Raman spectra of methane, ethylene, ethane, dimethyl ether, formaldehyde and propane for combustion applications

Abstract

Spontaneous Raman scattering measurements of temperature and major species concentration in hydrocarbon-air flames require detailed knowledge of the Raman spectra of the hydrocarbons present when fuels more complex than methane are used. Although hydrocarbon spectra have been extensively studied at room temperature, there are no data available at higher temperatures. Quantum mechanical calculations, when available are not sufficiently accurate for combustion applications. This work presents experimental measurements of spontaneous Stokes-Raman scattering spectra of methane, ethylene, ethane, dimethyl ether, formaldehyde and propane in the temperature range 300-860 K. Raman spectra from heated hydrocarbons jets have been collected with a higher resolution than is generally employed for Raman measurements in combustion applications. A set of synthetic spectra have been generated for each hydrocarbon, providing the basis for extrapolation to higher temperatures. The spectra provided here will enable simultaneous measurements of multiple hydrocarbons in flames. This capability will greatly extend the range of applicability of Raman measurements in combustion applications. In addition, the experimental spectra provide a validation dataset for quantum mechanical models.

Dual-resolution Raman spectroscopy for measurements of temperature and twelve species in hydrocarbon–air flames

“…Figure 1c) shows the Raman spectra of these hydrocarbons on the CO 2 and O 2 channels, attributed to CH 2 bending modes and to C 2 stretching modes. [11] Methane has only weak features in this spectral range, but DME, ethane and ethylene produce strong crosstalks onto the CO 2 and O 2 channels. Therefore, inaccuracies in hydrocarbons concentration measurements also affect CO 2 and O 2 .…”

“…To account for the spatial dependence of the element of the C matrix associated to the hydrocarbons, detailed Raman spectra are needed. In a previous work [11] we reported experimental Raman spectra for methane, ethane, ethylene, and DME in the 300-900 K range. Spectra of formaldehyde were also collected in the 400-900 K range, although no information was obtained regarding the temperature dependence of the integrated signal or its intensity compared to N 2 .…”

“…The spectrometer used in Ref. [11] had the same 4165 lines/mm grating of the spectrometer used in this work, but a five times narrower slit (100 μm), resulting in higher spectral resolution.…”

“…The synthetic spectra of Ref. [11] are treated as stick spectra, and convolved with an instrument function to obtain the experimental spectra in the lower and higher dispersion systems. The Table 1 Table 1 shows the standard deviation in the flame at the location where the CH 4 reaches its peak value (~4x10 -2 mol), corresponding to a temperature of ~900 K. The number density standard deviations are in between the values reported in the reactants and in the products.…”

“…shows the ambient temperature Raman spectra of methane, ethylene, ethane, formaldehyde, and DME in the C-H stretch region as measured by the previously reported Raman spectrometer[1,2,10,11,13], using a 1200 lines/mm holographic transmission grating (5.85 nm/mm linear dispersion). When only one of these hydrocarbons is present, the entire C-H stretch region is used as the hydrocarbon Raman channel, and an empirical calibration provides the temperature dependent values of the C-matrix column associated to the hydrocarbon channel.…”