Dual-Zone Catalyzed Substrate with Counterflow Urea Injection
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Solution Overview
Problem
Current exhaust gas treatment systems for internal combustion engines, while effective in reducing pollutants, can be improved to achieve further reductions in NOx emissions and efficiency.
Innovation Solution
A catalyzed substrate with a counterflow urea injector and a dual-zone configuration, featuring an oxidation catalyst zone and an SCR catalyst zone, where urea is injected counter to the exhaust flow to enhance NOx conversion by providing additional SCR catalyst volume and positioning it closer to the engine.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single-zone catalyst configuration is used, then the device complexity is reduced, but the NOx conversion efficiency is insufficient to meet stringent emission regulations
Solution Approach 1:
The catalyst substrate is divided into two distinct zones: an inlet zone containing oxidation catalyst and an outlet zone containing SCR catalyst. This segmentation allows each zone to perform its specific function optimally, with the oxidation zone converting CO and HC to CO2 and H2O, and the SCR zone reducing NOx to N2, thereby achieving high NOx conversion efficiency while maintaining manageable system complexity
Solution Approach 2:
Different catalytic materials are applied to different zones of the substrate based on local requirements. The inlet zone receives oxidation catalyst (Pt, Pd, or Rh) while the outlet zone receives SCR catalyst (Cu, Fe, or Zn on zeolite). This local quality approach ensures that each region has the appropriate catalyst for its specific chemical transformation task, maximizing overall NOx reduction performance
2Productivity
If SCR catalyst is positioned farther from the engine, then the oxidation of CO and HC is more complete, but the contact between urea and SCR catalyst is reduced, lowering NOx conversion
Solution Approach 1:
Instead of the conventional approach where urea is injected upstream and flows with the exhaust, this invention uses counterflow injection where urea is injected at the outlet end and flows opposite to the exhaust direction. This counterflow approach ensures that urea travels through the entire length of the substrate, maximizing contact with the SCR catalyst in the outlet zone and significantly improving NOx conversion efficiency
Solution Approach 2:
The substrate structure acts as an intermediary that facilitates interaction between the exhaust gas and counterflow-injected urea. The substrate's channel structure provides a controlled environment where urea and exhaust gases can mix and react efficiently, ensuring adequate contact between urea and the SCR catalyst despite the counterflow injection method
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 boosts NOx conversion efficiency by ensuring a higher percentage of urea contacts the SCR catalyst, leading to improved pollutant reduction and compliance with stringent emission regulations.
Implementation Method 1
an oxidation catalyst which comprises a platinum group metal (PGM) supported on a support and having a function to oxidise CO, hydrocarbons and NO to CO2, H2O and NO2 respectively
Implementation Method 2
an outlet zone extending from the outlet end, the outlet zone comprising a SCR catalyst
Data Source
AI summary
An exhaust system, and a catalyzed substrate, is disclosed. The system comprises a catalyzed substrate, a counterflow urea injector downstream of the catalyzed substrate, and a first selective catalytic reduction (SCR) catalyst downstream of the counterflow injector. The catalyzed substrate has an inlet end, an outlet end, an axial length extending from the inlet to the outlet, an inlet zone extending from the inlet, and an outlet zone extending from the outlet. The inlet zone comprises an oxidation catalyst and the outlet zone comprises a catalyst selected from the group consisting of a urea hydrolysis catalyst and a second SCR catalyst. The counterflow urea injector directs urea toward the outlet zone of the catalyzed substrate so that at least a portion of the urea contacts the outlet zone prior to contacting the first SCR catalyst.