NH3 Supply Control for SCR Catalyst Temperature
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Solution Overview
Problem
Existing exhaust gas purification systems for engines face challenges in efficiently controlling ammonia (NH3) supply to SCR catalysts, leading to excessive ammonia discharge or insufficient absorption, due to variations in NOx catalyst temperature, which affects NOx purification efficiency.
Innovation Solution
An exhaust gas purification controller that includes an NOx catalyst, an NOx catalyst regenerator, an SCR catalyst, an NH3 supplier, and an NH3 supply amount controller, which adjusts NH3 supply based on NOx catalyst temperature and regeneration status to optimize NH3 absorption and reduce excessive discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If NH3 supply to SCR catalyst is increased to improve NOx purification efficiency, then NOx conversion rate is improved, but excessive NH3 may be discharged to exhaust gas passage downstream SCR catalyst
Solution Approach 1:
The control device calculates the NH3 generation amount at the NOx catalyst based on detected NOx concentration and air-fuel ratio, then uses this feedback information to adjust the NH3 supply amount to the SCR catalyst, preventing both excessive NH3 discharge and insufficient NH3 supply for NOx purification
Solution Approach 2:
The system dynamically changes the NH3 supply parameter based on operating conditions (NOx concentration, air-fuel ratio, temperature) to optimize the balance between NH3 generation at NOx catalyst and NH3 consumption at SCR catalyst, resolving the contradiction between purification efficiency and NH3 discharge prevention
2Object-generated harmful factors
If NH3 supply to SCR catalyst is decreased to prevent excessive NH3 discharge, then NH3 discharge is inhibited, but NH3 supply may become insufficient for effective NOx purification
Solution Approach 1:
The control device continuously monitors NOx concentration and air-fuel ratio to calculate NH3 generation amount, then adjusts NH3 supply to SCR catalyst in real-time based on this feedback, ensuring sufficient NH3 is supplied for purification while preventing excessive discharge
Solution Approach 2:
The NH3 supply amount is made dynamic rather than fixed, adjusting continuously based on changing operating conditions (temperature, load, air-fuel ratio) to maintain optimal balance between preventing NH3 discharge and ensuring sufficient NH3 for purification
3Device complexity
If NH3 generation amount at NOx catalyst is not accurately calculated, then control simplicity is maintained, but sufficient inhibition of NH3 discharge or prevention of NH3 shortage cannot be achieved
Solution Approach 1:
The system replaces complex physical NH3 measurement devices with a calculation-based approach using readily available sensor data (NOx concentration, air-fuel ratio, temperature) to determine NH3 generation amount, achieving accurate control without additional complex hardware
Solution Approach 2:
The control device uses existing sensor measurements and built-in calculation capabilities to self-determine NH3 generation amount, eliminating the need for external complex measurement systems while maintaining control accuracy
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
The system ensures efficient NOx purification by accurately managing NH3 supply, considering temperature variations and regeneration states, thereby preventing ammonia discharge and maintaining effective NOx reduction.
Implementation Method 1
an NOx catalyst provided on an exhaust gas passage of an engine and configured to occlude NOx in an flowing-in exhaust gas in a state wherein an air-fuel ratio of the flowing-in exhaust gas is leaner than a stoichiometric air-fuel ratio and to reduce the occluded NOx to NH3 in a state wherein the air-fuel ratio of the flowing-in exhaust gas is richer than the stoichiometric air-fuel ratio
Implementation Method 2
an SCR catalyst provided on the exhaust gas passage downstream the NOx catalyst, and configured to purify NOx by a reaction with NH3
Implementation Method 3
an NH3 supplier configured to supply NH3 or a raw material for NH3 to the SCR catalyst and cause the SCR catalyst to absorb the NH3 or the raw material for NH3
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
An NH3 supply amount controller reduces and adjusts a supply amount of NH3 to an SCR catalyst by an NH3 supplier, when an exhaust gas flowing into an NOx catalyst has a rich air-fuel ratio and NOx occluded by the NOx catalyst is reduced to N2. A reduction amount of the supply amount of the NH3 controlled by the NH3 supply amount controller is set smaller when a temperature of the NOx catalyst detected or estimated by an NOx catalyst temperature detector is higher.