SCR Reductant Buffer Control via Dual Injection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge in diesel engine exhaust systems is controlling the reductant buffer level in SCR catalysts, as direct measurement is not possible, leading to sub-optimal NOx conversion and ammonia slip due to inadequate urea injection, which affects NOx conversion efficiency and fuel economy.
Innovation Solution
A method involving two reductant injections with varying amounts upstream of the exhaust gas aftertreatment device, followed by NOx conversion evaluations to adjust subsequent injections, allowing for open-loop experimentation to determine if the buffer is empty or full, thereby optimizing NOx conversion and maintaining the buffer at an optimal level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If urea injection levels are precisely controlled to maximize NOx conversion, then NOx conversion efficiency is improved, but ammonia slip increases if over-injection occurs
Solution Approach 1:
The patent implements a feedback control mechanism where NOx conversion efficiency is continuously monitored and used to adjust urea injection levels. By evaluating the actual NOx conversion and comparing it with target values, the system dynamically adjusts injection amounts to maintain optimal conversion while preventing over-injection that would cause ammonia slip.
Solution Approach 2:
The system changes injection parameters (amount, timing, duration) based on operating conditions and measured NOx conversion efficiency. By dynamically adjusting these parameters rather than using fixed injection levels, the system optimizes NOx conversion across varying conditions while avoiding ammonia slip from excessive injection.
2Productivity
If reductant buffer level is increased to ensure sufficient NOx conversion, then NOx conversion efficiency is improved, but system complexity increases due to indirect measurement requirements
Solution Approach 1:
The patent uses NOx conversion efficiency as an intermediary parameter to indirectly measure reductant buffer level. Instead of directly measuring buffer level, the system monitors how effectively NOx is being converted, which serves as a proxy indicator for buffer status, simplifying the measurement system while maintaining control accuracy.
Solution Approach 2:
The system replaces direct mechanical or physical buffer level sensing with a chemical performance-based measurement approach. By substituting direct level measurement with NOx conversion efficiency monitoring, the system avoids complex sensing hardware while gaining more meaningful operational data.
3Measurement precision
If open-loop experimentation is performed to determine buffer status, then measurement precision is improved, but loss of time occurs during experimentation
Solution Approach 1:
The patent performs partial experimentation by injecting reductant in controlled increments and evaluating NOx conversion at each step. Rather than exhaustive testing, the system uses sufficient but not excessive experimentation to determine buffer status, balancing measurement precision with time constraints by stopping once adequate information is obtained.
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 ensures maximum NOx conversion while minimizing ammonia slip, allowing for real-time adjustments to maintain the reductant buffer at an optimal level, independent of existing buffer management methods, and adaptable to varying engine conditions.
Implementation Method 1
Selective Catalytic Reduction (SCR) catalysts, in which NOx is continuously removed through active injection of a reductant into the exhaust gas mixture entering the catalyst
Implementation Method 2
NOx conversion resulting from said first and second reductant injections
Implementation Method 3
an injection system is used to supply it into the exhaust gas stream entering the SCR catalyst where it decomposes into hydro cyanic acid (NHCO) and gaseous ammonia (NH3)
Implementation Method 4
NOx conversion efficiency of an SCR catalyst is improved in the presence of adsorbed ammonia
Implementation Method 5
some of the adsorbed ammonia in the catalyst may desorb and slip from the catalyst
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The invention relates to a method for controlling a reductant buffer level in an exhaust gas after treatment device connectable downstream of an internal combustion engine, said method comprising the steps of: performing a first reductant injection of a first amount upstream said exhaust gas after treatment device, performing a second reductant injection of a second amount upstream said exhaust gas after treatment device, which second amount is different to said first amount, evaluating the NOx conversion resulting from said first and second reductant injections downstream said exhaust gas after treatment device to obtain a first and second result, controlling a further reductant injection in dependence of the first and second results from said first and second NOx conversion evaluations.