SCR Catalyst Ammonia Adsorption Control for Exhaust Purification
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Solution Overview
Problem
Conventional exhaust gas purification systems fail to effectively utilize ammonia adsorbed to SCR catalysts, leading to increased ammonia oxidation and inefficient NOx reduction, as the dosing of urea aqueous solution is not adjusted for saturated ammonia states, resulting in excessive ammonia discharge.
Innovation Solution
An engine exhaust gas purification apparatus with a control unit that calculates and adjusts the dosing of urea aqueous solution based on ammonia adsorption and NOx purification ratios, ensuring optimal utilization of ammonia for NOx reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the flow rate of urea aqueous solution is controlled based on engine operation state without considering ammonia adsorption, then the dosing control is simple, but the urea aqueous solution is not effectively utilized and ammonia discharge increases
Solution Approach 1:
The control unit calculates the amount of adsorbed ammonia based on the amount of produced ammonia and NOx purification ratio, then uses this feedback information to correct the dosing amount of urea aqueous solution. This closed-loop feedback mechanism optimizes urea utilization by adjusting dosing according to actual ammonia adsorption state.
2Reliability
If the flow rate of urea aqueous solution is increased to ensure sufficient ammonia supply, then NOx purification is maintained, but ammonia that does not contribute to NOx purification increases and is discharged to atmosphere
Solution Approach 1:
Instead of dosing urea aqueous solution in excess to ensure sufficient ammonia supply, the system calculates the precise dosing amount by subtracting the adsorbed ammonia amount from the produced ammonia amount. This partial action approach doses only the necessary amount of urea needed for NOx purification, avoiding excessive ammonia generation and discharge.
3Device complexity
If ammonia adsorption to SCR catalyst is not considered in dosing control, then the control system is simpler, but the amount of ammonia to be oxidized by oxidation catalyst increases
Solution Approach 1:
The control unit calculates the amount of adsorbed ammonia using feedback from the NOx purification ratio and produced ammonia amount, then corrects the dosing amount accordingly. This feedback mechanism provides an accurate picture of ammonia adsorption state without requiring direct measurement of adsorbed ammonia, maintaining control system simplicity while reducing ammonia oxidation requirements.
Solution Approach 2:
Instead of using a physical sensor to directly measure adsorbed ammonia (which would increase device complexity), the system substitutes this mechanical measurement approach with a calculation method based on readily available data (produced ammonia amount and NOx purification ratio). This substitution achieves the same control objective without adding complex measurement hardware.
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 reduces ammonia discharge into the atmosphere, enhances NOx purification efficiency, and optimizes urea solution usage, allowing for effective ammonia utilization and potential miniaturization of oxidation catalysts, thereby reducing weight and cost.
Implementation Method 1
a selective reduction catalyst disposed in an exhaust pipe of the engine to selectively reduce NOx by use of ammonia produced from a urea aqueous solution
Implementation Method 2
The ammonia which has passed through the SCR catalyst is oxidized by an oxidation catalyst disposed on an exhaust downstream side of the the SCR catalyst
Implementation Method 3
ammonia which does not reduce NOx in exhaust gas but is adsorbed to an SCR catalyst
Data Source
Figure 1
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AI summary
A control unit calculates an amount of produced ammonia from an amount of a dosed urea aqueous solution according to an engine operation state, and calculates a NOx purification ratio in the case of dosing the amount of the dosed urea aqueous solution according to the operation state to exhaust gas on an exhaust upstream side of an SCR catalyst. Moreover, the control unit estimates an amount of adsorbed ammonia to the SCR catalyst based on the produced ammonia amount and the NOx purification ratio. Then, the control unit subtracts the amount of the urea aqueous solution corresponding to the amount of the adsorbed ammonia from the amount of the dosed urea aqueous solution according to the operation state to correct the amount of the dosed urea aqueous solution, and controls the dosing of the urea aqueous solution based on the corrected amount of the dosed urea aqueous solution.