SCR Catalyst NH3 Preloading for Cold-Start NOx Control
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Solution Overview
Problem
The efficiency of selective catalytic reduction (SCR) catalysts in reducing NOx emissions is compromised when the amount of ammonia (NH3) stored within the catalyst is low, particularly during cold engine starts, leading to increased NOx emissions.
Innovation Solution
A vehicle operating method where urea is supplied to the SCR catalyst when the vehicle is in an off state and the SCR catalyst temperature is within a predetermined range, ensuring adequate NH3 storage for improved catalyst efficiency upon engine restart.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If urea is injected during engine operation to replenish NH3 storage, then NH3 storage is maintained during normal operation, but NH3 storage is insufficient during cold engine starts
Solution Approach 1:
The system performs preliminary action by injecting urea into the SCR catalyst during vehicle off-states (parking periods) to build up NH3 storage capacity before the engine is needed. This advance preparation ensures that adequate NH3 is available immediately upon engine restart, eliminating the delay that would otherwise occur during cold starts.
2Quantity of substance
If the vehicle remains off for extended periods, then NH3 storage can be built up, but the engine cannot operate to utilize the SCR system
Solution Approach 1:
The system utilizes vehicle off-states to perform preliminary urea injection and NH3 storage building. By injecting urea during parking periods when the engine is not running, the system prepares the SCR catalyst in advance, ensuring that NH3 storage is sufficient for immediate emission control upon engine restart without requiring extended idle operation.
3Productivity
If urea is injected at high temperatures, then urea decomposition is efficient, but NH3 storage capacity is reduced
Solution Approach 1:
The system changes the temperature parameter by selecting specific injection timing based on SCR catalyst temperature conditions. Urea is injected during vehicle off-states when the catalyst has cooled to moderate temperatures, optimizing the balance between urea decomposition efficiency and NH3 storage capacity. The controller monitors temperature and adjusts injection strategy accordingly.
4Quantity of substance
If the SCR catalyst temperature is too low, then NH3 storage is preserved, but urea decomposition is insufficient
Solution Approach 1:
The system optimizes the temperature parameter by timing urea injection to occur when the SCR catalyst temperature is within an optimal range during vehicle off-states. This ensures that the catalyst is warm enough to decompose urea effectively but not so hot that NH3 storage capacity is compromised, achieving the optimal balance between decomposition rate and storage retention.
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 enhances SCR catalyst efficiency during cold starts, adjusts NH3 storage to meet desired levels, and reduces the possibility of NH3 slip, thereby minimizing NOx emissions.
Implementation Method 1
supplying urea to a selective catalytic reduction (SCR) catalyst... The amount of NH3 that is stored within the SCR catalyst may be replenished by injecting urea upstream of the SCR catalyst
Implementation Method 2
The amount of NH3 that is stored within a washcoat of the SCR catalyst... the amount of NH3 that is stored in the SCR catalyst after a vehicle is in an off state may be increased
Implementation Method 3
A selective catalytic reduction (SCR) catalyst may be applied to reduce NOx emissions of a vehicle... SCR catalyst efficiency may be influenced by an amount of NH3 that is stored within a washcoat of the SCR catalyst
Data Source
AI summary
Methods and systems for improving NOx conversion efficiency of a selective catalytic reduction catalyst are described. In one example, an amount of NH3 stored in a SCR is adjusted after stopping an engine so that a desired amount of NH3 may be stored within the SCR when the engine is restarted.