Development of a Raman spectrometer for the characterization of gaseous hydrocarbons at high temperatures. (January 2022) - Dieter, K.
Highlights: Heating of gaseous hydrocarbons by inline heaters is limited by thermal decomposition. When using Raman spectroscopy for combustion research, ethanol has a spectral crosstalk towards species like CO2 and O2 . Ethanol shows strong variations in spectral shape and Raman cross section with variing temperature. Heating of hydrocarbons using a helium based rapid gas-mixing heating apparatus overcomes previous temperature limitations. Abstract: Spatially and temporally resolved information on thermochemical conditions in hydrocarbon/air flames requires concentration and temperature data obtained by spontaneous Raman/Rayleigh scattering. During the combustion of renewable and more complex fuels, such as ethanol, partially oxidized hydrocarbons are created as intermediates in concentrations large enough to have an influence on the turbulence-chemistry interaction. To obtain concentrations and temperature in flames at atmospheric pressure with a high spatial and temporal resolution, information on the temperature dependent shape and scattering cross section of the major as well as the minor intermediate species is required. Therefore, a novel gas heater based on mixing the hydrocarbons with helium at high temperatures in combination with a multipass Raman spectrometer were developed, able to characterize ro-vibrational Raman scattering of gaseous ethanol in the gaseous phase up to high temperatures and in different spectral regions. The setup is described, its performance evaluated and Raman spectra of gaseous ethanol at atmospheric pressure up to high temperatures is demonstrated.