Abstract:
A sensor for detecting particulate matter in an exhaust stream of an engine. The sensor may be a spark-plug-like device having an extended center electrode composed of a stainless steel or other material. The electrode may have a thin passivating layer formed on it. The layer may be grown or deposited on the electrode within the exhaust system. The sensor may detect charge transients indicative of particulate concentration in the exhaust stream. Information about particulate matter in the exhaust system along with other engine information may be processed for controlling or adjusting parameters of the engine to affect the particulate matter in the exhaust system.

Description:
BACKGROUND  
       [0001]     The present invention pertains to sensors and particularly to sensing particles in the air. More particularly, the invention pertains to sensing emissions.  
         [0002]     Many combustion devices produce particulate emissions. For example, diesel engines are increasing in popularity in many kinds of vehicles. In the meanwhile, environmental regulations relative to particulate emissions are becoming more stringent. Thus, there is need for minimizing emissions from diesel engines and other particulate emitting mechanisms.  
       SUMMARY  
       [0003]     The present invention is a sensor for detecting and monitoring particulate emissions. The sensor outputs a signal indicating an amount of such emissions. The signal may be sent to a processor or controller that outputs a control signal indicative of the amount of emissions. This signal may be sent to a controller of mechanism expelling the emissions to minimize the output of the emissions.  
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0004]      FIG. 1  is a graph showing typical engine exhaust mass and number weighted size distributions shown with Alveolar deposition;  
         [0005]      FIG. 2  reveals basic components of the particulate matter (PM) sensor;  
         [0006]      FIG. 3  is a side view of the PM sensor;  
         [0007]      FIG. 4  shows an implementation of the PM sensor in an engine; and  
         [0008]      FIG. 5  shows an insertion of the PM sensor in an exhaust pipe.  
         [0009]      FIG. 6  is a loop for engine control based on parameters of an engine including the particulate matter of its exhaust emissions. 
     
    
     DESCRIPTION  
       [0010]      FIG. 1  is a graph showing engine exhaust and the number of weighted size distributions shown with an alveolar deposition fraction. The graph illustrates an idealized diesel particulate matter (PM) number and mass weighted distribution. The PM follows a lognormal, trimodal size distribution with the concentration in any size range being proportional to the area under the corresponding curve in that range. The nuclei mode particles range in diameter from 0.005 to 0.05 micron (5-50 nm). They consist of metallic compounds, elemental carbon and semivolatile organic and sulfur compounds that form particles during exhaust dilution and cooling. The nuclei mode typically contains 1 to 20 percent of the particle mass and more than 90 percent of the particle number. The accumulation mode particles range in diameter from 0.05 to 0.5 micron (50 to 500 nm). Most of the mass, composed primarily of carbonaceous agglomerates and adsorbed materials, is found here. The course mode consists of particles larger than one micron in diameter and contains 5 to 20 percent of the PM mass. These relatively large particles are formed by re-entrainment of particulate matter, which has been deposited on cylinder and exhaust system surfaces.  
         [0011]     PM emissions contribute to the fine particle burden in the atmosphere, and the EPA has established a light-duty vehicle PM emission standard of 0.08 g/mile and has promulgated a regulation to limit the amount of particular matter with a diameter of 2.5 microns or less (such as the newer 0.1 micron standard being considered). To meet these standards, engine manufacturers have developed low-emission engines. Technological improvements may have reduced mass emissions, but it has been said the newer engines meeting the 1991 emissions limit requirements had dramatically increased numbers and volumes of very small nuclei mode particles when compared to similar engines meeting  1988  emissions limit requirements. These observations suggest that not only accumulation mode size particles, but also nuclei mode size particles, may pose future emission problems.  
         [0012]     Particles in the nuclei mode and in the accumulation mode appear to be formed by different mechanisms. Accumulation mode particles are primarily carbonaceous and are associated with rich combustion and poor subsequent oxidation during the engine cycle. On the other hand, most nuclei mode particles are not even formed until the exhaust combustion products dilute and cool. They consist of a complex, poorly understood mix of sulfuric acid and particularly burned fuel and lubricating oil. Formation of these two types of particles likely occurs under different engine operating conditions. One condition is heavy loads favoring carbonaceous accumulation mode particles. Another condition is light loads most likely favoring the formation of vapor phase precursors of nuclei mode particles. The precursors may not undergo gas to particle conversion until the exhaust cools and dilutes in the atmosphere.  
         [0013]     In order to meet future emission standards, diesel engines need to be fitted with combustion control systems. Also, an after treatment system including particle filters or traps will be needed. To make such combustion control systems and after treatment devices reasonably feasible to reduce particulate emissions from an engine, an effective exhaust particulate sensor is needed.  
         [0014]     Particulate traps are available but they are large, expensive and significantly reduce fuel economy. The reduction in fuel economy is due to additional back pressure in the exhaust system being applied to the engine.  
         [0015]     The present sensor  10  may be built upon an automotive spark plug  11 . To obtain a very good high temperature and a high pressure platform for the sensor, the sensor may be placed directly in the engine&#39;s exhaust pipe  18 , manifold or header  22 . If the engine  21  has a turbocharger  19 , as in  FIG. 4 , then the sensor  10  may be placed downstream from the turbocharger  19  to avoid harm to the turbocharger if sensor  10  releases some particles.  
         [0016]     The design of the sensor  10  may provide for low cost and high volume manufacturing of the sensor. The sensor design, as in  FIG. 2 , may use Swageloc™ fittings  12  and/or fabricated high temperature ceramic feed-through insulators  13  and/or connectors. A probe  14  of sensor  10  may be placed in the path of the exhaust of the engine. The length  15  and diameter  16  of probe  14  may be varied depending on the parameters of sensing and the engine. Probe  14  is pacivated with a very thin non-conductive coating or layer  17 . This coating or layer  17  accounts for the lack of electrical shorting by the soot layer accumulated by probe  14  during operation of the engine. “Pacivate” may be similar to “passivate”, although the term passivate and variants of it are used in the present description. The pacivation material may be composed of SiN4, cerium and the like. The thickness of the pacivation layer on probe  14  may be between 0.001 and 0.100 inch. A nominal thickness may be about 0.01 inch. The pacivation layer may be achieved with the exposure of the probe to high exhaust gas temperatures or may be coated with such layer vie a material added to the engine fuel.  
         [0017]     Sensor  10  with various dimensions is shown in  FIG. 3 . Examples of a length dimension  15  may be between 0.25 and 12 inches. A nominal value of dimension  15  may be about 3 to 4 inches. Examples of a thickness dimension  16  may be between {fraction (1/32)}′ and ⅜′. A nominal dimension  16  may be about ⅛′.  
         [0018]     An embodiment of sensor  10  may be a standard spark plug  11  (such as a Champion™ RJ19LM, though the model is not important) that has the outside electrode removed and has a 4 to 6 inch stainless steel extension  14  of about {fraction (1/8)} inch diameter welded to the center electrode. Sensor  10  may be mounted in the exhaust stream  23  near the exhaust manifold  22  or after the turbocharge  19 . The electrode  14  may be connected to a standard analog change amplifier in processor  26  to record charge transient  25  in the exhaust stream  23 . The charge transients may be directly proportional to the soot (particulate) concentration in the exhaust stream  23 . The extended electrode  14  may be pacivated with a very thin non-conducting surface layer  17 , so that the electrode  14  will develop an image charge from the exhaust particulates but will not be electrically shorted to the spark plug  11  base or the grounded exhaust pipe  18 . The pacivating layer  17  may be deposited or grown on the electrode  14 . The 304 stainless steel may grow this pacivating layer  17  spontaneously after a few minutes of operation in the exhaust stream  23  at elevated temperatures greater than 400 degrees C. (752 degrees F.). Other grades of stainless steel (e.g.,  316 ) might not spontaneously grow the pacivating layer  17 . However, a pacivating layer  17  of cerium oxide may be grown on these other grades of stainless steel by adding an organometalic cerium compound (about 100 ppm) to the fuel for the engine  21 .  
         [0019]     Other methods of pacivating the electrode  14  with a layer  17  may include sputter depositing refractory ceramic materials or growing oxide layers in controlled environments. The purpose of the pacivating layer on electrode  14  is to prevent electrical shorts between the electrode  14  and the base of spark plug  11  due to particulate buildups, so that sensor  10  may retain its image charge monitoring activity of the exhaust stream  23 . If electrode  14  did not have the pacivating layer  17 , sensor  10  may fail after a brief operating period because of a shorting of electrode  14  to the base of plug  11  due to a build up of conductive soot on the electrode  14 .  
         [0020]      FIG. 5  reveals an installation of sensor  10  in an exhaust pipe  18 . There may be a stainless steel collar  24  welded into the exhaust pipe  18 . Collar  24  may be fabricated with an oversized threaded access so that the sensor  10  could be easily changed with other sensors  10  having different probe styles. An adapting collar or insert  12  with external threads may fit the threaded collar  24  and internal threads may fit the threaded sensor  10 . Adapting collar  12  may be made from stainless steel and Macor™, a machineable glass ceramic from Corning™. The Macor™ adaptors  12  may provide electrical and thermal connection or isolation of sensor  10  relative to exhaust pipe  18  or wherever collar  24  is mounted. Additional sensors  20  may be mounted in the exhaust manifold  22  upstream from turbocharger  19 . Other sensors  30  may be mounted further down stream, e.g., about 2 meters, in exhaust pipe  18  from the turbocharger  19 . The additional sensors  20  and  30  may allow one to examine the effects of the turbocharger  19 , such as strong mixing, and residence time on a signal  25  from sensor  10 . In the long term sites downstream from turbocharger  19  may be good locations because of the reduced risk of damage to the turbocharger  19  in the event of a sensor  10  failure.  
         [0021]     Signals  25 , indicating an amount of particulate matter in the exhaust  23 , on the line from sensor  10  may go to a processor and/or controller  26 . Processor  26  may be connected to other particulate sensors  20  and  30 , engine sensors, and a fuel injection and intake manifold system  27 . Based on signals  25  from sensor  10  and possibly from sensors  20  and  30 , sensors in system  27  and engine  21 , for sensing some or all of, but not limited to, the following engine parameters (via line  37  to processor  26 ) such as fuel flow, EGR (exhaust gas recirculation), injection timing, needle lift, crankshaft angle, cylinder pressure, valve position and lift, manifold vacuum, fuel/air mixture, the intake properties of air  28  and other information from or about engine  21 , processor  26  may provide control information signals  29  to the fuel injection amount and timing, EGR percent, valve control, and intake manifold system  27 , and the like, as desired, so as to cause engine  21  to expel a reduced amount of particulate emissions by adjusting fuel mixture, injection timing, percent EGR, valve control, and so forth. Incidentally, exhaust  23  may enter turbocharger  19  and cause a turbine  31  to spin and turn a compressor  32  via a shaft  33 . Compressor  32  may compress incoming air  28  which goes in a more dense condition to system  27 .  
         [0022]     Initial concerns relative to sensor  10  were possible fouling by excessive soot and very high temperatures. However, operation of sensor  10  in an exhaust system has been reliable in view of operation of engine  21  under very heavy loads causing the observed exhaust  23  temperature to reach at least 670 degrees C. (1238 degrees F.) and resulting in a Bosch smoke number of exhaust  23  to be at least 5. The latter number may correspond to a particle mass concentration of 350 mg/m 3 .  
         [0023]     Sensor  10  may put out a reproducible rms signal representing its image charge monitoring of the exhaust  23 , which is correlated to exhaust smoke as characterized by the Bosch smoke number. Sensor  10  generally does not degrade due to soot build-up over a long period of time. Also, sensor  10  does not appear to degrade at various temperatures.  
         [0024]      FIG. 6  is one version of a loop for engine control based on the particulate matter of the exhaust emissions. Engine  21  may output an exhaust  23  which is sensed by sensor  10  which in turn may output an image charge signal  25  to processor  26  which may include an amplifier  34 , a data extractor  35 , and an output signal conditioner  36 , among other components of the processor. Signal  25  may go to a charge amplifier  34  which may output a real-time signal to a data extraction device  35  which may receive a crankshaft angle determination. Components  34 ,  35  and  36  may have other parameter inputs for improving engine control and performance. The output from device  35  may include an electronic indication of the PM concentration or concentrations. This signal may go to signal conditioning  36  which may, based on other various inputs of engine data (e.g., timing, temperature, percent EGR, valve position, other engine information) provide engine control voltage signals  29  (for engine timing, percent EGR, valve control, and the like) to the fuel injection and manifold system  27  of engine  21 .  
         [0025]     Although the invention has been described with respect to at least one illustrative embodiment, many variation and modifications will become apparent to those skilled in the art upon reading the present specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.