Exhaust System Feedforward Feedback Control NOx Reduction
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Solution Overview
Problem
Existing exhaust systems for internal combustion engines, such as those using Selective Catalytic Reduction (SCR), may fail to optimally control reductant injection due to neglecting critical factors like SCR catalyst temperature and exhaust flow rate, leading to sub-optimal NOX reduction and unnecessary reductant waste.
Innovation Solution
An exhaust system with sensors to monitor operational and performance parameters of the reduction catalyst, including temperature and flow rate, and a controller that adjusts reductant injection based on NOX production and catalyst performance, implementing both feedforward and feedback control mechanisms to optimize reductant use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If reductant injection is regulated based only on fuel flow, throttle setting, engine speed, and exhaust gas temperature, then the control system is simpler, but the NOX reduction efficiency is sub-optimal
Solution Approach 1:
The system implements feedback control by using sensors to measure actual NOX levels and NH3 slip downstream of the SCR catalyst, then feeding this information back to the controller to adjust reductant injection. This closed-loop feedback enables the system to optimize NOX reduction efficiency while adapting to real-time catalyst performance and operating conditions.
Solution Approach 2:
The system performs preliminary actions by proactively adjusting reductant injection based on predicted catalyst performance and operating conditions before sub-optimal reduction occurs. The controller uses feedforward control signals based on engine operating parameters and catalyst temperature to anticipate and prevent NOX reduction deficiencies.
2Measurement precision
If more sensors and control mechanisms are added to monitor catalyst temperature and flow rate, then the control precision improves, but the device complexity increases
Solution Approach 1:
The system uses feedback from temperature sensors and flow rate sensors to continuously monitor catalyst performance and adjusts reductant injection accordingly. This enables precise control of the SCR process by adapting to real-time changes in catalyst temperature and exhaust flow conditions.
Solution Approach 2:
The controller serves multiple functions by integrating data from various sensors (NOX sensors, NH3 sensors, temperature sensors, flow rate sensors) and coordinating reductant injection, EGR valve control, and diesel particulate filter management. This multi-functional approach reduces the need for separate dedicated control systems for each function.
3Reliability
If reductant injection is increased to ensure adequate NOX reduction, then the NOX emission compliance is improved, but reductant waste and ammonia slip increase
Solution Approach 1:
The system uses feedback from downstream NOX and NH3 sensors to precisely control reductant injection. When NOX reduction is adequate, the system reduces reductant injection to minimize waste and prevent ammonia slip. This closed-loop control ensures compliance while optimizing reductant utilization.
Solution Approach 2:
The system dynamically changes reductant injection parameters based on real-time monitoring of catalyst temperature, exhaust flow rate, and emission levels. By continuously adjusting injection rate, timing, and duration based on actual operating conditions, the system achieves optimal NOX reduction while minimizing reductant waste and ammonia slip.
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 precise control of reductant injection, maintaining desired NOX emission levels across varying conditions, optimizing reductant use, and minimizing ammonia slip, thereby enhancing the efficiency and responsiveness of the engine.
Implementation Method 1
SCR is a process where gaseous or liquid reductant (most commonly a solution of urea solid and water) is added to the exhaust gas stream of an engine and is adsorbed onto a catalyst. The reductant reacts with NOX in the exhaust gas to form H2O and N2
Implementation Method 2
The reductant reacts with NOX in the exhaust gas to form H2O and N2, which can be safely released to the atmosphere
Implementation Method 3
a first sensor located to generate a first signal indicative of an operational parameter of the reduction catalyst
Implementation Method 4
a second sensor located downstream of the reduction catalyst to generate a second signal indicative of a performance parameter of the reduction catalyst
Data Source
AI summary
An exhaust system for use with a combustion engine is disclosed. The exhaust system may have an exhaust passageway, and a reduction catalyst disposed within the exhaust passageway. The exhaust system may also have a first sensor located to generate a first signal indicative of an operational parameter of the reduction catalyst, and a second sensor located to generate a second signal indicative of a performance parameter of the reduction catalyst. The exhaust system may further have an injection device located to inject reductant upstream of the reduction catalyst, and a controller in communication with the combustion engine, the first sensor, the second sensor, and the injection device. The controller may be configured to determine a NOX production of the combustion engine, determine an amount of reductant that should be injected based on the NOX production and the first signal, and adjust the amount based on the second signal.