Dual-laser-induced Breakdown Thermometry via Sound Speed Measurement：A New Procedure for Improved Spatiotemporal Resolution.

Shen Li,Zhongshan Li,Chengdong Kong,Wubin Weng,Marcus Aldén

doi:10.3390/s20102803

Shen Li, Zhongshan Li + Show 3 more

Open Access

https://doi.org/10.3390/s20102803

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Abstract

Measurement of acoustic waves from laser-induced breakdown has been developed as gas thermometry in combustion atmospheres. In the measurement, two laser-induced breakdown spots are generated and the local gas temperature between these two spots is determined through the measurement of the sound speed between them. In the previous study, it was found that the local gas breakdown can introduce notable system uncertainty, about 5% to the measured temperature. To eliminate the interference, in present work, a new measurement procedure was proposed, where two individual laser pulses with optimized firing order and delay time were employed. With the new measurement procedure, the system uncertainty caused by local gas breakdown can be largely avoided and the temporal and spatial resolutions can reach up to 0.5 ms and 10 mm, respectively. The improved thermometry, dual-laser-induced breakdown thermometry (DLIBT), was applied to measure temperatures of hot flue gases provided by a multijet burner. The measured temperatures covering the range between 1000 K and 2000 K were compared with the ones accurately obtained through the two-line atomic fluorescence (TLAF) thermometry with a measurement uncertainty of ~3%, and a very good agreement was obtained.

Highlights

Nowadays, a pulsed laser can be focused to breakdown gases, which generates heat, optical emission, and acoustic emission
We propose to calibrate this distance by using the same setup at the laboratory conditions (23 °C, 1 atm), where the sound speed is known
Figure shows the temperature of the hot flue gas derived by dual-laser-induced breakdown thermometry (DLIBT), two-line atomic fluorescence (TLAF), and agreement between the temperatures measured by DLIBT and TLAF

Summary

Introduction

A pulsed laser can be focused to breakdown gases, which generates heat, optical emission, and acoustic emission. The optical emissions are used in the conventional laser-induced breakdown spectroscopy (LIBS) technique to realize in-situ element measurements in various application fields [1,2]. The acoustic emission from the laser-induced breakdown has gained more attention and been successfully applied for different purposes, such as the understanding of the propagation mechanism of the laser-generated shock wave, the nonlinear absorption of laser in the gas, and the detection of the particle size and concentration [2]. Lots of methods have been developed and employed for obtaining accurate temperature measurements in combustion atmospheres. A conventional simple method is the thermocouple-based thermometry, which is intrusive and requires corrections of radiative and conductive heat losses. Non-intrusive laser-based techniques have been developed for temperature measurements, such as Rayleigh scattering

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