Axial NOx Loading in Lean Burn Emission Control
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Solution Overview
Problem
Lean NOx traps face inefficiencies in NOx storage and purging due to uneven distribution of NOx along the axial length, exacerbated by uneven precious metal loading, leading to suboptimal emission control and thermal aging issues.
Innovation Solution
Implementing a method that estimates NOx storage along multiple axial positions of the emission control device and adjusts operating parameters to tailor reductant supply, using NOx traps with catalytic regions of varying metal concentrations to enhance storage and conversion capacities, and optimizing the distribution of catalytic metal to protect high-loaded zones from thermal aging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a lumped parameter model is used to control purging based on total NOx storage, then the control system is simple, but the NOx purging efficiency is reduced due to uneven NOx distribution along the axial length
Solution Approach 1:
The emission control device is divided into multiple axial zones (upstream, downstream, and intermediate regions) with different precious metal loadings. This segmentation allows each zone to be optimized for specific functions: upstream zones with higher loading for NOx storage, downstream zones with lower loading for purging efficiency, thereby resolving the contradiction between simple control and effective purging.
Solution Approach 2:
Different axial positions of the emission control device are assigned different precious metal loadings tailored to local requirements. The upstream portion has higher precious metal loading for NOx storage capacity, while downstream portions have lower loading to facilitate efficient purging and reduce thermal aging, thus improving overall purging efficiency without requiring complex control systems.
2Quantity of substance
If uneven precious metal loading is used in the emission control device, then NOx storage capacity is improved, but thermal aging resistance is reduced in high-loaded zones
Solution Approach 1:
The emission control device employs non-uniform precious metal loading where upstream zones have higher loading for maximum NOx storage capacity, while downstream zones have progressively lower loading. This local differentiation allows high-loaded zones to be protected from severe thermal aging by positioning them where temperature is lower, thus maintaining both high storage capacity and improved thermal durability.
Solution Approach 2:
The device is designed with pre-established precious metal loading gradients that anticipate thermal aging effects. By positioning higher-loaded zones upstream where they experience lower temperatures during operation, the design proactively protects these critical zones from thermal degradation before significant aging occurs, thereby extending device life and maintaining performance.
3Quantity of substance
If the emission control device is made larger to increase NOx storage capacity, then NOx storage capacity is improved, but device cost and complexity increase
Solution Approach 1:
Instead of uniformly increasing the entire device size, the invention optimizes local precious metal loading distribution. By concentrating higher loading in upstream zones where NOx storage is most critical and reducing loading in downstream zones, the device achieves maximum NOx storage capacity with a more compact overall structure, thereby reducing manufacturing cost and complexity while maintaining high storage capacity.
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 improves NOx purging efficiency and resistance to thermal aging, maintaining high NOx storage and conversion capacities while reducing costs associated with larger or more heavily loaded NOx traps.
Implementation Method 1
lean NOx traps may be used to stored NOx produced during lean exhaust air-fuel operating conditions
Implementation Method 2
catalytic converter that converts hydrocarbons, carbon monoxide and nitrogen oxides to carbon dioxide, water and nitrogen
Implementation Method 3
reacts to the stored oxidants during stoichiometric or rich operation
Data Source
AI summary
Disclosed is a method for controlling a lean burn engine coupled to an emission control device that stores oxidants during lean operation, and reacts the stored oxidants during stoichiometric or rich operation, the method comprising estimating amounts of NOx stored in the device along a plurality of axial positions of the device and adjusting an operating parameter based on said estimate.