New Diagnostic Techniques
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Laser absorption by a uniform medium
Tunable Diode Laser Based Absorption Sensor (TDLAS)
Tunable Diode Laser Based Absorption Sensor (TDLAS)
The study involves the application of tunable diode lasers (TDL) to extract the temperature distribution information using laser absorption spectroscopy (LAS).
The study involves the application of tunable diode lasers (TDL) to extract the temperature distribution information using laser absorption spectroscopy (LAS).
TDLAS based sensors can provide high-bandwidth, species specific, in-situ, quantitative data in the kinetics of chemical reactions and combustion characterisation (temperature, species concentrations and flow velocities)
The method is based on measurement of direct absorbance of a laser beam, resonant with an appropriate molecular transition. The measured absorbance can be related to the state properties of the absorbing media, using the Beer-Lambert law for absorption spectroscopy.
H2O vapour is selected as the absorbing species as it is a major combustion product and is naturally present in the combustion exhausts.
Species of interest in IR for combustion diagnostics
Ref: Bolshovet al., Spectrochimica Acta Part B: Atomic Spectroscopy (2015)
One line DAS thermometry setup with flame stabilized in a Mc Kenna burner as the absorbing medium
Schematic of the scanned wavelength TDLAS set-up for 2-line thermometry
The ratio of integrated absorbances for two transitions with different temperature dependence is a function of the gas temperature alone
Absorption spectrum generated using MAMLAS for 1% CH4 in air centered near 3392 nm at 0.1 bar and 300 K
MAMLAS - Simulation of absorption spectrum
MAMLAS - Simulation of absorption spectrum
At IIST we have developed a user interactive algorithm (Modeling and Analysis of Molecular Laser Absorption Spectroscopy- MAMLAS) for generating absorption spectrum of any species of interest in vapour phase, and at any thermodynamic condition. Some of the features of MAMLAS are the following:
The algorithm can simulation of absorption spectra of gases using data from HITRAN database
Selection of optimal absorption lines to ensure best possible SNR and sensitivity for the proposed applications
Can do analysis of absorption signals to estimate the absolute concentration and temperature accurately.
References:
A. Mahanti, A., Satheesh, K., Mishra, D., Sadanandan, R.: "Deep Learning based Absorption Tomography for Combustion Diagnostics", Proceedings of the 25th AIAA International Space Planes and Hypersonic Systems and Technologies Conference, May 2023, Banglore, India
Dibya Kanti Golui , B. Tech 2020 Report, "Tunable Diode Laser Absorption Based Sensors for Combustion Diagnostics: Molecular Spectroscopic Modeling & Thermometry", IIST
Parmar Pamraat Paragbhai , B.Tech 2019 Report, "Development of a TDLAS Sensor for High-speed Measurements of Gas Temperature", IIST
In collaboration with Dr. Satheesh K, Associate Professor, Laser Absorption Spectroscopy Lab, Department of Aerospace Engineering, IIST.
Related Project:
Title: "Development of a fast response TDLAS temperature sensor for high-temperature applications" (on going), PI: Dr. Rajesh Sadanandan, Co-PI: Dr. Satheesh K
Funding Agency: Aeronautics Research and Development Board (AR & DB), DRDO.
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