Raman/Rayleigh scattering and CO-LIF measurements in laminar and turbulent jet flames of dimethyl ether

Abstract

To reduce the impact of combustion of fossil fuels on air quality and climate change, dimethyl ether (DME) is a promising alternative diesel fuel candidate. Technical combustion processes, including formation of pollutants, are influenced by turbulence-chemistry interaction. Therefore, accurate prediction by computational combustion models of combustion systems burning DME must account for multiple scalars and scalar gradients. The testing of such models requires detailed experiments. Here a study is presented on the feasibility of simultaneous species and temperature measurements in turbulent dimethyl ether flames, using line-imaged Raman/Rayleigh scattering of the major species H 2 , O 2 , N 2 , CO, CO 2 , H 2 O, C 2 H 6 O and laser induced fluorescence of CO. The measurement system and data evaluation methods developed to investigate methane-air flames are extended to address dimethyl ether flames. The Raman signal intensity and spectral shape of the Raman scattering from dimethyl ether over a range of temperatures are presented, based on measurements in electrically heated flows and laminar jet flames. These data are used to develop an iterative method for data evaluation that allows determination of indispensable crosstalk correction terms for the concentration measurements of O 2 and CO 2. Issues of fluorescence interferences, mainly from C 2 radicals on the fuel-rich side of the reaction zone, and their corrections are discussed. Laminar flame calculations are used to investigate the role of the intermediate species (CH 4 , CH 2 O, C 2 H 4 , C 2 H 2 , C 2 H 6 , CH 3) in the reaction zone. In particular, their effect on the mixture fraction calculation and its relationship to the experimentally determined mixture fraction is examined. The impact of the intermediate species on deviations in concentration and temperature profiles due to species-specific Raman-and Rayleigh scattering cross-sections is demonstrated. Finally, species concentrations and temperature profiles from measurements in a turbulent piloted jet flame of dimethyl ether are shown.

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

“…The dominant feature is the peak at 2887 cm -1 attributed to the symmetric stretching modes of CH 2 (v 3 ), and CH 3 (v 16 ). At higher frequencies the spectra become more complex because of the interaction, asymmetric stretching modes v 10 , v 15 , v 22 , and v 1 (2967, 2968, 2973 and 2977 cm -1 ) of CH 3 , with CH 2 stretching modes v 2 (2962 cm -1 , symmetric) and v 23 (2968 cm -1 , asymmetric), and several combination and overtone modes. Comparison of the data collected in the two polarization directions shows that distinct, strongly polarized peaks are overlapped with a broad, much weaker, unpolarized component, centered around 2935 cm -1 and ~200 cm -1 broad.…”

“…This is the case for instance in DME-air flames where the combined mole fractions of methane, formaldehyde, acetylene, ethylene, ethane (combustion intermediates) reach 8% of the total mole fractions. [15] Figure 1a) shows the room temperature spectra of methane, ethylene, ethane, and DME, obtained with the spectrometer of Ref. [6] that has a 1200 lines/mm grating.…”

Comparative flame structure investigation of normal and inverse turbulent non-premixed oxy-fuel flames using experimentally recorded and numerically predicted Rayleigh and OH-PLIF signals

“…The constant species-specific cross sections for the main species CO 2 , CO, O 2 , CH 4 , H 2 O, H 2 and significant intermediates OH, O, H, C 2 H 4 , C 2 H 6 , C 3 H 8 , C 2 H 2 and CH 3 are evaluated following [28]. For details, refer to [14,21], which includes also an error estimation at the species cross sections.…”

A Study of Two Dimensional Tomography Reconstruction of Temperature and Gas Concentration in a Combustion Field Using TDLAS

“…In recent years, many diagnostic techniques used for measurement of combustion characterization, such as laser light scattering [1,2], molecular filtered Rayleigh scattering (FRS) [3], coherent anti-stokes Raman scattering (CARS) [4], planar laser induced fluorescence (PLIF/LIF) [5][6][7], have been reported. Although these techniques mentioned above have a number of advantages compared to traditional contact measurement, there are still some inevitable limitations.…”