SCR Catalyst Ammonia Dosage via Exhaust Pressure Control
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Solution Overview
Problem
Existing exhaust gas purification systems connected to internal combustion engines struggle to achieve optimal nitrogen oxide (NOx) reduction, particularly at varying operating conditions and high NOx concentrations, due to limitations in the use of selective catalytic reduction (SCR) catalysts.
Innovation Solution
The method involves adjusting the dosage rate of an ammonia-containing reducing agent upstream of the SCR catalyst based on absolute pressure, which is correlated with the pressure in the exhaust gas purification system, and optionally increasing the absolute pressure by actuating an exhaust gas retaining flap or altering the exhaust gas flow path, to enhance NOx conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the dosage rate of ammonia-containing reducing agent is increased to improve NOx conversion, then nitrogen oxide reduction efficiency is improved, but ammonia storage capacity and thermodynamic equilibrium of the SCR catalyst are not optimized under varying pressure conditions
Solution Approach 1:
The patent changes the parameter of absolute pressure in the exhaust gas purification system to optimize the SCR catalyst's performance. By controlling pressure as a variable parameter, the system adapts to different operating conditions and improves NOx conversion efficiency without simply increasing ammonia dosage rate.
Solution Approach 2:
The patent employs feedback control by continuously monitoring the absolute pressure and adjusting the ammonia-containing reducing agent dosage rate accordingly. This closed-loop approach ensures optimal NOx conversion while adapting to varying operating conditions and preventing ammonia slip.
2Productivity
If the absolute pressure in the exhaust gas purification system is increased to improve mass transfer and NOx conversion, then catalytic reaction efficiency is improved, but system complexity and control difficulty increase
Solution Approach 1:
The system uses the naturally varying absolute pressure in the exhaust gas purification system as a control parameter. Rather than adding complex active pressure control mechanisms, the invention leverages the existing pressure variations and their beneficial effect on mass transfer and catalytic reaction efficiency.
Solution Approach 2:
The patent utilizes absolute pressure as a controllable parameter that can be adjusted through simple means (such as exhaust gas flow path switching) to significantly improve the SCR catalyst's mass transfer and reaction efficiency without requiring complex pressure control systems.
3Reliability
If the dosage rate of reducing agent is set based on nominal levels to achieve target NOx conversion, then emission compliance is achieved, but performance degrades under high NOx concentrations and varying operating conditions
Solution Approach 1:
The patent introduces absolute pressure as an additional control parameter beyond the conventional ammonia dosage rate. By considering pressure variations, the system can maintain reliable emission compliance while adapting to high NOx concentrations and varying operating conditions that would otherwise degrade performance.
Solution Approach 2:
The system proactively adjusts the ammonia dosage rate based on predicted pressure conditions and operating parameters before suboptimal performance occurs. This preliminary adjustment ensures maintained NOx conversion efficiency even under challenging conditions like high NOx concentrations or transient operating states.
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 leads to improved NOx reduction capabilities, even at high NOx concentrations and challenging operating conditions, by optimizing the storage capacity and thermodynamic equilibrium of the SCR catalyst, thereby ensuring compliance with strict emission limits.
Implementation Method 1
selective catalytic reduction (SCR) catalyst for catalytic conversion of nitrogen oxides contained in the exhaust gas of an internal combustion engine with ammonia
Implementation Method 2
the absolute pressure in the exhaust gas purification system on the input side of the SCR catalyst is increased by increasing a flow resistance for exhaust gas flowing out of the SCR catalyst
Data Source
AI summary
A method for operating an exhaust gas purification system connected to an internal combustion engine of a motor vehicle is disclosed. The purification system includes an SCR catalyst for catalyzed reaction of nitrogen oxides contained in the exhaust gas of the internal combustion engine with ammonia. The method includes adding a reducing agent containing ammonia to the exhaust gas upstream of the SCR catalyst at a predeterminable dosage rate and determining a pressure value correlating with an absolute pressure in the exhaust gas purification system on the input side of the SCR catalyst. The dosage rate is specified at least as a function of the pressure value.