Dual Closed-Loop Reductant Dosing for NOx Conversion
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Solution Overview
Problem
Conventional exhaust after-treatment systems for internal combustion engines face challenges in efficiently reducing nitrogen oxides (NOx) emissions, particularly in cold temperatures and transient periods, due to slow response times and inefficiencies in reductant dosing, leading to ammonia slip and increased operating costs.
Innovation Solution
The implementation of a dual closed-loop reductant dosing system, which includes a first closed-loop system with an SCRF and a second closed-loop system downstream, utilizing multiple NOx sensors to dynamically adjust reductant dosing based on real-time NOx levels, ensuring nearly 100% NOx conversion and minimizing ammonia slip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional single-loop reductant dosing systems are used, then system complexity is reduced, but response time is slow and NOx conversion efficiency is insufficient
Solution Approach 1:
The patent divides the reductant dosing system into two separate closed-loop systems: a first closed-loop system with a first reductant doser and first SCR catalyst, and a second closed-loop system with a second reductant doser and second SCR catalyst. Each system independently controls reductant dosing based on its own NOx sensor feedback, allowing parallel processing of NOx reduction and improving overall conversion efficiency without creating a single point of bottleneck.
Solution Approach 2:
The patent transitions from a single-loop sequential control system to a dual-loop parallel control system. By adding another dimension of control (the second closed-loop system), the system can simultaneously optimize reductant dosing at different stages of the exhaust stream, improving response time and NOx conversion efficiency without excessive complexity.
2Productivity
If reductant dosing is increased to ensure complete NOx conversion, then NOx removal efficiency improves, but ammonia slip increases and operating costs rise
Solution Approach 1:
Each closed-loop system uses a NOx sensor to continuously monitor the NOx level downstream of the SCR catalyst and adjusts the reductant doser accordingly. The first NOx sensor monitors the exhaust stream after the first SCR catalyst, while the second NOx sensor monitors the exhaust stream after the second SCR catalyst. This feedback mechanism ensures precise reductant dosing that achieves complete NOx conversion without excessive ammonia slip, as the system responds in real-time to actual NOx levels.
Solution Approach 2:
The dual closed-loop system applies reductant dosing in controlled partial amounts at different stages rather than applying excessive reductant all at once. The first reductant doser provides initial NOx reduction, and the second reductant doser provides additional reduction only where needed, based on the NOx levels detected by the second NOx sensor. This partial action approach achieves complete NOx conversion while minimizing ammonia slip.
3Reliability
If reductant dosing is optimized for cold-start conditions, then cold-start performance improves, but response time during transient periods remains slow
Solution Approach 1:
The patent implements dynamic control of reductant dosing through two independently operable closed-loop systems that can respond differently to varying operating conditions. During cold-start conditions, the system can activate both loops to provide maximum NOx reduction capability. During transient periods, the system can dynamically adjust the dosing rates of individual loops based on real-time NOx levels and engine operating parameters, enabling fast response time while maintaining cold-start performance.
Solution Approach 2:
The first closed-loop system is positioned to provide preliminary NOx reduction early in the exhaust stream, preparing the exhaust gas for subsequent treatment by the second system. This preliminary action ensures that when transient high-NOx conditions occur, the system already has reductant dosing optimized and ready to respond immediately, improving overall response time while maintaining effectiveness during cold-start conditions.
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 achieves nearly 100% NOx conversion, improves cold-start performance, reduces reductant usage, and enhances response times, thereby meeting stringent emissions standards and reducing operational costs.
Implementation Method 1
SCR catalysts are configured to convert NOx (NO and NO2 in some fraction) into harmless nitrogen gas (N2) and water vapor (H2O). A reductant (typically ammonia (NH3) in some form) is added to the exhaust gas upstream of the catalyst. The NOx and ammonia pass over the catalyst and a catalytic reaction takes place in which NOx and ammonia are converted into N2 and H2O.
Implementation Method 2
The injected DEF spray is heated by the exhaust gas stream to trigger the decomposition of urea into ammonia.
Implementation Method 3
DOCs reduce the amount of CO and HC present in the exhaust gas via oxidation techniques
Data Source
AI summary
Exhaust after-treatment systems and methods are disclosed. An example system includes a selective catalytic reduction on filter (SCRF) and a selective catalytic reduction (SCR) catalyst positioned downstream of the SCRF. The system also includes a first reductant doser positioned upstream of the SCRF and a second reductant doser positioned downstream of the SCRF and upstream of the SCR catalyst. The system further includes first and second nitrogen oxide (NOx) sensors positioned upstream of the first reductant doser, a third NOx sensor positioned downstream of the SCRF and upstream of the second reductant doser, and a catalyst positioned upstream of the first reductant doser.