Oxidation Catalyst Degradation Diagnosis via HC Sensor
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Solution Overview
Problem
Existing methods for diagnosing the degradation of oxidation catalysts in diesel engine exhaust systems, particularly in excessive oxygen atmospheres, face challenges due to inaccuracies in measuring the conversion rate of unburned hydrocarbons, interference from nitrogen monoxide and nitrogen dioxide gases, and reliance on indirect diagnosis techniques that are prone to errors from temperature and exhaust gas flow rate variations.
Innovation Solution
A method involving a hydrocarbon gas sensor placed downstream of the catalyst, which generates a diagnosis index value by measuring the change in electromotive force after introducing a gas atmosphere with a higher hydrocarbon concentration than the steady-state operation, allowing for real-time diagnosis of catalyst degradation without calculating conversion rates or being influenced by interference gases, and using a threshold set based on the catalyst temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If indirect diagnosis methods using temperature sensors or oxygen sensors are used to diagnose catalyst degradation, then the diagnosis can be performed without additional HC sensors, but the measurement precision is reduced due to errors from temperature and flow rate variations
Solution Approach 1:
The patent introduces a hydrocarbon gas sensor as an intermediary measurement device that directly measures HC concentration downstream of the catalyst. This intermediary sensor provides accurate HC concentration data without being affected by temperature and flow rate variations that plague indirect methods using temperature or oxygen sensors.
Solution Approach 2:
The patent replaces indirect mechanical/thermal measurement methods (temperature sensors, oxygen sensors) with a chemical sensing method (HC sensor) that directly measures the concentration of hydrocarbon gases. This substitution eliminates the errors associated with temperature and flow rate variations in indirect methods.
2Temperature
If fuel injection is increased to accelerate heat generation for diagnosis, then the diagnosis can be performed at required temperature, but fuel consumption increases
Solution Approach 1:
The patent uses partial action by injecting fuel only for the specific purpose of catalyst heating during diagnosis periods, rather than continuous injection. The control unit manages fuel injection timing and quantity to achieve the minimum necessary temperature for accurate HC measurement without excessive fuel consumption.
Solution Approach 2:
The system performs preliminary heating of the catalyst using controlled fuel injection before conducting the actual degradation diagnosis. This preliminary action ensures the catalyst reaches the required temperature for accurate measurements without maintaining continuous high fuel injection.
3Device complexity
If conversion rate calculation is used to diagnose catalyst degradation, then the diagnosis can be performed without HC sensors, but the reliability is reduced due to interference from nitrogen monoxide and nitrogen dioxide gases
Solution Approach 1:
The patent introduces a hydrocarbon gas sensor as a specialized intermediary device that selectively measures HC concentration. This sensor acts as a mediator that distinguishes HC signals from interference gases like NO and NO2, providing reliable degradation diagnosis data that conversion rate calculations cannot achieve.
Solution Approach 2:
The HC sensor utilizes selective detection capabilities analogous to color changes, where the sensor responds specifically to hydrocarbon gases and distinguishes them from other exhaust components. This selective response enables reliable HC concentration measurement despite the presence of interference gases.
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 enables accurate, real-time diagnosis of oxidation catalyst degradation with minimal fuel consumption, avoiding errors associated with indirect methods and interference gases, ensuring timely replacement and maintaining engine performance compliance with environmental criteria.
Implementation Method 1
a target gas detecting element disposed downstream of the oxidation catalyst in the exhaust path, the target gas detecting element outputting an electromotive force corresponding to a concentration of the target gas as a detection signal of the target gas
Implementation Method 2
a catalyst which is provided in an exhaust path of an internal combustion engine and which oxidizes or adsorbs unburned hydrocarbon gas
Implementation Method 3
the unburned hydrocarbon gas is intentionally generated in the internal combustion engine
Data Source
AI summary
Provided is a method for accurately diagnosing a degree of degradation of an oxidation catalyst. A target gas detecting element configured to output an electromotive force corresponding to a concentration of a target gas is provided downstream of a catalyst in an exhaust path of an internal combustion engine. A sum of change amounts of an electromotive force in a time-variable profile thereof after the introduction of a gas atmosphere for diagnosis into the catalyst is set as a diagnosis index value. The gas atmosphere has been intentionally created in the engine and includes a target gas having a concentration higher than the concentration of a target gas during a steady operation state of the engine. The index value is then compared with a threshold corresponding to the temperature of the catalyst to diagnosis whether degradation exceeding an acceptable degree has occurred in the catalyst.