Exhaust Purification Addition Valve Two-Stage Urea Return Control
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Solution Overview
Problem
The existing exhaust gas purification systems for internal combustion engines face issues with urea solution freezing and subsequent clogging and abrasion in the addition valve due to the introduction of high-temperature exhaust gas and particulate matter, leading to increased particle diameter of precipitates which can cause valve clogging and abrasion.
Innovation Solution
An exhaust gas purification apparatus that employs a two-stage control mechanism to manage urea solution return, where a first control limits the initial urea solution return to prevent temperature rise and particle diameter increase, followed by a second control after a time lag to ensure thorough return when exhaust gas temperature is lower, thereby reducing PM intake and preventing clogging and abrasion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If urea solution is sucked back into the tank immediately after the internal combustion engine is stopped, then the addition valve receives cooling and urea solution is removed, but high-temperature exhaust gas flows into the addition valve causing temperature rise and PM intake which leads to precipitate aggregation and valve clogging
Solution Approach 1:
The system performs a first suck-back operation immediately after engine stop to remove most urea solution before PM aggregation can occur, then waits for temperature reduction before the second suck-back operation to彻底 remove remaining urea solution
Solution Approach 2:
The suck-back operation is divided into two distinct stages: first suck-back (immediate, limited duration) and second suck-back (delayed, thorough removal), allowing the system to address different aspects of the problem at different times
2Reliability
If urea solution remains in the addition valve after engine stop, then the addition valve is protected from freezing, but precipitates are produced from urea solution at high temperature causing abrasion and clogging
Solution Approach 1:
The first suck-back operation is performed immediately after engine stop to remove urea solution from the high-temperature zone of the addition valve before precipitates can form and aggregate
Solution Approach 2:
The system uses periodic suck-back operations with a specific time interval between them, allowing temperature to drop between operations to prevent precipitate aggregation while still removing urea solution
3Reliability
If the addition valve temperature rises after engine stop, then urea solution hydrolysis produces ammonia causing corrosion, but immediate suck-back causes PM intake and precipitate aggregation
Solution Approach 1:
The first suck-back operation is performed immediately after engine stop to remove urea solution from the addition valve before significant hydrolysis can occur, preventing ammonia generation and subsequent corrosion
Solution Approach 2:
The corrosion prevention strategy is segmented into two phases: immediate urea solution removal to prevent hydrolysis, followed by delayed thorough removal to clear any remaining urea solution after temperature reduction
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 effectively prevents or reduces abrasion and clogging in the addition valve by controlling the particle diameter of precipitates, ensuring efficient operation and extending the lifespan of the valve components.
Implementation Method 1
a pump configured to cause urea solution to flow in the urea solution channel
Implementation Method 2
the addition valve receives heat from the exhaust gas and components around the addition valve, so that the temperature of the addition valve temporarily becomes higher
Implementation Method 3
the rise in the temperature of the addition valve sometimes leads to hydrolysis of urea inside the addition valve, producing ammonia
Implementation Method 4
Urea solution freezes at, for example, approximately −11° C. When the outside air temperature is low, there is a possibility that urea solution may freeze in the addition valve and/or in a channel for supplying urea solution
Data Source
AI summary
An object is to prevent abrasion inside an addition valve and clogging of the addition valve due to an increase in the particle diameter of precipitates. A first control is performed by which a pump is caused to operate in such a way as to return urea solution contained in the addition valve and a urea solution channel to a tank by a predetermined quantity. After the lapse of a certain time after the end of the first control, a second control is performed by which the pump is caused to operate in such a way as to return the urea solution remaining in the addition valve and the urea solution channel thoroughly to the tank.