Optical Characterization of Dimethyl Ether (DME) for Laser-based Combustion Diagnostics

Abstract

Optical characteristics of dimethyl ether (DME) are presented, with emphasis on laser-based combustion diagnostics. OME is a well-known substance which has excellent properties as fuel for compression ignition (CI) engines. It is also believed to have suitable properties for laser diagnostics in CI engines, but reports of its optical properties are sparse in the literature. OM E has therefore been investigated by flame-emission, optical absorption, laser-induced fluorescence (UF), Raman spectroscopy, and rotational CARS. A preliminary evaluation of the potential for measuring NO in a OME flame is also presented. The Raman cross section of OME is more than twice as large as that of methane. DME absorbs in the VUV, but one absorption band extends into the UV where many tunable lasers radiate. This tail is displaced towards longer wavelengths with increasing temperature. Excitation at 193 nm yields a structured fluorescence between 350-550nm. The DME rotational CARS signal is -10 times weaker than that of nitrogen, and the non-resonant susceptibility is 9 times that of nitrogen.

Experimental and Theoretical Study of the Kinetics and Mechanism of the Reaction of OH Radicals with Dimethyl Ether

“…Photon densities under these conditions were <1 × 10 14 cm −2 . There is some controversy over DME absorption cross sections at 193 nm; Andersson et al 45 measured a cross-section of (7.2 ± 1.5) × 10 −18 cm 2 in an unpurged spectrometer with a deuterium lamp source, whereas synchrotron based measurements by Bremner et al 46 and Suto et al 47 show a threshold for absorption at ∼195 nm and absorption cross sections <1 × 10 −18 cm 2 at 193 nm. With a cross-section of 1 × 10 −18 cm 2 and a radical yield of two, photolysis of DME under our conditions would yield a secondary radical concentration of ∼1 × 10 11 molecule cm −3 (for [DME] = 5 × 10 14 molecule cm −3 ) and a pseudo-first-order rate coefficient for radical loss of 5−10 s −1 (for bimolecular radical−radical rate coefficients of (5−10) × 10 −11 cm 3 molecule −1 s −1 ), which is negligible compared to typical pseudo-first-order rate coefficients for OH loss of >1000 s −1 .…”

Investigation of Dimethyl Ether Combustion Instabilities in a Partially - Premixed Gas Turbine Model Combustor Using High-Speed Laser Diagnostics

“…The chemical properties and reaction parameters of DME under laminar flame conditions have been studied by many researchers. Andersson et al 9 used laser-based combustion diagnostics methods and determined the optical properties of DME, such as its flame emission spectrum and Raman cross-section area. Fisher, Dryer, and Curran investigated the reaction kinetics of DME with flow reactors at both high temperature (1000K to 1100K) 10 and low temperature (550K to 850K) 11 .…”

The ro-vibrational ν2 mode spectrum of methane investigated by ultrabroadband coherent Raman spectroscopy

“…Furthermore, the modeling of the CH 4 ν 2 Raman spectrum can serve as blueprint for heavier hydrocarbon molecules, such as ethane and dimethyl ether, which also have a Raman-active vibrational mode due to the bending of the H-C-H bond. 27,96 The availability of spectral data for such molecules could pave the way to the extension of ultrabroadband fs/ps CRS to the in situ investigation of oxy-fuel combustion in many practical applications. 97…”