Particulate Sensor Temperature Control for Exhaust Gas
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Solution Overview
Problem
Existing particulate sensors in diesel engines face challenges in maintaining consistent particulate accumulation rates due to varying mechanisms like electrophoretic, thermophoretic, and direct impact, which can lead to inaccurate readings and slow response times, especially when condensation occurs below the dew-point temperature.
Innovation Solution
A particulate sensing system with a heater element and processor that maintains a sensor temperature between the dew-point and burn-off temperatures, and applies zero-bias or electrophoretic voltage strategically to minimize thermophoretic and electrophoretic accumulation, ensuring consistent particulate detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the sensor temperature is maintained below the dew-point temperature to prevent overheating, then energy consumption is reduced, but condensation occurs causing wet particulate accumulation and erroneous readings
Solution Approach 1:
The patent dynamically adjusts the sensor temperature parameter based on exhaust temperature conditions. When exhaust temperature exceeds the dew-point, the sensor is heated above dew-point to prevent condensation and wet particulate accumulation. When exhaust temperature is below dew-point, the sensor remains cool to minimize energy consumption. This conditional parameter adjustment resolves the contradiction between energy efficiency and measurement accuracy.
2Loss of time
If electrophoretic voltage is applied to accelerate particulate accumulation, then response time is improved, but accumulation rate becomes inconsistent due to varying mechanisms
Solution Approach 1:
The patent implements dynamic control of the electrophoretic voltage based on real-time temperature monitoring. The system transitions between different voltage states (zero-bias, electrophoretic accumulation voltage) depending on whether the sensor temperature is above or below the dew-point and relative to exhaust temperature. This dynamic adjustment ensures consistent accumulation rates by preventing condensation-induced variability while maintaining accelerated accumulation when conditions permit.
3Measurement precision
If the sensor is heated to burn-off particulates to initiate from a known condition, then measurement accuracy is improved, but thermophoretic accumulation increases reducing response time
Solution Approach 1:
The patent employs periodic burn-off cycles rather than continuous heating. The sensor is heated to burn-off temperature periodically to restore a known clean condition, then operated at lower temperatures for normal measurement. This periodic action maintains measurement accuracy by eliminating accumulated particulates that would otherwise cause thermophoretic accumulation, while minimizing energy consumption and response time penalties during normal operation.
4Measurement precision
If zero-bias voltage is applied when exhaust temperature is below dew-point to prevent condensation, then measurement accuracy is maintained, but particulate accumulation rate becomes too slow
Solution Approach 1:
The patent changes the voltage parameter from zero-bias to electrophoretic accumulation voltage when the exhaust temperature exceeds the dew-point. This parameter transition enables faster particulate accumulation by utilizing electrophoretic mechanisms while ensuring that condensation does not occur. The system monitors temperature conditions and adjusts voltage accordingly, resolving the contradiction between maintaining accuracy through zero-bias and achieving productive accumulation rates.
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 reduces thermophoretic accumulation, prevents wet particulate contamination, and synchronizes accumulation mechanisms for predictable and accurate particulate detection, enhancing sensor response time and accuracy.
Implementation Method 1
The thermophoretic effect generally occurs when the surface temperature of the sensor is lower than the particulate or exhaust temperature 52. The processor is configured to operate the heater element to establish a sensor temperature greater than a dew-point temperature of the exhaust gas and less than a burn-off temperature of the sensor to reduce thermophoretic accumulation of particulates on the sensor.
Implementation Method 2
The electrophoretic accumulation is caused by a voltage applied across the electrodes that attracts charged particulates. The processor is further configured to apply an electrophoretic voltage across the first electrode and the second electrode if an exhaust temperature of the exhaust gas is greater than the dew-point temperature and the sensor temperature is less than the exhaust temperature.
Implementation Method 3
Typically, prior to operating the sensor to accumulate particulates, the sensor is heated to a sensor temperature effective to burn-off all or most of the particulates. The processor is configured to operate the heater element to establish a sensor temperature greater than a dew-point temperature of the exhaust gas and less than a burn-off temperature of the sensor
Data Source
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AI summary
A particulate sensing system (10) configured to detect particulates in exhaust gas (12) from a combustion process. Particulates are detected based on electrical conductivity between a first electrode (42) and a second electrode (44). A heater element (54) is provided to heat the first electrode (42) and the second electrode (44). The first electrode (42), the second electrode (44), and the heater element (54) cooperate to form a sensor (40). The heater element (54) is operated to establish a sensor (40) temperature greater than a dew-point temperature of the exhaust gas (12) and less than a bum-off temperature of the sensor (40) to reduce thermophoretic accumulation of particulates on the sensor (40). When the exhaust temperature (52) and the sensor (40) temperature are suitable for thermophoretic accumulation and electrophoretic accumulation of particulates, a voltage is applied across the electrodes to facilitate electrophoretic accumulation of particulates, and the heater element (54) is turned off so thermophoretic accumulation occurs.