Dual-Catalyst Exhaust System for NOx Purification
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Solution Overview
Problem
In diesel engines, the addition of multiple NOx trap catalysts or multilayered NOx trap catalysts increases exhaust pressure and complicates the structure, leading to performance deterioration and cost increases, while existing solutions for purifying NOx during lean combustion and cold starts are inefficient.
Innovation Solution
A dual-catalyst system is employed in the exhaust passage, where a high-temperature NOx adsorption catalyst with oxidation performance is followed by a low-temperature NOx adsorption catalyst, and a precious metal-based wall-flow filter is used downstream to efficiently purify NOx, HC, and CO with a simple structure, reducing catalyst complexity and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple NOx trap catalysts or multilayered NOx trap catalyst are added to purify NOx during cold start and lean combustion, then NOx purification performance is improved, but device complexity and exhaust pressure increase
Solution Approach 1:
The patent combines a high-temperature NOx adsorption catalyst with oxidation performance and a low-temperature NOx adsorption catalyst into a single integrated catalyst unit. The high-temperature catalyst layer performs oxidation of HC and CO while adsorbing NOx at elevated temperatures, and the low-temperature catalyst layer adsorbs NOx at lower temperatures, allowing both functions to coexist in one device without requiring multiple separate catalysts, thus improving NOx purification without increasing device complexity
Solution Approach 2:
The high-temperature NOx adsorption catalyst is designed to perform multiple functions: oxidizing hydrocarbons (HC), oxidizing carbon monoxide (CO), and adsorbing nitrogen oxides (NOx). This multi-functional catalyst replaces what would traditionally require separate oxidation catalysts and NOx trap catalysts, reducing the overall number of components needed while maintaining comprehensive purification performance
2Reliability
If multiple NOx trap catalysts or multilayered NOx trap catalyst are added to purify NOx during cold start and lean combustion, then NOx purification performance is improved, but exhaust pressure increases causing engine performance deterioration
Solution Approach 1:
By merging the high-temperature NOx adsorption catalyst with oxidation performance and the low-temperature NOx adsorption catalyst into one integrated unit, the patent reduces the total number of catalyst components in the exhaust system. This consolidation decreases exhaust flow resistance and backpressure compared to using multiple separate catalysts in series, thereby improving engine performance while maintaining effective NOx purification
3Reliability
If multiple NOx trap catalysts or multilayered NOx trap catalyst are added to purify NOx during cold start and lean combustion, then NOx purification performance is improved, but manufacturing cost increases
Solution Approach 1:
The patent integrates two catalyst functions (high-temperature NOx adsorption with oxidation and low-temperature NOx adsorption) into a single catalyst assembly, reducing the total number of parts that need to be manufactured, assembled, and installed. This consolidation lowers manufacturing complexity and associated costs compared to producing and installing multiple separate NOx trap catalysts, while still achieving comprehensive NOx purification across different temperature conditions
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 effectively purifies NOx, HC, and CO with reduced engine performance deterioration and catalyst costs by leveraging the temperature-dependent adsorption and oxidation capabilities of the catalysts, while minimizing exhaust pressure and optimizing precious metal usage.
Implementation Method 1
hydrocarbon (HC) and carbon monoxide (CO) exhausted from the internal combustion engine can be oxidized and purified by the high-temperature NOx adsorption catalyst having oxidation performance
Implementation Method 2
nitrogen oxides (NOx) can be adsorbed by the low-temperature NOx adsorption catalyst
Implementation Method 3
NOx emitted from the first catalyst on an upstream side of the second catalyst can be reliably reduced/purified by the precious metal of the second catalyst
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
In an exhaust pipe (5), an upstream-side catalyst (6) and a downstream-side catalyst (7) are provided in order from an upstream in an exhaust gas flow direction so as to communicate with each other. An open-flow honeycomb (6c) is provided in a casing (6a) of the upstream-side catalyst (6). In the open-flow honeycomb (6c), a NOx trap catalyst layer (6e) and a low-temperature NOx adsorption catalyst layer (6f) are formed in order from the upstream side in the exhaust gas flow direction. Moreover, in a casing (7a) of the downstream-side catalyst (7), a wall-flow filter (7c) is provided. Moreover, in the wall-flow filter (7c), a NOx reducing catalyst layer (7e) and a PM combustion catalyst layer (7f) are formed in order from the upstream side in the exhaust gas flow direction.