Abstract:
A particle sensor is provided having a first temperature sensing device having a sensing surface exposed to particles contained within a fluid. The sensing surface is at least partially coated with a catalyst for promoting an exothermic reaction with at least a portion of the particles. The particle sensor also has a second temperature sensing device positioned at a location substantially thermally isolated from thermal energy generated by the exothermic reaction.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This patent application is a Divisional of U.S. patent application Ser. No. 11/882,217, filed Jul. 31, 2007. Which is hereby fully incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure is directed to a particle sensor and, more particularly, to a particle sensor utilizing temperature sensing devices. 
       BACKGROUND 
       [0003]    Engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may exhaust a complex mixture of air pollutants. The air pollutants may include both gaseous and solid material, such as, for example, particulate matter. Particulate matter may include ash and unburned carbon particles and may sometimes be referred to as soot. 
         [0004]    Due to increased environmental concerns, among other things, exhaust emission standards may have become more stringent. The amount of particulate matter and gaseous pollutants emitted from an engine may be regulated depending on the type, size, and/or class of engine. In order to meet these emissions standards, engine manufacturers have pursued improvements in several different engine technologies, such as fuel injection, engine management, and air induction, to name a few. In addition, engine manufacturers have developed devices for treatment of engine exhaust after it leaves the engine. 
         [0005]    Engine manufacturers have employed exhaust treatment devices called particulate traps to remove the particulate matter from the exhaust flow of an engine. A particulate trap may include a filter designed to trap particulate matter. The use of the particulate trap for extended periods of time, however, may enable particulate matter to accumulate on the filter, thereby causing damage to the filter and/or a decline in engine performance. Systems have been developed to measure, or estimate, an amount of particulate matter that has accumulated on the filter. 
         [0006]    For example, one such system for soot detection is described in U.S. Patent Publication No. US2001/0051108 (the publication) by Schonauer. The publication describes an apparatus for detecting soot. The apparatus includes a porous ceramic element, a heater, a first temperature probe, and a second temperature probe. The heater applies a constant level of heat to the porous ceramic element that is equivalent to the minimum ignition temperature of soot. As exhaust gas containing soot passes through the pores of the ceramic element, the exhaust gas is heated to the soot ignition temperature combusting the soot and further increasing the temperature of the exhaust gas. Such a temperature increase is measured by the first temperature probe. At the same time, a portion of the exhaust gas is directed to a chamber through a filter, which filters most of the soot contained within the exhaust gas. Because the exhaust gas in the chamber contains such a small amount of soot, the temperature of exhaust gas in the chamber provides a baseline temperature for comparison with the temperature increase measured by the first temperature probe. Such a baseline temperature is measured by the second temperature probe. The difference between the two temperatures is directly related to the amount of soot contained within the exhaust gas. 
         [0007]    Although the apparatus described in the publication may detect the amount of soot contained within the exhaust gas, the design may be prone to inaccuracies. In particular, because the exhaust gas is heated to the ignition temperature of soot before reaching both temperature probes, any soot that is allowed to reach the second temperature probe may compromise soot level measurements. To isolate the second temperature probe from soot contained within the exhaust gas, a filtering element and an isolation chamber must be built within the sensor housing. Inherent manufacturing inconsistencies may limit the filtering capability of any filtering element, and unknown levels of soot may infiltrate the isolation chamber. These manufacturing inconsistencies may limit the accuracy of any soot level measurement by distorting the baseline temperature due to undesired soot combustion. 
         [0008]    In addition, the apparatus described in the publication may be limited to only the detection of soot because it relies on heating the exhaust gas to the ignition temperature of soot. However, it may be desired to detect the level of other types of pollutants contained within the exhaust gas. Preheating the exhaust gas to determine the level of such pollutants may not be preferred because the pollutants may have ignition temperatures that may be difficult to attain or may damage other equipment in the exhaust system. 
         [0009]    The disclosed apparatus is directed to overcoming one or more of the problems set forth above. 
       SUMMARY OF THE INVENTION 
       [0010]    In one aspect, the disclosure is directed toward a particle sensor. The particle sensor includes a first temperature sensing device having a sensing surface exposed to particles contained within a fluid. The sensing surface is at least partially coated with a catalyst for promoting an exothermic reaction with at least a portion of the particles. The particle sensor also includes a second temperature sensing device positioned at a location substantially thermally isolated from thermal energy generated by the exothermic reaction. 
         [0011]    Consistent with a further aspect of the disclosure, a method is provided for sensing particles in a fluid. The method includes promoting an exothermic chemical reaction between a catalyst and at least a portion of the particles contained within the a fluid. The method also includes sensing a parameter indicative of a temperature of the exothermic chemical reaction. The method further includes sensing a parameter indicative of a temperature of the fluid. In addition, the method includes determining a temperature difference between the sensed temperature of the exothermic chemical reaction and the sensed temperature of the fluid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a diagrammatic illustration of an exemplary disclosed power source and associated exhaust system; and 
           [0013]      FIG. 2  is a schematic diagram of a particle sensor for use with the exhaust system of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]      FIG. 1  illustrates an exemplary power source  10  including an internal combustion engine having multiple subsystems that cooperate to produce mechanical or electrical power output. For the purposes of this disclosure, power source  10  is depicted and described as a four-stroke diesel engine. One skilled in the art will recognize, however, that power source  10  may be any other type of internal combustion engine such as, for example, a gasoline or a gaseous fuel-powered engine. One subsystem included within power source  10  may be an exhaust system  12 . Other subsystems included within power source  16  may be, for example, a fuel system, an air induction system, a lubrication system, a cooling system, or any other appropriate system (not shown). 
         [0015]    Exhaust system  12  may remove or reduce the amount of pollutants in the exhaust produced by power source  10  and release the treated exhaust into the atmosphere. Exhaust system  12  may include an exhaust passage  14  which may be in fluid communication with an exhaust manifold  16  of power source  10 . Exhaust system  12  may also include an exhaust treatment device  18  fluidly connected to exhaust passage  14 , a particle sensor  20 , and a controller  22 . Exhaust treatment device  18  may be, for example, a catalytic device, a particulate trap, an attenuation device, or any device capable of removing pollutants from exhaust gas flowing through exhaust passage  14 . Although exhaust system  12  is illustrated including only one exhaust treatment device  18 , it is contemplated that exhaust treatment system  12  may include multiple exhaust treatment devices  18 , if desired. 
         [0016]    As illustrated in  FIG. 2 , particle sensor  20  may include a housing  24  enclosing a first temperature probe  26  and a second temperature probe  28 . Housing  24  may be secured to an interior surface  30  of exhaust passage  14  using any method or device such as, for example, welds, mechanical fasteners, or adhesives. It is contemplated that housing  24  may be any shape capable of permitting exhaust gas to flow freely. However, it may be desired to select a housing shape that produces minimal drag to reduce any backpressure that may adversely affect the performance of exhaust system  12 . Housing  24  may define passages  32  and  34  through which exhaust gas may flow. A wall member  36  may divide and reduce heat transfer between passages  32  and  34 . In addition, wall member  36  may be manufactured from any type of rigid material having strong insulating properties such as, for example, heat resistant ceramics or foams. 
         [0017]    First and second temperature probes  26  and  28  may be situated within passages  32  and  34  so that they are exposed to the exhaust gas flowing through housing  24 . In addition, first and second temperature probes may be for example, a thermocouple, a thermistor, or any other type of temperature sensing device capable of sending a signal indicative of an exhaust gas temperature to controller  22 . First and second temperature probes may communicate with controller  22  via communication lines  38  and  40 , respectively. It is contemplated that, for increased accuracy, first and second temperature probes  32  and  34  may have similar sensing properties. For example, in embodiments utilizing thermistors, first and second temperature probes  26  and  28  may have substantially similar resistance characteristics. Also, in embodiments utilizing thermocouples, first and second temperature probes  26  and  28  may have substantially similar voltage generating characteristics. 
         [0018]    An entire surface of first temperature probe  26  exposed to the exhaust gas may be coated with a catalyst. The catalyst may be any material capable exothermically reacting with a particular type of particle contained within the exhaust gas. The particle may be, for example, soot, sulfur, or any other type of emissions particle that may be regulated. In addition, the catalyst may be selected so that it may exothermically react only with the type of particle for which detection is desired. When a particular type of particle contained within exhaust gas encounters temperature probe  26 , the resulting exothermic reaction with the catalyst may increase the temperature of exhaust gas flowing through passage  32  by a magnitude directly related to the amount of the particle contained within the exhaust gas. 
         [0019]    Controller  22  may include one or more microprocessors, a memory, a data storage device, a communication hub, and/or other components known in the art and may be associated with exhaust system  12 . Controller  22  may receive signals from first and second temperature probes  26  and  28  and analyze the data to determine a difference between the temperature of exhaust gas flowing through passage  32  and the temperature of exhaust gas flowing through passage  34 . Controller  22  may compare the determined difference to algorithms, equations, tables, or charts stored in or accessible by controller  22  to determine the amount of the sensed particle contained within the exhaust gas. Based on the quantity of the particle, controller  22  may establish an output to influence the operation of other devices of exhaust system  12 . 
       Industrial Applicability 
       [0020]    The disclosed particle sensor may accurately detect the quantity of a particular type of particle such as, for example, soot that may be contained within an exhaust gas. In particular, the disclosed particle sensor may provoke an exothermal chemical reaction between the soot and a catalyst. The resulting temperature increase may be directly related to the amount of soot within the exhaust gas. The operation of particle sensor  20  will now be explained. 
         [0021]    Exhaust gas may flow through exhaust passageway  14  and enter sensor  20  via passages  32  and  34 . In passage  34 , first temperature probe  26  may be exposed to the exhaust gas flowing through passage  32 . The first temperature probe  26  may be coated with a catalyst that may exothermally react only with soot. As the exhaust gas encounters first temperature probe  26 , the catalyst may exothermically react with the soot increasing the temperature of the exhaust gas surrounding the reaction. First temperature probe  26  may send a temperature signal to controller  22  indicative of the increased exhaust gas temperature. 
         [0022]    In passage  34 , second temperature probe  28  may be exposed to exhaust gas flowing through passage  34 . Unlike first temperature probe  26 , an exposed surface of second temperature probe  28  may be left uncoated or coated with a chemically neutral material so that neither the exhaust gas nor particles within the exhaust gas may exothermically react with the exposed surface of second temperature probe  28 . In addition, wall member  36  may insulate second temperature probe  28  and the exhaust gas flowing through passage  34  from the heat generated by the exothermic reaction occurring in passage  32 . It is contemplated that wall member  36  may be omitted if second temperature probe  28  is positioned far enough from first temperature probe  26  to be unaffected by the exothermic reaction. This may allow second temperature  28  to sense a baseline temperature of the exhaust gas. Second temperature probe  28  may send a temperature signal to controller  22  indicative of the baseline exhaust gas temperature. 
         [0023]    Upon receiving the temperature signals from first and second temperature probes  26  and  28 , controller  22  may calculate the difference between the two sensed temperatures, which may be directly related to the amount of soot contained within the exhaust gas. Controller  22  may compare the calculated temperature difference to tables, graphs, and/or equations stored in its memory or accessible to controller  22  to determine the amount of soot contained within the exhaust gas. Once the amount of soot is determined, controller  22  may perform any number of predetermined actions. For example, controller  22  may actuate a regenerating device to regenerate a particulate trap filter or actuate a warning alarm if the level of soot in the exhaust gas exceeds a predetermined threshold. It should be understood that particle sensor  20  may be located anywhere within exhaust passageway  14  depending on the desired use of particle sensor  20 . 
         [0024]    Because the disclosed sensor does not preheat the exhaust gas before exposing the temperature probes to the exhaust gas, the disclosed sensor may generate more accurate readings. In particular, the disclosed sensor may not need to filter the soot before exposing the second temperature probe to the exhaust gas, and special devices such as filters and isolation chambers may not be necessary to generate an accurate baseline temperature reading. Without elements that require such tight manufacturing tolerances, inherent manufacturing inconsistencies may have less of an impact on the sensor&#39;s accuracy. 
         [0025]    In addition, because the sensor relies on exothermic chemical reactions the sensor may not be limited to the detection of only soot. In particular, because the catalyst may generate the temperature increase, the types of particles which may be detected by the sensor may only be limited by the variety of catalysts known in the art. 
         [0026]    It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed apparatus without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.