Ammonia Storage Management for SCR Catalysts
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Solution Overview
Problem
Existing emission control systems for diesel engines face challenges in managing ammonia storage in SCR catalysts, leading to sub-optimal NOx conversion efficiency due to insufficient ammonia storage during vehicle-off to vehicle-on transitions and thermal events, such as DPF regeneration, which results in increased NOx emissions.
Innovation Solution
A method is implemented where ammonia is injected during a final exhaust blowdown after a vehicle-off event to reach a predetermined storage level, and additional ammonia is injected upon a vehicle-on event if the stored amount is below the target, with further injections following thermal events to maintain optimal NOx conversion efficiency by adjusting the injection rate based on temperature and storage depletion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If closed loop storage control is used to manage ammonia storage in SCR catalyst, then ammonia storage is maintained under normal conditions, but ammonia storage becomes insufficient during vehicle-off to vehicle-on transitions and thermal events
Solution Approach 1:
The system performs preliminary action by injecting ammonia during the final exhaust blowdown before vehicle-off to preemptively maintain ammonia storage in the SCR catalyst. This advance action ensures sufficient ammonia is available when the vehicle restarts, avoiding the lag inherent in closed-loop control that only reacts after storage is detected as insufficient.
Solution Approach 2:
The system uses feedback by monitoring ammonia storage levels in the SCR catalyst and adjusting injection strategies accordingly. When ammonia storage falls below threshold levels following thermal events or vehicle-off periods, the system detects this condition and implements corrective injection to replenish storage, creating a closed-loop adaptation to transient conditions.
2Reliability
If ammonia is stored in SCR catalyst for optimal NOx conversion, then NOx conversion efficiency increases, but ammonia desorbs during thermal events causing ammonia slip and increased NOx emissions
Solution Approach 1:
The system performs preliminary action by replenishing ammonia storage proactively following thermal events before the vehicle restarts. By detecting that a thermal event has occurred and ammonia storage is likely depleted, the system injects ammonia in advance during the final blowdown, ensuring storage is restored before normal operation resumes, thus maintaining conversion efficiency without excessive slip.
Solution Approach 2:
The system changes operational parameters by adjusting ammonia injection timing and quantity based on thermal event detection. Following thermal events, the system implements a specific injection strategy that accounts for the temperature history and expected storage depletion, optimizing the balance between maintaining sufficient storage for conversion and avoiding over-injection that would cause slip during the thermal event.
3Object-affected harmful factors
If active ammonia injection is delayed until after cold start to avoid emissions, then ammonia storage builds up safely, but ammonia storage remains under-stored following vehicle-on event
Solution Approach 1:
The system performs preliminary action by injecting ammonia during the final exhaust blowdown at the end of cold start operation. This timing allows the exhaust system to reach sufficient temperature for effective ammonia injection while still capturing the ammonia storage benefit before vehicle-off, preemptively preparing the SCR catalyst for the upcoming vehicle-on event without delaying storage buildup.
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 proactive approach ensures sufficient ammonia storage in the SCR catalyst, minimizing delays in regaining optimal NOx conversion efficiency after cold starts and thermal events, thereby reducing NOx emissions and maintaining efficient catalyst performance.
Implementation Method 1
ammonia is stored in the SCR catalyst to convert NOx into nitrogen and water
Implementation Method 2
Ammonia that is used as a reductant in the catalyst may be desorbed from the SCR catalyst when the temperature increases resulting in ammonia slip from the catalyst
Data Source
AI summary
Various systems and methods are described for managing ammonia storage in an SCR catalyst. In one example approach, a method comprises, in response to a vehicle-off event, injecting ammonia during a final exhaust blowdown until a predetermined value of ammonia is stored in the SCR catalyst; and in response to a subsequent vehicle-on event when an amount of ammonia stored in the SCR catalyst is less than the predetermined value, injecting ammonia until the predetermined value of ammonia is stored in the SCR catalyst.