Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
1999-06-07
2001-02-06
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S274000, C060S286000, C060S295000, C060S301000
Reexamination Certificate
active
06182444
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a system and method for controlling reductant injection upstream of an active lean NOx catalyst for use with an internal combustion engine.
BACKGROUND OF THE INVENTION
In order to meet current emission regulations, active lean NOx catalyst systems with externally added reducing agents are used. In such systems, regulated emissions, such as certain nitrogen oxides, are reduced to nitrogen and water in the catalyst when a reducing agent containing hydrocarbons is added. In order to obtain maximum fuel economy while meeting emission regulations, it is necessary to inject just enough reductant to promote the chemical reactions without increasing hydrocarbon emissions by injecting too much reductant.
In certain circumstances, it may be desirable to have multiple lean NOx catalysts coupled in series to accommodate, for example, packaging and manufacturing constraints. In this case, dual reductant injection may be used for injecting reducing agent upstream of each catalyst.
One method for controlling reductant injection upstream of first and second lean NOx catalysts uses a NOx sensor located downstream of each catalyst. In this method, reductant is injected upstream of the first NOx catalyst in accordance with a control dependent on engine operating parameters. Similarly, reductant is injected upstream of the second NOx catalyst in accordance with a strategy identical to the first NOx catalyst. Both the reductant injection strategies rely on a downstream NOx sensor for the reductant control, and thereby the exhaust air/fuel ratio control. Such a system is described is U.S. Pat. No. 5,771,686.
The inventors herein have recognized a disadvantage with the above system. The above system does not indicate a method for determining the quantity of NOx entering the second catalyst. In addition, the above system does not exploit available benefits of having multiple catalyst with individual reductant injection control. In other words, the above method uses the same reductant control strategy for each catalyst, thereby requiring sensors for each catalyst. The inventors herein have recognized that improvements are possible by recognizing the physical couplings and eliminating unnecessary sensor duplications.
SUMMARY OF THE INVENTION
An object of the invention claimed herein is to provide a system and method for controlling multiple reductant injection upstream of serially placed lean NOx catalysts that maximizes nitrogen oxide conversion with minimum reductant injection.
The above object is achieved, and disadvantages of prior approaches is overcome, by the instant invention.
By realizing that the product of the first catalyst efficiency and the first reductant injection quantity is proportional to the necessary reductant injection quantity for the second catalyst, it is possible to eliminate the need for additional sensors. In other words, based on the efficiency of the first catalyst and the amount of reductant injected into the first catalyst, it is possible to calculate the amount of reductant necessary for the second catalyst. This intrinsically takes into account the amount of nitrogen oxides exiting the first catalyst, and the amount of unused reductant exiting the first catalyst, each of which will enter the second catalyst.
An advantage of the present invention is improved emission control.
Another advantage of the present invention is improved nitrogen oxide conversion efficiency.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.
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Fulton Brien Lloyd
Goodliff Simon
Vantine Katie Jo
Denion Thomas
Ford Global Technologies Inc.
May Roger L.
Nguyen Tu M.
Russell John D.
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