Zoned Oxidation Catalyst for Lean-Burn Engine Emissions
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Solution Overview
Problem
Catalysts for oxidizing carbon monoxide (CO) and hydrocarbons (HC) in lean-burn engines typically require expensive platinum group metals (PGMs) and struggle to maintain efficient conversion throughout entire legislated emission test cycles, especially during temperature fluctuations.
Innovation Solution
A three-zone platinum group metal catalyst arrangement with varying PGM loadings and washcoat components along the substrate monolith, where the first zone has a higher PGM loading at the inlet, the second zone acts as a heat buffer, and the third zone maintains light-off during cool-down phases, using a higher thermal capacity washcoat to retain heat.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a standard uniform catalyst is used, then the structure is simple and manufacturing is easy, but the conversion efficiency drops during cool-down phases and total PGM usage is high
Solution Approach 1:
The catalyst substrate is divided into multiple zones along the flow direction, with each zone having different PGM loadings and washcoat thermal capacities. This segmentation allows the catalyst to maintain high conversion efficiency throughout the entire substrate length during both hot and cool phases of the emission test cycle.
Solution Approach 2:
Different zones of the catalyst substrate are assigned different local properties: upstream zones have higher PGM loadings and lower thermal capacity for rapid light-off, while downstream zones have lower PGM loadings and higher thermal capacity for heat retention during cool-down phases.
2Reliability
If high PGM loading is used throughout the catalyst, then conversion efficiency is maintained during cool-down phases, but total PGM usage and cost increase
Solution Approach 1:
PGM loading is optimized locally in each zone rather than uniformly throughout. Downstream zones that require heat retention during cool-down phases have higher thermal capacity washcoats and can operate with lower PGM loadings, while upstream zones have higher PGM loadings for rapid light-off, minimizing total PGM usage while maintaining reliability.
Solution Approach 2:
The washcoat thermal capacity parameter is varied along the substrate length to optimize performance. By increasing thermal capacity in downstream zones, the system maintains conversion efficiency during cool-down phases without requiring high PGM loadings throughout the entire catalyst.
3Quantity of substance
If low PGM loading is used throughout the catalyst, then PGM cost is reduced, but conversion efficiency drops during acceleration phases
Solution Approach 1:
The catalyst is segmented into zones with different PGM loadings matched to specific operating conditions. Upstream zones experience higher temperatures during acceleration and are designed with higher PGM loadings and lower thermal capacity for rapid light-off and high conversion efficiency, while downstream zones use lower PGM loadings appropriate for cooler operating conditions.
Solution Approach 2:
PGM loading is locally optimized for each zone's specific thermal and flow conditions. Upstream zones have higher PGM concentrations to handle the high-temperature, high-flow conditions during acceleration, reducing the need for high PGM loading throughout the entire catalyst.
4Speed
If the catalyst is designed for rapid light-off, then acceleration phase performance is improved, but heat retention during cool-down phases deteriorates
Solution Approach 1:
The catalyst substrate is segmented into zones with different thermal capacities. Upstream zones have lower thermal capacity washcoats that heat up quickly for rapid light-off during acceleration, while downstream zones have higher thermal capacity washcoats that retain heat during cool-down phases, resolving the contradiction between fast light-off and heat retention.
Solution Approach 2:
The thermal capacity of the washcoat is varied locally along the substrate length. Upstream zones use materials with lower thermal capacity for rapid heating, while downstream zones use materials with higher thermal capacity for heat retention, allowing both rapid light-off and good heat retention performance in different locations.
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 achieves better CO and HC conversion over legislated emission test cycles with reduced or even lower total PGM usage compared to standard catalysts, maintaining efficiency during both acceleration and deceleration phases.
Implementation Method 1
the first zone can rapidly reach its operating temperature at high exhaust gas temperatures
Implementation Method 2
the second zone stores heat for operating conditions involving a low exhaust gas temperature
Implementation Method 3
a catalyst for oxidising carbon monoxide (CO) and hydrocarbons (HC)
Data Source
AI summary
An exhaust system for a lean-burn internal combustion engine comprises a catalyst for oxidising carbon monoxide and hydrocarbons comprising a flow-through substrate monolith comprising a first platinum group metal (PGM) zone containing at least one PGM supported on a surface area-increasing washcoat component, a second PGM zone containing at least one PGM supported on a surface area-increasing washcoat component, a third PGM zone containing at least one PGM supported on a surface area-increasing washcoat component wherein both the PGM loading in the first PGM zone and the PGM loading in the third PGM zone is greater than the PGM loading in the second PGM zone and wherein the first PGM zone comprises a washcoat loading that is less than a washcoat loading of the third PGM zone.