Ammonia Dosing for SCR Catalyst Storage Management
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Solution Overview
Problem
Existing methods for injecting ammonia into diesel engine exhaust gas streams to reduce NOx emissions face challenges such as insufficient injection leading to low conversions, excessive ammonia slip, and improper dosing due to factors like temperature, space velocity, and storage levels, especially during active regeneration of the diesel particulate filter.
Innovation Solution
A method that determines imminent regeneration events and adjusts ammonia dosing based on parameters like distance to be driven, exhaust gas temperature, and current storage levels to maintain optimal NOx conversion efficiency and prevent ammonia slip, involving calculations to fill the catalyst storage to a selected level and adjusting the ammonia quantity accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the ammonia injection rate is increased to reduce NOx emissions, then NOx conversion efficiency is improved, but ammonia slip increases and is released to the atmosphere
Solution Approach 1:
The system performs preliminary action by storing ammonia on the DPF and catalyst surfaces before regeneration events occur. Ammonia is dosed in advance during base operation and low-temperature conditions, building up a reservoir that can be utilized when regeneration occurs and temperature rises, preventing the need to over-dose during critical periods.
Solution Approach 2:
The ammonia dosing strategy dynamically adjusts injection rates based on real-time conditions including exhaust temperature, space velocity, current storage level, and predicted regeneration timing. The system transitions between different dosing modes (base operation, pre-regeneration, during regeneration) to optimize conversion while minimizing slip under varying operating conditions.
2Object-generated harmful factors
If the ammonia injection rate is decreased to prevent ammonia slip, then ammonia slip is reduced, but NOx conversion efficiency decreases
Solution Approach 1:
The system accumulates ammonia storage on the DPF and catalyst surfaces during base operation and low-temperature periods before regeneration events. This preliminary accumulation ensures sufficient ammonia is available when regeneration occurs, maintaining high conversion efficiency without requiring excessive dosing during the regeneration event itself.
Solution Approach 2:
The system continuously monitors exhaust temperature, space velocity, and estimated ammonia storage levels to adjust dosing rates in real-time. This feedback mechanism ensures ammonia is dosed at optimal rates to maintain conversion efficiency while preventing slip, dynamically responding to changing operating conditions.
3Duration of action of moving object
If a high quantity of ammonia is stored on the vehicle to last the service life, then sufficient ammonia supply is ensured for the entire service life, but the storage system size and cost increase
Solution Approach 1:
The DPF and SCR catalyst structures serve dual functions: their primary functions (particulate filtration and catalytic conversion) plus an additional function as ammonia storage media. By utilizing the porous structures of these existing components for ammonia adsorption, the system eliminates the need for separate dedicated ammonia storage tanks, reducing overall system volume and cost.
Solution Approach 2:
The system changes the operational parameters of existing components (DPF and catalyst) by utilizing their adsorption characteristics to store ammonia. By operating these components in a mode that leverages their surface area and porosity for ammonia retention, the system achieves extended ammonia supply duration without increasing physical storage capacity.
4Reliability
If ammonia is dosed during active regeneration when exhaust temperature and flow rate increase, then NOx reduction continues during regeneration, but the stored ammonia on the DPF is depleted
Solution Approach 1:
The system performs preliminary ammonia dosing during base operation and low-temperature conditions, building up storage on the DPF and catalyst surfaces before regeneration events. This ensures sufficient ammonia is available when regeneration occurs and temperature rises, maintaining conversion efficiency without depleting reserves unnecessarily.
Solution Approach 2:
The ammonia dosing strategy dynamically adjusts based on predicted regeneration timing and current storage levels. When regeneration is anticipated, the system modifies dosing rates to optimize the balance between maintaining conversion during the upcoming regeneration event and preserving sufficient ammonia reserves for the duration of the regeneration process.
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 method ensures efficient NOx reduction while preventing ammonia slip by optimizing ammonia injection rates and storage levels, ensuring sufficient ammonia supply for the vehicle's service life and compliance with emission regulations.
Implementation Method 1
selective catalytic reduction systems (SCR systems) are used to reduce oxides of Nitrogen (NOx) emitted from engines. Nitrogen oxides can be reduced by ammonia (NH3), yielding N2, H2O and CO2. In the aftertreatment process, NOx reacts with the ammonia, which is injected into the exhaust gas stream upstream of an SCR Catalyst.
Implementation Method 2
the quantity of ammonia should be nearly depleted at the end of the service life of the vehicle. Thus, the injection of ammonia should be sufficient to reduce the NOx, and should also correspond to the storage capabilities of the SCR system.
Data Source
AI summary
A method (10) for injecting ammonia (NH3) into exhaust gas upstream of a catalyst of an aftertreatment system includes the steps of determining whether a regeneration event is imminent (14) on the basis of predetermined parameters, and determining whether dosing parameters are met (22). The method (10) further includes the steps of calculating an amount of NH3 to fill the catalyst (18) and adjusting a quantity of NH3 dosed (22) before the regeneration event occurs.