Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
1999-07-12
2001-10-23
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S277000, C060S286000, C060S295000, C060S301000
Reexamination Certificate
active
06305160
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a system and method for controlling ammonia injection upstream of a selective reduction catalyst for use with an internal combustion engine.
BACKGROUND OF THE INVENTION
In order to meet some emission regulations, selective catalytic reduction systems using externally added reducing agents can be used. In such a system, regulated emissions, such as certain nitrogen oxides, or NOx, can be reduced in a oxygen-rich environment to nitrogen and water over a catalyst when a reducing agent, such as ammonia, is added. In addition to controlling nitrogen oxide emissions, the amount of excess ammonia, or ammonia slip, must be managed. Ammonia slip occurs when ammonia in excess of that used to reduce the nitrogen oxides passes through the catalyst unaffected and exits the catalyst (as ammonia slip).
One method for regulating nitrogen oxide emissions and ammonia slip is to use an after-catalyst NOx sensor to detect nitrogen oxide concentration. Control of NOx emissions are allegedly achieved by varying reductant injection until the level or quantity of nitrogen oxides as measured by the sensor falls within an acceptable limit. The amount of reductant injected to keep NOx emissions within the acceptable limit needs to be balanced with an ammonia slip limit. This can be measured and controlled by an after-catalyst ammonia sensor. Such a system is disclosed in U.S. Pat. No. 5,233,934. Alternatively, ammonia slip can be calculated and controlled using an algorithm. Such a system is disclosed in U.S. Pat. No. 4,751,054.
The inventors herein have recognized a disadvantage with the above systems. The above systems attempt to control nitrogen oxide emission level, while limiting ammonia slip. However, these systems do not consider NOx conversion efficiency. While NOx conversion efficiency and after-catalyst NOx emission levels are related, there is an important distinction in their use for reductant control strategy. In general, as maximum NOx conversion is approached with increasing ammonia addition (i.e., increasing NH
3
/NOx mole ratio), ammonia starts to slip. After maximum NOx conversion is attained, ammonia slip increases more rapidly with increasing NH
3
/NOx. For example, if a NOx emission level is regulated to a specific concentration value, then at high feed gas NOx levels, the demand for NOx reduction can easily result in attaining a NOx conversion where ammonia slip is likely excessive and prone to go out of control.
In other words, because a catalyst experiences widely varying levels of engine NOx, controlling to a specific concentration value results in widely varying, and less than optimum, NOx conversion efficiency. Thus, prior art methods are insufficient.
SUMMARY OF THE INVENTION
An object of the invention claimed herein is to provide a system and method for controlling ammonia injection upstream of a selective reduction catalyst to obtain a desired level of nitrogen oxide conversion efficiency while keeping ammonia slip as low as possible.
The above object is achieved, and disadvantages of prior approaches overcome by the method of controlling a reductant injection upstream of a catalyst coupled to an internal combustion engine, the method comprising the steps of: generating a reductant injection quantity based at least on an engine operating condition; determining a nitrogen oxide conversion efficiency of the catalyst; and adjusting said injection quantity to obtain a predetermined value of said nitrogen oxide conversion efficiency.
By controlling reductant injection based on operating the catalyst at a desired nitrogen oxide conversion efficiency value, low nitrogen oxide emissions are obtained, and ammonia slip is kept low, even when the operating conditions vary widely and rapidly such as those for vehicle driving.
In other words, it is possible to reduce NOx significantly and keep ammonia slip low by regulating NOx conversion efficiency rather than NOx emission level. Controlling NOx conversion efficiency is particularly useful where NOx production and flow rate vary widely and quickly such as for vehicle engines.
An advantage of the present invention is optimum reduction in NOx while keeping ammonia slip low without need for an ammonia sensor or an algorithm estimate to adjust ammonia slip.
Another advantage of the present invention is improved reduction in NOx emissions while keeping ammonia slip low.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.
REFERENCES:
patent: 4403473 (1983-09-01), Gladden
patent: 4751054 (1988-06-01), Watanabe
patent: 4854123 (1989-08-01), Inoue
patent: 5201802 (1993-04-01), Hirota et al.
patent: 5233934 (1993-08-01), Krigmont et al.
patent: 5367875 (1994-11-01), Aboujaoude et al.
patent: 5369956 (1994-12-01), Daudel et al.
patent: 5406790 (1995-04-01), Hirota et al.
patent: 5524432 (1996-06-01), Hansel
patent: 5540047 (1996-07-01), Dahlheim et al.
patent: 5605042 (1997-02-01), Stutzenberger
patent: 5709080 (1998-01-01), Arora et al.
patent: 5806310 (1998-09-01), Daidou et al.
patent: 5809774 (1998-09-01), Peter Hoblyn et al.
patent: 5845487 (1998-12-01), Fraenkle et al.
Adams Karen Marie
Hammerle Robert Henry
Laing Paul Matthew
Denion Thomas
Ford Global Technologies Inc.
Russell John D.
Trieu Thai Ba
LandOfFree
Emission control system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Emission control system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Emission control system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2556093