Patent Publication Number: US-2013227934-A1

Title: Aftertreatment burner air supply system

Description:
TECHNICAL FIELD 
     The present system and method relate to efficient regeneration of a diesel particulate filter used in the exhaust system of a diesel engine. Specifically, the system and method relate to supplying a burner with precise amounts of fuel and air for properly increasing and maintaining exhaust temperature for efficient filter regeneration. 
     BACKGROUND 
     Diesel engines are efficient, durable and economical. Diesel exhaust, however, can harm both the environment and people. To reduce this harm, governments, such as the United States and the European Union, have proposed stricter diesel exhaust emission regulations. These environmental regulations require diesel engines to meet the same pollution emission standards as gasoline engines. Typically, to meet such regulations and standards, diesel engine systems require equipment additions and modifications. 
     For example, a lean burning engine provides improved fuel efficiency by operating with an amount of oxygen in excess of the amount necessary for complete combustion of the fuel. Such engines are said to run “lean” or on a “lean mixture.” However, the increase in fuel efficiency is offset by the creation of undesirable pollution emissions in the form of nitrogen oxides (NO x ). Nitrogen oxide emissions are regulated through regular emission testing requirements. One method used to reduce NO x  emissions from lean burn internal combustion engines is known as selective catalytic reduction. When used to reduce NO x  emissions from a diesel engine, selective catalytic reduction involves injecting atomized urea into the exhaust stream of the engine in relation to one or more selected engine 
     Another method for reducing NO x  emissions is exhaust gas recirculation (EGR), which is a technique that re-circulates a portion of an engine&#39;s exhaust gas back to the engine cylinders. Engines employing EGR recycle part of the engine exhaust back to the engine air intake. The oxygen depleted exhaust gas blends into the fresh air entering the combustion chamber. Reducing the oxygen produces a lower temperature burn, reducing NO x  emissions by as much as 50%. The recycled exhaust gas can then be cooled. This “cooled EGR”, can create an even greater reduction in emissions by further lowering the combustion temperatures. When used with a DPF (diesel particle filter), emissions can be reduced up to 90%. 
     The DPF includes a diesel oxidation catalyst (DOC), which is a ceramic material that heats up in the DPF. Over time, soot and particulate matter accumulates in the DPF, which is cleaned of particulate matter at periodic intervals through a regeneration process. Regeneration is the process of removing the accumulated soot from the filter. This is done either passively (from the engine&#39;s exhaust heat in normal operation or by adding a catalyst to the filter) or actively by introducing very high heat (more than 600° C. to burn off the particulate matter) into the exhaust system. The high temperatures need to be maintained continuously from 10 up to 30 minutes for effective regeneration. 
     Commonly, DPF regeneration systems rely on upstream fuel injection (in-cylinder or in-exhaust) and combustion of the injected fuel in the DOC positioned between the fuel injector and the DPF to create the necessary temperature rise. However, effective DPF regeneration becomes problematic under driving conditions that produce low engine exhaust temperatures, such as observed in stop-and-go traffic. Low temperatures create few opportunities for the DOC to reach the required temperatures needed to initiate and maintain the DPF regeneration. Furthermore, active regeneration events may be interrupted if the temperature at the DOC inlet falls below the required temperature limit (250° C. to 300° C. to burn fuel), making it impossible for the DOC to support the regeneration process. Thus, there is a need for improving the light-off of the DOC during conditions when the exhaust temperature is low and transient. 
     One method for doing this is to change the engine operation to increase the exhaust temperature. Another method is to add a burner into the exhaust system. If a burner is used, then it needs to be supplied with precise amounts fuel and air to operate properly. Delivering the precise amount of air at the correct pressure can be done by many means, each with their own impact to product cost and engine fuel efficiency. 
     In an effort the sustain the proper exhaust heat and fuel combustion for effective regeneration, the present system incorporates a burner for heating a portion of the exhaust gas. However, for the burner to operate efficiently, precise amounts of fuel and air must be provided. Delivery of precise amounts of air at the correct volume and pressure can be accomplished by various means, including use of a positive displacement pump device or by use of a pressure increasing device (blower) and a pressure regulator, each option having its own impact on product cost and engine fuel efficiency. 
     The present system and methods solve these and other problems in providing a system and method for particulate filter regeneration using a burner that is supplied with precise amounts of fuel and air for heating the exhaust stream, thereby providing effective and efficient DPF regeneration. 
     SUMMARY 
     A system and method for regenerating a diesel particulate filter, is disclosed. Generally, the system comprises an exhaust system for a diesel engine having a fresh air intake and an exhaust gas output, a burner fluidly connected to the exhaust gas output, a feed line connected to the air intake and the burner, an air flow delivery device such as a positive displacement pump or blower positioned within the feed line, an air flow regulating valve fluidly connected within the feed line for controlling the air flow from the air intake to the burner, and, the particulate filter fluidly connected in the exhaust gas output after the burner. 
     In another embodiment, the system may also include a pressure regulator within the feed line and the burner. The pressure regulator controls the final pressure to the burner under conditions where the pump is not required. In addition to the pressure regulator, the system may include a bypass line, which diverts air flow around the pump under pressure conditions where the pump is not required. In this embodiment, the system further includes a three-way regulating valve having an inlet for receiving the boost air feed, and a first and second outlet, which are fluidly connected to the bypass line and the pump, respectively, for independent operation. 
     A method for regenerating a diesel engine particulate filter, is also disclosed. The method comprises the steps of providing an exhaust system for a diesel engine having a fresh air intake stream and an exhaust gas output stream, channeling a portion of the exhaust gas output stream toward a burner connected to the particulate filter, delivering a pre-determined volume of boost air from the fresh air intake stream to the burner, maintaining a pre-determined regeneration temperature of the exhaust gas output stream from the burner to the particulate filter, and, regenerating the particulate filter. 
     These and other embodiments and their advantages can be more readily understood from a review of the following detailed description and the corresponding appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic drawing of an system for regenerating a diesel particulate filter used in an exhaust treatment system of an engine; 
         FIG. 2  is a schematic drawing of another embodiment of system for regenerating a diesel particulate filter used in the exhaust treatment system of an engine in accordance with the present disclosure; and, 
         FIG. 3  is a schematic drawing of yet another embodiment of a system for regenerating a diesel particulate filter used in the exhaust treatment system of an engine in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Generally speaking, and with reference to the engine exhaust system  10  schematic of  FIG. 1 , a turbocharged, internal combustion engine  12 , having a fresh air intake  12   a  and an exhaust gas output  12   b,  is shown. The engine exhaust system  10  incorporates an exhaust treatment system, including an EGR cooler  14 , an turbocharger  16  with a turbocharger compressor  18  and a charge air cooler  20 . Such structures will be generally referenced herein and identified in the drawing figures but, as each of these exhaust treatment structures is commonly understood by those skilled in the art, a detailed discussion of the operation of each will not be presented. 
     The present exhaust treatment system also includes a diesel particulate filter (DPF)  22 , which is used to collect particulate matter from the exhaust gas output  12   b . Eventually, the DPF needs to be cleaned or regenerated for effective and continued operation. One method of filter regeneration is to use high temperature exhaust gases. Increasing exhaust temperatures can be accomplished by several means, including adding a burner or burner nozzle  24  to the exhaust system. Because the burner  24  needs to be supplied with precise amounts of fuel and air to operate properly, means have been developed to accomplish providing the necessary air supply. One means includes incorporating air flow/pressure delivery device, such as a positive displacement pump or pressure increasing blower, to the exhaust gas system and in particular, to the air intake. A second means includes incorporating the positive displacement pump or blower and a pressure regulator to the system. The terms “pump” and “blower” are used interchangeable throughout, but it should be understood they relate to an air flow delivery device. The pressure regulator may also be used when the boost air bypasses the pump or blower. 
     Accordingly, the present system provides for delivering a pre-determined amount of air at the correct pressure to the burner  24  for effective and efficient DPF  22  regeneration, including under conditions of low engine speed and power levels. 
     With reference to  FIG. 1 , an embodiment of the exhaust system incorporating a DPF  22 , which is proceeded by a burner  24 , is shown. The exhaust system  10  incorporates a feed line  30  which is located after the turbocharger compressor  18  in the fresh air intake  12   a . The feed line  30  directs an unregulated boost air feed into the positive displacement pump or blower  26 , depending on which is being used, which then directs the desired air flow into the burner  24 . The positive displacement pump  26  delivers a specific air flow volume based on a given pump speed. By measuring the pressure and temperature of the unregulated boost air, the pump speed can be calculated and selected to deliver a specific mass flow of air. An engine control unit (ECU) (not shown) may be electronically coupled to and control operation of the positive displacement pump  26 , while sensors (not shown) may also be incorporated into system for reading the pressure and temperature of the unregulated boost air, thus working in conjunction with the ECU for operation of the pump. For further pressure and flow control, an air flow regulating valve or check valve  32  is fluidly connected within the feed line  30  for controlling the air flow through the feed line to the burner  24 . The check valve may also be controlled through the ECU. 
     With reference to  FIG. 2 , another embodiment of the system is shown incorporating a positive displacement pump or blower  26 , a bypass line  34  and a pressure regulator  36 . When the air boost pressure is higher than the burner pressure requirement, it may be advantageous to control the pressure of the air being generated from the positive displacement pump or blower  26 . In this instance, a pressure regulator  36  can be installed within the feed line  30  between the positive displacement pump or blower  26  and the burner  24 . The pressure regulator  36  in conjunction with the check valve  32 , controls the air flow and pressure to the burner  24 . The burner  24  can then operate properly to increase the exhaust gas temperature to levels required for effective DPF  22  regeneration. 
     Alternatively, rather than having the boost air flow through the pump  26 , the bypass line  34  may be activated. The bypass line  34  diverts the air flow around the pump  26  if the boost air pressure is at a level high enough to meet the burner pressure requirement without the need to activate the pump. Controlling whether the boost air flows through the pump  26  or the bypass line  34  can be accomplished through operation of a regulating device, such as a three-way regulating valve  38  incorporated into the feed line  30 . The regulating valve  38  includes an inlet  38   a  and a first and second outlets  38   b,    38   c,  wherein the inlet and outlets are fluidly connected to the feed line  30 . In one embodiment, the bypass line  34  is fluidly connected to the first outlet  38   b,  while the pump  26  is connected to the second outlet  38   c  of the three-way regulating valve  38 . The arrangement of the regulating valve  38 , pump  26  and bypass line  34  can vary depending on the engine and exhaust system requirements. Operation of the regulating valve  38  may be controlled by real-time signals from the ECU (not shown). Signals for the regulating valve  38  are based on pressure and air flow readings of the boost air. Sensors (not shown), either temperature or pressure, are used to feed information to the ECU about the characteristics of the air flow, which in turn operates the regulating valve  38  to either send boost air through the bypass line  34  or the pump or blower. 
     In many instances, the air requirement of the burner  24  is approximately 10% of the total engine air flow requirement. However, at low engine speed and power levels, such as during stop-and-go driving conditions, the pump or blower  26  is required to supply the burner  24  with the necessary air flow and pressure to heat the exhaust gas stream to regenerate the DPF  22 . Any extra air drawn into the pump or blower  26  requires matching through the turbocharger  16 . Therefore, when using the pump or blower, it may be advantageous to draw the boost air directly from the fresh air intake  12   a  so the turbocharger  16  and turbocharger compressor  18  are not affected. Alternatively, there may be enough boost air pressure to supply the burner  24  using a bypass line, without requiring a pump or blower, as previously discussed. Operation of the pump or blower may be controlled by real-time signals from the ECU (not shown), as previously discussed. 
       FIG. 3  illustrates an embodiment where the fresh boost air can be drawn before it reaches the turbocharger compressor  18  or alternatively, after the turbocharger compressor. In this embodiment, there are two separate feed lines, a first feed line  40  connected directly to the fresh air intake  12   a  and leading to the positive displacement pump or blower  26 . There is also a first air flow regulating valve  44 , which regulates the air flow from the pump or blower  26  to the main feed line  30  and ultimately to the burner  24 . This arrangement would be useful in particular during conditions of low engine speeds and power levels, when extra air is required to feed the burner  24 . This embodiment is advantageous in that the boost air is taken directly from the air intake  12   a  and before it reaches the turbocharger compressor  18 , thus mitigating the affect on the turbocharger. The air is then channeled through the pressure regulator  36 , and ultimately to the burner  24 . 
     In another embodiment, also shown in  FIG. 3 , there is a second feed line  42  connected after the turbocharger compressor  18 . This feed line  42  also includes a second air flow regulating valve  46 , which regulates the boost air flow to the main feed line  30 , through the pressure regulator  36  and to the burner  24 . This arrangement is similar to the embodiment of  FIG. 2 . Because a pump or blower is not used in this arrangement, the pressure regulator  36  controls the final air pressure to the burner  24 . This arrangement is useful during periods of full engine speeds and power levels.