DOC Deterioration Diagnosis via NOx Purification Rates
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Solution Overview
Problem
Existing diagnostic methods for deterioration of Diesel Oxidation Catalysts (DOC) in exhaust systems are inaccurate due to the difficulty in directly detecting NO2 in exhaust gases, leading to unreliable diagnosis of DOC deterioration.
Innovation Solution
A diagnostic device that calculates low and high temperature NOx purification rates and hydrocarbon purification rates based on NOx values at upstream and downstream sides of the SCR catalyst, and determines DOC deterioration by analyzing these rates and heat generation differences across the DOC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the value of NO2 is estimated by multiplying a ratio of NO2 to NO by the detection value of the NOx sensor, then the diagnosis can be performed without direct NO2 detection, but the diagnosis accuracy deteriorates because the ratio changes with running condition
Solution Approach 1:
The patent segments the NOx purification process into two distinct temperature ranges (low temperature and high temperature) and calculates separate purification rates for each range. This segmentation allows the system to account for temperature-dependent variations in the NO2/NO ratio, thereby maintaining diagnosis accuracy across different running conditions while avoiding direct NO2 detection
Solution Approach 2:
The patent changes the diagnostic approach from using a single static NO2/NO ratio to calculating dynamic purification rates that vary with temperature. By adjusting the diagnostic parameters (purification rate calculations) based on temperature conditions, the system maintains accuracy across varying running conditions without requiring direct NO2 measurement
2Device complexity
If the DOC deterioration is diagnosed using estimated NO2 values, then the diagnostic system can be simplified, but the reliability of deterioration determination deteriorates
Solution Approach 1:
The patent introduces purification rate calculations as an intermediary step between NOx sensor measurements and DOC deterioration determination. By using purification rates (calculated from upstream and downstream NOx values at different temperatures) as the intermediary metric, the system maintains reliable deterioration diagnosis without requiring complex direct NO2 detection hardware
Solution Approach 2:
The patent replaces the need for direct NO2 detection hardware with a computational approach that uses standard NOx sensors and temperature-based purification rate calculations. This substitution maintains diagnostic reliability while simplifying the physical sensor 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
Enables precise diagnosis of DOC deterioration, unaffected by changes in engine running conditions, improving the accuracy of NO2 producing capability assessment and HC purification rate determination.
Implementation Method 1
an oxidation catalyst (Diesel Oxidation Catalyst: DOC) for oxidizing hydrocarbons (HC) and carbon monoxide (CO) contained in an exhaust gas and also oxidizing nitrogen monoxide (NO) to produce nitrogen dioxide (NO2)
Implementation Method 2
oxidize at least hydrocarbons and nitrogen monoxide contained in an exhaust gas... calculate a hydrocarbon purification rate of the oxidation catalyst based on at least a difference in exhaust gas heat quantity
Implementation Method 3
a selective catalytic reduction (SCR) catalyst for selectively reducing and purifying nitrogen compounds (NOx) contained in the exhaust gas
Implementation Method 4
configured to reduce and purify NOx contained in the exhaust gas with ammonia being a reducing agent
Data Source
AI summary
A diagnostic device includes: a diesel oxidation catalyst (DOC) for oxidizing hydrocarbon (HC) and nitrogen monoxide in an exhaust gas; a selective catalytic reduction (SCR) catalyst for reducing and purifying NOx contained in the exhaust gas; a NOx purification rate calculation unit which calculates, based on NOx values at upstream and downstream sides of the SCR catalyst, a low temperature NOx purification rate and a high temperature NOx purification rate; a HC heat generation rate calculation unit which calculates an HC purification rate based on at least the difference between the exhaust gas heat quantities at upstream and downstream sides of the DOC; and a deterioration determination unit which determines the deterioration in the NO2 producing capability of the DOC based on the calculated low temperature NOx purification rate, the calculated high temperature NOx purification rate, and the calculated HC purification rate.