NOx Model for Real-Time Exhaust Emission Estimation
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Solution Overview
Problem
Commercially available NOx sensors for SCR systems are expensive and have operational drawbacks, such as limited accuracy and sensitivity to environmental and operating conditions, making them unsuitable for determining optimal reductant dosing levels, especially during low idle conditions or engine warm-up, and increasing maintenance costs.
Innovation Solution
A method to estimate engine-out NOx content using a control unit that determines engine speed, engine load, intake oxygen level, fuel pressure, and fuel quantity, applying these parameters to a NOx model to predict NOx levels without relying on NOx sensors, utilizing local and global NOx emission models to derive a global model for real-time NOx emission estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If commercially available NOx sensors are used to determine reductant dosing levels, then NOx measurement capability is provided, but system cost and maintenance requirements increase
Solution Approach 1:
The patent creates a virtual copy of the NOx sensor function through a computational model that replicates NOx measurement capabilities using existing sensor data (oxygen, temperature, pressure) and engine parameters. This software-based copy eliminates the need for expensive physical NOx sensors while maintaining measurement functionality.
Solution Approach 2:
The patent replaces the mechanical/physical NOx sensor system with a computational/software-based system. The physical sensor hardware is substituted by an algorithm that processes available data to estimate NOx levels, thereby eliminating the mechanical measurement device while achieving the same functional goal.
2Measurement precision
If NOx sensors are used to determine reductant dosing levels, then NOx detection is enabled, but operational reliability deteriorates under certain engine conditions
Solution Approach 1:
The patent implements a dynamic model that adapts to changing engine conditions (temperature, load, speed) rather than relying on a static sensor. The computational approach adjusts its calculations based on real-time engine parameters, maintaining reliability across varying operating conditions where physical sensors fail.
Solution Approach 2:
The patent changes the measurement parameters from direct NOx concentration detection to using correlated parameters (oxygen level, temperature, pressure, engine load) that can be reliably measured across all engine conditions. By measuring different parameters and computing NOx from them, the system achieves reliability where direct NOx sensing fails.
3Measurement precision
If NOx sensors are positioned in the exhaust stream for accurate measurement, then NOx content detection is improved, but exposure to high temperatures and dew point reduces sensor lifespan
Solution Approach 1:
The patent introduces an intermediary computational layer between the harsh exhaust environment and the measurement function. Instead of placing a sensor directly in the hot exhaust stream, the system uses intermediate parameters (oxygen, temperature, pressure) that can be measured in safer locations and computes NOx through calculation, protecting the measurement system from environmental damage.
Data Source
AI summary
Methods are provided for estimating the NOx content of exhaust gas produced by an internal combustion engine. The method includes determining one or more operating parameters. The method further includes applying the determined operating parameter(s) to a global NOx model. The global NOx model may be derived using a plurality of steady state data points relating to local NOx emission models. The steady state data points may be derived using a plurality of set and variable operating parameters. The global NOx model allows for prediction of the engine-out NOx content of exhaust gas in real time and without a NOx sensor, even if engine operating parameters change.