SCR Catalyst Cold-Start Dosing with Water Adsorption Compensation
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Solution Overview
Problem
Existing exhaust aftertreatment systems for internal combustion engines, particularly during cold starts, face inefficiencies due to water condensation in the exhaust system, which affects the adsorption and conversion of nitrogen oxides by SCR catalysts, leading to suboptimal emissions control.
Innovation Solution
A method involving pre-cold start assessment of SCR catalyst conditions, including water condensation and adsorption, followed by controlled addition of compensatory reducing agents based on catalyst state and water evaporation, to optimize nitrogen oxide reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If water condensation is allowed to occur in the exhaust system during cold start, then the SCR catalyst can store reducing agent, but nitrogen oxide conversion efficiency deteriorates due to water adsorption on catalyst surface
Solution Approach 1:
The system determines the pre-operating state of the SCR catalyst before cold start, including pre-existing water and reducing agent amounts, and uses this information to plan compensatory reducing agent addition during the cold start phase, ensuring optimal nitrogen oxide conversion despite water condensation
Solution Approach 2:
The control strategy dynamically adjusts reducing agent dosing based on changing parameters during cold start, including exhaust gas temperature, water condensation/evaporation rates, and catalyst surface conditions, to maintain optimal conversion efficiency throughout the transient phase
2Productivity
If compensatory reducing agent is added during cold start, then nitrogen oxide conversion efficiency improves, but reducing agent consumption increases
Solution Approach 1:
The system continuously monitors actual nitrogen oxide conversion during cold start and compares it with target values, then adjusts compensatory reducing agent dosing accordingly, adding reducing agent only when and where needed to correct conversion deficiencies rather than applying fixed dosing
Solution Approach 2:
The control strategy applies partial compensatory reducing agent dosing only during specific cold start phases where conversion efficiency falls below target, rather than continuous full dosing, thereby reducing overall reducing agent consumption while maintaining adequate conversion performance
3Productivity
If water evaporation is accelerated to clear catalyst surface, then nitrogen oxide conversion improves, but energy consumption increases
Solution Approach 1:
The system leverages the natural heat from exhaust gas flow and the exothermic oxidation reactions occurring on the catalyst surface to drive water evaporation, rather than applying external heating energy, allowing the catalyst system to self-clear water accumulation using its own operational heat
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
Enhances exhaust gas treatment efficiency by accurately determining and adjusting reducing agent dosage, reducing emissions and improving catalyst performance during cold starts.
Implementation Method 1
Water condenses from the exhaust gas in the exhaust gas duct of the exhaust system which is located upstream of the first SCR catalyst
Implementation Method 2
The exhaust gas pipe is heated, causing the water condensed from the exhaust gas to evaporate upstream of the first SCR catalyst
Implementation Method 3
This water is then at least partially carried with the exhaust gas to the first SCR catalyst and adsorbed onto a first catalyst surface of the first SCR catalyst
Implementation Method 4
Exhaust gas is applied to the first SCR catalyst, causing nitrogen oxides to be adsorbed by the first SCR catalyst
Implementation Method 5
at least a partial reduction of nitrogen oxide components stored on the first catalyst surface occurs as a result of heating of the first catalyst surface caused by an exothermic reaction of water on the catalyst surface
Data Source
Figure 1
Figure 2
Figure 3a~3f
AI summary
The invention relates to a method for operating an exhaust system (20) for an internal combustion engine (10) of a motor vehicle (K), into which exhaust system exhaust gas (14) that is emitted by the internal combustion engine (10) is admitted. In the method, the exhaust gas (14) is supplied to at least one first SCR catalytic converter (30) in the exhaust system (20). The method relates to a cold start of the internal combustion engine (10), wherein at least one prior operating state at least of the first SCR catalytic converter (30), which existed at a time prior to the cold start and is ascertained by means of a computing device (12), is taken into consideration in the method. Aside from a water quantity that was adsorbed on the first SCR catalytic converter (30) prior to the cold start, a reducing agent quantity that was adsorbed on the first SCR catalytic converter (30) prior to the cold start, which quantity is assigned to the prior operating state and is also referred to as a prior reducing agent quantity, is also taken into consideration in order to determine an actual reducing agent quantity on the first SCR catalytic converter (30). A compensation reducing agent quantity can thus be metered as required, said compensation reducing agent quantity characterizing a differential value between a setpoint reducing agent quantity and the actual reducing agent quantity and being admixed to the exhaust gas (14) upstream of the first SCR catalytic converter (30). Further aspects of the invention relate to an internal combustion engine (10) having an exhaust system (20) and to a motor vehicle (K) having an internal combustion engine (10).