Two-Stage Catalyst Regeneration for NOx Reduction
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Solution Overview
Problem
After a deceleration event in gasoline engines, the three-way catalytic converter becomes saturated with oxygen, leading to reduced NOx emission reduction due to lack of stored HC and CO, and prior methods of open loop rich operation either deplete oxygen too much or not enough, causing inefficiencies in subsequent feedback control.
Innovation Solution
Implementing a two-stage regeneration method where the engine operates open loop rich for a predetermined time after deceleration, followed by feedback control around a rich stoichiometric value for a preselected time, gradually returning to stoichiometry, ensuring proper oxygen balance in the catalyst.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the engine operates open loop rich of stoichiometry for a predetermined time after deceleration to deplete catalyst oxygen storage, then the catalyst oxygen storage is depleted, but the stored oxygen may be fully depleted causing inability to oxidize HC and CO during subsequent rich transients
Solution Approach 1:
The system performs a preliminary open-loop rich operation for a predetermined time after deceleration to partially deplete catalyst oxygen storage, but intentionally stops before complete depletion. This preliminary action prepares the catalyst for subsequent closed-loop control by creating optimal initial conditions without eliminating the oxygen buffer needed for emission oxidation during rich transients.
Solution Approach 2:
After the preliminary open-loop rich operation, the system transitions to closed-loop feedback control using the downstream oxygen sensor. The feedback controller adjusts the air/fuel ratio to maintain an average rich condition, continuously monitoring and adjusting based on sensor output to prevent both complete oxygen depletion and excessive oxygen storage that would cause NOx breakthrough.
2Quantity of substance
If the engine operates open loop rich of stoichiometry to deplete catalyst oxygen storage, then oxygen storage is reduced, but insufficient depletion leaves too much oxygen causing NOx breakthrough during lean transients
Solution Approach 1:
The predetermined open-loop rich operation serves as a preliminary action that partially depletes catalyst oxygen storage to an optimal level. This preliminary depletion is sufficient to prevent NOx breakthrough during subsequent lean transients but insufficient to deplete oxygen completely, thereby maintaining the ability to oxidize HC and CO during rich transients.
Solution Approach 2:
The system changes the air/fuel ratio parameter from stoichiometric to rich during the predetermined open-loop period, then transitions to feedback control that maintains an average rich condition. This parameter change strategy optimizes the catalyst oxygen storage level to simultaneously prevent NOx breakthrough and maintain oxidation capability.
3Reliability
If feedback control immediately resumes at stoichiometry after deceleration, then emission control is maintained, but the saturated catalyst cannot reduce NOx during lean transients
Solution Approach 1:
Instead of immediately resuming stoichiometric feedback control, the system performs a preliminary open-loop rich operation to modify catalyst oxygen storage levels. This preliminary action creates optimal conditions for subsequent feedback control by reducing excess oxygen that would otherwise prevent NOx reduction during lean transients.
Solution Approach 2:
The system dynamically adjusts the control strategy based on engine operating conditions. After deceleration, it temporarily operates in open-loop rich mode, then transitions to closed-loop feedback control that maintains an average rich condition rather than immediately returning to stoichiometric control. This dynamic adaptation allows the catalyst to properly reduce NOx while maintaining overall emission control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively oxidizes HC and CO and reduces NOx emissions by maintaining optimal oxygen storage in the catalyst, preventing breakthroughs and ensuring compliance with emission regulations.
Implementation Method 1
Gasoline engines are equipped with three-way catalytic converters to oxidize CO and HC engine emissions and reduce NOx emissions
Implementation Method 2
O2 also will be stored in ceria compounds in the catalyst
Implementation Method 3
HC and CO will reduce NOx in the exhaust stream over precious metal catalyst surfaces
Implementation Method 4
CO and HC emissions will be oxidized and NOx emissions reduced
Data Source
AI summary
A system and method are described for reducing NOx emissions following deceleration fuel shut off (DFSO). The method comprises: cutting off fuel to the engine during a deceleration event; open loop operating the engine air/fuel ratio rich of stoichiometry for a predetermined time after the deceleration event; feedback controlling the air/fuel ratio on average near a value rich of stoichiometry for a preselected time after said predetermined time; and feedback controlling the air/fuel ratio returning to stoichiometry after the preselected time.