SDPF Controller NH3 Slip Detection
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Solution Overview
Problem
The existing exhaust gas purification systems using selective catalytic reduction (SCR) catalysts on diesel particulate filters (SDPFs) face challenges in accurately detecting ammonia (NH3) slip, leading to misdiagnosis of NOx purification efficiency and increased costs due to incorrect urea injection and sensor limitations, especially under varying driving conditions.
Innovation Solution
An exhaust gas purification system that includes a controller to detect NH3 slip in real-time using NOx sensor values and model values, adjust urea injection, and improve the reliability of on-board diagnostics (OBD) by calculating the amount of ammonia slip and optimizing urea injection, while including a catalytic converter and a reducing agent injector to maintain optimal NOx purification efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If urea injection is increased to maintain NOx purification efficiency, then NOx purification is improved, but NH3 slip increases and causes false OBD diagnosis
Solution Approach 1:
The patent introduces a model-based estimation system as an intermediary to calculate NH3 slip amount. Instead of directly measuring NH3 slip which causes false diagnoses, the system uses a mathematical model that incorporates NOx sensor data, urea injection amount, and engine operating conditions to indirectly determine NH3 slip. This intermediary calculation allows the system to distinguish between actual NH3 slip and sensor measurement errors.
Solution Approach 2:
The patent implements a feedback control mechanism where the calculated NH3 slip amount is continuously fed back to adjust urea injection. The controller compares the calculated NH3 slip with threshold values and modifies urea injection accordingly. This closed-loop feedback prevents both over-injection (which causes NH3 slip) and under-injection (which reduces NOx purification), while using model-based calculations to avoid false feedback from NH3 slip.
2Loss of information
If NH3 slip is detected to reduce urea injection, then NH3 slip decreases, but NOx purification efficiency deteriorates
Solution Approach 1:
The patent changes the parameter used for control decisions from raw NOx sensor measurements to calculated NH3 slip amounts derived from a mathematical model. By transforming the control parameter from direct sensor readings to model-based calculations that account for multiple factors (engine load, temperature, urea injection rate), the system can make more accurate control decisions that prevent both NH3 slip and NOx purification deterioration.
3Extent of automation
If NOx sensor is used to monitor purification efficiency, then OBD diagnosis is enabled, but NH3 slip is misrecognized as NOx causing false diagnosis
Solution Approach 1:
The patent introduces a model-based estimation system as an intermediary between the NOx sensor and the OBD diagnosis logic. Instead of directly interpreting NOx sensor readings as pure NOx concentrations, the system uses a mathematical model to separate the contributions of actual NOx and NH3 slip. This intermediary calculation layer allows accurate OBD diagnosis while compensating for the NOx sensor's inability to distinguish between NOx and NH3 slip.
Solution Approach 2:
The patent replaces the direct mechanical/sensor-based measurement approach with a computational/model-based approach. Instead of relying solely on the physical NOx sensor to accurately measure NOx concentrations, the system substitutes a mathematical model that processes sensor data along with engine operating parameters to calculate true NOx levels and NH3 slip amounts, thereby eliminating the measurement precision limitations of the sensor alone.
4Measurement precision
If reducing agent injection is optimized to prevent NH3 slip, then measurement accuracy is improved, but system complexity increases due to real-time calculation requirements
Solution Approach 1:
The patent performs preliminary calculations of NH3 slip amount using a mathematical model that incorporates pre-stored engine operating condition data and reducing agent injection parameters. By pre-calculating and storing the relationships between these parameters, the system can quickly determine NH3 slip in real-time without requiring complex real-time modeling computations, thus reducing the computational burden on the control system.
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 effectively reduces NH3 slip, maintains optimal NOx purification efficiency, prevents incorrect measurement of NH3 as NOx, and improves the reliability of OBD diagnosis across various driving conditions by determining the influence of NH3 slip on NOx purification efficiency in real-time.
Implementation Method 1
the NOx contained in the exhaust gas is reduced by the SCR catalyst through an oxidation-reduction reaction with the reducing agents
Implementation Method 2
A selective catalytic reduction catalyst on diesel particulate filter (SDPF) absorbs particulate matter contained the exhaust gas
Data Source
AI summary
An exhaust gas purification system, which includes an engine and an exhaust pipe that is connected to an exhaust manifold of the engine, includes: a catalyst converter disposed at a rear side the engine on the exhaust pipe; a selective catalytic reduction on diesel particulate filter (SDPF) disposed at a rear side of the catalyst converter on the exhaust pipe; a reducing agent injector disposed between the catalyst converter and the SDPF on the exhaust pipe and injecting a reducing agent; and a controller controlling an amount of the reducing agent injected from the reducing agent injector.