Crossflow PNA-SCR Catalyst Thermal Coupling
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Solution Overview
Problem
Current diesel engine exhaust aftertreatment systems face challenges in reducing NOx emissions at low temperatures due to thermal lag between the passive NOx adsorber (PNA) and selective catalytic reduction (SCR) catalyst, which delays the warm-up of the SCR catalyst and reduces NOx conversion efficiency.
Innovation Solution
Integrating the PNA and SCR catalysts into a single cross-flow substrate assembly with alternating flow directions, allowing for thermal coupling and faster heat transfer between the two components, thereby minimizing thermal lag and enhancing NOx conversion at lower temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the PNA and SCR catalysts are integrated into a single cross-flow substrate assembly with thermal coupling, then the warm-up speed of the SCR catalyst is improved and NOx conversion efficiency is enhanced, but the device complexity increases due to the integrated alternating layer structure
Solution Approach 1:
The patent merges the PNA and SCR catalysts into a single integrated substrate assembly with alternating layers. The PNA substrate and SCR substrate are positioned adjacent to each other within the same housing, allowing thermal coupling through their shared structure. This integration enables heat transfer from the PNA to the SCR catalyst, accelerating warm-up and improving cold-start NOx conversion efficiency while consolidating what would traditionally be separate components.
2Reliability
If conventional separate PNA and SCR catalyst systems are used, then the device complexity is lower, but thermal lag occurs between the PNA and SCR catalyst, reducing NOx conversion efficiency at low temperatures
Solution Approach 1:
The integrated substrate assembly acts as a thermal intermediary between the PNA and SCR catalyst. By positioning the PNA and SCR substrates adjacent to each other within the same housing structure, heat generated by the PNA during cold-start conditions is directly transferred to the SCR catalyst through the shared substrate material. This eliminates the thermal lag that would occur with separate systems, ensuring the SCR catalyst reaches operational temperature quickly for effective NOx conversion.
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 enables quicker warm-up of the SCR catalyst, improving NOx conversion efficiency during cold starts and low-load operations, and reduces NOx emissions to levels below 0.02 g/hp-hr, while maintaining consistent catalyst temperatures for optimal performance.
Implementation Method 1
The plurality of first substrate layers comprise a passive NOx adsorber washcoat
Implementation Method 2
The plurality of second substrate layers comprise a selective catalytic reduction washcoat
Implementation Method 3
The plurality of second substrate layers are thermally coupled with the plurality of first substrate layers
Data Source
AI summary
An exhaust aftertreatment system includes a cross-flow selective catalytic reduction catalyst. The cross-flow selective catalytic reduction catalyst includes a housing and a substrate assembly. The substrate assembly includes a plurality of first substrate layers defining a plurality of first flow channels and a plurality of second substrate layers defining a plurality of second flow channels. The exhaust aftertreatment system includes a passive NOx adsorber. The passive NOx adsorber includes a housing. The housing includes an inlet in exhaust gas receiving communication with the plurality of first flow channels of the cross-flow selective catalytic reduction catalyst. The housing includes an outlet in exhaust gas providing communication with the plurality of second flow channels of the cross-flow selective catalytic reduction catalyst. The passive NOx adsorber includes a substrate positioned in the housing. The substrate includes a passive NOx adsorber washcoat.