| Method for using partial homogeneous charge compression ignition in a diesel internal combustion engine for nox trap regeneration -> Monitor Keywords |
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Method for using partial homogeneous charge compression ignition in a diesel internal combustion engine for nox trap regenerationRelated Patent Categories: Power Plants, Internal Combustion Engine With Treatment Or Handling Of Exhaust Gas, By Means Producing A Chemical Reaction Of A Component Of The Exhaust Gas, Having Means For Regenerating, Replacing, Or Feeding Liquid Or Solid Reagent Or CatalystMethod for using partial homogeneous charge compression ignition in a diesel internal combustion engine for nox trap regeneration description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060201143, Method for using partial homogeneous charge compression ignition in a diesel internal combustion engine for nox trap regeneration. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The invention relates to a method for controlling a diesel internal combustion engine being able to run in a conventional mode and in a partial Homogeneous Charge Compression Ignition mode (pHCCI). The invention further relates to a method for operating the engine in a rich pHCCI-mode. BACKGROUND AND SUMMARY OF THE INVENTION [0002] A major problem for engine manufacturers all over the world is to combine the features of low fuel consumption and low emissions of particulate matter (PM), unburned hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO.sub.x). Generally speaking, there are two different ignition systems for Internal Combustion engines (IC-engines), Spark Ignition (SI) and Compression Ignition (CI) of which the latter is the one generally used for diesel engines. CI-engines, e.g. diesel engines, have an advantage in view of SI-engines regarding the fuel consumption. In order to further reduce the harmful emissions in CI-engines, it has been suggested to run the engines in a partial Homogeneous Charge Compression Ignition mode (pHCCI) instead of the conventional mode. The pHCCI mode differs from the conventional mode in that the fuel is more evenly distributed in the piston chamber and more diluted by gases from the Exhaust Gas Recirculation (EGR) system while ignited. In the conventional mode the difference in concentrations of fuel, at different locations in the combustion chamber, will cause the ignition to start at substantially one location. Hence, the ignition will start at the place being most beneficial for a combustion reaction, i.e., when the pressure and temperature in the combustion chamber are high enough to ignite the combustion mixture at the location where the air/fuel mixture (A/F-mixture) is right. Furthermore, the way the fuel is combusted in the combustion chamber will contribute to maintain a lower temperature throughout the combustion which causes less production of NO.sub.x. In the conventional mode, having heterogeneous charge compression ignition combustion, the burnt gas temperature will be highly heterogeneous with very high local temperatures values creating high NO.sub.x emissions. However, when performing this lean pHCCI, like in conventional lean modes, there is still a production of NO.sub.x which will be absorbed by a NO.sub.x-adsorbing catalyst in an exhaust gas treatment system. To regenerate the NO.sub.x-adsorbing catalyst, there is a need to use a rich combustion mode. In U.S. Pat. No. 6,276,130, it is described how an engine is controlled to be run in a Homogeneous Charge Compression Ignition (HCCI) mode and while being run in this mode, it can switch between a first, lean A/F-mixture whereby NO.sub.x is adsorbed to a second, rich A/F-mixture whereby NO.sub.x is released. [0003] However, there are still several problems associated with the regeneration according to U.S. Pat. No. 6,276,130. One major problem is that the suggested mode of operating the engine will have a very small operating window in respect of engine load and speed for fulfilling all the required parameters as set in the patent. This means there will be a need to change from the HCCI-mode rather often and to frequently use the less desirable conventional rich mode. Furthermore, in conventional rich mode, there is always a great risk of oil dilution, i.e. the part of the fuel being injected adheres to the liner of the cylinder and mixes with the oil, when using a rich A/F-mixture. U.S. Pat. No. 6,276,130 is silent as to how this problem can be solved. [0004] Hence, there is a need for an improved and better method for controlling a diesel engine in order to regenerate a NO.sub.x-adsorbing catalyst associated with the engine. [0005] The invention relates to a method for regenerating a NO.sub.x-adsorbing catalyst coupled downstream of a diesel internal combustion engine, the engine having at least one cylinder, the method including: operating the engine in a lean partial homogeneous charge compression ignition (PHCCI) mode; providing an indication that the catalyst needs to be regenerated; and in response to said indication, switching engine operation to rich PHCCI mode, said rich PHCCI mode characterised in that a ratio of recirculated exhaust gases of 20 to 55% in the gas being admitted to an engine cylinder, said rich pHCCI mode being further characterised in that the central axis of a fuel spray in a main injection for each working cycle is directed towards a piston bowl cavity, said main injection comprising at least 70% of the fuel to be injected in each working cycle. [0006] The indication that the NO.sub.x-adsorbing catalyst needs to be regenerated can be based on several different criteria: Direct measurements of the amount of NO.sub.x stored in the NO.sub.x-absorbent exceeding a certain value, the use of mathematical models based on relevant parameters to estimate a value of stored NO.sub.x, having a schedule of regeneration cycles to be performed etc. For the purpose of the invention, it is not important how the determination that there shall be a change of pHCCI mode from lean to rich A/F-mixture is arrived at, the invention will work for any suitable way of indicating that a change of modes shall occur. [0007] It is further described that the EGR ratio used in the rich pHCCI mode is from 20 to 55%, i.e. 20 to 55% of the exhaust gases are recirculated mixed with air in order to form the gas admitted to the cylinder, the so called combustion gas. This interval of EGR will allow the rich pHCCI to be performed in a wider range than have been achieved before. Hence, this novel way of controlling the engine will increase the possibility to use rich pHCCI for the engine. [0008] One of the great benefits of this rich pHCCI mode is the reduction of oil dilution associated with the rich regeneration of the NO.sub.x-absorbent. As is evident from the claims, the major part of the fuel to be injected is injected in the main injection for each working cycle wherein the central axis of the injected fuel is directed towards the piston bowl cavity. Hence, by using rich pHCCI instead of a rich, conventional mode is it possible to avoid injecting fuel in such a way that it hits the liner of the cylinder which leads to oil dilution problems due to fuel sticking to said liner. Usually when running a diesel engine in a rich mode, there is an early pilot injection and/or one or more late, large post injections. These kinds of injections are usually associated with oil dilution problems. The present idea does not use any large post or pilot injections and avoids or diminishes the problem with oil dilution. As a result of decreased oil dilution, wear of the piston and cylinder will diminish, losses of power due to increased friction between the piston and the cylinder can be avoided and less frequent change of oil will be needed. [0009] Hence, using the method of the present invention provides the advantage of less oil dilution. [0010] A further aspect of the invention is that the rich pHCCI mode is allowed to have a Filter Smoke Number (FSN) value from 0.5 to 3.5. By allowing a higher soot formation, during the rich pHCCI mode, than what is common today, it is possible to extend the rich pHCCI operating window with a beneficial fuel economy and less oil dilution compared to conventional rich combustion mode. As engines have been controlled earlier, they have been forced to switch to conventional mode for regeneration when reaching a certain soot formation as taught for example in U.S. Pat. No. 6,276,130. In contrast to the intuition of a person skilled in the art, whose intuitive thinking would tell him to seek for solutions which suppress the soot formation, it has been surprisingly acknowledged that the allowance of higher soot formation in rich pHCCI may contribute to an overall positive effect with benefits concerning oil dilution and fuel economy. However, since there is allowed a relatively high rate of soot production, this mode of operation is advantageously combined with some kind of soot filter or other exhaust gas treating device adapted to convert the soot to harmless emissions. The FSN number can be measured using the method and instrumentation described in the manual for AVL 415S Variable Sampling Smoke Meter, ID number AT0699E, available from the AVL LIST GMBH, Graz, Austria. [0011] In yet another aspect of the invention, the main injection of said rich pHCCI mode is injected in the interval of 30 degrees Before Top Dead Center (BTDC) to 15 degrees After Top Dead Centre (ATDC), preferably in the interval of 30 degrees BTDC to 9 degrees ATDC. By defining the crank angle interval during which the main injection will occur it can be derived at which angles the fuel shall be injected in order to assure that the main axis of the fuel spray will be directed towards the piston bowl cavity. [0012] In another aspect of the invention, the temperature of said gas being admitted to the cylinder, i.e. the temperature of the combustion gas entering the cylinder, during said rich pHCCI mode is in the interval of 60 to 200 degrees Celsius, preferably in the interval of 60 to 130 degrees Celsius. In order to achieve a more homogeneous fuel mixture, it is suggested to use a relatively low temperature of the inlet gas in order to let the injected fuel have time to spread and mix with the combustion gas in the combustion chamber. A lowering of the temperature of the combustion gas will result in a reduction of soot formation which in turn will widen the operation window for rich pHCCI combustion. [0013] In a further aspect of the invention, the rich pHCCI mode further comprises a pilot and/or a post injection in a working cycle wherein the fuel injected in the pilot and/or post injection vaporises before it reaches a liner of a cylinder wall, if it is directed towards the liner. The use of a small pilot and/or post injection may contribute to stabilise the combustion and widen the operating window in which it is possible to perform rich pHCCI. To avoid that the fuel reaches the liner it is important that these injections are relatively small. It may also help if the injected fuel is atomised so that the fuel may mix with the combustion gas and diffuse into the gas. [0014] In yet another aspect of the invention there is only one single main injection injected in each working cycle in the rich pHCCI mode. Hence, all fuel injected in a working cycle in said rich pHCCI mode is injected in the main injection. By injecting all the fuel at one time, in the main injection, it can be assured that all the fuel will be directed towards the piston bowl cavity. For a large part of the operating area, this will be the optimal injection strategy for lowest fuel consumption and emissions during the regeneration. [0015] The above advantages and other advantages, and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings, and from the claims. BRIEF DESCRIPTION OF DRAWINGS [0016] The advantages described herein will be more fully understood by reading an example of an embodiment in which the invention is used to advantage, referred to herein as the Description of Preferred Embodiment, with reference to the drawings, wherein: [0017] FIG. 1 is a schematic drawing of a cylinder of an engine; [0018] FIG. 2 is a schematic drawing of an engine set up with an exhaust gas treating system; [0019] FIG. 3 is a graph of PHCCI and rich pHCCI operation window; [0020] FIG. 4 is a graph of the rich pHCCI operation window indicating rate of soot formation in different areas; [0021] FIG. 5 is a graph of the regeneration timing with rich pHCCI; and Continue reading about Method for using partial homogeneous charge compression ignition in a diesel internal combustion engine for nox trap regeneration... 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