Lean NOx Trap with Zinc-Loaded Wall Flow Filter
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Solution Overview
Problem
Current exhaust systems for internal combustion engines face challenges in reducing NOx, H2S, particulate, CO, and hydrocarbon emissions while maintaining effective catalytic performance and filtration, especially under stringent regulatory standards.
Innovation Solution
An exhaust system incorporating a lean NOx trap with a wall flow monolithic substrate having a pre-coated porosity of 40% or greater, featuring an oxidation catalytic zone with platinum group metals loaded on a support containing zinc compounds and alkaline earth metal oxides, which enhances H2S reduction without compromising CO and hydrocarbon oxidation performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a lean NOx trap is used to reduce NOx emissions, then NOx conversion efficiency is improved, but hydrogen sulfide (H2S) emissions increase due to non-selective reduction pathways
Solution Approach 1:
The patent converts the harmful H2S produced by non-selective reduction in the lean NOx trap into a beneficial byproduct. By positioning a wall-flow filter downstream, the H2S that would otherwise be emitted is captured and converted into elemental sulfur through catalytic oxidation, transforming a harmful emission into a useful sulfur product that can be removed from the system.
Solution Approach 2:
The wall-flow filter acts as an intermediary component between the lean NOx trap and the exhaust system. It captures H2S from the exhaust stream and facilitates its conversion to elemental sulfur through catalytic oxidation on the filter walls, preventing H2S emission while maintaining the NOx reduction function of the upstream trap.
2Object-affected harmful factors
If catalytic materials are added to reduce multiple pollutants, then emission reduction performance is improved, but back pressure increases
Solution Approach 1:
The wall-flow filter is designed to perform multiple functions simultaneously: it filters particulate matter through physical trapping in the wall-flow structure, oxidizes H2S to elemental sulfur on the catalytic coating, and provides a substrate for sulfur storage. This multi-functionality eliminates the need for separate devices, reducing overall system back pressure while achieving comprehensive emission control.
Solution Approach 2:
The patent merges the functions of particulate filtration, H2S oxidation, and sulfur storage into a single wall-flow filter component. By combining these functions in one device rather than using separate components, the system reduces cumulative back pressure while achieving multiple emission reduction goals simultaneously.
3Reliability
If sulfur is stored in the NOx trap during standard operation, then NOx conversion is maintained, but trap performance deteriorates and requires high temperature regeneration
Solution Approach 1:
The patent extracts sulfur from the NOx trap by capturing H2S in the wall-flow filter downstream. This prevents sulfur accumulation in the NOx trap, maintaining its performance without requiring high-temperature regeneration. The sulfur is removed from the system through oxidation to elemental sulfur in the wall-flow filter, eliminating the need for thermal desorption.
4Productivity
If high porosity substrate is used to maintain flow, then exhaust gas flow is improved, but catalytic activity decreases
Solution Approach 1:
The wall-flow filter utilizes a porous substrate structure with controlled porosity (30-70%) that balances exhaust gas flow and catalytic activity. The porous walls provide sufficient surface area for catalytic oxidation of H2S while maintaining adequate permeability for exhaust gas flow. The catalytic materials are deposited on the porous walls, creating a high surface-area-to-volume ratio that enhances catalytic activity without blocking flow paths.
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
The system effectively reduces NOx, H2S, particulate, CO, and hydrocarbon emissions while maintaining efficient oxidation catalytic activity and filtration, even under challenging drive cycles, without increasing back pressure.
Implementation Method 1
an exhaust system for an internal combustion engine, the exhaust system comprising a lean NOx trap and a wall flow monolithic substrate having a pre-coated porosity of 40% or greater and comprising an oxidation catalytic zone
Implementation Method 2
the oxidation catalytic zone comprising a platinum group metal loaded on a first support
Implementation Method 3
the first support comprising at least one inorganic oxide and a zinc compound, wherein the first support comprises at least one alkaline earth metal compound at a loading in the range of 3.18 to 7.06 g/L
Data Source
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AI summary
An exhaust system for an internal combustion engine, the exhaust system comprising, a lean NOx trap, and a wall flow monolithic substrate having a pre-coated porosity of 40% or greater, and comprising an oxidation catalytic zone, the oxidation catalytic zone comprising a platinum group metal loaded on a first support, the first support comprising at least one inorganic oxide and a zinc compound.