SCR Control via NO2/NO Ratio Estimation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for reducing NOx and particulate emissions in combustion engines face challenges in precise control, particularly in real-time monitoring and adjustment of ammonia injection in SCR systems, due to temperature effects and uncertainty in NOx composition, leading to difficulties in maintaining optimal emissions control.
Innovation Solution
A method for estimating the molar ratio of CO2 to NOx in the exhaust gases using a map based on residence time in an oxidation catalyst, with corrections for catalyst aging, to improve the efficiency of SCR systems by optimizing ammonia injection and monitoring system performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the quantity of urea injected is increased to reduce NOx emissions, then NOx reduction effectiveness is improved, but the risk of ammonia slip and system complexity increases
Solution Approach 1:
The invention changes the parameter being monitored from absolute NOx concentration to the ratio between NO2 and NO concentrations. This ratio parameter provides direct information about oxidation catalyst performance and ammonia availability, enabling simplified control of urea injection quantity without requiring complex closed-loop control systems.
Solution Approach 2:
The invention uses the NO2/NO ratio as an intermediary parameter that indirectly indicates the state of the oxidation catalyst and the availability of stored ammonia. This intermediary measurement simplifies the control problem by providing a single parameter that captures the essential system state without requiring direct measurement of multiple variables.
2Productivity
If temperature of exhaust gases is increased to favor reaction kinetics in SCR catalyst, then reduction reaction efficiency is improved, but ammonia storage capacity in catalyst decreases due to desorption
Solution Approach 1:
The invention implements feedback control by continuously monitoring the NO2/NO ratio in the exhaust gases and using this information to adjust the urea injection rate. The ratio provides real-time feedback on the balance between ammonia storage and reaction kinetics, allowing the control system to optimize urea injection to maintain efficient NOx reduction while preventing ammonia slip.
3Measurement precision
If closed-loop control based on downstream NOx sensor is used to adapt urea injection, then emission control precision is improved, but response time is insufficient for transient engine states
Solution Approach 1:
The invention performs preliminary action by measuring the NO2/NO ratio upstream of the SCR catalyst, before the actual NOx reduction takes place. This upstream measurement provides advance information about the system state and ammonia availability, allowing the control system to adjust urea injection in advance of transient changes, thereby improving response time compared to downstream sensing.
4Productivity
If the quantity of ammonia stored in catalyst is increased to enhance NOx reduction, then reduction capacity is improved, but risk of ammonia slip increases
Solution Approach 1:
The invention changes the control parameter from absolute ammonia quantity to the NO2/NO concentration ratio. This ratio parameter naturally balances ammonia storage and reaction rates, as it reflects the actual chemical state of the system. By controlling urea injection to maintain an optimal NO2/NO ratio, the system automatically adjusts ammonia storage to match reaction demands, preventing both insufficient reduction and excessive ammonia slip.
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 enables more precise control of NOx reduction, accounting for catalyst aging and temperature effects, thereby enhancing the effectiveness of SCR systems in reducing emissions and detecting potential malfunctions in real-time.
Implementation Method 1
an oxidation catalyst placed upstream of means for treating gases resulting in a reduction of nitrogen oxides
Implementation Method 2
The SCR catalyst then serves to promote the reduction of NOx by NH3 according to the following 3 reactions
Implementation Method 3
chemical conversion by reduction of nitrogen oxides using a reducing agent
Implementation Method 4
ammonia being obtained by thermolysis/hydrolysis of urea in the exhaust line according to the following reactions: (NH2)2CO → HNCO + NH3: thermolysis at 120°C
Implementation Method 5
HNCO + H2O → CO2 + NH3: hydrolysis at 180°C
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
The invention relates to a method for controlling a system for the treatment of exhaust gases in an exhaust line of an internal combustion engine. The invention is characterised in that it consists in estimating the molar ratio of nitrogen dioxide to nitrogen monoxide at the inlet of an NOx selective reduction catalyst based on a cartography that is dependent on the residence time of the exhaust gases in an oxidation catalyst disposed upstream of the gas treatment means leading to a reduction in nitrogen oxides.