Rotational Raman spectroscopy for in situ temperature and composition determination in reactive flows

摘要

For the design and modelling of reactive flows, profound knowledge of temperature and species concentration is essential.Here, optical, non-invasive sensing techniques are frequently chosen, yet they often require elaborate experimental effortor inhibit other disadvantages. To circumvent these drawbacks, we developed a mobile, fiber-based sensor system, utilizinglinear rotational Raman spectroscopy. This technique requires neither sampling from or tracers inside the reactive flow noran external temperature or composition calibration. It simultaneously yields point-wise information on temperature andspecies concentration.To extract these quantities of interest the acquired, background-corrected spectra are matched to simulated spectra via aleast-square fit algorithm. Such an approach constitutes an ill-posed inverse problem as multiple solutions could explainthe measured data. Conventional least-square approaches only yield a set of parameters minimizing the residuum, butneglect uncertainties arising from the ill-posedness. Here, Bayesian inference offers many advantages: besides pointestimatesit allows to determine the corresponding uncertainties. Furthermore, prior knowledge about quantities of interestor model parameters can be included in the evaluation to establish a more advanced analysis routine.Using these tools, the benefits and limits of the rotational Raman technique are evaluated by the investigation of a flamefrom a premixed methane/air laminar flat-flame burner regarding the flame temperature and species concentrations of therotational Raman-active and, therefore, detectable gas species N_2, O_2 and CO_2. In addition, two different backgroundcorrectionapproaches are applied and compared using Bayesian inference and inter-parameter correlations.