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

Abstract

Abstract Optical characteristics of dimethyl ether (DME) are presented, with emphasis on laser-based combustion diagnostics. DME 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. DME has therefore been investigated by flame-emission, optical absorption, laser-induced fluorescence (LIF), Raman spectroscopy, and rotational CARS. A preliminary evaluation or the potential for measuring NO in a DME flame is also presented. The Raman cross section of DME 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.