Chirped Pulse Quantum Cascade Laser Thermometry
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Solution Overview
Problem
Current thermometry techniques in combustion environments lack sufficient temporal resolution and are not calibration-free, making it difficult to accurately measure rapid temperature fluctuations in gases within engines and shock tubes without invasive methods.
Innovation Solution
A sensor system utilizing a pulsed laser with intrapulse spectroscopy, specifically a chirped pulse quantum cascade laser, to rapidly scan across H2O transition lines, allowing for high temporal and spatial resolution temperature measurements independent of gas composition and pressure changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional thermometry techniques are used in combustion environments, then temperature measurements can be obtained, but the temporal resolution is insufficient and calibration is required
Solution Approach 1:
The patent employs pulsed laser operation with repetition rates up to several MHz, where each pulse performs a complete spectral scan. This periodic action enables high temporal resolution measurements by capturing temperature information at discrete time points throughout rapid combustion processes, directly resolving the contradiction between measurement precision and productivity.
Solution Approach 2:
The patent replaces traditional mechanical scanning systems with electro-optical modulation of the laser frequency within each pulse. This substitution eliminates mechanical inertia limitations, enabling temporal resolution in the microsecond range and achieving both high measurement precision and productivity simultaneously.
2Measurement precision
If invasive measurement methods are used, then temperature can be measured in combustion environments, but the measurement process interferes with the system being studied
Solution Approach 1:
The patent uses optical radiation (laser) to probe the combustion environment remotely, replacing invasive physical probes. This non-contact measurement approach eliminates system interference while maintaining high temperature measurement accuracy through absorption spectroscopy of H2O transition lines.
Solution Approach 2:
The patent uses H2O molecules in the combustion gas as an intermediary medium. The laser measures temperature by detecting absorption features of water vapor naturally present in the combustion environment, avoiding direct interaction with the hot gas while achieving accurate temperature measurements.
3Loss of information
If conventional spectroscopy methods are used, then gas composition information can be obtained, but the temporal resolution is too slow for rapidly evolving combustion processes
Solution Approach 1:
The patent performs complete spectral scans within each laser pulse at repetition rates up to several MHz, capturing gas composition information at microsecond time intervals. This periodic measurement approach minimizes information loss about rapidly changing combustion conditions while maintaining comprehensive spectral data.
Solution Approach 2:
The patent pre-tunes the laser to cover the spectral region containing H2O transition lines before each pulse. This preliminary preparation enables immediate measurement upon pulse initiation, reducing the time required to capture gas composition information during rapid combustion events.
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
The system provides precise, non-invasive temperature measurements with high temporal resolution, overcoming limitations of traditional methods by using a calibration-free approach that can capture temperature changes in rapidly evolving systems, such as internal combustion engines and shock tubes.
Implementation Method 1
tuning a beam of coherent electromagnetic radiation to a range of peak absorbance in the material. The beam can be transmitted through the material and chirped at a rate of less than 5 microseconds. An intrapulse absorbance of the beam can be measured.
Data Source
AI summary
A system and method for rapid thermometry using intrapulse spectroscopy can include a laser for propagating pulses of electromagnetic radiation to a region. Each of the pulses can be chirped. The pulses from the region can be detected. An intrapulse absorbance spectrum can be determined from the pulses. An instantaneous temperature of the region based on the intrapulse absorbance spectrum can be determined.