Spectral observation of fuel additives in gasoline-ethanol blends using a Fourier-transform Raman spectrometer prototype

The combination of fossil fuels with bio-fuels, specially ethanol and methanol, has acquired relevance and attention in several countries in recent years. A variety of factors have induced this trend: market prices, constant geopolitical events, new sustainability policies and laws, etc. The fuels used in the automotive industry, including bio-fuels, normally contain additives as anti-shock agents and as octane booster. These additives may endanger (beside the high volatility implied) public health or environment due to the nature of its chemical composition. Raman spectral information from different additives, specially toluene, contained in E10 gasoline-ethanol blends has been obtained by using an own-design Fourier-Transform Raman spectrometer (FT-Raman). This information has been also compared with Raman spectra from pure additives and with standard Raman lines in order to validate its accuracy in frequency. The spectral information is presented in the range of 0 cm−1 to 3500 cm−1 with a resolution of 1.66 cm−1. The Raman spectra obtained shows a reduced frequency deviation (less than 0.4 cm−1 when compared to standard Raman spectra from different calibration materials, e.g. cyclohexane and toluene, without compensation for instrumental response). The Fourier-Transform Raman spectrometer prototype used for the spectral analysis, consisting of a Michelson interferometer and a self-designed photon counter cooled down on a three stage Peltier element arrangement, is able to extract high resolution and precise Raman spectra from the additives in the fuels analyzed. The proposed FT-Raman prototype has no additional complex hardware or software control. The mechanical and thermal disturbances affecting the FT-Raman system are mathematically compensated by extracting the optical path information from the generated interference pattern of λ = 632.8nm Helium-Neon laser (HeNe laser), which is used at the spectrum evaluation. This allows the device to be used in complicated environments where certain level of security is required (e.g. fuel production, storage, transportation, etc.).