SCR Dosing Strategy Switching for Ammonia Slip Control
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Solution Overview
Problem
Current methods for feeding ammonia in SCR systems for reducing nitrogen oxide emissions in internal combustion engines face challenges due to temperature dependency, aging, and measurement inaccuracies, leading to suboptimal utilization and increased wear on control systems.
Innovation Solution
A method involving a first dosing strategy that monitors storage catalytic converter loading and adjusts ammonia feed based on target conversion rates, switching to a second strategy if deviations exceed a threshold, disregarding storage capacity to ensure precise ammonia delivery and prevent slippage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a storage catalytic converter is used to store excess ammonia, then the maximum storage quantity can be utilized and metering system wear is reduced, but the storage is subject to temperature dependency, aging, and measurement inaccuracies that reduce utilization or make it impossible
Solution Approach 1:
The patent implements a dynamic switching mechanism between two dosing strategies. The control unit monitors boundary conditions (temperature, aging, measurement accuracy) and dynamically switches between storage-based dosing (first strategy) and direct injection dosing (second strategy). This dynamic adaptation allows the system to maintain reliable ammonia dosing regardless of storage converter conditions, resolving the contradiction between storage reliability and adaptability to varying conditions.
2Manufacturing precision
If stoichiometric metering of ammonia is achieved, then conversion rate is maximized and ammonia slip is minimized, but very high outlay in terms of control technology is required and dosing accuracy is unachievable
Solution Approach 1:
The patent segments the dosing control into two distinct strategies with different levels of complexity. The first strategy uses storage-based dosing with simplified control, while the second strategy uses direct injection with more precise control. The control unit selects the appropriate strategy based on boundary conditions, achieving high dosing precision when needed without always requiring complex control technology, thus resolving the contradiction between dosing precision and control complexity.
3Manufacturing precision
If the metering system operates very frequently to maintain precise ammonia delivery, then dosing accuracy is improved, but wear and energy consumption of the metering system increase
Solution Approach 1:
The storage catalytic converter performs preliminary ammonia storage, allowing the metering system to operate less frequently. The storage converter acts as a buffer that can supply ammonia during periods when the metering system is not actively dosing, thereby reducing wear and energy consumption while maintaining dosing accuracy through the complementary second dosing strategy when precise delivery is required.
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 achieves precise ammonia dosing, reducing nitrogen oxide emissions and minimizing wear on control systems by adapting to changing conditions and ensuring accurate ammonia delivery.
Implementation Method 1
an SCR catalytic converter for performing a selective catalytic reduction of nitrogen oxide compounds in the exhaust gas
Implementation Method 2
a storage catalytic converter for the storage of reducing agent
Data Source
AI summary
A method for feeding reducing agent to an exhaust gas mass flow in an exhaust gas treatment device provides a reducing agent feed port, a storage catalytic converter storing reducing agent and an SCR catalytic converter for selective catalytic reduction of nitrogen oxygen compounds in exhaust gas. A first dosing strategy is followed, loading of the storage catalytic converter with reducing agent is monitored and a first target conversion rate is determined based on current loading. Reducing agent is fed according to the first target conversion rate. A current conversion rate obtained with the SCR catalytic converter is determined. The current conversion rate is compared to the first target conversion rate and any deviation is registered. A further dosing strategy, not considering the loading of the storage catalytic converter, is used if the deviation exceeds a first threshold value. A motor vehicle and a stationary installation are also provided.