Abstract:
An internal combustion engine system having a non-catalyzed particulate filter receiving products of combustion at a temperature of frequently above 600° C. and an excess of oxygen of between 0.5 and 0.8% from a stoichiometric diesel engine. A NO x  reduction catalyst is positioned downstream of the particulate filter. The engine system may include a turbocharger and the particulate filter and NO x  reduction catalyst may be positioned either upstream of the turbine or downstream of the turbine or alternatively the particulate filter upstream of the turbine and the NO x  reduction catalyst downstream of the turbine.

Description:
GOVERNMENT RIGHTS IN PATENT  
       [0001]    This invention was made with Government support under contract DE-FC26-05NT42416 awarded by the Department of Energy. The U.S. government may have certain rights in this invention. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to the field of internal combustion engine systems, and more particularly to, engine systems having exhaust aftertreatment devices. 
       BACKGROUND OF THE INVENTION 
       [0003]    Internal combustion engines come in a number of forms, the most common of which are spark-ignited, gasoline-fueled engines and compression-ignition, diesel-fueled engines. The spark-ignited, gasoline-fueled engine meters fuel into air, controlled by a throttle valve, to produce a mixture in the combustion chamber that is as close to stoichiometric as possible. The stoichiometric air-fuel ratio is the mass ratio at which all the fuel and all the air are combined in the combustion process. For gasoline-fueled, spark-ignited engines; this air-fuel ratio is 14.7-1. Operation at this condition enables appropriate exhaust aftertreatment using a three-way catalyst to reduce oxides of nitrogen in the engine exhaust. 
         [0004]    The compression-ignition, or diesel type engine, is used in many commercial and industrial power applications because of outstanding durability and fuel economy superior to the spark-ignited, gasoline-fueled engine. The diesel engine utilizes the heat of compression of intake air into which a timed and metered quantity of fuel is injected to produce combustion. The nature of the diesel engine cycle is that it has a variable air-fuel ratio that can, under part power conditions, rise to levels significantly above stoichiometric. This results in enhanced part power fuel economy since only the quantity of fuel needed for particular power levels is supplied to the engine. 
         [0005]    One of the issues with an engine of this type is the impact on emissions. In addition to generation of carbon monoxide and nitrous oxide, there is the generation of particulates in the form of soot. A number of approaches have been employed to reduce particulates while at the same time reducing oxides of nitrogen to evermore stringent levels mandated by the federal government. 
         [0006]    Stoichiometric diesel engines have been proposed to achieve this balance since they enable the use of automotive style catalysts to reduce oxides of nitrogen. By operating the engine at or near stoichiometric, generally around 14.7 ratio of air to fuel, a three-way catalyst may be employed. However, operation at this air fuel ratio causes a substantial increase in diesel particulates. Accordingly, diesel particulate filters must be employed to filter out the particulates, but generation of particulates is significant enough that frequent regeneration of the filters through temporary heating or other means is necessary to remove the collected particulate matter. 
         [0007]    Accordingly a need exists in the art to provide an engine system of this type having a superior ability to regenerate a diesel particulate filter. 
       SUMMARY OF THE INVENTION 
       [0008]    In one form, the invention includes an internal combustion engine system having an internal combustion engine with an air intake and an exhaust for products of combustion, the products of combustion having an excess of oxygen and a temperature greater than approximately 600° C. A non-catalyzed particulate filter receives products of combustion from the exhaust and a NO x  reduction catalyst downstream from and receiving fluid from the particulate filter reduces the oxides of nitrogen. 
         [0009]    In another form, the invention includes a method of operating an internal combustion engine system including the steps of operating an air breathing, fuel consuming, internal combustion engine to produce products of combustion in an exhaust with a temperature greater than approximately 600° C. and an excess of oxygen. The products of combustion are passed over a non-catalyzed particulate filter and subsequently passed over a NO x  reduction catalyst. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic drawing of an internal combustion engine embodying the present invention; 
           [0011]      FIG. 2  is a schematic drawing of an alternate embodiment of the present invention; and 
           [0012]      FIG. 3  is still another alternative embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]      FIG. 1  shows a power system having as its foundation an air breathing, fuel consuming, internal combustion engine  10  in which one or more pistons reciprocate within an engine block and are connected to a crankshaft for producing a rotary output. Each piston forms part of a variable volume combustion chamber that receives air for combustion from an intake system  12 . The products of combustion pass through an exhaust system  14 . In typical fashion, poppet valves (not shown to simplify the understanding of the invention) are actuated by camshafts to open at the appropriate point in the cycle to permit intake of air or allow exhaust of the products of combustion. As herein shown, the internal combustion engine is a compression ignition or diesel type. This engine is usually characterized by having a significantly high compression ratio for intake air so that a hydrocarbon fuel will self-ignite upon injection into the air heated by the compression process. In such an engine, a fuel system  13  delivers a metered quantity of fuel at the appropriate time interval to produce the desired power. Fuel system  13  produces the fuel quantity and timing in response to selected engine operating parameters and command from a fuel system controller (not shown). 
         [0014]    In an attempt to further increase the efficiency of the engine  10 , a turbocharger, identified by reference character  16  may be employed. Turbocharger  16  has a compressor  18  receiving intake air through conduit  20  and pressurizing it for delivery via conduit  17  to the intake system  12 . Consequently, the air entering the combustion chamber of the internal combustion engine  10  is at a higher density than obtainable from ambient air pressures and can produce greater power. An intercooler  19  receives the air at an increased pressure and temperature from compressor  18  and cools it to increase the charge density and enable greater power output. 
         [0015]    The compressor  18  is driven by a shaft  22  connected to a turbine  24  receiving the products of combustion from exhaust line  23  to be driven into rotation and thus drive compressor  18 . The inlet to turbine  24  may employ variable geometry of different types to attempt to maintain gas velocity as high as possible for lower flow conditions experienced under part-power. The exhaust gases that have passed over turbine  24  exit the system through exhaust line  26  where they may be subjected to exhaust aftertreatment, as described below, to reduce products in the exhaust system that are considered to be harmful to the environment. 
         [0016]    A diesel particulate filter  28  is interposed in exhaust line  26  and a three-way NO x  catalyst  30  is provided in exhaust line  26  downstream of diesel particulate filter  28 . Internal combustion engine  10  is operated as a stoichiometric diesel engine in that the ratio of combustion air to fuel consumed by the engine  10  is approximately stoichiometric, which is usually about 14.7 to 1. The mixture is based on air mass to fuel mass flow in the exhaust. Stoichiometric means that the mixture contains only the proper amount of oxygen to consume all of the fuel in the combustion process. However, because combustion is not complete, the exhaust from a stoichiometric engine contains some oxygen which is typically 0.5 to 0.8% even though the overall fuel air ratio is stoichiometric. The oxygen thus contained in the engine exhaust is balanced by a similar amount of carbon monoxide and hydrogen so that there is no excess oxygen since this would prevent the NO x  reduction catalyst  30  from removing NO x  in the engine exhaust. By operating the engine  10  in a stoichiometric manner, its exhaust is very hot and is generally greater than approximately 600° C. 
         [0017]    The diesel particulate filter  28  is absent a catalytic treatment and may be a wall-flow monolithic particulate filter. It should be apparent to those skilled in the art that other forms of uncatalyzed particulate filters may also be employed. The most common particulate filter is made of cordierite (a ceramic material that is also used as catalytic converter support (core). Cordierite filters provide excellent filtration efficiency, are (relatively) inexpensive, and have thermal properties that simplifiy vehicle packaging. The second most popular filter material is silicon carbide or SiC. 
         [0018]    Because the exhaust of the engine  10  is hot, the small amount of oxygen present is able to continuously oxidize the collected particulate matter on the particulate filter  28 . This occurs because the particulate filter  28  has no catalytic treatment since the presence of the catalyst would cause the oxygen to preferentially react with carbon monoxide and hydrogen and leave the carbon collected by the filter unreacted. After the exhaust gas has passed through the particulate filter, the NO x  reduction catalyst  30  (or three-way catalyst, is employed to eliminate oxides of nitrogen and other harmful components, such as carbon monoxide and hydrocarbons in the exhaust. By placing the uncatalyzed particulate filter  28  ahead of the NO x  reduction catalyst  30 , the temperature is sufficiently high to cause the accumulated carbon on the particulate filter  28  to oxidize. 
         [0019]    As shown in  FIG. 1 , the particulate filter  28  and the NO x  catalyst  30  are placed downstream of the turbine in exhaust line  26 . In  FIG. 2  however, the particulate filter  28  is placed upstream of turbine  24  in exhaust line  23  and the NO x  catalyst  30  placed downstream of turbine  24 . This may be done to place the diesel particulate filter in a fluid stream that is sufficiently hot to maintain a continuous oxidization of carbon particles collected on the particulate filter  28 . It should be noted that in this embodiment also, the NO x  catalyst  30  is downstream of the uncatalyzed particulate filter  28 . 
         [0020]      FIG. 3  shows still another arrangement in which both the particulate filter  28  and NO x  catalyst  30  are placed upstream of turbine  24  in exhaust line  23 . Again, it is noted that the uncatalyzed particulate filter  28  is upstream of NO x  catalyst  30  to provide maximum temperature and oxygen for continuous oxidization of the carbon particles thus accumulated. 
         [0021]    Although the engine system is shown incorporating a turbocharger  16 , it should be apparent to those skilled in the art that the engine  10  may also be operated without a turbocharger and still realize the benefits of the uncatalyzed particulate filter upstream of the NO x  catalyst. 
         [0022]    Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.