SCR Catalyst Ammonia Control for Exhaust Gas Purification
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Solution Overview
Problem
In exhaust gas control systems with SCR catalysts, ammonia is adsorbed onto the catalyst after engine stop, leading to its desorption and discharge when the engine restarts, reducing the NOx purification rate and increasing atmospheric ammonia emissions.
Innovation Solution
An exhaust gas control system with an addition valve and temperature increase treatment unit that controls ammonia addition based on engine operation states, ensuring ammonia is not added during temperature increase treatments to prevent desorption, and adding ammonia only when necessary to maintain NOx reduction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ammonia is added from the addition valve after engine stop, then the NOx purification rate is enhanced immediately after restart, but ammonia is discharged into the atmosphere during temperature increase treatment
Solution Approach 1:
The system performs preliminary action by adding ammonia before engine stop when temperature increase treatment is not executed, so that ammonia is already adsorbed on the SCR catalyst when the engine restarts. This eliminates the need to add ammonia after restart, preventing ammonia discharge during temperature increase treatment while maintaining high NOx purification rate.
Solution Approach 2:
The control unit monitors the execution state of temperature increase treatment and adjusts the timing of ammonia addition accordingly. When temperature increase treatment is executed, the system feedback-controls to prohibit ammonia addition after engine stop, thereby preventing ammonia discharge while maintaining system efficiency.
2Temperature
If temperature increase treatment is executed immediately after engine restart, then the exhaust gas control element temperature is recovered, but the SCR catalyst temperature rises abruptly causing ammonia desorption
Solution Approach 1:
The system performs preliminary ammonia addition before engine stop, so that ammonia is already adsorbed on the SCR catalyst. This timing strategy ensures that when temperature increase treatment occurs after restart, there is no additional ammonia available to desorb, thereby preventing ammonia discharge while still allowing temperature recovery.
Solution Approach 2:
The control unit applies preliminary anti-action by prohibiting ammonia addition after engine stop when temperature increase treatment is detected. This preemptive measure counteracts the potential harmful effect of ammonia desorption during temperature increase, eliminating the contradiction between temperature recovery and ammonia stability.
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 NOx purification rate immediately after engine restart while reducing ammonia discharge into the atmosphere, optimizing the use of ammonia and maintaining system efficiency.
Implementation Method 1
a selective reduction NOx catalyst (which may also be referred to as an 'SCR catalyst' below) having a function to selectively reduce NOx in exhaust gas with ammonia as a reducing agent
Implementation Method 2
ammonia is adsorbed onto the SCR catalyst after the operation stop of the internal combustion engine
Implementation Method 3
execute temperature increase treatment that increases temperature of the exhaust gas flowing into the exhaust gas control apparatus so as to increase temperature of the exhaust gas control element
Implementation Method 4
an addition valve provided in the exhaust passage, the addition valve being configured to add an additive that is ammonia or a precursor of ammonia toward the selective reduction NOx catalyst
Data Source
AI summary
An exhaust gas control apparatus has an exhaust gas control element other than an SCR catalyst. A temperature increase treatment unit executes temperature increase treatment that increases temperature of exhaust gas flowing into the exhaust gas control apparatus so as to increase the temperature of the exhaust gas control element to a specified target temperature. In this case, when operation of the internal combustion engine is stopped while the temperature increase treatment unit is not executing the temperature increase treatment, addition of an additive to the SCR catalyst from an addition valve is executed after operation stop of the internal combustion engine. When operation of the internal combustion engine is stopped while the temperature increase treatment unit is executing the temperature increase treatment, addition of the additive to the SCR catalyst from the addition valve is not executed after operation stop of the internal combustion engine.