SCR Dosing Pressure Control for Leakage Prevention
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Solution Overview
Problem
SCR systems in vehicles face issues with reducing agent leakage and crystallization when the dosing unit is closed, leading to degraded performance and potential costly repairs due to undesired deposits in the exhaust system, especially at low exhaust temperatures where the reducing agent does not react effectively.
Innovation Solution
The method involves reducing the pressure of the reducing agent in the dosing unit from a higher pressure level to a lower level during non-continuous dosing and maintaining the pressurizing device's operation to minimize leakage and ensure quick pressure restoration when dosing resumes, using techniques such as adjusting the pump's RPM or valve configuration to control the pressure effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the dosing unit is kept closed to prevent reducing agent leakage, then leakage is reduced, but the system cannot deliver reducing agent when needed and performance degrades
Solution Approach 1:
The dosing unit transitions from a static closed state to a dynamic system that can switch between closed and open states based on operational requirements. The control unit dynamically adjusts the dosing unit's state to match engine operating conditions, enabling the system to prevent leakage during idle periods while maintaining dosing capability when needed.
Solution Approach 2:
The system changes the pressure parameter of the reducing agent based on operational state. During closed periods, pressure is reduced to minimize leakage. When dosing is required, pressure is increased to enable effective dosing. This dynamic pressure adjustment resolves the contradiction between preventing leakage and maintaining dosing capability.
2Productivity
If the dosing unit is opened to dose reducing agent, then dosing capability is maintained, but reducing agent leakage occurs causing crystallization and deposits
Solution Approach 1:
The system takes preliminary action by reducing pressure before closing the dosing unit to prevent leakage. The control unit anticipates potential leakage issues and proactively adjusts pressure parameters to minimize the risk of crystallization and deposits before they can occur.
Solution Approach 2:
The system converts the potentially harmful effect of pressure differential into a beneficial control mechanism. By carefully managing pressure changes during dosing and closed periods, the system prevents the harmful crystallization effect while maintaining the necessary dosing function.
3Reliability
If pressure is reduced to prevent leakage during non-dosing, then leakage is minimized, but pressure restoration time increases when dosing resumes
Solution Approach 1:
The system implements periodic pressure adjustment cycles, switching between reduced pressure during closed periods and elevated pressure during dosing periods. The control unit manages these periodic transitions to optimize both leakage prevention and rapid pressure restoration when needed.
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 the risk of reducing agent leakage and crystallization, maintaining system performance and preventing costly repairs by ensuring minimal pressure loss and efficient operation of the SCR system, even during periods of non-dosing.
Implementation Method 1
a pump (230) arranged so as to pressurize said reducing agent to a suitable pressure, e.g. a pressure between 5 and 15 bars, e.g. 9 bars, during dosing of said reducing agent to said exhaust duct
Implementation Method 2
Another such operating case in which no dosing occurs can be when a prevailing temperature of a surface of or component in the exhaust duct from the vehicle engine is lower than a given predetermined temperature. Dosed reducing agent could not be vaporized to the desired extent in this case
Implementation Method 3
in which catalytic converter said reductant and NO x gas can react and be converted into nitrogen and water
Data Source
Figure 1~2a
Figure 2b
Figure 3a~3b
AI summary
The invention concerns a method for an SCR system comprising a dosing unit (250) for dosing reducing agent into an engine exhaust duct (290) upstream of a SCR catalytic converter (270) for reducing the NOx level in an exhaust flow from said engine, wherein said SCR system comprises a pressurizing device (230) for feeding reducing agent from a container (205) to said dosing unit (250) arranged so as to dose said reducing agent to said exhaust duct (290) under pressure. The method comprises the step of: reducing, during periods of non-continuous dosing of reducing agent during continued maintained operation of said pressurizing device (230), the pressure (s301; s320) of said reducing agent at the dosing unit (250) compared to the pressure during continuous dosing. The invention also concerns a computer program product containing program code (P) for a computer (200; 210) for implementing a method according to the invention. The invention also concerns an SCR system and a motor vehicle that is equipped with said SCR system.