Open AccessSensitivity, stability, and precision of quantitative Ns-LIBS-based fuel-air-ratio measurements for methane-air flames at 1–11 bar
Author(s) -
Paul S. Hsu,
Mark Gragston,
Yue Wu,
Zhili Zhang,
Anil K. Patnaik,
Johannes Kiefer,
Sukesh Roy,
James R. Gord
Publication year - 2016
Publication title -
applied optics
Language(s) - English
Resource type - Journals
ISSN - 0003-6935
DOI - 10.1364/ao.55.008042
Subject(s) - laser induced breakdown spectroscopy , materials science , bar (unit) , laser , methane , nanosecond , analytical chemistry (journal) , optics , sensitivity (control systems) , atmospheric pressure , spectroscopy , hydrogen , plasma , chemistry , physics , organic chemistry , chromatography , quantum mechanics , electronic engineering , meteorology , engineering
Nanosecond laser-induced breakdown spectroscopy (ns-LIBS) is employed for quantitative local fuel-air (F/A) ratio (i.e., ratio of actual fuel-to-oxidizer mass over ratio of fuel-to-oxidizer mass at stoichiometry, measurements in well-characterized methane-air flames at pressures of 1-11 bar). We selected nitrogen and hydrogen atomic-emission lines at 568 nm and 656 nm, respectively, to establish a correlation between the line intensities and the F/A ratio. We have investigated the effects of laser-pulse energy, camera gate delay, and pressure on the sensitivity, stability, and precision of the quantitative ns-LIBS F/A ratio measurements. We determined the optimal laser energy and camera gate delay for each pressure condition and found that measurement stability and precision are degraded with an increase in pressure. We have identified primary limitations of the F/A ratio measurement employing ns-LIBS at elevated pressures as instabilities caused by the higher density laser-induced plasma and the presence of the higher level of soot. Potential improvements are suggested.