Snapper valve for hot end systems with burners

A system for controlling the temperature of an exhaust stream includes a main exhaust passageway adapted to receive the exhaust stream from an engine. A bypass passage includes an inlet and an outlet in communication with the main exhaust passageway. The outlet is located downstream from the inlet. A burner is positioned within the bypass passage for treating the exhaust passing through the bypass passage. A valve is positioned within the main exhaust passageway downstream from the inlet and upstream from the outlet. The valve is operable to vary the exhaust flow through the burner. A controller selectively operates the burner to maintain a desired exhaust temperature downstream of the outlet.

FIELD

The present disclosure generally relates to a system for treating exhaust gases. More particularly, a flow diverter and burner arrangement for increasing an exhaust gas temperature is discussed.

BACKGROUND

In an attempt to reduce the quantity of NOXand particulate matter emitted to the atmosphere during internal combustion engine operation, a number of exhaust aftertreatment devices have been developed. A need for exhaust aftertreatment systems particularly arises when diesel combustion processes are implemented. Typical aftertreatment systems for diesel engine exhaust may include one or more of a diesel particulate filter (DPF), a selective catalytic reduction (SCR) system, a hydrocarbon (HC) injector, and a diesel oxidation catalyst (DOC).

During engine operation, the DPF traps soot emitted by the engine and reduces the emission of particulate matter (PM). Over time, the DPF becomes loaded and begins to clog. Periodically generation or oxidation of the trapped soot in the DPF is required for proper operation. To regenerate the DPF, relatively high exhaust temperatures in combination with an ample amount of oxygen in the exhaust stream are needed to oxidize the soot trapped in the filter.

The DOC is typically used to generate heat to regenerate the soot loaded DPF. When hydrocarbons (HC) are sprayed over the DOC at or above a specific light-off temperature, the HC will oxidize. This reaction is highly exothermic and the exhaust gases are heated during light-off. The heated exhaust gases are used to regenerate the DPF.

Under many engine operating conditions, however, the exhaust gas is not hot enough to achieve a DOC light-off temperature of approximately 300° C. As such, DPF regeneration does not passively occur. Furthermore, NOXadsorbers and selective catalytic reduction systems typically require a minimum exhaust temperature to properly operate.

A burner may be provided to heat the exhaust stream upstream of the various aftertreatment devices. Known burners have successfully increased the exhaust temperature of relatively small displacement internal combustion engines for automotive use. However, other applications including diesel locomotives, stationary power plants, marine vessels and others may be equipped with relatively large diesel compression engines. The exhaust mass flow rate from the larger engines may be more than ten times the maximum flow rate typically provided to the burner. While it may be possible to increase the size of the burner to account for the increased exhaust mass flow rate, the cost, weight and packaging concerns associated with this solution may be unacceptable. Therefore, a need may exist in the art for an arrangement to increase the temperature of the exhaust output from a large diesel engine while minimally affecting the cost, weight, size and performance of the exhaust system. It may also be desirable to minimally affect the pressure drop and/or back pressure associated with the use of a burner.

SUMMARY

A system for controlling the temperature of an exhaust stream includes a main exhaust passageway adapted to receive the exhaust stream from an engine. A bypass passage includes an inlet and an outlet in communication with the main exhaust passageway. The outlet is located downstream from the inlet. A burner is positioned within the bypass passage for treating the exhaust passing through the bypass passage. A valve is positioned within the main exhaust passageway downstream from the inlet and upstream from the outlet. The valve is operable to vary the exhaust flow through the burner. A controller selectively operates the burner to maintain a desired exhaust temperature downstream of the outlet.

A system for controlling the temperature of an exhaust from an engine includes a bypass passage having an inlet in communication with a main exhaust passageway in receipt of an exhaust stream from the engine. The bypass passage also includes an outlet in communication with the main exhaust passageway at a location downstream from the inlet. A burner is positioned within the bypass passage for heating the exhaust passing through the bypass passage. A valve is positioned within the main exhaust passageway downstream from the inlet and upstream from the outlet. The valve is operable to vary the exhaust flow through the burner. An exhaust aftertreatment device is located downstream of the outlet in receipt of a mixed exhaust supplied from the bypass passage and the main exhaust passageway.

DETAILED DESCRIPTION

FIG. 1depicts a diesel exhaust gas aftertreatment system10for treating the exhaust output by engine12to a main exhaust passageway14. An intake passage16is coupled to engine12to provide combustion air thereto. A turbocharger18includes a driven member20positioned in an exhaust stream flowing through main exhaust passageway14as well as a drive member22positioned within intake passage16and in communication with intake air. During engine operation, the exhaust stream causes driven member20to rotate. Because drive member22is fixed for rotation with driven member20, intake air is compressed within intake passage16prior to entry into engine12.

Exhaust aftertreatment system10also includes a valve and burner arrangement26positioned downstream from turbocharger18and upstream from a number of exhaust aftertreatment devices. In the exemplary aftertreatment system depicted inFIG. 1, the aftertreatment devices include a hydrocarbon injector28, a diesel oxidation catalyst30, a diesel particulate filter32, a urea injector34and a selective catalytic reduction system36.

It is contemplated that engine12is configured as a relatively large displacement diesel compression engine having an exhaust mass flow rate ranging from 3000 to 20,000 kg per hour depending on engine operating speed. It should be appreciated that this mass flow rate range is merely exemplary and that the teachings of the present disclosure may be applied to other engines having different exhaust mass flow rates. It is further contemplated that engine12typically operates as a lean-burn engine having exhaust temperatures oftentimes less than 300° C. As previously mentioned, proper operation of many of the exhaust aftertreatment devices occurs when the exhaust gas temperature entering the aftertreatment device exceeds 300° C. Accordingly, burner and valve arrangement26is provided upstream of the exhaust aftertreatment devices.

Burner and valve arrangement26includes a burner40and a valve42positioned within parallel portions of system10. In particular, burner40is positioned within a bypass passage44having an inlet46positioned upstream of valve42and in communication with main exhaust passageway14. A bypass outlet48is positioned downstream of valve42and in communication with main exhaust passageway14. Bypass outlet48is upstream from each of exhaust aftertreatment devices28,30,32,34and36. As such, burner40may be used to heat the exhaust to an elevated temperature that will enhance the efficiency of DOC30and SCR system36.

Burner40may include one or more injectors52for injecting fuel as well as one or more oxygenators54. One or more igniters55function to ignite the injected fuel and oxygen together with unburned fuel already carried in the exhaust. Alternatively, each injector52may be a combined injector that injects both fuel and oxygen. A controller56is provided to monitor and control the flow of the fuel and/or oxygen through injectors52,54as well as the operation of igniters55.

Valve42is a passive snap-action valve positioned within a tubular portion60of main exhaust passageway14downstream of bypass inlet46and upstream of bypass outlet48. Valve42is depicted inFIGS. 2 and 3to include a spring anchor64, a valve spring66, an external lever arm68, a valve flap70, a valve support shaft or axle72and an attachment point74protruding from axle72.

Valve flap70has first and second arcuate edges substantially conforming to an interior arcuate surface of tube60. Flap70additionally has linear side edges76and78which provide clearance80,82between flap70and an interior surface of tube60when the flap is in the closed position shown inFIGS. 2 and 3. Bias element or spring66extends between a spring anchor64on tube60and attachment point74of external lever arm68. Spring66biases flap70toward the closed positioned shown inFIG. 2. When in the fully closed position, flap70resides at an angle other than 90° to a plane extending normal to the longitudinal axis of tube60. The angle of the flap with respect to a cross-sectional normal plane of tube60is designated A.

In operation, exhaust pressure acts on flap70from the left as viewed inFIGS. 2-5. When the exhaust pressure is sufficient to overcome the bias force of spring66, the flap70will start to rotate about axle72. The torque on valve flap70is determined by the bias spring force multiplied by a distance d. Distance d is the distance between the axis of spring66and axle72. The spring force increases as the valve flap opens and spring66stretches. However, d gets shorter as the valve continues to open resulting in the torque approaching zero as the longitudinal axis of the spring approaches an “over-center” position. Distance d reduces as the spring axis approaches intersection with a longitudinal axis of axle72. This nearly over-center positioning of the valve flap70as shown inFIGS. 4 and 5results in a substantially horizontal position of the flap when in the fully open position. This positioning, in turn, minimizes back pressure in the tube when the valve is in the fully open position. Additionally, it is to be noted that the tube itself supplies the stop mechanism for the valve flap in both its fully closed and fully opened positions. In the fully closed position, the arcuate edges of flap70contact the interior surface of tube60to define that position. Conversely, when in the fully opened position, as shown inFIGS. 4 and 5, flap70utilizes its lateral linear side edges (76and78ofFIG. 3) to come into contact with the inner surface of tube60to thereby provide a stop position for the fully opened position of flap70.

Rotating the valve flap such that the spring approaches the over-center condition also results in an easier maintenance of the valve in the fully opened position. It should be appreciated that the configuration of valve flap70is merely exemplary and that other snap-action valves are contemplated for use within burner and valve arrangement26. Specifically, U.S. Pat. No. 7,434,570 and U.S. Patent Application Publication Nos. 2008-0223025 and 2008-0245063 are herein incorporated by reference and depict alternate suitable valves.

Controller56is also in receipt of signals from various sensors84associated with aftertreatment system10and engine12. For example, sensors84may include individual sensors for collecting specific data or may broadly refer to data available over a CAN bus. When engine12and aftertreatment system10are used in a vehicle, the information provided to controller56may include battery voltage and ignition switch position data. Additional sensors including a mass air flow sensor, air flow and fuel flow sensors associated with injector52, a fuel pressure sensor, an air pressure sensor, a burner inlet temperature sensor, a burner outlet temperature sensor and/or an exhaust gas temperature sensor downstream of bypass outlet48may also be associated with aftertreatment system10and in communication with controller56.

It should be appreciated that exhaust aftertreatment system10may be operated in a number of different modes. In a first mode of operation, controller56may be in receipt of a command to operate burner40in an active mode. This mode of operation may be entered when the vehicle ignition is on and other sensor data indicates that engine12is combusting fuel. During operation of engine12, controller56commands burner40to maintain a desired exhaust gas temperature. The control temperature data may be provided by a sensor86(FIG. 1) at the burner outlet. Alternatively or additionally, an exhaust gas temperature sensor88may be positioned further downstream from the interconnection of bypass outlet48and main exhaust passageway14to determine the temperature of the mixed exhaust gas entering DOC30. Controller56may operate burner40to maintain a desired mixed exhaust temperature as indicated by sensor88. Burner control continues until controller56indicates that engine12has ceased operation and/or the ignition switch is in the off position.

It should be noted that valve42is passively operated and that the position of flap70varies based on exhaust fluid pressure applied to flap70. The angle of flap70at the closed position, the initial preload and rate of spring66, as well as the position of axle72will be determined and defined to assure that the proper flow of exhaust is diverted into bypass passage44and burner40. Controller56may selectively actuate injectors52,54and igniters55to heat the exhaust gas flowing through bypass outlet48to maintain a target temperature.

In another mode of operation, burner40may be used to perform active regeneration of DPF32after engine12has been shut off. In certain operating conditions, engine12will cool more rapidly than desired if continued passive regeneration of DPF32is desired. Accordingly, controller56may activate burner40to heat the exhaust gas within main exhaust passageway14to regenerate DPF32after engine12has been shut off. The burner40heats the exhaust gas when the exhaust flow has effectively been stopped.

Another mode of operating exhaust aftertreatment system10includes monitoring the use of fresh air inputs to engine12or exhaust aftertreatment system10that are not heated by the combustion process of engine12. Such systems may include a dynamic brake where relatively cold ambient air may be pumped through engine12when combustion does not occur in an attempt to retard the vehicle. The cool air is then provided to DOC30, DPF32and/or SCR system36. Some of the components within the exhaust aftertreatment devices30,32and36may be adversely affected when exposed to a thermal shock such as during dynamic engine braking. Accordingly, it may be desirable to operate burner40during engine braking to assure that the exhaust gas entering the aftertreatment devices will be at or above a minimum temperature.

During times when engine12operates at a relatively high load and/or operating speed, it is contemplated that valve42will be in a substantially open condition and that the temperature of the exhaust within main exhaust passageway14will exceed a predetermined minimum temperature for proper operation of exhaust aftertreatment devices30,32and36. Accordingly, controller56will maintain burner40at an idle state where fuel is not injected through injector52and igniters55are not energized. When engine12operates at lower loads and lower operating speeds, the exhaust gas temperature will likely decrease. Once controller56determines that the exhaust gas temperature upstream from DOC30is at or below a predetermined threshold, burner40will be operated in its active mode to maintain either a desired burner outlet temperature or a mixed gas temperature upstream from the exhaust aftertreatment devices.