Model-Based Urea Dosing for SCR Ammonia Slip Control
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Solution Overview
Problem
Selective Catalyst Reducer (SCR) performance degrades over time, leading to inefficiencies in NOx conversion and ammonia storage, especially at high temperatures, which affects emission control in diesel engines, necessitating an adaptive urea dosing strategy to maintain emission standards.
Innovation Solution
A model-based method to determine SCR operating conditions, adjust urea dosing, and recalibrate based on ammonia storage and slip, using temperature and exhaust flow rate data to predict SCR age and optimize NOx conversion, incorporating engine parameters like air mass flow and NOx flow rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If SCR operates at high temperature, then NOx conversion efficiency is improved, but ammonia storage capacity degrades and ammonia slip increases
Solution Approach 1:
The patent implements dynamic urea dosing control that adjusts dosing rates based on real-time SCR temperature, ammonia storage levels, and aging state. The controller continuously adapts dosing parameters to maintain optimal ammonia storage across varying temperature conditions, preventing both ammonia deficiency at low temperatures and ammonia slip at high temperatures.
Solution Approach 2:
The system changes operational parameters by adjusting urea dosing rates according to SCR temperature and aging state. The controller modifies dosing parameters dynamically to compensate for temperature effects on ammonia storage capacity, ensuring adequate ammonia availability for NOx conversion while preventing excessive ammonia slip.
2Duration of action of stationary object
If SCR operates for extended periods, then emission control is maintained, but SCR performance degrades due to aging
Solution Approach 1:
The system performs preliminary characterization of SCR aging by monitoring temperature-time exposure history and calculating an aging state parameter. This preliminary assessment allows the controller to proactively adjust urea dosing strategies before significant performance degradation occurs, extending the effective service life of the SCR system.
Solution Approach 2:
The patent implements feedback control by continuously monitoring SCR outlet ammonia levels and NOx conversion efficiency, then adjusting urea dosing rates accordingly. The system uses feedback from temperature sensors and emission measurements to adapt dosing parameters in real-time, compensating for aging effects and maintaining emission control performance.
3Quantity of substance
If urea dosing is increased, then ammonia storage in SCR is improved, but ammonia slip increases
Solution Approach 1:
The system applies local quality control by adjusting urea dosing rates according to specific SCR zones and operating conditions. Different dosing strategies are applied based on local temperature conditions, ammonia storage levels, and SCR aging state, optimizing ammonia distribution to prevent both storage deficiency and excessive slip.
Solution Approach 2:
The controller implements partial dosing by applying urea at optimized rates rather than maximum dosing. The system calculates precise dosing amounts needed to achieve target ammonia storage levels, avoiding excessive urea injection that would lead to ammonia slip while ensuring adequate ammonia availability for NOx conversion.
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 effectively controls ammonia slippage and NOx conversion, ensuring emission standards are met regardless of SCR age by dynamically adjusting urea dosing, thereby extending the effective life of the SCR and reducing atmospheric emissions.
Implementation Method 1
a selective catalyst reducer with a urea doser to trap NOx in the SCR until operating conditions of the SCR permit the NOx to be treated with exposure to ammonia, such as from urea, to change NOx to N2 gas for emission to the atmosphere
Implementation Method 2
When the SCR is operating at low temperature, ammonia is absorbed by the SCR
Data Source
AI summary
A method to control NH3 slippage and NOx conversion in an electronic controlled internal combustion engine exhaust system equipped with a selective catalyst reducer, a diesel particulate filter, a diesel oxidation catalyst and a urea doser.