System for particulate matter sensor signal processing

A system having a particulate matter sensor in an exhaust stream of an engine upstream from a particulate filter and another such sensor downstream from the filter. There may also be an exhaust gas recirculation (EGR) control on the engine. The amount of particulate matter in or loading of the filter may be determined by the upstream filter. The working condition of the filter may be determined by the downstream sensor. The filter may have a heater and control for providing operational and particulate matter burn-off temperatures to the filter. A processor may be connected to the sensors, the EGR control and the filter heater control.

BACKGROUND

The invention pertains to processing particle sensor data and particularly to data of engines. More particularly, the invention pertains to processing particle mass sensor data of engine exhaust events.

SUMMARY

The invention may include a processor for analysis of exhaust events of an engine to attain information about the engine's operation.

DESCRIPTION

Real-time exhaust events from individual diesel engine cylinders can provide a particular perspective into an engine's operation. Processing data about the exhaust events may reduce the real-time behavior of particulate emissions into usable control signals. The processing (e.g., algorithms) may use a combination of time-windowed (time domain) and frequency domain analysis of the real-time exhaust particulates to create profiles of the individual cylinder behavior in order to compare one cylinder to another and to compare one engine cycle to another. Instantaneous and time averaged results may be useful. Individual cylinder variations from one engine cycle to another cycle and variations among cylinders may be indicative of poor engine operation. These variations may be controlled for better overall performance and lower overall emissions. Other useful information such as engine running speed and exhaust flow rate, which are typically difficult to measure directly, may also be deduced from the time and/or frequency domain data.

The smoke emitted from a diesel engine is normally charged as a weak plasma generated in the combustion process. The charged particulates emitted from the cylinder during the exhaust cycle stream pass a conductive probe connected to a charge amplifier which records the concentration of particles as a function of time (i.e., time-domain). A signal representing this concentration may then be digitized and passed to a microprocessor for analysis. Data collected by the microprocessor, possibly coupled with a synchronizing signal from the engine control unit (ECU), may be time windowed and pulses from individual cylinders identified and analyzed for a baseline, peak height and integrated peak area. These may be direct measures of particulate matter (PM) emitted from an individual cylinder. The real time data stream may also be converted to the frequency domain by the use of Fourier transform, sine-cosine analysis, La Place transform, and so on. In the frequency domain, the primary frequency peak may be a measure of the engine running speed, and the peak height may be related to the total particulates. This signal processing is needed for signal amplification, noise reduction, and to clarify the charge signal. In a properly running engine where all of the cylinders are equally timed and of equal magnitude, there may be few harmonic frequencies. In poorly running engines, the non-repetitive nature of the cylinder-to-cylinder and cycle-to-cycle variability may cause many harmonic frequencies and overtones.

FIG. 1ashows a particulate matter sensor arrangement for an exhaust system of an engine10. Engine10may have an exhaust pipe101which is connected to the exhaust system of engine10and to a particulate matter (PM) or diesel particulate filter (DPF)102. Associated with and situated adjacent to the DPF102may be a controller103and/or heater103for operation of the DPF102, such as the heater103being turned on in the DPF102to control the temperature of the DPF102for operation and/or to burn off trapped diesel particulates or particulate matter. Particulate matter sensors105and/or106may be situated in the exhaust pipe101. Sensor105may be closer to the engine10than sensor106. In some arrangements, just one of sensor105or106may be present. A tail pipe104may be connected to the output of the DPF102. Situated in the tailpipe104may be a particulate matter sensor107.

An EGR valve110may have an exhaust gas conveyance111such as a pipe or tube connected to the exhaust pipe101and an exhaust gas conveyance device112such as a pipe or tube connected to an intake system120of the engine10. Sensor105may be connected proximate to tube111. Sensor106may be connected proximate to the input of the DPF102. In summary, sensors105and106may be regarded as upstream from DPF102and sensor107as downstream relative to DFP102. Sensors105,106and/or107may be connected to a signal processing electronics module113for providing signals indicating an amount or mass of sensed particulate matter or diesel particulates in an exhaust gas stream114before entering DPF102and in an exhaust gas stream115after DPF102, respectively. EGR valve110may be connected to the signal processing electronics I13for receiving signals to open or close the valve110, as indicated by the signals from sensors105and/or106. Sensor107may be primarily for determining the presence of particulate matter in the exhaust gas stream115and for indicating whether the DPF102is in a failure mode or has failed. Particulate matter in the exhaust gas stream115may be an indication of a failed or non-working DPF102. For a well-operating DPF102, sensor107should not be detecting any particulate matter in stream115.

Signal processing electronics module or processor113may output signals130having information about exhaust flow velocity, amount of loading of the PM filter, failure indication of the PM filter, time to clean the PM filter, optimal EGR operation, and so forth.

Sensor105or sensor106may be used for determining the loading of the DPF102. Sensor105may also be used for controlling the EGR valve110so as to reduce exhaust emissions in stream114. However, sensor106may generally be used for merely determining the loading of the DPF102. Either sensor105or106, or both sensors, along with signal processing electronics113, may provide sensor signals which are integrated mathematically over time so as to determine the total mass accumulation of particulate matter in the DPF102. Since an actual determination of the amount of particulate matter in the DPF102may be obtained with the present system, a model and/or related calculation is not necessarily needed for obtaining, for instance, an estimated determination of particulates or particulate matter in the DPF102.

FIG. 1bshows a flow diagram of data acquisition and processing for engine10. The diagram may also be regarded as a version of a loop for engine control based on the particulate matter of the exhaust emissions. Engine10may output an exhaust11which is sensed for particulate matter and other engine-related data by a transducer probe12. In the engine exhaust11may be a particulate matter (PM) concentration in the may be detected in the gas composition13. Other parameters that may be detected in the exhaust include, but not limited to, pressure, temperature, vibration, engine speed, percent of exhaust gas recirculation (EGR), and oil type. Three different engines10under test have included a John Deere™ 4045T implement, a Caterpillar™ C12 truck engine, and a Volkswagon TDI Euro IX engine. The 4045T is a turbocharged 4.5 liter diesel, the C12 is a naturally aspirated 12.0 liter diesel, and the TDI is a 1.9 liter diesel. This variety of engines for testing may validate some of the consistent results of data acquisition and analysis.

The PM transducer probe12may have a spark-plug-like support as shown inFIG. 2. The PM probe12may provide an output based on the charge measured by the probe. Probe12may be placed in a path of the exhaust11of the engine10. The length and geometry of probe12may vary depending on the parameters of the sensing electronics, sensor optimization, and the engine. Probe12may be passivated with a very thin nonconductive coating or layer. This coating or layer may prevent electrical shorting by the soot layer accumulated on the probe12during the operation of engine10. The passivation material may be composed of SiN4, cerium or other oxide, and/or the like. The thickness of the passivation layer on probe12may be between 0.001 and 0.010 inch. A nominal thickness may be about 0.01 inch. The passivation layer may be achieved with the probe exposed to high exhaust temperatures or may be coated with a layer via a material added to the engine's fuel.

Sensor or probe12may have various dimensions and electrode shapes. Examples of a length dimension may be between 0.25 and 12 inches. A nominal value of the length may be about 3 to 4 inches. Examples of a thickness or diameter dimension may be between 1/32 inch and ⅜ inch. A nominal thickness may be about ⅛ inch. The probe may also be non-cylindrical or may have a ball at the end of the probe to optimize the signal.

An example of the probe may include a standard spark plug housing that has the outside or ground electrode removed and has a 4 to 6 inch metal extension of about 1/8  inch thickness or diameter welded to a center electrode. Sensor12may be mounted in the exhaust stream11near the exhaust manifold or after the turbocharger of the engine10. The sensing electrode may be connected to an analog charge amplifier15of a processing electronics30. The charge transients14from the electrode or probe12may be directly proportional to the soot (particulate) concentration in the exhaust stream11. The extended electrode may be passivated with a very thin non-conducting layer on the surface of the electrode exposed to the exhaust gas11of the engine12. A304type stainless steel may grow the passivating layer on the probe12spontaneously after a few minutes of operation in the exhaust stream at temperatures greater than 400 degrees C. (750 degrees F.). However, a passivating layer of cerium oxide may instead be grown on the probe or electrode12situated in the exhaust11, by adding an organometallic cerium compound (about 100 PPM) to the fuel for the engine10.

Other approaches of passivating the probe or electrode12with a layer may include sputter depositing refractory ceramic materials or growing oxide layers in controlled environments. Again, the purpose of growing or depositing the passivating layer on probe or electrode12situated in the exhaust11is to prevent shorts between the probe and the base of the spark-plug like holder due to PM buildups, so that sensor or probe12may retain its image charge monitoring activity of the exhaust stream11. If the electrode did not have the passivating layer on it, probe12may fail after a brief operating period because of an electrical shorting of the electrode to the support base of the sensor due to a build-up of soot or PM on the electrode.

Processing electronics30may include charge amplifier15, a data extractor17, an output conditioner19, or other averaging or FFT processing electronics. Charge amplifier15ofFIG. 1may be designed and situated in terms of gain, frequency response, and location. The output16may be a real-time signal indicating the amount of PM in the exhaust11. Signal16may go to a data extractor unit17. A crankshaft angle signal may be entered at input40of unit17for associating the specific amounts of PM at particular crankshaft angles for engine10analysis. An output18may provide an average PM concentration of exhaust11. Also, PM concentrations on a cylinder-by-cylinder basis may be revealed at output18.

Output18may go to an output conditioner unit19, which may provide an engine control, diagnostic and/or engine control voltage signal20which may go to engine10or DPF loading or failure determination.

FIG. 3is a schematic of a data acquisition arrangement for an engine10. Sensor module21on engine10may provide engine data22via an engine control unit (ECU)98to a processor23. ECU98may have a bidirectional connection99to fuel and air intake system94which includes an intake manifold95. Also, ECU98may have a bidirectional connection96to an exhaust gas recirculation unit93. ECU98may have an input connection97from an output of the processor23. Data22may include information relative to engine parameters of RPM, load, turbocharger pressure (except the VW™), needle lift (Deere™ only), crank angle, and other parameters about the engine. An exhaust system24, including an exhaust manifold92, for conveying exhaust gas11, may have sensors25,26,27,28and29connected to processor23. An output of processor23may go to an oscilloscope31for data readings and plot observation and to a data acquisition (DAQ) module32. Sensors25-29may have amplifier, converter interface, and/or conditioning circuits35-39, respectively, to prepare the signal for entry to processor23. There may be a smoke sensor probe33in exhaust system24connected to a Bosch™ meter34. A two-stage dilution tunnel41may be situated at exhaust system24for providing a connection to a diffusion charger (DC)43, a photoelectric aerosol sensor (PAS)44and a condensation particle counter (CPC)45.

A device46may be situated between sensors25and26. The Bosch™ meter probe33and the two-stage dilution tunnel may be situated between sensors26and27. A catalytic converter47(used for the VW™ engine) may be situated between sensors27and28. Between sensors28and29may be a PM trap48(for the Caterpillar™ engine) or a muffler49(for the VW™ engine) situated in exhaust system24. With the described data acquisition system inFIG. 3, various data and plots may be taken as shown in the ensuing Figures.

FIG. 4is a plot of data taken from the Deere™ engine10showing cylinder pressure, crank angle, needle lift and soot at 1400 rpm, with no EGR and a 90 percent load versus time on the abscissa axis. Cylinder pressure is shown by a curve51and indicated by relative figures on the right ordinate axis. Curve52shows signal amplitude from a PM charge sensor by figures on the left ordinate axis. Curve53is a crank angle line. Curve54reveals needle lift with relative magnitude revealed in the right ordinate axis. Indicator line116indicates one engine cycle along the abscissa of the graph. Downward spikes of curve52may identify action of cylinders1,2,3and4as indicated by designations55,56,57and58, respectively. Data for curves51,53and54may come from the sensor module21. The data for curve52may come from soot charge sensor25.

FIG. 5areveals real time capture by a particulate matter sensor in terms of volts versus time with curve59.FIG. 5bshows a waveform60of signal to frequency of a processed smoke signal.FIG. 5cshows a waveform61of signal to time of a processed smoke signal.

FIG. 6reveals the charge sensor signal upstream of the catalytic converter47by curve62as indicated by charge sensor27and by curve63as indicated by sensor28for the VW™ TDI Euro IV engine. The graph is in terms of signal millivolts versus decimal fractions of seconds. Dimensions64and65indicate a cycle of the VW™ engine10, each of which are about 0.06 seconds and equivalent to about 2000 RPM.

FIG. 7ais a correlation and/or sensor response as a function of a Bosch smoke number for the Deere™ engine running at 1400 RPM with no EGR as indicated by triangles and with 15 percent of EGR as indicated by circles. It may be noted that correlation of data points or curves66and67, respectively, for non EGR and some EGR is relatively good. The graph shows the sensor response of, for instance sensor26, in volts RMS versus the Bosch smoke number. At the start of curves66and67, up to about Bosch smoke number2, a little change in sensor voltage seems to cause a large change in the Bosch smoke number. The greatest disparity between curves66and67appears before the smoke number2. After the Bosch smoke number2, the relationship between the sensor responses appears almost linear.

FIG. 7bis a graph showing volume concentration (μm3per cc) versus an aetholometer reading (mg per m3) for a comparison of 10 percent and 25 percent loads. An aetholometer is a real time instrument that responds to black carbon. The data117may be fitted with a curve118having an equation “y=2022.2×”. A correlation “R2” of the curve to the data is about 0.8876.FIG. 7cis a graph showing a sensor signal in volts versus a mass concentration in mg per m3. The signal to mass relationship data119were fitted to a curve121have a relationship expressed by the equation “y=0.0004×2+0.0099×+0.0001”. The correlation “R2” of the curve to the data is about 0.8565.

FIG. 8reveals an optical PM detector71and a PM charge sensor12in an exhaust pipe75. PM charge sensor or probe12may have an electrode73and a housing74to support the electrode73and a housing74to support the electrode73in an exhaust pipe75. The optical PM sensor71may have a light source76, a bright red LED (e.g., a Lumex™ no. LTL-2F3VRNKT). Light77may be transmitted through a quartz rod78to inside of the exhaust pipe75. A holder or support housing79may support the quartz rod78in exhaust pipe75. Rod78may be about ¼ inch in diameter and 4 inches long. Light rays77may impinge PM particles80in the exhaust stream11and reflect light rays81which may be conveyed by a quartz rod82to a light detector83(e.g., a Burr-Brown™ photodiode no. OPT301). Rod82may have similar dimensions as rod78. Rod82may be supported by a holder or support housing84in exhaust pipe75. An increase of a number of PM particles80per unit volume of exhaust11may indicate an increase of reflected light81to detector83for a greater reading, and vice versa. Rods78and82may operate as thermal isolations between the hot exhaust pipe75and the emitter76and detector83electronics, respectively. In tests using sensor71that may be noted in this description, no attempts are made to keep rods78and82clean in the exhaust pipe75.

FIG. 9is a graph of a charge sensor12signal85, cylinder pressure signal86, and an optical sensor71signal87showing magnitude versus time in seconds on the abscissa axis for the Deere™ engine10. The left ordinate axis shows the magnitude of the charge sensor12signal85. The right ordinate axis shows the magnitude of the cylinder pressure signal86and the optical sensor71signal87. One may note a correlation shown by dashed line88of peaks of signals85and87as a puff smoke. These peaks appear to be aligned with a cylinder pressure peak of signal86. Also, an impact of PM particle80loading on the optical sensor71causing a change in magnitude of signal87as shown by arrow89.

FIG. 10ashows a comparison between the charge sensor signal85and optical sensor signal87at the same location.FIG. 10shows small period of time (i.e., 0.4 to 0.6 seconds relative to 0 to 3.5 seconds) ofFIG. 9for signals85and87. Dimensions64and65each reveal a length of a cycle. The length of a cycle is shown by dimension64or65. It may be noted that there is very little difference between the times that the charge sensor12signal85and optical sensor71signal87peaks occur as shown by dashed lines91.FIG. 10bshows a comparison of charge signals85and optical signals87resulting in a correlation coefficient of 0.69 for a straight line fit.

FIG. 11a is a graph comparing the charge sensor signal85with the cylinder pressure signal86at the same location.FIG. 11bis a graph where a comparison of the charge signals85and pressure signals86is plotted to determine a correlation between the signals. The correlation coefficient of the signals85and86is about 0.0003 for a straight line fit.

The particle size distribution from engines follows a lognormal, multi-modal 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 semi-volatile 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.

Although the invention has been described with respect to at least one illustrative example, many variations 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.