Diesel Exhaust Soot Sensor System and Method

Abstract

Systems and methods to determine when regeneration of a diesel particulate filter (DPF) are presented. Such determination is made by indirectly determining soot accumulation in the DPF by monitoring soot accumulation on a regeneration burner spark plug based on the correlation between spark plug fouling and DPF soot loading. An ion current sensing circuit is used during periods of no flame to determine soot loading on the spark plug. When soot loading on the spark plug approaches an amount that could cause fouling of the spark plug, the ignition controller initiates a hot spark to burn the soot off the spark plug. The number of such cleaning events is tracked and used to determine when the DPF soot loading is at a level that regeneration should be initiated. Temperature rise across the DPF is monitored and used to adjust the number spark plug cleaning events needed before initiating regeneration.

1 . A method of regenerating a diesel particulate filter (DPF) with a fuel fired heater having a spark plug to initiate flame in a burner thereof, comprising the steps of:
 counting a number of cleaning events of the spark plug; and   initiating regeneration when the number of cleaning events of the spark plug is greater than or equal to a predetermined threshold.   
     
     
         2 . The method of  claim 1 , further comprising the steps of:
 providing a bias voltage to the spark plug;   monitoring a leakage current across a spark gap of the spark plug; and   initiating the cleaning event when the step of monitoring determines that the leakage current exceeds a predetermined current threshold.   
     
     
         3 . The method of  claim 1 , further comprising the steps of:
 determining a value of resistance across a spark gap of the spark plug; and   initiating the cleaning event when the step of determining indicates that the resistance is less than a predetermined resistance.   
     
     
         4 . The method of  claim 1 , further comprising the steps of:
 monitoring a temperature rise across the DPF during the regeneration; and   reducing the predetermined threshold when the step of monitoring determines that the temperature rise across the DPF exceeds a predetermined maximum temperature threshold.   
     
     
         5 . The method of  claim 1 , further comprising the steps of:
 monitoring a temperature rise across the DPF during the regeneration; and   increasing the predetermined threshold when the step of monitoring determines that the temperature rise across the DPF is less than a predetermined minimum temperature threshold.   
     
     
         6 . The method of  claim 1 , further comprising the steps of:
 monitoring a temperature rise across the DPF during the regeneration;   determining an operating condition of a diesel engine from which exhaust flows to the DPF; and   increasing the predetermined threshold when the step of monitoring determines that the temperature rise across the DPF is less than a predetermined minimum temperature threshold and when the step of determining determines that the diesel engine is not idling.   
     
     
         7 . The method of  claim 1 , further comprising the steps of:
 monitoring a temperature rise across the DPF during the regeneration;   reducing the predetermined threshold when the step of monitoring determines that the temperature rise across the DPF exceeds a predetermined maximum temperature threshold; and   increasing the predetermined threshold when the step of monitoring determines that the temperature rise across the DPF is less than a predetermined minimum temperature threshold.   
     
     
         8 . The method of  claim 7 , further comprising the step of determining an operating condition of a diesel engine from which exhaust flows to the DPF, and wherein the step of increasing is performed only when the step of determining determines that the diesel engine is not idling. 
     
     
         9 . A regeneration system for a diesel particulate filter (DPF) positioned to capture particulates in an exhaust flow from a diesel engine, comprising:
 a burner configured to be positioned upstream of the DPF in the exhaust flow, the burner including at least one spark plug positioned in the exhaust flow therethrough to ignite a flame therein during regeneration;   an ignition controller operably coupled to the at least one spark plug to control sparking thereof during regeneration, the ignition controller including means for determining a level of soot accumulation on the spark plug, the ignition controller being configured to initiate a cleaning event of the spark plug when the level of soot accumulation exceeds a predetermined threshold; and   wherein the ignition controller counts each cleaning event of the spark plug and initiates regeneration when the number of cleaning events exceeds a predetermined number.   
     
     
         10 . The regeneration system of  claim 9 , wherein the means for determining a level of soot accumulation on the spark plug comprises a power source configured to provide a bias voltage to a positive terminal of the spark plug at least when no regeneration is commanded and a current sense circuit for monitoring a leakage current flowing across a spark gap of the spark plug, and wherein the ignition controller initiates the cleaning event when the leakage current exceeds a predetermined maximum current threshold. 
     
     
         11 . The regeneration system of  claim 9 , further comprising a plurality of temperature sensors positioned to monitor a temperature rise across the DPF during regeneration, and wherein the ignition controller monitors the temperature rise across the DPF during regeneration and changes the predetermined number of cleaning events needed before subsequent regenerations will be initiated when the temperature rise is outside of expected values. 
     
     
         12 . The regeneration system of  claim 11 , wherein the ignition controller decreases the predetermined number of cleaning events needed before subsequent regenerations will be initiated when the temperature rise across the DPF is greater than a predetermined maximum temperature threshold. 
     
     
         13 . The regeneration system of  claim 11 , wherein the ignition controller increases the predetermined number of cleaning events needed before subsequent regenerations will be initiated when the temperature rise across the DPF is less than a predetermined minimum temperature threshold. 
     
     
         14 . The regeneration system of  claim 11 , further comprising an engine speed sensor operatively coupled to the ignition controller, and wherein the ignition controller increases the predetermined number of cleaning events needed before subsequent regenerations will be initiated when the temperature rise across the DPF is less than a predetermined minimum temperature threshold and the engine speed sensor indicates that the engine is not idling during the regeneration. 
     
     
         15 . A diesel particulate filter (DPF) system for removing particulates from diesel engine exhaust, comprising:
 a diesel particulate filter (DPF) having an inlet and an outlet;   a burner having an exhaust inlet for receiving diesel engine exhaust and a burner outlet coupled to the inlet of the DPF, the burner including a spark plug exposed to an exhaust flow through the burner;   an ignition controller having a primary power source operably coupled through triggering circuitry to the spark plug to control sparking thereof, the ignition controller further including a secondary power source configured to provide a bias voltage to a positive electrode of the spark plug and an ion current sensing circuit operatively coupled between the secondary power source and the spark plug;   wherein the ignition controller is configured to initiate a cleaning event when the ion current sensing circuit senses a current flow greater than a predetermined maximum leakage current threshold when not commanding regeneration of the DPF; and   wherein the ignition controller counts each cleaning event of the spark plug and initiates regeneration of the DPF by turning on the burner when the number of cleaning events exceeds a predetermined number.   
     
     
         16 . The DPF system of  claim 15 , further comprising a plurality of temperature sensors positioned to monitor a temperature rise across the DPF during regeneration, and wherein the ignition controller monitors the temperature rise across the DPF during regeneration and changes the predetermined number of cleaning events needed before subsequent regenerations will be initiated when the temperature rise is outside of expected values. 
     
     
         17 . The DPF system of  claim 16 , wherein the ignition controller decreases the predetermined number of cleaning events needed before subsequent regenerations will be initiated when the temperature rise across the DPF is greater than a predetermined maximum temperature threshold. 
     
     
         18 . The DPF system of  claim 16 , wherein the ignition controller increases the predetermined number of cleaning events needed before subsequent regenerations will be initiated when the temperature rise across the DPF is less than a predetermined minimum temperature threshold. 
     
     
         19 . The DPF system of  claim 16 , further comprising an engine speed sensor operatively coupled to the ignition controller, and wherein the ignition controller increases the predetermined number of cleaning events needed before subsequent regenerations will be initiated when the temperature rise across the DPF is less than a predetermined minimum temperature threshold and the engine speed sensor indicates that the engine is not idling during the regeneration. 
     
     
         20 . The DPF system of  claim 15 , wherein the ignition controller initiates a cleaning event by gating the triggering circuitry to generate a hot spark at the spark plug to burn off accumulated soot. 
     
     
         21 . A method of measuring soot flowing in an exhaust pipe having a spark plug positioned therein such that it accumulates soot thereon, the accumulated soot creating a path for electrical leakage current from a center electrode to a ground plane on a shell of the spark plug, the method comprising the steps of:
 providing a bias voltage to the spark plug;   monitoring the leakage current;   initiating a sparking event to clean the soot from the spark plug when the step of monitoring determines that the leakage current exceeds a predetermined current threshold; and   counting a number of sparking events to clean the soot from the spark plug, the number of sparking events being indicative of an amount of soot flowing in the exhaust pipe.   
     
     
         22 . The method of  claim 21 , further comprising the step of initiating regeneration of a diesel particulate filter (DPF) positioned to filter soot flowing in the exhaust pipe when the number of cleaning events reaches a predetermined threshold. 
     
     
         23 . The method of  claim 22 , wherein the step of initiating regeneration comprises the step of turning on a fuel fired heater to initiate flame in a burner thereof to regenerate the DPF. 
     
     
         24 . The method of  claim 22 , wherein the step of initiating regeneration comprises the step of injecting hydrocarbon fuel into the exhaust pipe to cause a catalytic reaction in a Diesel Oxidation Catalyst positioned upstream of the DPF to regenerate the DPF. 
     
     
         25 . The method of  claim 22 , wherein the step of initiating regeneration comprises the step of modifying operating parameters of a diesel engine in such a manner to cause an exhaust temperature to rise to a level sufficient to regenerate the DPF. 
     
     
         26 . The method of  claim 21 , further comprising the steps of:
 positioning the spark plug downstream of a diesel particulate filter (DPF) positioned to filter soot flowing in the exhaust pipe; and   providing an indication of a lack of effectiveness of the DPF and possible existence of a crack in a filter substrate when the number of sparking events exceeds a predetermined threshold.