustion center of gravity being determined from at least one current measured value for the engine operation. The untreated NOx emissions are calculated from the value for the position of the combustion center of gravity and the values for the recorded fuel quantity and air mass. The parallel determination of air mass, fuel mass and recirculated exhaust gas mass is especially costly. [0007] The combustion center of gravity uses the first law of thermodynamics to describe the state in the combustion chamber in which 50% of the fuel energy introduced has been converted. The position of the center of gravity is the associated crank angle position (i.e., a crank angle position of the piston) at which 50% of the quantity of fuel participating in the combustion has been converted into heat. [0008] Therefore, one object of the present invention is to provide an improved method for determining or minimizing nitrogen oxide emissions. [0009] This and other objects and advantages are achieved by the method according to the invention, in which a mean gas temperature in the cylinder is determined during a combustion operation in the combustion chamber, so that a gradient of the mean gas temperature is calculated. The untreated nitrogen oxide emission level from the internal combustion engine is determined from a value for the gradient of the mean gas temperature and/or from a position of the gradient of the mean gas temperature in the combustion chamber. According to the invention, the untreated nitrogen oxide emission level (NOx emission) formed in the compression-ignition internal combustion engine is directly related to the gradient of the mean gas temperature in the cylinder. Accordingly, the engine parameters are set in such a manner as to achieve a profile of the gradient with which lower NOx emissions are formed during combustion. [0010] Furthermore, the method according to the invention is distinguished by the fact that a mean gas temperature in the cylinder is determined during a combustion operation in the combustion chamber, so that the untreated nitrogen oxide emission level from the internal combustion engine is determined from a maximum value for the mean gas temperature in the combustion chamber and/or from a position of the maximum value for the mean gas temperature. According to the present invention, the untreated nitrogen oxide emission level (NOx emission) formed in the compression-ignition internal combustion engine is directly related to the maximum value for the mean gas temperature in the cylinder. Accordingly, the engine parameters are set in such a manner that a defined maximum value is set during combustion or a predetermined maximum value is not exceeded. This allows simplified determination of the NOx emissions, in which the cost of measurement technology is reduced. [0011] The method according to the invention is also distinguished by the fact that a mean gas temperature in the cylinder is determined in the combustion chamber, and the untreated nitrogen oxide emission level from the internal combustion engine is determined from a value for a mean gas temperature when the intake valve is closed and/or a value for a final compression temperature in the combustion chamber. According to the invention, the untreated NOx emission level formed in the compression-ignition internal combustion engine is directly related to the value for the mean gas temperature which is determined prior to commencement of the combustion, at the instant at which the intake valve closes and/or at the end of compression. As a result, an accurate, simplified determination of the NOx emissions is achieved, so that the outlay on measurement technology is likewise reduced. [0012] According to one embodiment of the invention, the mean gas temperature is determined in a defined crank angle range. It is preferable to select a crank angle range in which the mean gas temperature in the cylinder has a virtually linear profile. This achieves accurate determination of the NOx emissions, since evaluation in a narrow crank angle range is reliable and less complex. Consequently, the outlay on measurement technology can be reduced. [0013] In a further configuration of the invention, a quantity of a reducing agent for the downstream exhaust gas aftertreatment system is determined from the untreated nitrogen oxide emission level which has been determined. Accordingly, the exhaust gas aftertreatment is optimized and, by way of example, a metered quantity for an SCR catalytic converter is varied. [0014] According to a further configuration of the invention, the metered quantity of fuel is injected into the combustion chamber in such a manner that a predetermined gradient of the mean gas temperature in the combustion chamber and/or a predetermined position of the maximum value for the mean gas temperature is established in the combustion chamber. Consequently, the mean gas temperature can be altered in such a manner that according to the invention the formation of the NOx emissions takes place at a minimal level or is as far as possible minimized. In this case, a predetermined rise in the gas temperature per unit time or a predetermined position of the maximum value is set. Accordingly, a predetermined maximum temperature value for the mean gas temperature, at which the formation of NOx emissions rises, cannot be exceeded. [0015] According to a further configuration of the invention, the metered quantity of fuel is injected into the combustion chamber in such a manner that a combustion center of gravity is at a defined crank angle position. In this case, increased formation of NOx can be avoided. [0016] According to a further configuration of the invention, an exhaust gas recirculation quantity for setting a defined oxygen concentration in the combustion chamber is set as a function of a combustion center of gravity. In this case, the required exhaust gas recirculation rate is calculated from the determined untreated NOx emission level from the internal combustion engine, and the exhaust gas recirculation is adjusted until a defined oxygen concentration results in the combustion chamber. [0017] In one configuration of the method according to the invention, a drop in the oxygen concentration which is required for nitrogen oxide reduction is calculated from the calculated untreated nitrogen oxide emission level, so that an exhaust gas recirculation device is set in such a manner that after combustion air has been mixed with recirculated exhaust gas, a defined oxygen concentration is produced in a cylinder charge upstream of or in the combustion chamber. As a result, targeted and rapid control of the internal combustion engine is achieved at the respective load point, so that the formation of untreated NOx emissions is reduced. It is preferable for desired values for the oxygen concentration to be stored in an engine map of the internal combustion engine in the engine control device. [0018] According to a further configuration of the invention, the oxygen concentration of the combustion air before it enters the combustion chamber is measured by means of an oxygen sensor, and a defined oxygen concentration of the combustion air upstream of or in the combustion chamber is set by means of the exhaust gas recirculation device as a function of the measured concentration. The use of the oxygen sensor brings about targeted and rapid control of the internal combustion engine to lower the formation of untreated NOx emissions at the respective load point. [0019] In one configuration of the method according to the invention, the oxygen concentration of the exhaust gases emerging from the combustion chamber is measured by means of an oxygen sensor. The oxygen concentration of the combustion air before it enters the combustion chamber is calculated from this signal. An exhaust gas recirculation rate and a measured combustion air quantity, and a defined oxygen concentration of the combustion air upstream of or in the combustion chamber is set by means of the exhaust gas recirculation device as a function of the calculated concentration. As a result, targeted and rapid control of the internal combustion engine so as to reduce the formation of untreated NOx emissions at the respective load point, taking into account the last combustion operation, is achieved by the use of the oxygen sensor in the exhaust manifold. [0020] Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS [0021] FIG. 1 shows a cross section through a cylinder of a direct injection compression-ignition internal combustion engine; [0022] FIG. 2 diagrammatically depicts a mean gas temperature of an internal combustion engine shown in FIG. 1 as a function of a crank angle; Continue reading about Method for operating a compression-ignition internal combustion engine... Full patent description for Method for operating a compression-ignition internal combustion engine Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method for operating a compression-ignition internal combustion engine patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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