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Thermometry by vibrational Raman spectroscopy of nitrogen: Identification and impact of spatial averaging effects
Author(s) -
Kiefer Johannes,
Stodt Malte F. B.,
Fritsching Udo
Publication year - 2021
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.6104
Subject(s) - raman spectroscopy , principal component analysis , raman scattering , chemistry , spectral line , spectroscopy , analytical chemistry (journal) , combustion , approximation error , work (physics) , computational physics , optics , statistics , mathematics , physics , thermodynamics , chromatography , quantum mechanics , astronomy
Thermometry utilizing the vibrational spectrum of nitrogen is a very common tool in combustion diagnostics via spontaneous and coherent Raman scattering spectroscopy. In the presence of strong temperature gradients, however, it is likely that hot and cold gas portions contribute to the signal. This is known as spatial averaging, and it can result in severe measurement errors. The present work proposes and demonstrates two straightforward approaches that allow the identification of spatial averaging as well as estimating the resulting error. For this purpose, simulated Raman spectra are considered in order to avoid any impact from experimental artifacts. The first approach utilizes difference spectra, whereas the second one is based upon principal component analysis (PCA). Two scenarios were tested: (1) spectra of 50:50 mixtures exhibiting a common mean temperature and (2) spectra of mixtures with systematically varied fractions of hot (2000 K) and cold (300 K) gas. It is shown that the resulting measurement error can be as high as 500 K.