Method and device for measuring the concentration of soot particles in an exhaust gas, in particular from an internal combustion engine

Abstract

The present invention relates to a method and a sensor ( 1 ) for collecting soot in an exhaust stream from an internal combustion engine by means of a resistive type planar probe positioned in the gas stream and having at least one face provided with electrodes connected to an electronic device for measuring soot concentration in the gas stream. The gas stream upstream from the planar probe is deflected by means of a protection shield ( 3 ) completely covering the planar probe and having a single soot-collection window ( 5 ) arranged in a wall of the protection shield ( 3 ) that is situated downstream from the planar probe in the gas stream, in such a manner as to: protect the planar probe from a direct frontal impact of soot and any debris contained in the gas stream; and generate a turbulent flow and reduce the speed of the gas stream downstream from the planar probe so as to select soot particles as a function of their size.

1 . A method of collecting soot in a gas stream, in particular an exhaust stream from an internal combustion engine, by means of a planar probe, preferably of resistive or capacitive type, positioned in the gas stream and having at least one face provided with electrodes connected to an electronic device for measuring soot concentration in the gas stream, the method being characterized in that the gas stream upstream from the planar probe is deflected by means of a protection shield completely covering the planar probe and having a single soot-collection window formed in a wall of the protection shield that is situated downstream from the planar probe in the gas stream, in such a manner as to:
 protect the planar probe from a direct frontal impact of soot and any debris contained in the gas stream; and   generate a turbulent flow and reduce the speed of the gas stream downstream from the planar probe so as to select soot particles as a function of their size;   thus resulting in mechanical protection of the planar probe and a uniform deposit of soot on said planar probe.   
     
     
         2 . A method according to  claim 1 , characterized in that the soot that is collected is selected by means of the protection shield so that the largest dimension of the collected soot particles is less than or equal to 5 μm. 
     
     
         3 . A method according to  claim 1 , characterized in that soot is collected in a collection zone on the first face of the planar probe facing the collection window formed in the protection shield. 
     
     
         4 . A method according to  claim 1 , characterized in that the protection shield is of right tubular shape having a longitudinal axis (X-X′), and of cross-section that presents a closed regular geometrical shape inscribed within a circle centered on the longitudinal axis of the protection shield. 
     
     
         5 . A method according to  claim 4 , characterized in that the longitudinal axis (X-X′) of the shield extends perpendicularly to the flow direction of the gas stream, and in that the planar probe extends longitudinally inside the protection shield along its longitudinal axis (X-X′). 
     
     
         6 . A soot sensor for measuring soot concentration in a gas stream, in particular an exhaust stream from an internal combustion engine, the sensor comprising a resistive type planar probe made up of a plane substrate of insulating material and having:
 on a first face at least two conductive electrodes separated from each other by a determined distance and each connected to an electrical connection track; and   at least one resistor for regenerating the electrodes and for measuring the temperature of the gas stream, said resistor being connected at its terminals to two electrical connection tracks;   the sensor being characterized in that it includes a protection shield covering the planar probe over all of the faces of its substrate and including a single open soot-collection window for collecting soot arranged in a wall of the protection shield situated downstream from the planar probe in the gas stream, the collection window enabling soot to be deposited on at least one collection zone on the first face of the planar probe when the sensor is positioned in a gas stream.   
     
     
         7 . A soot sensor according to  claim 6 , characterized in that the collection zone on the first face of the planar probe and the collection window arranged in the protection shield are arranged facing each other. 
     
     
         8 . A soot sensor according to  claim 6 , characterized in that the collection zone on the first face of the planar probe and the collection window arranged in the protection shield ( 3 ) are of rectangular shape, and the ratio of the length h of the collection zone to the height H of the collection window lies in the range 0.2 to 3, and preferably in the range 1 to 2. 
     
     
         9 . A sensor according to  claim 6 , characterized in that the protection shield is of right tubular shape presenting a longitudinal axis (X-X′) and of cross-section presenting a closed regular geometrical shape inscribed in a circle centered on the longitudinal axis along which the shield extends. 
     
     
         10 . A sensor according to  claim 9 , characterized in that the protection shield presents a cylindrical shape of circular cross-section, the planar probe being arranged in the inside space of the shield so as to extend along its longitudinal axis (X-X′). 
     
     
         11 . A sensor according to  claim 10 , characterized in that the collection window covers an angular sector lying in the range 45° to 180° in a horizontal plane perpendicular to the longitudinal axis (X-X′) of the protection shield. 
     
     
         12 . A sensor according to  claim 6 , characterized in that the collection window is subdivided into at least two openings by at least one reinforcing element extending between two opposite sides of the collection window. 
     
     
         13 . A sensor according to  claim 6 , characterized in that the planar probe does not make contact with the protection shield so as to enable the gas stream that penetrates via the collection window to flow inside the shield and over each of the faces of the probe. 
     
     
         14 . A sensor according to  claim 6 , characterized in that the regeneration resistor is positioned on a second face of the planar probe in a manner that is symmetrical to the soot collection zone on the first face of said planar probe relative to the longitudinal midplane of the probe. 
     
     
         15 . A sensor according to  claim 6 , characterized in that it includes a support body for the planar probe and a protection shield, the support body including indexing means for indexing the position of the sensor in a gas stream such that the collection window situated on the downstream side in the stream flow direction. 
     
     
         16 . A sensor according to  claim 15 , characterized in that the position indexing means comprise a flat on a cylindrical surface of the support body.