Patent Application
20130227934
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.
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 (NOx). Nitrogen oxide emissions are regulated through regular emission testing requirements. One method used to reduce NOx emissions from lean burn internal combustion engines is known as selective catalytic reduction. When used to reduce NOx 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 NOx emissions is exhaust gas recirculation (EGR), which is a technique that re-circulates a portion of an engine'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 NOx 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'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.
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.
Generally speaking, and with reference to the engine exhaust system 10 schematic of
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 12b. 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
With reference to
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 38a and a first and second outlets 38b, 38c, 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 38b, while the pump 26 is connected to the second outlet 38c 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 12a 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.
In another embodiment, also shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 61367667 | Jul 2010 | US | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US11/34605 | 4/29/2011 | WO | 00 | 4/5/2013 |
