EXHAUST GAS TREATMENT SYSTEM WITH EMISSION CONTROL DURING FILTER REGENERATION
An exhaust gas treatment system for an engine includes an exhaust gas inlet tube configured to receive an exhaust gas from the engine. A particulate filter, a heat exchange system and first and second selective catalytic reduction (SCR) devices are in fluid communication with the exhaust gas inlet tube. The particulate filter is configured to undergo thermal regeneration when the exhaust gas in the particulate filter is heated above a regeneration temperature. The controller is configured to control a temperature difference, between a present temperature of the second SCR device and a predefined optimal second SCR temperature, to be within a predefined threshold during the thermal regeneration of the particulate filter. The controller may be configured to direct an injector to inject a reductant into the first SCR device when the temperature difference is below the predefined threshold, thereby controlling a NOx emission in the exhaust gas.
The present invention relates generally to an exhaust gas treatment system for a vehicle and a method for controlling the exhaust gas treatment system.
BACKGROUNDInternal combustion engines produce a number of emissions, including various oxides of nitrogen, referred to collectively herein as NOx gases. NOx gases are created when nitrogen and oxygen molecules present in engine intake air are exposed to high temperatures of combustion. Exhaust gas treatment systems are used in vehicles in order to reduce and manage the NOx gases created in the combustion process. Exhaust gas treatment systems generally employ a selective catalytic reduction (SCR) device which uses a reductant, such as ammonia, capable of reacting with NOx gases in combination with excess oxygen in order to reduce the NOx gases.
Exhaust gas treatment systems also employ particulate filters to filter out particles or particulate matter produced by the engine. On regular intervals, the particulate filter has to be thermally regenerated in order to remove the accumulated particles. As the temperature of the particulate filter is increased, the temperature of the SCR device is also increased, resulting in ammonia being desorbed from the SCR device. The ammonia may pass through the particulate filter and be oxidized to form NOx gases, thereby increasing NOx emissions during the thermal regeneration of the particulate filter.
SUMMARYAn exhaust gas treatment system for an engine producing an exhaust gas includes an exhaust gas inlet tube configured to receive the exhaust gas from the engine. A particulate filter, a heat exchange system and first and second selective catalytic reduction (SCR) devices are in fluid communication with the exhaust gas inlet tube. The heat exchange system is positioned downstream of the particulate filter. The first and second SCR devices are positioned upstream and downstream of the heat exchange system, respectively. The particulate filter is configured to undergo thermal regeneration when the exhaust gas in the particulate filter is heated above a regeneration temperature. A first temperature sensor is operatively connected to the second SCR device and configured to determine a present second SCR temperature (TS2) of the second SCR device. A controller is operatively connected to the first temperature sensor and configured to determine whether the thermal regeneration is taking place in the particulate filter. The controller is configured to control the temperature difference (TS2−TO) between the present second SCR temperature (TS2) and a predefined optimal second SCR temperature (TO) to be within a predefined threshold during the thermal regeneration of the particulate filter.
An injector is operatively connected to the first SCR device and configured to selectively inject a reductant into the first SCR device. The reductant is configured to travel to the second SCR device. The controller may be configured to direct the injector to inject the reductant when the temperature difference (TS2−TO) is below a predefined threshold, thereby controlling the NOx emission in the exhaust gas during the thermal regeneration of the particulate filter. In one example, the predefined optimal second SCR temperature (TO) is between approximately 200 and 220° Celsius. In another example, the predefined optimal second SCR temperature (TO) is approximately 220° Celsius and the predefined threshold is approximately 10° Celsius.
The controller being configured to control the temperature difference (TS2−TO) to be within a predefined threshold includes directing the heat exchange system to transfer heat from the exhaust gas when the temperature difference (TS2−TO) is above the predefined threshold. Thus, the exhaust gas treatment system uses the heat exchange system to control the present second SCR temperature (TS2) of the second SCR device during the thermal regeneration of the particulate filter.
First and second pressure sensors may be positioned upstream and downstream of the particulate filter, respectively. The first and second pressure sensors are configured to determine a differential pressure across the particulate filter. The controller may be configured to determine whether the thermal regeneration is taking place in the particulate filter by determining when the differential pressure across the particulate filter is above a predefined threshold pressure.
A second temperature sensor is operatively connected to and configured to determine a present filter temperature (TF) of the particulate filter. The controller may be configured to determine whether the thermal regeneration is taking place in the particulate filter by determining whether the present filter temperature (TF) of the particulate filter has elapsed a predefined amount of time at a predefined temperature. In one example, the predefined amount of time is 30 minutes and the predefined temperature is 550 Celsius.
The first SCR device may include a first catalyst and the particulate filter may include a plurality of channels having respective walls. The first SCR device and the particulate filter may be disposed in a common housing such that the first catalyst is coated on the respective walls of the plurality of channels of the particulate filter. First and second NOx sensors may be positioned upstream and downstream of the particulate filter, respectively. The first and the second NOx sensors are configured to determine respective amounts of NOx in the exhaust gas upstream and downstream of the particulate filter.
The heat exchange system may include an inlet portion configured to receive the exhaust gas from the particulate filter. An outlet portion of the heat exchange system is configured to transmit the exhaust gas to the second SCR device. An interior cavity connects the inlet and outlet portions and defines a central passageway and a bypass passageway. A heat exchange device is positioned within the bypass passageway and configured to transfer heat from the exhaust gas.
A bypass valve is selectively movable between a plurality of positions to selectively permit the exhaust gas entering the second SCR device to include a first portion from the central passageway and a second portion from the bypass passageway. The bypass valve may be positioned such that the first portion is approximately 100% and the second portion is approximately 0% when the temperature difference (TS2−TO) is below the predefined threshold. The bypass valve may be positioned such that the first portion is approximately 60% and the second portion is approximately 40% when the temperature difference (TS2−TO) is above the predefined threshold.
A coolant circuit may be operatively connected to the heat exchange system such that the heat exchange device is configured to selectively transfer heat from the exhaust gas to the coolant circuit. A method for controlling operation of the exhaust gas treatment system is provided.
The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.
Referring to the drawings, wherein like reference numbers correspond to like or similar components throughout the several figures, a portion of a vehicle 10 is shown in
Referring to
Referring to
Referring to
The NOx reduction reaction takes place as the exhaust gas 14 passes through the first and second SCR device 24, 26. Referring to
The particulate filter 20 is used to filter out particles or particulate matter produced by the engine 12. These particles may include soot, hydrocarbons, ashes and sulphuric acid. Referring to
Referring to
The exhaust treatment system 16 includes one or more sensors at various locations for sensing the temperature, pressure and other properties of the system 16. Referring to
Referring to
On regular intervals, the particulate filter 20 has to be regenerated in order to remove the accumulated particles. The particulate filter 20 is configured to undergo thermal regeneration when the exhaust gas 14 in the particulate filter 20 is heated above a regeneration or combustion temperature, thereby allowing the particles to combust or burn. In one example, the regeneration temperature is between 600-750° C. Any suitable method of performing regeneration may be employed, including but not limited to, using a fuel burner, using resistive heating coils and using microwave energy. As the temperature of the particulate filter 20 is increased, the temperature of the first SCR device 24 is also increased, resulting in the reductant 28, such as ammonia, being desorbed from the first SCR device 24. The ammonia may pass through the particulate filter 20 and be oxidized to form NOx gases (various oxides of nitrogen), thereby increasing NOx emissions during thermal regeneration of the particulate filter 20.
Referring to
Execution of algorithm 200 is described below with reference to
In another embodiment, the controller 60 may be configured to determine whether the thermal regeneration is taking place in the particulate filter 20 by determining whether the present filter temperature (TF) of the particulate filter 20 (as determined by the second temperature sensor 50 shown in
If thermal regeneration is not taking place, the algorithm 200 is exited as indicated by line 210. If thermal regeneration is taking place, the algorithm 200 proceeds to step 204. In step 204 of
In sub-step 204A, the controller 60 determines the present second SCR temperature (TS2) of the second SCR device 26, based on the first temperature sensor 48 operatively connected to the second SCR device 26. In sub-step 204B of
In sub-step 204C, the controller 60 directs the heat exchange system 22 to transfer heat from the exhaust gas 14 when the temperature difference (TS2−TO) is above the predefined threshold. In one example, the predefined optimal second SCR temperature (TO) is between approximately 200 and 220° Celsius. In another example, the predefined optimal second SCR temperature (TO) is approximately 220° Celsius and the predefined threshold is approximately 10° Celsius. In this case, if the present second SCR temperature (TS2) is above 230° Celsius, the controller 60 directs the heat exchange system 22 to transfer heat from the exhaust gas 14 until the present second SCR temperature (TS2) is within approximately 10° Celsius of the optimal second SCR temperature (TO), or (TS2−TO)≦10.
Thus, the exhaust gas treatment system 16 uses the heat exchange system 22 to maintain an optimal temperature of the second SCR device 26 during the thermal regeneration of the particulate filter 20. As shown by line 206, algorithm 200 loops back to step 204 until the temperature difference (TS2−TO) is no longer above the predefined threshold.
In step 208 of
The controller 60 may determine the amount of the reductant 28 to be injected by the injector 29 based upon a number of combination factors. The factors may include, but are not limited to, the respective amounts of NOx in the exhaust gas 14 upstream and downstream of the particulate filter 20, the present second SCR temperature (TS2), the amount of first and second catalysts 44, 36 in the first and second SCR devices 24, 26, respectively, and the exhaust flow rate at the exhaust gas inlet tube 18 of the engine 12.
Referring to
Referring to
Referring to
The controller 60 may direct the bypass valve 74 to the second position 76B when the temperature difference (TS2−TO) is above the predefined threshold. In the second position 76B, the first portion 78 may be approximately 60% and the second portion 80 may be approximately 40%. The controller 60 may also direct the bypass valve 74 to a third position 76C, in which the first portion 78 is approximately 0% and the second portion 80 is approximately 100%. As shown in
Referring to
The coolant circuit 82 may transfer heat between various vehicle components, including the engine 12, the exhaust system 16, a heater core 94, and the vehicle transmission (not shown). The heater core 94 allows heat to be transferred from the coolant 84 leaving the engine 12 to the passenger compartment (not shown) of the vehicle 10. The coolant circuit 82 may include a heater core bypass 98 in parallel with the heater core 94, and a heater core bypass valve 96 configured to control flow of coolant 84 through the heater core 94 and the heater core bypass 98. The coolant circuit 82 may include flow restrictors, such as restrictor 99, placed at various locations within the circuit 82. The vehicle 10 may include various other components known to those skilled in the art, including but not limited to, a radiator, transmission heat exchanger and thermostat (not shown).
The controller 60 of
The detailed description and the drawings or figures are supportive and descriptive of the invention, but the scope of the invention is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claimed invention have been described in detail, various alternative designs and embodiments exist for practicing the invention defined in the appended claims.
Claims
1. An exhaust gas treatment system for an engine producing an exhaust gas, the system comprising:
- an exhaust gas inlet tube configured to receive the exhaust gas;
- a particulate filter in fluid communication with the exhaust gas inlet tube and configured to undergo thermal regeneration when the exhaust gas in the particulate filter is heated above a regeneration temperature;
- a heat exchange system in fluid communication with the exhaust gas inlet tube and positioned downstream of the particulate filter;
- a first selective catalytic reduction (SCR) device in fluid communication with the exhaust gas inlet tube and positioned upstream of the heat exchange system;
- a second selective catalytic reduction (SCR) device in fluid communication with the exhaust gas inlet tube and positioned downstream of the heat exchange system;
- a first temperature sensor operatively connected to and configured to determine a present second SCR temperature (TS2) of the second SCR device;
- a controller operatively connected to the first temperature sensor and configured to determine whether the thermal regeneration is taking place in the particulate filter; and
- wherein the controller is configured to control a temperature difference (TS2−TO) between the present second SCR temperature (TS2) and a predefined optimal second SCR temperature (TO) to be within a predefined threshold during the thermal regeneration of the particulate filter.
2. The exhaust gas treatment system of claim 1, further comprising:
- an injector operatively connected to and configured to selectively inject a reductant into the first SCR device, the reductant being configured to travel to the second SCR device; and
- wherein the controller is configured to direct the injector to inject the reductant when the temperature difference (TS2−TO) is below the predefined threshold, thereby controlling a NOx emission in the exhaust gas.
3. The exhaust gas treatment system of claim 1, wherein the predefined optimal second SCR temperature (TO) is between approximately 200 and 220° Celsius.
4. The exhaust gas treatment system of claim 1, wherein the predefined optimal second SCR temperature (TO) is approximately 220° Celsius and the predefined threshold is approximately 10° Celsius.
5. The exhaust gas treatment system of claim 1, wherein the controller being configured to control the temperature difference (TS2−TO) to be within a predefined threshold includes:
- the controller being configured to direct the heat exchange system to transfer heat from the exhaust gas when the temperature difference (TS2−TO) is above the predefined threshold.
6. The exhaust gas treatment system of claim 1, further comprising:
- first and second pressure sensors positioned upstream and downstream of the particulate filter, respectively, and configured to determine a differential pressure across the particulate filter; and
- wherein the controller is configured to determine whether the thermal regeneration is taking place in the particulate filter by determining when the differential pressure across the particulate filter is above a predefined threshold pressure.
7. The exhaust gas treatment system of claim 1, further comprising:
- a second temperature sensor operatively connected to and configured to determine a present filter temperature (TF) of the particulate filter; and
- wherein the controller is configured to determine whether the thermal regeneration is taking place in the particulate filter by determining whether the present filter temperature (TF) of the particulate filter has elapsed a predefined amount of time at a predefined temperature.
8. The exhaust gas treatment system of claim 7, wherein the predefined amount of time is 30 minutes and the predefined temperature is 550 Celsius.
9. The exhaust gas treatment system of claim 1, wherein:
- the first SCR device includes a first catalyst;
- the particulate filter includes a plurality of channels having respective walls; and
- the first SCR device and the particulate filter are disposed in a common housing such that the first catalyst is coated on the respective walls of the plurality of channels of the particulate filter.
10. The exhaust gas treatment system of claim 1, further comprising:
- first and second NOx sensors positioned upstream and downstream of the particulate filter, respectively; and
- wherein the first and the second NOx sensors are configured to determine respective amounts of the NOx emission in the exhaust gas upstream and downstream of the particulate filter.
11. The exhaust gas treatment system of claim 1, wherein the heat exchange system includes:
- an inlet portion configured to receive the exhaust gas from the particulate filter;
- an outlet portion configured to transmit the exhaust gas to the second SCR device;
- an interior cavity connecting the inlet and outlet portions and defining a central passageway and a bypass passageway;
- a heat exchange device positioned within the bypass passageway and configured to transfer heat from the exhaust gas; and
- a bypass valve selectively movable between a plurality of positions to selectively permit the exhaust gas entering the second SCR device to include a first portion from the central passageway and a second portion from the bypass passageway.
12. The exhaust gas treatment system of claim 11, wherein the bypass valve is positioned such that the first portion is approximately 100% and the second portion is approximately 0% when the temperature difference (TS2−TO) is below the predefined threshold.
13. The exhaust gas treatment system of claim 11, wherein the bypass valve is positioned such that the first portion is approximately 60% and the second portion is approximately 40% when the temperature difference (TS2−TO) is above the predefined threshold.
14. The exhaust gas treatment system of claim 11, wherein the heat exchange device includes:
- a plurality of plates having respective spaces between the plurality of plates, the respective spaces defining a first flow path for the exhaust gas;
- wherein the plurality of plates each define at least one respective slot, the at least one respective slot being aligned to fit at least one tube configured for flow of a coolant.
15. The exhaust gas treatment system of claim 8, further comprising:
- a coolant circuit operatively connected to the heat exchange system; and
- wherein the heat exchange device is configured to selectively transfer heat from the exhaust gas to the coolant circuit.
16. A vehicle comprising:
- an engine;
- an exhaust gas inlet tube in fluid communication with and configured to receive an exhaust gas from the engine;
- a particulate filter in fluid communication with the exhaust gas inlet tube and configured to undergo thermal regeneration when the exhaust gas in the particulate filter is heated above a regeneration temperature;
- a heat exchange system in fluid communication with the exhaust gas inlet tube and positioned downstream of the particulate filter;
- a first selective catalytic reduction (SCR) device in fluid communication with the exhaust gas inlet tube and positioned upstream of the heat exchange system;
- a second selective catalytic reduction (SCR) device in fluid communication with the exhaust gas inlet tube and positioned downstream of the heat exchange system;
- an injector operatively connected to and configured to selectively inject a reductant into the first SCR device, the reductant being configured to travel to the second SCR device;
- a first temperature sensor operatively connected to the second SCR device and configured to determine a present temperature of the second SCR device;
- a controller operatively connected to the first temperature sensor and configured to determine whether the thermal regeneration is taking place in the particulate filter;
- wherein the controller is configured to control a temperature difference (TS2−TO) between the present second SCR temperature (TS2) and a predefined optimal second SCR temperature (TO) to be within a predefined threshold during the thermal regeneration of the particulate filter; and
- wherein the controller is configured to direct the injector to inject the reductant when the temperature difference is below the predefined threshold, thereby controlling a NOx emission in the exhaust gas.
17. A method for controlling operation of an exhaust gas treatment system in an engine producing exhaust gas, the method comprising:
- operatively connecting an exhaust gas inlet tube to the engine for receiving the exhaust gas;
- operatively connecting a particulate filter and heat exchange system for fluid communication with the exhaust gas inlet tube, the particulate filter being configured to undergo thermal regeneration when the exhaust gas in the particulate filter is heated above a regeneration temperature;
- operatively connecting first and second selective catalytic reduction (SCR) devices for fluid communication with the exhaust gas inlet tube, the first and second SCR devices being positioned upstream and downstream of the heat exchange system, respectively;
- operatively connecting an injector to the first SCR device for selective injection of a reductant into the first SCR device;
- detecting when the thermal regeneration is taking place in the particulate filter;
- controlling the temperature difference between the present SCR temperature and a predefined optimal SCR temperature to be within a predefined threshold during the thermal regeneration of the particulate filter; and
- directing the injector to inject the reductant when the temperature difference is below the predefined threshold, thereby controlling a NOx emission in the exhaust gas.
18. The method of claim 17, wherein controlling the temperature difference to be within a predefined threshold during the thermal regeneration of the particulate filter includes:
- determining a present second SCR temperature of the second SCR device based on a first temperature sensor operatively connected to the second SCR device;
- determining whether the temperature difference between the present SCR temperature and a predefined optimal SCR temperature is above or below the predefined threshold when the thermal regeneration is taking place in the particulate filter; and
- directing the heat exchange system to transfer heat from the exhaust gas when the temperature difference is above the predefined threshold.
19. The method of claim 16, further comprising:
- positioning first and second pressure sensors upstream and downstream of the particulate filter, respectively, for determining a differential pressure across the particulate filter; and
- wherein said detecting when the thermal regeneration is taking place in the particulate filter includes determining when the differential pressure is above a predefined threshold pressure.
Type: Application
Filed: May 31, 2013
Publication Date: Dec 4, 2014
Inventors: Eugene V. Gonze (Pinckney, MI), Michael J. Paratore, JR. (Howell, MI), Joshua Clifford Bedford (Farmington Hills, MI)
Application Number: 13/906,940
International Classification: F01N 3/021 (20060101);