Exhaust Aftertreatment NO2/NOx Ratio Monitoring via Oxygen Consumption
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing exhaust aftertreatment systems for heavy-duty diesel engines face challenges in monitoring and improving NOx emissions, particularly in determining the performance of diesel oxidation catalysts (DOC) and selective catalytic reduction (SCR) systems, which are temperature-dependent and require effective oxygen and NO2/NOx ratio management.
Innovation Solution
The system employs wide-band oxygen sensors and NOx sensors upstream and downstream of the oxidation catalyst to determine oxygen consumption and NO2 generation, calculating the NO2/NOx ratio to evaluate the oxidation catalyst's performance and detect potential faults, ensuring optimal operation and SCR conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If oxidation catalyst performance is monitored using traditional methods, then system complexity is reduced, but measurement precision of NO2/NOx ratio and oxygen consumption is insufficient
Solution Approach 1:
The exhaust aftertreatment system is segmented into multiple monitoring zones with dedicated sensors: upstream oxygen sensor before DOC, downstream oxygen sensor after DOC, upstream NOx sensor before SCR, and downstream NOx sensor after SCR. This segmentation enables precise measurement of oxygen consumption and NO2/NOx ratio at different locations, resolving the measurement precision issue while organizing complexity through functional zonation.
Solution Approach 2:
Wide-band oxygen sensors are introduced as intermediary measurement devices that provide continuous lambda values for calculating oxygen consumption. These sensors act as mediators between the exhaust gas composition and the control system, enabling precise determination of DOC performance without requiring direct measurement of all exhaust parameters simultaneously.
2Reliability
If multiple sensors are deployed to monitor oxygen consumption and NO2 generation, then evaluation accuracy of oxidation catalyst improves, but device complexity increases
Solution Approach 1:
The control unit performs multiple evaluation functions using the sensor data: it calculates oxygen consumption across DOC, determines NO2 generation, computes NO2/NOx ratios, and evaluates catalyst health status. This multi-functionality consolidates what would otherwise require separate monitoring systems into a single integrated control unit, improving reliability without proportionally increasing complexity.
Solution Approach 2:
The system implements continuous feedback loops where sensor measurements feed into real-time calculations of DOC performance metrics. The control unit continuously monitors oxygen consumption and NO2/NOx ratio, comparing against thresholds to detect catalyst degradation or faults. This feedback mechanism enhances evaluation reliability by providing ongoing verification rather than single-point checks.
3Speed
If real-time monitoring of oxygen consumption is implemented, then detection speed of catalyst faults improves, but energy consumption increases
Solution Approach 1:
The control unit performs oxygen consumption and NO2/NOx ratio calculations at periodic intervals based on engine operating conditions rather than continuously at maximum processing rate. This periodic evaluation maintains fast fault detection capability for critical issues while reducing computational energy consumption during steady-state operation, balancing speed and energy usage.
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 allows for real-time monitoring and evaluation of the oxidation catalyst's efficiency, enabling effective NOx reduction and improving the overall performance of the exhaust aftertreatment system by maintaining an optimal NO2/NOx ratio, thus enhancing NOx conversion efficiency and reducing emissions.
Implementation Method 1
an oxidation catalyst arranged upstream of a selective catalytic reduction (SCR) catalyst... determining, via a first oxygen sensor and a second oxygen sensor, a consumption of oxygen in the oxidation catalyst due to oxidation reactions
Implementation Method 2
a first wide-band oxygen sensor arranged to monitor an exhaust gas feedstream upstream of the oxidation catalyst, and a second wide-band oxygen sensor arranged to monitor the exhaust gas feedstream downstream of the oxidation catalyst
Implementation Method 3
a downstream NOx sensor arranged to monitor an exhaust gas feedstream downstream of the oxidation catalyst... determine an engine-out NO2 concentration in the exhaust gas feedstream upstream of the oxidation catalyst
Data Source
Figure 1
Figure 2
AI summary
An exhaust aftertreatment system and associated method for purifying an exhaust gas feedstream of a lean-burn or other compression-ignition internal combustion engine is described. An instruction set is executable to determine an engine-out NO2 concentration upstream of an oxidation catalyst and determine a first parameter associated with 02 concentration. A consumption of oxygen in the oxidation catalyst due to oxidation reactions is determined, and a concentration of NO2 generated by the oxidation catalyst is determined based upon the consumption of oxygen in the oxidation catalyst. A concentration of NO2 downstream of the oxidation catalyst is determined. A NO2/NOx ratio in the exhaust gas feedstream downstream of the oxidation catalyst is determined based upon the concentration of NO2 downstream of the oxidation catalyst and the NOx concentration measured by the downstream NOx sensor. The oxidation catalyst is evaluated based upon the NO2/NOx ratio.