NOx Trap Capacity Estimation via Oxygen Proxy
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Solution Overview
Problem
Lean-burning engines face challenges in reducing nitrogen oxides (NOx) emissions due to the high cost of NOx sensors required for determining the NOx storage capacity of NOx traps, which are essential for efficient purging and emissions control.
Innovation Solution
Estimating the NOx storage capacity of NOx traps using oxygen storage capacity measurements from upstream and downstream oxygen sensors by operating the engine at specific air/fuel ratios and temperatures, allowing for a more accurate and cost-effective determination of NOx trap efficiency without the need for expensive NOx sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If NOx sensors are used to measure NOx emissions behind the NOx trap, then the accuracy of NOx storage capacity determination is improved, but the cost of the emissions system increases significantly
Solution Approach 1:
The patent uses oxygen sensors to indirectly measure NOx storage capacity by monitoring oxygen concentration changes during rich-to-lean transitions. Instead of directly measuring NOx with expensive NOx sensors, the system creates a proxy measurement using oxygen sensors, which are cheaper and already present in the emissions system. The oxygen storage capacity serves as a surrogate indicator for NOx storage capacity.
Solution Approach 2:
The patent introduces oxygen concentration measurements as an intermediary parameter to determine NOx storage capacity. Rather than directly measuring NOx, the system measures oxygen concentration upstream and downstream of the NOx trap during controlled rich-to-lean transitions. The change in oxygen storage capacity serves as a mediator to infer NOx storage capacity, avoiding the need for direct NOx sensing.
2Reliability
If the engine operates at rich air/fuel ratio for extended periods to purge the NOx trap, then the NOx storage capacity is restored, but the fuel economy decreases
Solution Approach 1:
The patent implements periodic rich-to-lean transitions to periodically regenerate the NOx trap storage capacity. Rather than continuous rich operation, the system performs controlled periodic excursions to rich conditions followed by returns to lean operation. This periodic action restores NOx storage capacity while minimizing the time spent in fuel-inefficient rich mode, thereby balancing trap performance with fuel economy.
Solution Approach 2:
The patent performs preliminary assessment of NOx storage capacity using oxygen sensor measurements before initiating rich-to-lean transitions. By monitoring oxygen storage capacity trends during normal lean operation, the system can predict when NOx storage capacity will be depleted and schedule regenerative transitions at optimal times, avoiding unnecessary rich operation and preserving fuel economy while ensuring trap performance is maintained.
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 method provides a repeatable and robust estimation of NOx storage capacity, enabling efficient purging of NOx traps while reducing emissions and lowering the overall cost of emissions systems by eliminating the need for NOx sensors.
Implementation Method 1
measuring an oxygen uptake by the catalytic device... An oxygen storage capacity of the catalytic device may be measured while at the diagnostic temperature
Implementation Method 2
The engine can then be configured to produce a rich exhaust containing carbon monoxide, hydrogen gas and various hydrocarbons to reduce the NOx in the trap
Data Source
AI summary
Performance characteristics of a catalytic device are determined based on a particle size of a particulate component of the catalytic device. In this way, aging of a catalytic device can be accounted for in the calculation of performance characteristics.