Nested SCR and CUC Catalyst Housing for Lean-Burn Engine Thermal Management
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Solution Overview
Problem
In lean-burn engines, the temperature of the selective catalytic reduction (SCR) catalyst needs to be maintained between 250 to 400°C for optimal performance, while the clean-up catalyst (CUC) requires a higher temperature, posing challenges in positioning and heat management due to the production of carbon dioxide interrupting the NH3-NOx purifying reaction and the need for a clean-up catalyst to be positioned behind the SCR catalyst.
Innovation Solution
A lean-burn engine after-treatment system with a multiple catalyst bed configuration, including an SCR catalyst housing surrounded by a CUC housing, and a double pipe system with perforations and heat-insulating materials to manage exhaust gas flow and heat transfer, allowing the SCR catalyst temperature to be maintained between 250 to 400°C and the CUC temperature to be higher than 250°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the CUC is positioned behind the SCR catalyst to purify CO, then the CO purification performance is improved, but the SCR catalyst temperature becomes difficult to maintain at 250-400°C due to heat loss
Solution Approach 1:
The patent implements a nested catalyst bed structure where the SCR catalyst housing is positioned inside the CUC housing. This allows the SCR catalyst to be surrounded by the CUC housing which captures and retains heat, thereby maintaining the SCR catalyst temperature at 250-400°C while the CUC remains positioned behind the SCR catalyst for effective CO purification.
Solution Approach 2:
The patent introduces a heat-insulating material as an intermediary layer between the catalyst housings and the external environment. This heat-insulating material acts as a thermal barrier that reduces heat loss from the SCR catalyst and CUC, maintaining optimal operating temperatures for both catalysts while allowing them to be positioned in the required sequence.
2Temperature
If the SCR catalyst is positioned at the front of the vehicle to ensure adequate temperature, then the SCR catalyst temperature is maintained, but the system complexity and space requirements increase
Solution Approach 1:
The nested configuration allows the SCR catalyst housing to be placed inside the CUC housing, creating a compact integrated structure. This reduces the overall space requirement and simplifies the system layout compared to having separate housings positioned far apart, while still maintaining the SCR catalyst at adequate temperature through the heat-retaining effect of the surrounding CUC housing.
Solution Approach 2:
The patent merges the SCR catalyst housing and CUC housing into a single integrated assembly where the SCR housing is positioned inside the CUC housing. This combination reduces the number of separate components and simplifies installation and packaging, while the thermal interaction between the two housings helps maintain SCR catalyst temperature.
3Reliability
If multiple catalyst housings are arranged in sequence, then the purification function is improved, but the heat loss increases making temperature control difficult
Solution Approach 1:
By nesting the SCR catalyst housing inside the CUC housing, the patent creates a configuration where the outer CUC housing acts as a thermal envelope for the inner SCR housing. This reduces the surface area exposed to the external environment and minimizes heat loss from both catalysts, while still maintaining the sequential purification function for both NOx and CO.
Solution Approach 2:
The heat-insulating material serves as an intermediary thermal barrier that reduces heat loss from the catalyst housings to the surrounding environment. This allows the system to maintain higher operating temperatures with reduced energy loss, improving thermal efficiency while preserving the sequential purification function of multiple catalysts.
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 optimizes the temperature range for both SCR and CUC catalysts, enhancing the purification performance and reducing heat loss, allowing the SCR catalyst to be positioned closer to the rear of the vehicle, thus improving fuel efficiency and engine performance.
Implementation Method 1
heat-insulating materials to manage exhaust gas flow and heat transfer
Implementation Method 2
a double pipe including a first pipe that is connected to a front end of the APC housing and a rear end of a three-way catalyst (TWC) housing and a second pipe that surrounds the first pipe and is connected to the first housing; At least one perforation may be formed in each of inner and outer surfaces of the first pipe, the APC housing, and the SCR catalyst housing
Implementation Method 3
a selective catalytic reduction (SCR) catalyst housing that surrounds the APC housing
Implementation Method 4
a clean-up catalyst (CUC) that purifies CO using low-temperature oxygen storage capacity (OSC)
Data Source
AI summary
A lean-burn engine after-treatment system includes: a multiple catalyst bed including an APC catalyst housing, an SCR catalyst housing that surrounds the APC catalyst housing, and a CUC housing that surrounds the SCR catalyst housing; a first housing surrounding the multiple catalyst bed; a double pipe including a first pipe that is connected to a front end of the APC catalyst housing and a rear end of a TWC housing, and a second pipe that surrounds the first pipe and is connected to the first housing; and an exhaust-gas treatment unit connected to a rear end of the CUC housing. At least one perforation is formed in each of inner and outer surfaces of the first pipe, the APC catalyst housing, and the SCR catalyst housing, and an inner surface of the CUC housing.