Compact SCR Monolith Upstream of Wall-Flow Filter
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Solution Overview
Problem
Existing exhaust systems for lean-burn combustion engines face challenges in efficiently reducing NOx and soot emissions while minimizing cost, weight, and backpressure, particularly due to limitations in catalyst loading and heat management.
Innovation Solution
A compact SCR flow-through monolith is positioned upstream of a close-coupled SCR wall-flow filter, creating a synergistic effect that enhances NOx conversion and soot combustion efficiency without the need for additional catalyst, thus reducing system cost and weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple separate exhaust gas treatment components are used, then NOx and particulate matter reduction capability is improved, but system cost, volume, and weight increase
Solution Approach 1:
The patent combines an SCR catalyst and a particulate filter into a single integrated component. The SCR catalyst is applied to the walls of the wall-flow filter substrate, merging two separate functions (NOx reduction and soot filtration) into one unified device, thereby reducing system weight and volume while maintaining pollutant reduction capability
Solution Approach 2:
The integrated component performs multiple functions simultaneously: the wall-flow filter structure provides soot filtration while the SCR catalyst coating provides NOx reduction. This multi-functional design eliminates the need for separate components, directly addressing the weight and cost penalties of using multiple separate treatments
2Reliability
If thick washcoat is applied to wall-flow filter, then catalyst loading and NOx conversion capability are improved, but channel narrowing and back pressure increase
Solution Approach 1:
The SCR catalyst is applied selectively to the walls of the wall-flow filter channels rather than uniformly throughout. This localized application provides sufficient catalyst loading for NOx conversion while preserving the open channel structure and avoiding excessive back pressure that would result from a thick uniform washcoat
3Reliability
If SCR catalyst is applied to wall-flow filter surface, then NOx reduction is improved, but system heating time increases due to increased mass
Solution Approach 1:
By applying catalyst locally to the channel walls rather than as a thick uniform layer, the system achieves adequate NOx reduction capability while minimizing the total mass that requires heating. This localized approach reduces thermal inertia and shortens the time to reach operating temperature
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 combined system achieves higher NOx conversion and soot combustion efficiency compared to conventional SCR systems, while maintaining high temperature stability for consistent filter regeneration and reducing fuel consumption.
Implementation Method 1
An SCR process involves the conversion of NOx, in the presence of a catalyst and a reducing agent, typically anhydrous ammonia, aqueous ammonia, or urea, into elemental nitrogen (N2) and water.
Implementation Method 2
The first method converts NOx in a diesel exhaust gas into more benign substances, also known as Selective Catalytic Reduction (SCR).
Implementation Method 3
To regenerate the filter, the accumulated carbon-based soot must be removed from the filter, for example by periodically combusting the soot by passive or active oxidation at high temperatures.
Implementation Method 4
the accumulated carbon-based soot must be removed from the filter, for example by periodically combusting the soot by passive or active oxidation at high temperatures.
Data Source
AI summary
A system for treating exhaust gases from a combustion engine and a method for using the same results in improved NOx conversion during engine startup. The system includes a compact SCR flow-through monolith installed upstream of a close-coupled SCR wall-flow filter, wherein the compact SCR flow-through monolith may be extruded or made of a thin-walled substrate, such that the SCR flow-through monolith has a smaller volume with lower heat capacity and higher catalyst loading relative to the SCR wall-flow filter.