Lean catalyst and particulate filter control system and method

Details Lean catalyst and particulate filter control system and method Lean catalyst and particulate filter control system and method

1999-08-24

2001-03-13

Denion, Thomas (Department: 3748)

Power plants

Internal combustion engine with treatment or handling of...

By means producing a chemical reaction of a component of the...

C060S295000, C060S311000, C422S178000

Reexamination Certificate

active

06199375

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a system and method for controlling an engine having both a lean NOx catalyst for reducing exhaust NOx in an oxygen rich environment and a particulate filter for removing carbon particles, or soot.
BACKGROUND OF THE INVENTION
In order to meet future emission regulations in vehicles having a compression ignition engine, it may be necessary to use lean NOx catalysts in combination with particulate filters.
A NOx catalyst reduces NOx emissions continuously, even in an oxygen rich environment. For an active NOx catalyst to maximize NOx reduction, a reducing agent, for example, diesel fuel or urea, needs to be present. The optimum amount of reducing agent for the NOx catalyst is typically based on engine operating conditions and catalyst conditions. These conditions typically include engine speed, engine load, and catalyst temperature.
A particulate filter, also commonly used with compression ignition engines, is used to prevent soot, or carbon particles, from exiting the tailpipe. Since the particulate filter has a limited storage capacity, it is periodically regenerated. In one approach, during the regeneration process, exhaust temperature is increased to ignite carbon particles stored in the particulate filter. By burning the stored carbon particles, the filter is regenerated and able to again store the carbon particles. In addition, the burning of the carbon particles causes an increase in temperature.
The inventor herein has recognized a disadvantage when combining the above systems, for example, by placing the NOx catalyst downstream of the particulate filter. In this configuration, when the particulate filter is being regenerated, excess reductants are made available to the NOx catalyst since reductants are released from the particulate filter during the regeneration process. Thus, reductant is fed to the NOx catalyst in excess of that needed to reduce NOx. This can result in increased HC and CO emissions.
SUMMARY OF THE INVENTION
An object of the present invention is to control a particulate filter regeneration of a particulate filter coupled to a compression ignition engine having a downstream lean NOx catalyst.
The above object is achieved and disadvantages of prior approaches overcome by a method for managing regeneration of a particulate filter communicating with an engine exhaust upstream of a catalyst, the method comprising: regenerating the particulate filter; determining an reductant amount released by the particulate filter; and discontinuing said regeneration when said reductant amount is greater than a predetermined value.
By discontinuing regeneration when a reductant amount released during regeneration is too large, it is possible to prevent excess reductant from passing through the catalyst unused. In other words, when the catalyst cannot effectively utilize the reductant, regeneration is terminated, thereby improving overall emission control.
An advantage of the above aspect of the present invention is reduced emissions.
In another aspect of the invention, the method comprises: regenerating the particulate filter, determining an initial reductant amount based on operating conditions, generating and adjusted reductant amount by adjusting said initial reductant amount when regenerating the particulate filter, and discontinuing said regeneration when said adjusted reductant amount is less than a predetermined value.
By discontinuing regeneration when adjusted reductant amount is less than a predetermined value, it is possible to prevent excess reductant from passing through the catalyst unused.
An advantage of the above aspect of the present invention is reduced emissions.


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