SCR Catalyst Efficiency Determination via Exhaust Gas Recirculation

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Solution Overview

Problem

Existing exhaust gas after-treatment systems, particularly those using selective catalytic reduction (SCR) catalysts in lean burn internal combustion engines, face challenges in efficiently converting nitrogen oxides (NOX) without adequate ammonia presence, requiring precise control and monitoring to maintain system efficiency and prevent malfunctions.

Innovation Solution

A method involving an exhaust gas recirculation system with a controller that detects pollutant concentrations, calculates theoretical efficiency, and activates alerts or limp-home modes when efficiency drops, using a single NOX sensor to manage urea injection and recirculation for effective NOX conversion in SCR catalysts.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single NOX sensor is used to monitor exhaust gas composition, then system complexity and cost are reduced, but the ability to accurately determine AT device efficiency is compromised

Engineering Contradiction:

Improvesensor quantityVSAvoidefficiency determination accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent uses exhaust gas recirculation (EGR) as an intermediary mechanism to transport treated exhaust gas back to the sensor location. This allows the single NOX sensor to indirectly monitor downstream conditions by measuring the composition of recirculated gas, enabling efficiency determination without requiring direct downstream sensing

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system implements a feedback loop where the NOX sensor continuously monitors exhaust composition, the controller calculates AT device efficiency based on sensor readings and EGR flow rates, and the system adjusts operations or alerts users when efficiency thresholds are not met. This closed-loop feedback enables accurate monitoring with minimal hardware

Inventive Principle:

Principle #23Feedback

2Reliability

If exhaust gas recirculation is implemented to maintain continuous operation, then system availability is improved, but the complexity of efficiency calculation increases

Engineering Contradiction:

Improvecontinuous operationVSAvoidcalculation complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The system pre-establishes the mathematical relationships and efficiency calculation algorithms in the controller before operation. The controller is pre-programmed with the formulas that relate NOX concentrations, EGR flow rates, and AT device efficiency, allowing real-time calculations to be performed using stored computational models rather than complex real-time derivations

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent replaces complex physical monitoring systems with mathematical modeling. Instead of using multiple sensors or complex physical measurement devices to directly measure efficiency, the system uses computational models that calculate efficiency based on readily available sensor data and EGR flow measurements, substituting mechanical complexity with computational simplicity

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical 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

This approach ensures continuous operation of the after-treatment system by maintaining theoretical efficiency above a predetermined value, alerting users to potential malfunctions, and reducing emissions by optimizing NOX conversion in SCR catalysts, even with varying engine conditions.

Implementation Method 1

The SCR is configured to convert nitrogen oxides (NOX) into diatomic nitrogen (N2) and water (H2O) with the aid of the NO2 generated by another exhaust AT device

Methodology Applied

Scientific EffectSelective catalytic reduction: Catalysis

Implementation Method 2

The SCR conversion process additionally requires a predetermined amount of ammonia (NH3) to be present in the exhaust gas flow

Methodology Applied

Scientific EffectChemical reduction: Reduction

Implementation Method 3

typically the diesel oxidation catalyst (DOC)

Methodology Applied

Scientific EffectOxidation: Oxidation

Implementation Method 4

recirculating, via an exhaust gas recirculation (EGR) passage, a portion of the treated exhaust gas from the exhaust gas passage to the intake passage

Methodology Applied

Scientific EffectGas recirculation: Convection

Data Source

PatentUS10337383B2Selective catalyst reduction efficiency determination

Publication Date: 2019.07.02 GM GLOBAL TECHNOLOGY OPERATIONS LLC

AI summary

A method for an engine employing an after-treatment (AT) system with an AT device for treating an engine exhaust gas includes detecting an actual concentration of a pollutant in the exhaust gas upstream of the AT device. The method additionally includes treating the exhaust gas via the AT device and directing the treated gas to an exhaust gas passage. The method also includes recirculating a portion of the treated exhaust gas from the exhaust gas passage to the engine's intake passage and determining efficiency of the AT device, after recirculating the portion of the treated exhaust gas, using the detected actual pollutant concentration. Furthermore, the method includes maintaining operation of the AT system when the determined AT device efficiency is at or above a predetermined value and activating a sensory signal indicative of the AT device having malfunctioned when the determined AT device efficiency is below the predetermined value.