Low Pressure EGR Control for NOx Variations
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Turbocharged engines face challenges in maintaining desired NOx emissions levels due to variations in NOx levels in low pressure EGR systems caused by after-treatment operating conditions, affecting engine fuel economy and transient emissions.
Innovation Solution
An engine control system adjusts actuators, such as fuel injectors and EGR valves, in response to NOx mass flow rates in low pressure EGR passages, optimizing NOx emissions by adjusting fuel injection timing and EGR flow rates between high and low pressure EGR loops based on SCR efficiency and NOx concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If low pressure EGR is used to reduce engine charge temperature, then cooling effect is improved, but NOx emissions control becomes more difficult due to variations in NOx mass flow rate
Solution Approach 1:
The control system continuously monitors NOx mass flow rate in the low pressure EGR passage and uses this feedback to dynamically adjust actuator positions. This closed-loop control compensates for variations in EGR constituent composition, maintaining desired NOx emissions levels while preserving the cooling benefit of low pressure EGR
Solution Approach 2:
The system changes operating parameters (actuator positions, fuel injection timing, EGR flow rates) in response to detected NOx mass flow rate variations. By dynamically adjusting these parameters, the system maintains optimal balance between charge temperature reduction and NOx emissions control
2Speed
If high pressure EGR is used to increase EGR mass fraction induction rate, then response speed to load changes is improved, but engine charge temperature increases
Solution Approach 1:
The system dynamically selects between high pressure and low pressure EGR sources and adjusts their respective flow rates based on real-time operating conditions. This dynamic EGR strategy allows the system to exploit the fast response of high pressure EGR when needed while using low pressure EGR for cooling when appropriate
Solution Approach 2:
The system applies different EGR strategies to different operating conditions rather than using a single uniform approach. By tailoring the EGR source selection and flow rate distribution to specific operating scenarios, the system optimizes both response speed and charge temperature control for each condition
3Object-generated harmful factors
If SCR efficiency increases to reduce tailpipe NOx, then NOx emissions are improved, but NOx mass flow rate in low pressure EGR decreases affecting engine control
Solution Approach 1:
The control system monitors NOx mass flow rate in the low pressure EGR passage and detects changes caused by varying SCR efficiency. This feedback enables the system to compensate for reduced NOx in EGR by adjusting actuator positions and fuel injection timing to maintain desired engine NOx levels
Solution Approach 2:
The system uses the NOx sensor downstream of the SCR catalyst to automatically adjust engine operation and EGR flow rates, enabling self-regulation of NOx emissions without external intervention. The control system adapts to changing SCR efficiency and compensates accordingly
Data Source
AI summary
Methods and systems for operating an engine that includes a low pressure EGR passage and a selective reduction catalyst are disclosed. In one example, an actuator is adjusted in response to a NOx mass flow rate in the low pressure EGR passage.