Urea Injection Control for SCR DPF Ash Accumulation
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Solution Overview
Problem
In SCR integral diesel particulate filters, the increasing collection of soot and accumulation of ash reduce the contact area with exhaust gases, leading to a decrease in NH3 storage, which deteriorates control precision and results in ammonia slip, affecting NOx purification performance.
Innovation Solution
A control unit that calculates the effective volume of the SCR integral diesel particulate filter based on ash accumulation and soot collection, determines the necessary urea injection amount by reflecting these changes, and adjusts the NH3 storage control to maintain optimal NH3 levels, preventing ammonia slip and improving NOx purification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If an SCR integral diesel particulate filter is used to reduce weight and improve NOx purification, then weight reduction and fuel consumption enhancement are achieved, but as soot collection and ash accumulation increase, the contact area between exhaust gas and SCR catalyst decreases, leading to reduced NH3 storage and control precision deterioration
Solution Approach 1:
The control unit performs preliminary calculations of effective volume based on ash accumulation and soot collection amounts before determining the urea injection amount. By proactively adjusting the NH3 storage target value according to predicted filter state changes, the system maintains control precision despite the inherent volume reduction from soot and ash accumulation in the integrated filter structure.
Solution Approach 2:
The system continuously monitors differential pressure across the filter to estimate soot collection amount and uses vehicle travel distance to estimate ash accumulation. This feedback mechanism allows the control unit to dynamically adjust the effective volume calculation and NH3 storage target, compensating for the gradual contact area reduction in the integrated filter and maintaining precise NH3 storage control throughout the filter's operational life.
2Device complexity
If the SCR catalyst and DPF are integrated to improve package efficiency and reduce cost, then device complexity and cost are reduced, but the effective volume of the filter reduces due to ash accumulation, thereby reducing NH3 storage capacity
Solution Approach 1:
The system dynamically adjusts the effective volume parameter based on accumulated ash and soot amounts rather than using a fixed value. The control unit continuously updates the effective volume calculation as the filter operates, allowing the NH3 storage target to adapt to the changing internal conditions of the integrated filter. This dynamic adjustment compensates for the reduced storage capacity inherent in the integrated design, maintaining optimal NH3 storage levels despite the compact structure.
3Device complexity
If a general NH3 reaction rate model is applied to the SCR integral diesel particulate filter, then the model is simple to implement, but as soot collection and ash accumulation increase, the control precision of NH3 storage deteriorates and ammonia slip occurs
Solution Approach 1:
The system changes the effective volume parameter based on soot collection amount (from differential pressure) and ash accumulation (from travel distance). By adjusting this key parameter dynamically, the NH3 storage target calculation adapts to the actual filter conditions without requiring a completely complex reaction rate model. This parameter adjustment approach maintains reliability in preventing ammonia slip while keeping the control system relatively simple.
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 precision of urea injection, stabilizes exhaust gas treatment, reduces fuel consumption, and improves the commercial value by preventing ammonia slip and maintaining optimal NOx purification performance.
Implementation Method 1
an SCR catalyst and a diesel particulate filter (DPF) are separated... a method of determining a urea injection amount, a necessary amount of NH3 is calculated according to a stoichiometric ratio (NH3/NOx), which is a ratio of NH3 and an amount of NOx that are exhausted from an engine
Implementation Method 2
an SCR integral diesel particulate filter that purifies NOx and that collects a particulate material including soot and ash
Data Source
AI summary
An apparatus and method for controlling a urea injection amount of a vehicle provides precision improvement of urea injection by determining a urea injection amount according to a collection amount of soot that is collected at an SCR integral diesel particulate filter and an accumulation amount of ash. The method includes: detecting a collection amount of soot that is collected at the SCR integral diesel particulate filter and calculating an effective volume of the SCR integral diesel particulate filter according to enlargement of an accumulation amount of ash; calculating an NH3 target storage amount by reflecting the soot collection amount and an effective volume decrement according to ash accumulation; and providing urea injection by determining an NH3 storage control amount and determining a urea necessary injection amount according to the NH3 target storage amount.