SCR Dosing Control via Lowest Conversion Rate Selection
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Solution Overview
Problem
Existing exhaust gas treatment systems face challenges in precisely adding ammonia stoichiometrically to mobile internal combustion engines, leading to reducing agent slip and inefficient nitrogen oxide conversion due to dynamic changes in power output, temperature, and other factors, which can result in environmental odor issues and increased consumption.
Innovation Solution
A method involving the calculation of conversion rate specifications based on engine power output, nitrogen oxide mass flow, and SCR catalytic converter performance, with the selection of the lowest conversion rate to prevent reducing agent slip, and precise dosing of ammonia or its precursor, such as urea, to ensure efficient nitrogen oxide conversion without excess ammonia release.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a reducing agent is added to convert nitrogen oxide compounds in exhaust gas, then nitrogen oxide conversion efficiency is improved, but reducing agent slip occurs causing odor nuisance and increased consumption
Solution Approach 1:
The patent implements a feedback control system that continuously monitors nitrogen oxide concentration downstream of the SCR catalytic converter and adjusts the reducing agent dosing amount accordingly. The control unit calculates the required dosing amount based on the measured nitrogen oxide concentration and converts this into a corresponding dosing signal, creating a closed-loop control that prevents reducing agent slip while maintaining high conversion efficiency.
Solution Approach 2:
The patent dynamically adjusts the dosing amount parameter of the reducing agent based on changing operating conditions. The control system modifies the dosing amount in real-time according to the measured nitrogen oxide concentration, engine power output, and temperature conditions, ensuring optimal conversion efficiency without excess reducing agent that would cause slip.
2Reliability
If ammonia dosing is increased to ensure complete nitrogen oxide conversion, then exhaust gas standards are met, but reducing agent consumption increases and slip occurs
Solution Approach 1:
The downstream nitrogen oxide sensor provides feedback on the actual conversion performance, allowing the control unit to precisely adjust the reducing agent dosing amount. This feedback mechanism ensures that exactly the required amount of reducing agent is dosed to meet exhaust gas standards, preventing both under-dosing (non-compliance) and over-dosing (increased consumption and slip).
Solution Approach 2:
The patent applies partial action by dosing only the minimum required amount of reducing agent needed to achieve complete nitrogen oxide conversion. Rather than dosing in excess to ensure compliance, the feedback-controlled system calculates and applies precisely the stoichiometric amount needed, eliminating waste while maintaining reliability.
3Loss of substance
If reducing agent dosing is decreased to avoid reducing agent slip, then consumption is reduced, but nitrogen oxide conversion becomes incomplete and exhaust gas standards are not met
Solution Approach 1:
The downstream nitrogen oxide sensor provides critical feedback that prevents under-dosing. By continuously monitoring nitrogen oxide concentration after the SCR converter, the system ensures that sufficient reducing agent has been dosed to achieve complete conversion. If conversion is incomplete, the feedback signal triggers increased dosing, thereby maintaining reliability while optimizing consumption.
Solution Approach 2:
The feedback control system enables the exhaust gas treatment device to self-regulate the reducing agent dosing amount. The system automatically adjusts dosing based on actual conversion performance, eliminating the need for conservative over-dosing strategies and achieving both reduced consumption and maintained conversion completeness through intelligent self-control.
4Measurement precision
If multiple conversion rate specifications are calculated based on different parameters, then dosing precision is improved, but system complexity increases
Solution Approach 1:
The patent segments the dosing control into multiple independent calculation paths, each based on different parameters (engine power output, nitrogen oxide mass flow, nitrogen oxide quantity ratio). Each segment calculates a conversion rate specification independently, and the control unit selects the lowest value. This segmentation allows comprehensive consideration of multiple factors while maintaining manageable system complexity through modular calculation structures.
Solution Approach 2:
The patent applies partial action by calculating multiple conversion rate specifications but only implementing the lowest one for actual dosing control. Rather than combining all calculation results or implementing all control paths simultaneously, the system selectively uses the most conservative (lowest) specification, achieving high dosing precision through selective application while avoiding the full complexity of integrating all calculation methods.
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 effectively prevents reducing agent slip, ensures efficient nitrogen oxide conversion, and allows for precise control of ammonia dosage, meeting exhaust gas standards while minimizing ammonia consumption and environmental impact.
Implementation Method 1
a reducing agent containing ammonia or a reducing agent precursor that can be converted into ammonia is added to the exhaust gas and the nitrogen oxide compounds are converted into nitrogen and water in an SCR catalytic converter
Implementation Method 2
The aqueous urea solution is converted thermally in the exhaust gas and/or hydrolytically in a hydrolysis catalytic converter to form ammonia
Implementation Method 3
an oxidation catalytic converter (blocking catalytic converter) arranged downstream of the SCR catalytic converter
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a method for adding a reducing agent to an exhaust gas treatment device which comprises a feed port and an SCR catalytic converter for converting nitrogen oxide compounds in the exhaust gas, said method comprising at least the following steps: a) calculating following set conversion rates that indicate which portion of the nitrogen oxide compounds present in the exhaust gas can be converted by the SCR catalytic converter: a.1) a first set conversion rate that is determined from the power output of a connected internal combustion engine; a.2) a second set conversion rate that is determined from the mass flow of nitrogen oxide compounds in the purified exhaust gas; and a.3) a third set conversion rate that is determined from a ratio of a quantity of nitrogen oxide compounds upstream of the SCR catalytic converter and a quantity of nitrogen oxide compounds downstream of the SCR catalytic converter; b) selecting the lowest set conversion rate; c) determining the dosing quantity of reducing agent for the selected set conversion rate; and d) dosing the determined dosing quantity into the exhaust gas treatment device.