Methods for determining when to regenerate exhaust gas particulate filters

Abstract

Methods for determining when to regenerate an exhaust gas particulate filter ( 10 ), for regenerating, and for calibrating a pressure drop across such filters are disclosed. An example method involves reducing a first amount of particulates ( 52 ) accumulated in the filter to a residual amount RA DP . The method also includes measuring the residual amount RA DP by exciting the microwave resonant cavity ( 126 ) in which the filter resides with microwave radiation ( 182 ) and then monitoring the microwave cavity response. The method also includes using the measured value of RA DP to calibrate a pressure drop threshold ΔP TH SO that it is representative of a limit (T DP ) of particulate accumulation in the filter. The methods may also include regenerating the filter a number of times and each time re-setting the pressure drop threshold ΔP TH based on measurements of RA DP taken after each filter regeneration.

1 . A method of determining when to regenerate an exhaust gas particulate filter disposed in a microwave resonant cavity, the filter having a particulate mass accumulation limit, comprising:
 a) reducing a first amount of particulates accumulated in the filter to a first residual amount;   b) measuring the first residual amount by exciting the microwave resonant cavity with microwave radiation and monitoring a cavity response; and   c) using the measured first residual amount to determine a pressure drop threshold representative of the particulate mass accumulation limit in the filter.   
   
   
       2 . The method according to  claim 1 , wherein the filter comprises a diesel particulate filter, and wherein the first residual amount is either less than or equal to about 3 g/l at a filter temperature of about 300° C., or is less than or equal to about 9 g/l at a filter temperature of about 25° C. 
   
   
       3 . The method according to  claim 1 , further comprising:
 measuring a pressure drop across the filter as the filter accumulates a second amount of particulates; and   reducing the second amount of accumulated particulates to a second residual amount when the measured pressure drop equals the pressure drop threshold.   
   
   
       4 . The method according to  claim 1 , wherein reducing at least one of the first and second amounts of particulates includes applying heat to the filter. 
   
   
       5 . The method according to  claim 1 , further comprising:
 performing a temperature measurement of the filter; and   performing a temperature correction to the measured first residual amount based on the temperature measurement.   
   
   
       6 . The method according to  claim 1 , further comprising performing at least one of acts a) through c) while the filter and microwave resonant cavity are operably arranged in an engine exhaust system. 
   
   
       7 . The method according to  claim 1 , further comprising:
 operably arranging the filter and the microwave resonant cavity in an engine exhaust system;   operating the engine exhaust system and measuring a pressure drop across the filter as the filter accumulates a second amount of particulates; and   reducing the second amount of accumulated particulates to a second residual amount when the measured pressure drop equals the pressure drop threshold.   
   
   
       8 . The method according to  claim 7 , further comprising:
 measuring the second residual amount by exciting the microwave resonant cavity with microwave energy and monitoring the cavity response; and   using the measured second residual amount to re-set the pressure drop threshold.   
   
   
       9 . A method of regenerating an exhaust gas particulate filter disposed in a microwave resonant cavity, wherein the filter accumulates particulates when operably arranged in an engine exhaust system, the method comprising:
 a) measuring a first residual amount of particulates in the filter by exciting the microwave resonant cavity with microwave radiation and monitoring the cavity response;   b) using the measured first residual amount to establish a pressure drop threshold across the filter that is representative of a predetermined amount of particulate accumulation in the filter;   c) operating the engine and monitoring the pressure drop across the filter as the filter accumulates particulates; and   d) when the pressure drop reaches the pressure drop threshold, thermally regenerating the filter to reduce the particulate accumulation to a second residual amount.   
   
   
       10 . The method according to  claim 9 , further comprising:
 performing a temperature measurement of the filter; and   calibrating the measurement of at least one of the first and second residual amounts based on the temperature measurement.   
   
   
       11 . The method according to  claim 9 , further comprising repeating acts a) through d) one or more times. 
   
   
       12 . The method according to  claim 9 , wherein at least one of the first and residual amounts is one of i) about 3 g/l or less at a filter temperature of about 300° C., and ii) about 9 g/l or less at a filter temperature of about 25° C. 
   
   
       13 . The method according to  claim 9 , further comprising performing at least one of acts a) through d) while the filter resides within the engine exhaust system. 
   
   
       14 . The method according to  claim 9 , wherein the microwave resonant cavity defines a microwave cavity resonance peak, and wherein monitoring the cavity response further includes measuring a frequency shift in the microwave cavity resonance peak due to the presence of particulates in the filter. 
   
   
       15 . The method according to  claim 9 , further comprising maintaining the filter at a substantially constant temperature when monitoring the cavity response. 
   
   
       16 . The method according to  claim 9 , wherein the filter comprises a diesel particulate filter. 
   
   
       17 . A method of calibrating a pressure drop across an exhaust gas particulate filter disposed in a microwave resonant cavity, wherein the filter accumulates particulates that cause a pressure drop when the filter is operably arranged in an engine exhaust system, the method comprising:
 a) reducing an initial amount of accumulated particulates in the filter to be equal to or less than a residual amount, wherein the initial amount is greater than the residual amount   b) measuring the residual amount by exciting the microwave resonant cavity with a microwave signal having at least one microwave frequency and measuring at least one of a microwave signal resonant frequency shift and a microwave signal attenuation;   c) based on the measured residual amount, establishing a pressure drop threshold across the filter that corresponds to an allowable amount of accumulated particulates;   d) measuring the pressure drop across the filter while the filter is operably arranged in the engine exhaust system; and   e) reducing the accumulated particulates to be within the residual amount when the pressure drop reaches the pressure drop threshold.   
   
   
       18 . The method according to  claim 17 , wherein the residual amount is either less than or equal to about 3 g/l at a filter temperature of about 300° C., or is less than or equal to about 9 g/l at a filter temperature of about 25° C. 
   
   
       19 . The method according to  claim 17 , further comprising generating and receiving the microwave signal using first and second high-temperature coaxial probes arranged at one end of the microwave resonant cavity. 
   
   
       20 . The method according to  claim 17 , further comprising measuring a temperature of the filter and performing a correction of the measured residual amount based on the measured temperature.