SCR Catalyst Cold-Start Dosing With Stored Water Compensation
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Solution Overview
Problem
Existing methods for exhaust gas aftertreatment, particularly following a cold start of an internal combustion engine, are inefficient in nitrogen oxide reduction due to condensation of water in the exhaust system, leading to suboptimal operation of SCR catalytic converters.
Innovation Solution
A method that determines the preoperational state of the SCR catalytic converter before a cold start, adsorbs condensed water, heats it to evaporate and facilitate exothermic reactions, and adjusts the amount of reducing agent based on actual and target amounts to optimize nitrogen oxide conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If water condenses in the exhaust system during cold start, then water is removed from exhaust gas, but nitrogen oxide reduction efficiency deteriorates due to suboptimal SCR converter operation
Solution Approach 1:
The patent determines the preoperational state of the SCR catalytic converter before cold start (including pre-existing water and NOx amounts) and uses this information to adjust reducing agent metering during subsequent operation. This preliminary assessment allows the system to compensate for the detrimental effects of cold-start condensation on SCR efficiency.
Solution Approach 2:
The system continuously monitors the actual amount of reducing agent adsorbed on the catalyst surface and compares it with a target amount. Based on this feedback loop, the metering device adjusts the reducing agent injection rate to optimize nitrogen oxide conversion efficiency even during cold start conditions when water condensation occurs.
2Productivity
If reducing agent is added to exhaust gas for nitrogen oxide reduction, then nitrogen oxide conversion is enhanced, but reducing agent consumption increases leading to potential waste
Solution Approach 1:
The system determines the actual amount of reducing agent adsorbed on the SCR catalyst surface and compares it with a target amount. The metering device adjusts reducing agent injection based on this feedback, preventing both deficiency (which would reduce conversion efficiency) and excess (which would waste reducing agent).
Solution Approach 2:
The patent dynamically adjusts the reducing agent metering rate based on changing operating conditions including exhaust gas temperature, flow rate, and the determined preoperational state of the catalyst. This parameter adaptation ensures optimal reducing agent utilization across different operating conditions.
3Productivity
If the SCR catalytic converter operates during cold start, then nitrogen oxide reduction is attempted, but performance is suboptimal due to low temperature conditions
Solution Approach 1:
The system determines the preoperational state of the SCR catalytic converter including its temperature and existing water/nitrogen oxide amounts before cold start. This information is used to predict and compensate for the temporary performance degradation during cold start conditions.
Solution Approach 2:
The system continuously monitors converter performance and adjusting reducing agent metering to maintain optimal nitrogen oxide conversion efficiency despite temperature fluctuations during cold start and warm-up periods.
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
Improves exhaust gas aftertreatment by accurately metering reducing agent, delaying exothermic reactions, and enhancing nitrogen oxide trapping, resulting in a more efficient and low-emission operation of the internal combustion engine.
Implementation Method 1
the exhaust gas guide tube (22) is heated, whereby the water condensed out of the exhaust gas evaporates upstream of the first SCR catalytic converter (30)
Implementation Method 2
there is an at least partial reduction of nitrogen oxide constituents stored on the first catalyst surface as a consequence of the catalyst surface being heated by an exothermic reaction of the water on the catalyst surface
Implementation Method 3
nitrogen oxides are adsorbed by the first SCR catalytic converter while water is condensed out of the exhaust gas
Data Source
AI summary
A method for operating an exhaust system includes supplying exhaust gas to a first SCR catalytic converter. The method relates to a cold start, wherein a prior operating state of the first SCR catalytic converter existing prior to the cold start ascertained by a computer is considered. Aside from a water quantity that was adsorbed on the first SCR catalytic converter prior to the cold start, a reducing agent quantity that was adsorbed on the first SCR catalytic converter prior to the cold start, which quantity is assigned to the prior operating state is also taken into consideration to determine an actual reducing agent quantity on the first SCR catalytic converter. A compensation reducing agent quantity is metered as required and characterizes a differential value between a setpoint quantity and the actual reducing agent quantity, and being admixed to the exhaust gas upstream of the first SCR catalytic converter.