SCR Catalyst Segmentation for Uniform Reducing Agent Mixing
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Solution Overview
Problem
The existing exhaust purification systems face challenges in accurately controlling the injection of reducing agents in SCR catalysts due to non-uniform mixing of reducing agents with exhaust gas, leading to ammonia slip and reduced NOx purification efficiency, especially in vehicles with limited space for catalyst installation.
Innovation Solution
An exhaust purification system that calculates the amount of ammonia adsorbed in SCR catalysts by considering flow uniformity, allowing for precise control of reducing agent injection through a controller that divides the SCR catalyst into slices and cells, ensuring uniform flow and accurate injection based on ammonia adsorption and reaction rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the SCR catalyst is closely approached to the first catalyst to save space, then the installation space is reduced, but the reducing agent cannot be uniformly mixed with exhaust gas leading to ammonia slip
Solution Approach 1:
The SCR catalyst is divided into multiple slices along the exhaust gas flow direction, with each slice containing multiple cells. This segmentation allows the reducing agent to be injected and mixed in a staged manner, improving uniformity even in a compact space configuration.
Solution Approach 2:
Different regions of the SCR catalyst are designed with different characteristics - the front slices receive the injected reducing agent for mixing, while rear slices provide additional purification capacity. This local differentiation optimizes both space utilization and mixing uniformity.
2Reliability
If excess reducing agent is injected to ensure NOx purification, then the purification rate is improved, but ammonia slip increases
Solution Approach 1:
A rear NOx sensor monitors the exhaust gas after the SCR catalyst and provides feedback to the controller. The controller adjusts the reducing agent injection amount based on this feedback, ensuring optimal purification while preventing excessive ammonia injection that would cause slip.
Solution Approach 2:
Instead of injecting the full required reducing agent amount at one location, the system injects reducing agent partially at the front, allowing natural mixing and diffusion to distribute it through the catalyst slices, thereby achieving uniform distribution without excessive local concentration.
3Volume of moving object
If the distance between reducing agent injector and SCR catalyst is short to save space, then the installation space is reduced, but the reducing agent mixing uniformity deteriorates
Solution Approach 1:
The SCR catalyst is segmented into multiple slices along the flow direction, creating extended contact length within a compact volume. This allows sufficient mixing distance to be achieved while maintaining short overall catalyst-injector spacing.
Solution Approach 2:
The catalyst structure utilizes three-dimensional cell arrangements within each slice, creating multiple flow paths and increasing the effective mixing surface area without increasing the linear distance between injector and catalyst outlet.
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 approach reduces ammonia slip and improves NOx purification efficiency by ensuring the right amount of reducing agent is injected, optimizing the performance of the SCR catalysts and enhancing space efficiency in vehicle installations.
Implementation Method 1
nitrogen oxide included in the exhaust gas may be reduced through oxidation-reduction reaction with the reducing agent in the DeNOx catalyst
Implementation Method 2
when an engine is operated in an atmosphere having a lean air-fuel ratio, the LNT may adsorb the nitrogen oxide included in the exhaust gas
Implementation Method 3
when the engine is operated in an atmosphere having a rich air-fuel ratio, the LNT may desorb the adsorbed nitrogen oxide
Data Source
AI summary
Provided is an exhaust purification system that may include: a first catalyst installed on a rear exhaust pipe of an engine; a selective catalytic reduction (SCR) catalyst installed on the rear exhaust pipe of the first catalyst; a reducing agent injector which is installed on an exhaust pipe between the first catalyst and the SCR catalyst and configured to inject a reducing agent; and a controller configured to control an amount of reducing agent injected from the reducing agent injector. /The controller may calculate a total amount of ammonia adsorbed in the SCR catalyst, a required amount of reducing agent based on a total amount of ammonia adsorbed in the SCR catalyst, and the amount of nitrogen oxide introduced into the SCR catalyst, and then control a reducing agent injector to inject the required amount of reducing agent.