Particulate Matter Sensor Diagnosis via Liquid Injection
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Solution Overview
Problem
Verifying the operation of particulate matter sensors downstream of a device that holds exhaust constituents is challenging due to the particulate filter's tendency to trap exhaust components, which can lead to unreliable efficiency measurements.
Innovation Solution
Injecting a liquid, such as urea, into the exhaust system before the dewpoint temperature is exceeded to saturate the particulate filter and deposit on the sensor, allowing for conductivity changes to verify sensor operation, with the method conserving liquid by using existing system components and only injecting externally if necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If particulate matter sensors are positioned downstream of a particulate filter to measure filter efficiency, then the sensor can provide indication of particulate matter exiting the filter, but the sensor operation becomes difficult to verify because the particulate filter traps exhaust constituents
Solution Approach 1:
The system performs preliminary action by injecting liquid into the exhaust stream before the downstream particulate matter sensor to intentionally create a detectable signal change. This proactive approach allows verification of sensor functionality by causing a known change (liquid deposition) that should produce a measurable response from the sensor, thereby confirming the sensor is operational before actual particulate matter measurements are taken.
Solution Approach 2:
Liquid is introduced as an intermediary substance to mediate between the difficult-to-verify downstream sensor and the verification system. The liquid serves as a test agent that deposits on the sensor surface, creating a detectable conductivity or signal change that confirms sensor operation without requiring direct observation of the sensor's internal workings or reliance on upstream sensor comparisons.
2Reliability
If liquid is injected into the exhaust system to deposit on the particulate matter sensor for verification, then sensor operation can be diagnosed, but liquid consumption increases
Solution Approach 1:
The system utilizes the existing exhaust stream and its natural flow characteristics to deliver the liquid to the downstream sensor without requiring additional pumping or forced delivery mechanisms. The exhaust gas flow itself serves the dual purpose of carrying the liquid and providing the thermal environment for evaporation, allowing the system to diagnose sensor operation using resources already present in the exhaust system.
Solution Approach 2:
The system changes physical parameters by controlling the evaporation of injected liquid through temperature management. By injecting liquid at controlled rates and allowing it to evaporate in the hot exhaust stream, the system creates optimal deposition conditions on the sensor surface. This parameter control ensures efficient use of liquid while maintaining reliable diagnostic capability.
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 effectively diagnoses the operation of particulate matter sensors, even when located downstream, providing a reliable method to assess sensor functionality and conserve diagnostic fluids by utilizing existing exhaust system components.
Implementation Method 1
depositing at least some of the liquid on the particulate matter sensor
Implementation Method 2
saturate a particulate filter, SCR, and/or catalyst with the liquid
Data Source
AI summary
A method for diagnosing a particulate matter sensor is described. In one example, a liquid is purposefully injected into the exhaust system to verify operation of the particulate matter sensor. Reliability of particulate matter diagnostics may be improved by way of the approach, at least during some conditions.