Segmented Catalytic Article with Gradient Oxygen Storage
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Solution Overview
Problem
Maintaining the composition of exhaust gas within a three-way catalyst (TWC) at a stoichiometric balance is challenging due to time lags in adjusting the air-to-fuel ratio, leading to inefficient NOx reduction, CO oxidation, and HC treatment, especially when the engine operates under transient conditions.
Innovation Solution
A close-coupled catalytic article comprising an upstream and downstream substrate with different TWC compositions, where the downstream substrate has a higher oxygen storage component (OSC) loading than the upstream substrate, allowing for effective oxygen absorption and release to maintain stoichiometric balance despite air-to-fuel ratio oscillations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single TWC substrate is used, then the device complexity is reduced, but the ability to maintain stoichiometric balance during transient conditions deteriorates
Solution Approach 1:
The catalytic article is divided into two distinct substrates: an upstream substrate with lower OSC loading (0.5-2.0 g/in³) and a downstream substrate with higher OSC loading (2.0-4.0 g/in³). This segmentation allows each substrate to perform specialized functions - the upstream substrate handles initial catalysis while the downstream substrate provides oxygen buffering during transient conditions, thereby maintaining stoichiometric balance without excessive complexity.
Solution Approach 2:
Different regions of the catalytic article are assigned different OSC loadings tailored to their specific functional requirements. The upstream substrate uses lower OSC loading to minimize oxygen storage demands during steady-state operation, while the downstream substrate uses higher OSC loading to provide oxygen buffering capacity during transient rich conditions, optimizing performance locally in each region.
2Reliability
If the OSC loading is increased to maintain stoichiometric balance during transient conditions, then the exhaust gas treatment efficiency improves, but the cost of the catalytic article increases
Solution Approach 1:
The total OSC quantity is segmented between two substrates with different loading levels. The downstream substrate contains the majority of OSC (2.0-4.0 g/in³) to handle transient conditions, while the upstream substrate contains minimal OSC (0.5-2.0 g/in³) for steady-state operation. This segmentation achieves reliable stoichiometric balance during transients while optimizing the total quantity of OSC used.
Solution Approach 2:
The OSC loading parameter is varied spatially across the catalytic article, with the upstream substrate using lower loading (0.5-2.0 g/in³) and the downstream substrate using higher loading (2.0-4.0 g/in³). This parameter change optimizes the balance between reliability during transient conditions and the total quantity of OSC required, reducing overall cost while maintaining performance.
3Quantity of substance
If the upstream substrate has high OSC loading, then oxygen storage capacity is improved, but the operating temperature increases reducing catalyst durability
Solution Approach 1:
The oxygen storage function is segmented between two substrates. The upstream substrate uses low OSC loading (0.5-2.0 g/in³) to minimize oxygen storage demands and keep operating temperature low, preserving catalyst durability. The downstream substrate uses high OSC loading (2.0-4.0 g/in³) to provide the necessary oxygen storage capacity during transient conditions, thus resolving the temperature-capacity trade-off through functional segmentation.
Solution Approach 2:
The OSC loading is optimized locally for each substrate's operational context. The upstream substrate operates in a region where low OSC loading (0.5-2.0 g/in³) suffices for steady-state catalysis, maintaining lower temperatures and higher durability. The downstream substrate operates in a region requiring high oxygen storage (2.0-4.0 g/in³) to buffer transient rich conditions, providing the necessary capacity where it is most needed.
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 configuration reduces hydrocarbon, NOx, and CO emissions by over 25% by enabling efficient treatment of exhaust gases, even with time lags in air-to-fuel ratio adjustments, by ensuring sufficient oxygen storage to absorb or release oxygen as needed.
Implementation Method 1
the downstream substrate has a higher oxygen storage component (OSC) loading than the upstream substrate, allowing for effective oxygen absorption and release to maintain stoichiometric balance despite air-to-fuel ratio oscillations
Implementation Method 2
Three-way catalysts (TWCs) are intended to catalyse three simultaneous reactions: (i) oxidation of carbon monoxide to carbon dioxide
Implementation Method 3
oxidation of carbon monoxide to carbon dioxide
Implementation Method 4
Three-way catalysts (TWCs) are intended to catalyse three simultaneous reactions: (ii) oxidation of unburned hydrocarbons to carbon dioxide and water
Implementation Method 5
oxidation of unburned hydrocarbons to carbon dioxide and water
Implementation Method 6
Three-way catalysts (TWCs) are intended to catalyse three simultaneous reactions: (iii) reduction of nitrogen oxides to nitrogen and oxygen
Implementation Method 7
reduction of nitrogen oxides to nitrogen and oxygen
Data Source
AI summary
A close-coupled catalytic article, and its use in an exhaust system for internal combustion engines, is disclosed. The close-coupled catalytic article for the treatment of an exhaust gas comprising: an upstream substrate and a downstream substrate, wherein the upstream substrate is spaced apart from the downstream substrate, wherein the upstream substrate comprises a first three-way catalyst (TWC) composition and the downstream substrate comprises a second TWC composition, the first and second TWC compositions each comprising an oxygen storage component (OSC), wherein a loading of the OSC in the downstream substrate is greater than a loading of the OSC in the upstream substrate and is at least 2.2 g/in3.