Exhaust Purification System with Downstream NOx Estimation
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Solution Overview
Problem
Existing exhaust purification systems for internal combustion engines face challenges in accurately controlling the injection amount of urea water due to variability in NOx purification rate caused by exhaust composition, temperature, and catalyst degradation, leading to inefficient NOx reduction and excessive NH3 slip.
Innovation Solution
An exhaust purification system that includes a selective reduction catalyst, a reducing agent supply system, a downstream NOx sensor, an upstream NOx sensor, and estimation and control mechanisms to model the NOx concentration downstream of the catalyst, allowing for precise determination of the reducing agent supply based on the identified purification coefficient and error minimization, thereby optimizing NOx purification and minimizing NH3 slip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the injection amount of urea water is increased to improve NOx purification rate, then more NH3 is available for reduction, but excessive NH3 slip occurs when the purification rate exceeds optimal levels
Solution Approach 1:
The system uses downstream NOx sensor output to identify the purification coefficient and estimate downstream NOx concentration, creating a feedback loop that adjusts urea water injection amount to maintain optimal purification rate and prevent NH3 slip
Solution Approach 2:
The system dynamically changes the purification coefficient parameter based on identified values from sensor data, adjusting the control strategy to match actual catalyst performance and operating conditions
2Ease of operation
If conventional exhaust purification systems are used with fixed control strategies, then system complexity is low, but accurate control of urea water injection is difficult due to variability in purification rate
Solution Approach 1:
The system replaces complex mechanical adjustment mechanisms with an electronic identification and estimation system that uses sensor data and algorithms to determine optimal injection amounts, achieving accurate control through computational methods rather than mechanical means
3Measurement precision
If downstream NOx sensor is used to detect NOx concentration, then purification rate can be monitored, but the sensor output is affected by both NOx and NH3 making accurate measurement difficult
Solution Approach 1:
The system extracts the purification coefficient information from the mixed sensor signal by identifying the relationship between upstream NOx input and downstream sensor output, separating the useful purification rate information from the NH3 interference
Solution Approach 2:
The purification coefficient acts as an intermediary parameter that translates the mixed sensor signal into meaningful NOx purification rate information, enabling accurate measurement despite NH3 presence in the exhaust
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
The system achieves improved NOx purification rates and reduced NH3 slip by accurately estimating the NOx concentration downstream of the catalyst, ensuring optimal reducing agent supply and maintaining high NOx purification performance even during transient engine states.
Implementation Method 1
a selective reduction catalyst that purifies NOx in the exhaust under the presence of NH3
Implementation Method 2
NOx is selectively reduced by this NH3
Implementation Method 3
NH3 is generated by thermal decomposition or hydrolysis of this urea water by the heat of the exhaust
Implementation Method 4
NH3 is generated by thermal decomposition or hydrolysis of this urea water by the heat of the exhaust
Implementation Method 5
a NOx sensor that detects the concentration of NOx
Implementation Method 6
an NH3 sensor that detects the concentration of NH3
Data Source
AI summary
An exhaust purification system is provided that can appropriately grasp the NOx concentration or NH3 concentration on a downstream side of a selective reduction catalyst. A separation filter of the system models a downstream NOx estimated value (NOx_DW_hat) of the catalyst with a value obtained by multiplying a coefficient (Kscr) by an output (NOx_UP) of an upstream-side NOx sensor. The separation filter includes transient extraction filters that block a stationary component and allow a frequency band corresponding to an increase-decrease request of drive power from the driver to pass from the downstream NOx sensor output (Ynox) and upstream NOx sensor output (NOx_UP), and calculate filter values (Ynox_f, NOx_UP_f) of each; and an identifier that identifies the coefficient (Kscr) so that error (eid) between the filter value (Ynox_f) and a value (NOx_DW_hat_f) obtained by multiplying the purification coefficient (Kscr) by the filter value (NOx_UP_f) becomes a minimum.