Exhaust Flow Rate Estimation Using NOx Sensor Feedback
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Solution Overview
Problem
Existing methods for estimating exhaust flow rate in large internal combustion engines, such as high horse power engines, are inaccurate due to complex tuning requirements and fail to account for variations in altitude, engine-to-engine differences, and flow restrictions in aftertreatment systems.
Innovation Solution
A system and method using a NOx sensor to measure oxygen fractions in exhaust gas, combined with a fuel rate signal, to determine the air-fuel ratio and subsequently the exhaust flow rate, allowing for more accurate calculations irrespective of altitude and engine variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If exhaust flow rate is estimated using engine speed density model or speed/torque pre-tuned table, then the estimation can be obtained, but the accuracy is insufficient for large engines and fails to account for altitude changes, engine variations, and flow restrictions
Solution Approach 1:
The patent replaces complex mechanical tuning and calibration systems with an electronic control system that uses sensors (NOx sensor, mass airflow sensor) and electronic processing to determine exhaust flow rate. The controller electronically calculates exhaust flow rate based on real-time sensor data, eliminating the need for complex mechanical tuning procedures while improving accuracy across different engine conditions including altitude variations and engine-to-engine variations.
2Measurement precision
If conventional estimation methods are used, then the system is simple to implement, but the accuracy deteriorates under varying altitude, engine variations, and flow restrictions
Solution Approach 1:
The patent implements a feedback-based measurement system using NOx sensors and mass airflow sensors that continuously monitor exhaust conditions and provide real-time data to the controller. The controller uses this feedback information to dynamically calculate and adjust exhaust flow rate determinations, enabling accurate measurements across varying altitude conditions, engine-to-engine variations, and flow restrictions without requiring system redesign or retuning.
Solution Approach 2:
The patent changes the measurement parameters from engine operating conditions (speed, torque) to direct exhaust composition measurements (NOx concentration, oxygen concentration, mass airflow). This parameter change enables the system to accurately determine exhaust flow rate regardless of altitude changes, engine variations, or flow restrictions, as the measurements are taken directly from the exhaust stream rather than inferred from engine operating parameters.
3Reliability
If speed/torque pre-tuned table method is used, then initial setup is straightforward, but the method fails to account for flow restrictions due to filter or catalyst plugging
Solution Approach 1:
The patent uses feedback from NOx sensors and mass airflow sensors to continuously monitor actual exhaust flow conditions. When flow restrictions occur due to filter or catalyst plugging, the sensors detect changes in exhaust composition and flow characteristics, and the controller adjusts the exhaust flow rate determination accordingly. This maintains measurement reliability and enables detection of flow restrictions without complicating system operation.
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 provides a simple, drop-in solution for determining exhaust flow rate with higher accuracy, overcoming the limitations of conventional methods by using actual measurements from NOx and fuel-rate sensors, thus enabling more precise engine efficiency assessment and reductant injection in SCR systems.
Implementation Method 1
a first sensor configured to measure an amount of NOx gases in the exhaust gas... determine an air-fuel ratio from the first sensor signal
Data Source
AI summary
A system for determining an exhaust flow rate of an exhaust gas produced by an engine comprises a first sensor configured to measure an amount of NOx gases in the exhaust gas. A controller is communicatively coupled to the first sensor. The controller is configured to receive a first sensor signal from the first sensor. The controller is also configured to receive a fuel rate signal corresponding to a rate of fuel consumption by the engine. The controller is configured to determine an air-fuel ratio from the first sensor signal and determine a fuel rate from the fuel rate signal. Furthermore, the controller is configured to determine the exhaust flow rate from the air-fuel ratio and the fuel rate.