Abstract:
A system to measure a parameter of a particulate laden gas flow may include a conduit enclosed by a boundary wall directing the particulate laden gas flow and a sensor configured to measure the parameter. The system may also include an annular averaging chamber extending radially outwardly from the conduit. The averaging chamber may be positioned such that the sensor is fluidly coupled to the conduit through the averaging chamber. The system may further include a porous element extending around the conduit. The porous element may be positioned such that the averaging chamber is fluidly coupled to the conduit through the porous element.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to a system to measure the parameters of a gas flow including particulate matter. 
       BACKGROUND 
       [0002]    In some applications, there is a need to measure parameters (such as, for example, pressure, velocity, mass flow rate, etc.) of a gaseous flow stream containing particulate matter (such as, for example, soot, etc.) in a real-time manner. The particulate matter in the flow stream, however, tends to settle and negatively impact the parameter measurements. For example, in an engine application where a pressure transducer is used to measure the time varying (or transient) pressure of exhaust flowing through a venturi, particulate matter in the exhaust (collectively referred to herein as soot) may impact the pressure measurements. 
         [0003]    Published U.S. Patent Application No. 2009/0084193 to Cerabone et al. (“the &#39;193 application”) discloses an apparatus for measuring an exhaust gas recirculation flow of an internal combustion engine. The apparatus of the &#39;193 application includes a venturi pipe through which the recirculated exhaust gas flows. The apparatus further includes a differential pressure sensor that is in fluid communication with the venturi pipe through passages that connect to the venturi pipe. Although the &#39;193 application discloses an apparatus that purportedly serves to measure the mass flow of exhaust through the venturi, in some cases particulate matter may collect in the passages that couple the pressure sensor to the venturi pipe, and eventually clog these passages. 
         [0004]    The systems and methods of the present disclosure may help address the foregoing problems and/or other problems existing in the art. 
       SUMMARY 
       [0005]    In one aspect, a system to measure a parameter of a particulate laden gas flow is disclosed. The system may include a conduit enclosed by a boundary wall directing the particulate laden gas flow and a sensor configured to measure the parameter. The system may also include an annular averaging chamber extending radially outwardly from the conduit. The averaging chamber may be positioned such that the sensor is fluidly coupled to the conduit through the averaging chamber. The system may further include a porous element extending around the conduit. The porous element may be positioned such that the averaging chamber is fluidly coupled to the conduit through the porous element. 
         [0006]    In another aspect, a method of measuring a parameter of a particulate laden gas flow is disclosed. The method may include directing the particulate laden gas through a conduit and detecting a signal indicative of the parameter using a sensor. The sensor may be fluidly coupled to the conduit through an averaging chamber and a porous element. The averaging chamber may be an annular chamber that extends radially outwardly from the conduit and is positioned such that the sensor is fluidly coupled to the conduit through the averaging chamber, and the averaging chamber is fluidly coupled to the conduit through the porous element. 
         [0007]    In yet another aspect, an exhaust gas recirculation system of an engine is disclosed. The system may include a venturi tube configured to direct exhaust gas containing particulate matter therethrough. The system may also include a hollow cylindrical porous element extending around a portion of the venturi tube and a pressure sensor fluidly coupled to the venturi tube through the porous element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  graphically illustrates an exemplary engine with an exhaust gas recirculation (EGR) system; 
           [0009]      FIG. 2  is a cross-sectional view of an embodiment of a venturi tube that may be used in the EGR system of  FIG. 1 ; 
           [0010]      FIG. 3A  is a perspective view of an exemplary channel member that may be used with the venturi tube of  FIG. 2 ; 
           [0011]      FIG. 3B  is a cross-sectional view of the channel member of  FIG. 3A ; 
           [0012]      FIG. 3C  is a cross-sectional view of another embodiment of a channel member that may be used with the venturi tube of  FIG. 2 ; 
           [0013]      FIG. 4A  is an enlarged view of a region of the venturi tube of  FIG. 2  showing an embodiment of a filter element disposed therein; 
           [0014]      FIG. 4B  is perspective view of the filter element of  FIG. 4A ; 
           [0015]      FIG. 5  graphically illustrates a low pass pneumatic filter of the venturi tube of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Although the systems and methods described herein are broadly applicable to the measurement of any parameter of a particulate laden gas flow in any application, for the sake of brevity, these concepts will be described with reference to an exhaust gas recirculation system of an engine. 
         [0017]      FIG. 1  illustrates an engine  10  with an exhaust gas recirculation (EGR) system  30  according to the present disclosure. Engine  10  may be any type of engine configured to produce power by combusting a fuel (such as, for example, diesel fuel, gasoline, etc.). Engine  10  may have one or more combustion chambers that combust the fuel and produce exhaust. Engine  10  may include an intake system  14  for delivering air and/or other gases to the combustion chambers and an exhaust system  12  for directing the exhaust gases away from combustion chambers. Intake system  14  may include various components for directing intake air (and/or other gases) into the combustion chambers. For example, intake system  14  may include, among other components, a compressor  22  of a turbocharger  20  configured to compress the intake air. Although not illustrated in  FIG. 1 , intake system  14  may include various other components that may assist in directing the intake air to the combustion chambers (such as, for example, valves, compressors, filters, heat exchangers, etc.). Exhaust system  12  may include various components configured to extract energy from the exhaust gases (exhaust) and direct the exhaust away from the engine  10 . For example, exhaust system  12  may include a turbine  24  of turbocharger  20 . Turbine  24  may be powered by the exhaust and operate the compressor  22 . Exhaust system  12  may also include an aftertreatment system (not shown) configured to reduce the amount of undesirable constituents in the exhaust emitted by the engine  10 . 
         [0018]    EGR system  30  may direct some of the exhaust from the exhaust system  12  to mix with air passing through the intake system  14 . EGR system  30  may include several components configured to treat and measure the recirculated exhaust before being directed to the intake system  14 . These components may include, among others, an EGR cooler  32  and a venturi tube  34 . The EGR cooler  32  may include any component (such as, for example, a heat exchanger) configured to cool the exhaust passing therethrough. The venturi tube  34  may be configured to measure the exhaust flow through the EGR system  30 . Although  FIG. 1  illustrates the exhaust as being drawn from the exhaust system  12  downstream of the turbine  24  and directed to the intake system  14  upstream of the compressor  22 , this is only exemplary. In other embodiments, EGR system  30  may fluidly couple the exhaust system  12  to the intake system  14  at other locations. In addition to the components shown in  FIG. 1 , EGR system  30  may include various other components, including, but not limited to, valves, filters, mixers, etc., and these components may be arranged in any order relative to one another. 
         [0019]    It is known that the mass flow rate of a fluid flowing through a pipe may be measured using a venturi tube. A venturi tube measures the mass flow rate by making use of the Venturi effect. The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of a pipe. By measuring the pressure of the fluid at the inlet and at the constricted section (that is, the pressure drop of the fluid), the flow rate can be calculated based on the law of conservation of energy and the Bernoulli theorem. Venturi tube  34  includes a constricted section (throat  38 ) positioned between an inlet  36  and an outlet  42 . The exhaust in EGR system  30  enters venturi tube  34  through the inlet  36 , flows through the throat  38 , and exits the venturi tube  34  through the outlet  42 . As the exhaust flows through the throat  38 , the velocity of the exhaust increases at the expense of its pressure. Pressure sensors  44 ,  46 , fluidly coupled to the inlet  36  and the throat  38 , respectively, measure the pressure of the exhaust flowing through the inlet  36  and the throat  38 . Based on the measured pressure, a controller  48  (in electrical communication with the pressure sensors  44 ,  46 ) may determine the pressure drop and the mass flow rate of exhaust flowing through the venturi tube  34 . 
         [0020]    Pressure sensors  44  and  44  may be any device configured to measure the pressure of a gas. Although two separate pressure sensors  44  and  46  are described as being coupled to the inlet  36  and the throat  38 , this is only exemplary and other configurations (such as, for example, a differential pressure sensor coupled to the inlet and the throat, etc.) may be used to measure the pressure drop of the exhaust at the throat  38 . Further, although not illustrated in  FIG. 1 , EGR system  30  may also include other components, such as, for example, a valve (in communication with the controller  48 ) configured to control the amount of exhaust redirected through the EGR system  30  based on the measured mass flow rate and/or other engine parameters. 
         [0021]    Any type of venturi tube known in the art may be used to measure the mass flow rate of exhaust flowing through EGR system  30 .  FIG. 2  illustrates an embodiment of the venturi tube  34  that may be used in EGR system  30 . Venturi tube  34  includes a tubular structure with a throat  38 , having a reduced diameter, positioned between the inlet  36  and the outlet  42 . The diameter of the inlet  36 , the throat  38 , and the outlet  42  may be any value and may be selected based on the application. A passageway  54  may fluidly couple the inlet  36  to pressure sensor  44  (see  FIG. 1 ), and a passageway  56  may fluidly couple the throat  38  to pressure sensor  46 . As the exhaust flows through the venturi tube  34 , the passageways  54  and  56  transmit the pressure of the exhaust to the pressure sensors  44  and  46 . The pressure sensors  44 ,  46  are thus exposed to the pressure proximate the opening of the passageways  54 ,  56  into the venturi tube  34 . For example, pressure sensor  46  is exposed to (and therefore measures) the pressure of the exhaust flowing around the opening of passageway  56  into the throat  38 . 
         [0022]    It is known that flow discontinuities (such as, for example, bends and other flow disruption features that disturb the flow of a fluid) at an upstream location change the characteristics of fluid flow for a finite distance downstream of the discontinuity. This finite distance is typically expressed as a ratio of the length of pipe to the diameter (L/D ratio) of the pipe. That is, a discontinuity in the exhaust stream upstream of passageway  56  affects the characteristics of exhaust flow across the throat  38 . Therefore, the pressure (and other characteristics) of the exhaust at all locations along the diameter, or at all locations along the circumference, of the throat  38  may not be the same. To ensure that the pressure measured by pressure sensor  46  is a true representation of the pressure of the exhaust at the throat  38 , the passageway  56  is coupled to the throat  38  through an averaging chamber  68 . 
         [0023]    Averaging chamber  68  is an annular chamber formed around throat  38 , and positioned between the passageway  56  and the throat  38 . Coupling the pressure sensor  46  to the throat  38  through an averaging chamber  68  (annularly disposed around the throat  38 ) exposes the pressure sensor  46  to an average pressure in the throat  38 . If the pressure distribution of the exhaust in throat  38  is non-uniform due to an upstream flow discontinuity (or due to any other reason), the averaging chamber  68  averages (or assists in averaging) the pressure of the exhaust in the throat  38 . Thus, pressure sensor  46  measures an average pressure of the exhaust in the throat  38 . The size of the averaging chamber  68  depends on the application. The factors that may play a role in the size of the averaging chamber  68  may include, among others, the expected exhaust pressure, expected pressure variation around the throat  38 , frequency of the pressure transient, etc. For example, in an application where the variation in pressure around the throat  38  is high, a relatively larger averaging chamber  68  may be provided. In an application where the pressure of the exhaust through the throat  38  changes relatively fast with time, the size of the averaging chamber  68  may be relatively smaller to ensure that the pressure sensor  46  measures the transient characteristics of the exhaust pressure at the throat  38 . A large averaging chamber  68  in such an application may act as a filter that filters the high frequency pressure pulses passing therethrough. In some embodiments, the size of the averaging chamber  68  may be selected to ensure sufficient averaging of the pressure without filtering the transient pressure pulses. In some embodiments, a vibration damping packing material may be disposed inside the averaging chamber  68 . The averaging chamber  68  may be formed by attaching a channel member  66  to the throat  38 . 
         [0024]      FIG. 3A  illustrates a perspective view of an exemplary channel member  66  that may be attached to the throat to form the averaging chamber  68 .  FIG. 3B  illustrates a cross-sectional view of the channel member  66  along plane  3 B. In the description that follows, reference will be made to both  FIGS. 3A and 3B . Channel member  66  may be a ring shaped element having a generally C-shaped cross-sectional shape. Channel member  66  may include a base section  66   a  with two legs  66   b  that extend from either end of the base section  66   a . Although not a requirement, in some embodiments, as illustrated in  FIG. 3B , the legs  66   b  may extend substantially perpendicular to the base section  66   a . The channel member  66  may be attached to the venturi tube  34  at terminal ends  66   c  of the legs  66   b . The channel member  66  may be attached to the venturi tube  34  by any method (welding, brazing, adhesive attach, etc.) suitable for the operating environment of the venturi tube  34 . The base section  66   a  may include an opening  52  to engage with the passageway  56  coupled to the pressure sensor  46 . In some embodiments, more than one opening  52  may be provided in the base section  66   a . In these embodiments, multiple passageways may couple the averaging chamber  68  to the pressure sensor  46 . For example, in some embodiments, channel member  66  may include two openings  52  (that are separated by, for example, 90°), and a passageway  56  having a Y-configuration may couple to the two openings  52  at one end and to the pressure sensor  46  at the opposite end. Multiple openings  52  positioned around the base section  66   a  may assist in averaging the pressure around the throat  38 . In an application where the size of the averaging chamber  68  is selected to be small to prevent filtering of pressure pulses, multiple openings  52  may provide the desired averaging. 
         [0025]    Although a channel member  66  having a generally C-shaped cross-sectional shape is illustrated in  FIG. 3B , in general, the channel member  66  may have any shape that forms an averaging chamber  68  around throat  38 . The channel member  66  may also have any size. The size of the channel member  66  may depend on the desired size of the averaging chamber  68 . In some embodiments, the depth (d) of the averaging chamber  68  may vary from between about 1-10 mm and its width (w) may vary between about 10-50 mm. The channel member  66  may be formed by any material. In some embodiments, the material of the venturi tube  34  and the channel member  66  may be the same to minimize the coefficient of thermal expansion (CTE) mismatch induced stresses in the weld (or other attachment medium) between the two components. In some embodiments, the passageway  56  may also be made of a material having a similar CTE to reduce CTE mismatch induced stresses. In some embodiments, the channel member  66  may be configured to form the throat  38  of the venturi tube  34 .  FIG. 3C  illustrates a cross-sectional view of another exemplary embodiment of channel member  166  in which the ends of the legs  66   b , opposite the base  66   a , extend substantially perpendicularly from the legs  66   b  to form the walls  38   b  of the throat  38 . A coupling  52   a  may also be provided at opening  52  to enable of coupling of passageway  56  to channel member  166 . 
         [0026]    With reference to  FIG. 2 , as exhaust in EGR system  30  flows through the venturi tube  34 , soot in the exhaust may settle on the walls of the venturi tube  34 . This settling of the soot may be caused by known mechanisms such as thermophoresis (in which soot migrates towards the lower temperature walls), pressure pulses acting as a pneumatic hammer (caused by repeated opening and closing of the exhaust valve), etc. The soot settling on the walls of the venturi tube  34  may clog the passageways  54 ,  56  and thereby impact the measurement of pressure by the pressure sensors (or any other sensor) coupled to these passageways. Thus, the soot in the exhaust may impact the measurement of exhaust pressure. To minimize this impact, a porous element or a filter element  60  may be positioned between the averaging chamber  68  and the throat  38 . 
         [0027]      FIG. 4A  illustrates an enlarged view of the averaging chamber  68  (location identified in  FIG. 2 ) showing the filter element  60  positioned between the averaging chamber  68  and the throat  38 . Filter element  60  may include a porous material coupled to the channel member  66  such that the pores of the filter element  60  fluidly couple the throat  38  to the averaging chamber  68 . In some embodiments, the filter element  60  is coupled to the channel member  66  such that a surface  60   a  of the filter element  60  exposed to the throat  38  is substantially flush with the walls  38   b  of the throat  38 . Positioning the surface  60   a  substantially flush with the walls  38   b  may ensure that the filter element  60  does not affect the exhaust flow pattern (and thereby the pressure distribution) in the throat  38 . The filter element  60  may be coupled to the channel member  66  by any method. In some embodiments, the filter element  60  may be positioned such that it spans across substantially the entire opening of the averaging chamber  60  into the throat  38 . In such embodiments, substantially all the exhaust that enters the averaging chamber  60  from the throat  38  passes through the filter element  60 . In some embodiments, the filter element  60  may be attached to the channel member  66  by welding, brazing, soldering, using a high temperature adhesive, etc. In some embodiments, the filter element  60  may be interference fitted to the channel member  66 . Although not illustrated herein, in some embodiments, the legs  66   b  (for example, at the terminal ends  66   c ) of the channel member  66  may include a step or another feature to hold the filter element  60  substantially flush with the throat walls  38   b . Although filter element  60  is described as being attached to the channel member  66 , this is only exemplary. In some embodiments, the filter element  60  may be attached (welded, etc.) to the venturi tube  34 , with the channel member  66  placed over the filter element  60  and attached to the venturi tube  34 . 
         [0028]      FIG. 4B  illustrates a perspective view of the filter element  60 . In some embodiments, the filter element  60  may have a hollow cylindrical shape. When installed in the channel member  66 , the internal surface  60   a  of the cylindrical filter element  60  may form the walls of the throat  38 . Although a cylindrically shaped filter element  60  is described herein, it should be noted that, in general, the filter element  60  can have any shape and configuration. For example, in an application without an averaging chamber  68 , or in an application in which the averaging chamber  68  has a different shape, the filter element  60  may have a different shape. The filter element  60  may be made of any material and may have any pore size. The size of the pores may be selected to be small enough to block soot from passing therethrough while being large enough to transmit pressure therethrough. In general, the size of the pores may depend on the application. The factors that dictate the pore size may be similar to the factors that dictate the size of the averaging chamber  68 . In general, for application in which increased flow stability is desired, a smaller pore size may be used, and in applications where dynamic response is desired, a filter element  60  with a larger pore size may be employed. In some embodiments, the pore size of the filter element  60  and the size of the averaging chamber  68  may be tuned to achieve desirable properties. In some embodiments, the filter element  60  may be made of sintered stainless steel with a pore size between about 10 and 50 microns, and have a total open area between about 30 and 50% of surface  60   a.    
         [0029]    With reference to  FIG. 2 , in some embodiments, 3-way valves  62   a ,  62   b , fluidly coupled to purge lines  57   a ,  57   b , may be provided in passageways  54 ,  56  downstream of averaging chambers  58 ,  68 . The purge lines  57   a ,  57   b  may be coupled to a source of compressed air or another gas. In such embodiments, the 3-way valves  62   a ,  62   b  may be periodically activated to direct a burst of air (or another gas) into the passageways  54 ,  56  through the purge lines  57   a ,  57   b . This burst of air may flow upstream through the passageways  54 ,  56  into the venturi tube  34  to clear the pores of the filter elements  60 . These air burst may be of a relatively short duration (for instance, 1-3 seconds) and may occur at times when the pressure sensors  44 ,  46  are inactive. The air bursts may be especially suitable for applications where flow measurement times are separated by periods where there is no interest in flow measurement. 
         [0030]    With reference to  FIG. 2 , in some embodiments, a low pass pneumatic filter  70  may be incorporated downstream of the averaging chamber  68  to minimize the exposure of the pressure sensor  46  to high frequency noise.  FIG. 5  illustrates a pneumatic filter  70  that may be positioned between averaging chamber  68  and the pressure sensor  46 . In some embodiments, the pneumatic filter  70  may be a part of the passageway  56 , while in other embodiments, the pneumatic filter may be a separate part that is fluidly coupled to the passageway  56 . The pneumatic filter  70  may include a tubular component with sections having different lengths and diameters. For instance, pneumatic filter  70  may include a first section  70   a  having a first length L 1  and a first diameter D 1 , positioned upstream of a second section  70   b  having a larger second diameter D 2  and a second length L 2 , and a third section  70   c  having a third diameter D 3  and a third length L 3  positioned downstream of the second section  70   b . In some embodiments, the second diameter D 2  may be larger than the first and the third diameters D 1 , D 3 , and the second length L 2  may be smaller than the first and the third lengths L 1 , L 3 . In some embodiments, the second diameter D 2  may be smaller than the diameter of passageway  56 . The relative dimensions of the first, second, and third sections  70   a ,  70   b ,  70   c  of the pneumatic filter  70  may be selected to block high frequency pulses (≧about 100 Hz) without affecting the low frequency pressure pulses (≦20 Hz) passing therethrough. While the exact dimensions of the different sections of the pneumatic filter  70  may vary with the particular application, in an exemplary application in an EGR system  30 , the first and third diameters D 1 , D 3  may be between about 1-2 mm, the first and third lengths L1, L3 were between about 10-15 mm, and the second diameter D 2  and second length L 2  may be between 3-7 mm and 5-8 mm respectively. 
         [0031]    As illustrated in  FIG. 2 , in some embodiments, a channel member  64  may also be positioned annularly around the inlet  36  to form an averaging chamber  58  around the inlet  36 . A filter element  60  may be positioned to fluidly couple the averaging chamber  58  to the inlet  36 . In some embodiments, a pneumatic filter  80  may also be positioned downstream of the averaging chamber  58  to block high frequency pressure pulses from reaching the pressure sensor  44 . Since the channel member  64 , averaging chamber  58 , and the pneumatic filter  80  function in a similar manner to the channel member  66 , averaging chamber  68 , and the pneumatic filter  70  discussed previously, for the sake of brevity, they are not described in more detail herein. 
       INDUSTRIAL APPLICABILITY 
       [0032]    The disclosed systems and methods to measure the parameters of a particulate laden gas flow may be used in any application where it is desired to measure the parameters of the gas flow. The disclosed system may be especially useful where it is desired to measure transient parameters of gas flow in a real-time manner. The disclosed system may promote accurate measurements of an average value of the parameter and may reduce the impact of the particulate matter in the measurements. To illustrate some of the novel aspects of the disclosed system, an application in an EGR system of an engine exhaust system is described below. 
         [0033]    A portion of exhaust flowing through the exhaust system  12  of the engine may be re-directed to the intake system  14  through an EGR system  30 . In EGR system  30 , the exhaust may be passed through a venturi tube  34  to determine the mass flow rate of the re-directed exhaust. The venturi tube  34  determines the mass flow rate by measuring the pressure drop of the exhaust between two regions (the inlet  36  and the throat  38 ) of the venturi tube  34  using pressure sensors  44 ,  46 . To measure an average value of the pressure at a region, the pressure sensors  44 ,  46  are fluidly coupled to the regions through averaging chambers  58 ,  68  which assist in averaging the pressure of the exhaust around a circumference of the region. To prevent particulate matter in the exhaust from entering and clogging the averaging chambers  58 ,  68 , or the passageways  54 ,  56  to the pressure sensors  44 ,  46 , a porous element  60  is provided at the entrance to the averaging chambers  58 ,  68 . To minimize the impact of high frequency pressure pulses (or noise) on the pressure measurements, pneumatic filters  70 ,  80  are also provided between the pressure sensors  44 ,  46  and the averaging chambers  58 ,  68 . 
         [0034]    Averaging the pressure in a region using an averaging chamber  58 ,  68  may help ensure that a pressure sensor  44 ,  46  provides an accurate representation of the exhaust pressure in the region. Inhibiting the plugging of the passages  54  and  56  by particulate matter may help ensure that the pressure measured by the pressure sensors  44 ,  46  is accurate. 
         [0035]    It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed systems and methods without departing from the scope of the disclosure. Other embodiments of the disclosed systems and methods will be apparent to those skilled in the art from consideration of the specification and practice of the systems and methods disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.