SCR Hydrolysis Catalyst Temperature Control via Observer
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Solution Overview
Problem
Existing SCR systems face inefficiencies due to inadequate control over ammonia release and storage, leading to reduced NOx conversion and potential urea deposits, as current methods struggle to accurately determine internal hydrolysis catalyst states for optimized dosing strategies.
Innovation Solution
A method involving a selective catalytic reduction system with a hydrolysis catalyst, DEF dosing unit, and a controller using measurement data from sensors to derive characteristics associated with system states, outputs, and biases, allowing for precise control of DEF injection and ammonia management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If DEF is dosed onto a hydrolysis catalyst to produce ammonia for NOx reduction, then ammonia is generated to convert NOx, but the DEF cooling effect slows down or prevents thermolysis of urea and hydrolysis of isocyanic acid, creating a lag in ammonia release
Solution Approach 1:
The system performs preliminary heating of the hydrolysis catalyst before dosing DEF to ensure the catalyst reaches sufficient temperature for immediate thermolysis and hydrolysis reactions. This preliminary action prevents the cooling lag by pre-establishing the thermal conditions necessary for rapid ammonia generation when DEF is introduced.
Solution Approach 2:
The system uses sensors to monitor the hydrolysis catalyst temperature and ammonia storage levels, feeding this information back to the controller. The controller adjusts DEF dosing timing and hydrolysis catalyst heating power based on this feedback to maintain optimal temperatures that prevent reaction lag while managing ammonia production rates.
2Quantity of substance
If DEF dosing is increased to improve ammonia availability for NOx conversion, then more ammonia is available for reduction, but urea deposits form in the exhaust passage and ammonia slip events occur
Solution Approach 1:
The system dynamically adjusts dosing parameters including DEF injection timing, injection duration, and hydrolysis catalyst temperature based on real-time sensor feedback. By changing these parameters, the system optimizes ammonia generation rates to match exhaust flow conditions, ensuring complete urea decomposition and preventing both deposit formation and ammonia slip.
Solution Approach 2:
The system transitions from static DEF dosing to dynamic dosing where injection rates and timing are continuously adjusted based on exhaust temperature, flow rate, and ammonia storage levels. This dynamic control ensures optimal ammonia availability across varying operating conditions while preventing harmful effects.
3Ease of operation
If embedded models are used to control DEF dosing based on temperature information, then dosing decisions can be made, but the models cannot accurately determine internal temperature profiles of the hydrolysis catalyst for optimized control
Solution Approach 1:
The system introduces an observer as an intermediary computational element that processes sensor measurements and model data to estimate internal hydrolysis catalyst temperature profiles. This observer acts as a mediator between available external measurements and the required internal state information, providing accurate temperature profile estimates without requiring direct internal sensors.
Solution Approach 2:
The system replaces direct physical measurement of internal temperature with a computational estimation approach using an observer. Instead of using mechanical/physical sensors inside the catalyst, the system uses mathematical models and available sensor data to compute internal temperature profiles, achieving accurate measurement without physical intrusion.
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 the control over ammonia storage and release, improving NOx conversion efficiency and reducing urea deposits, thereby optimizing the SCR system's performance and minimizing ammonia slip.
Implementation Method 1
DEF is dosed onto a hydrolysis catalyst and hydrolysed to ammonia
Implementation Method 2
a hydrolysis catalyst; a DEF dosing unit configured to inject DEF onto the hydrolysis catalyst
Implementation Method 3
The ammonia passes into a SCR catalyst where it reacts with the exhaust gas, wherein any nitrogen oxides (NOx) present in the exhaust gas are converted to nitrogen and water
Implementation Method 4
The DEF contains urea which undergoes a hydrolysis and/or thermolysis within the exhaust passage whereby ammonia is produced
Data Source
AI summary
Selective catalytic reduction systems are known and are generally included in exhaust systems of diesel engines in order to treat the exhaust gases of such engines. Such systems involve the introduction of diesel exhaust fluid (DEF) into exhaust gas flowing in an exhaust passage of an engine. When dosing DEF onto a hydrolysis catalyst in a SCR system, the DEF will under certain conditions cool the hydrolysis catalyst sufficiently to either slow down or effectively prevent ammonia release, which creates a lag or delay in the function of the hydrolysis catalyst. This limits the amount of control which can be exerted over ammonia storage in the SCR catalyst, and NOx conversion. In a first step, a set of measurement data is received from one or more sensors provided in the system. Subsequently, a first set of characteristics associated with a state of a component of the catalytic system, a second set of characteristics associated with an output of the catalytic system and a third set of characteristics associated with a bias and a scaling factor in the system are derived. In a third step, the derived sets of characteristics are used to control the catalytic system.