Comparative spectral analysis of commercial fuel-ethanol blends using a low-cost prototype FT-Raman spectrometer

The use of bio-fuels and fuel blends, specially in automotive industry, has been increasing substantially in recent years due to market prices and trends on sustainable development policies. Different spectral analysis techniques for quality control, production, purity, and counterfeit detection have been reported as non-invasive, fast, and price accessible. Raman spectra from three different commercial binary E10 fuel-ethanol blends has been obtained by using a low-cost Fourier-Transform Raman spectrometer (FT-Raman). Qualitative comparison between the commercial fuel blends and a laboratory-prepared fuel blend have been performed. The characteristic Raman lines from some additives contained in the commercial gasoline have been also observed. The spectral information is presented in the range of 0 cm-1 to 3500 cm-1 with a resolution of 1.66 cm-1. These Raman spectra shows reduced frequency deviation (less than 0.4 cm-1 when compared to standard Raman spectra from cyclohexane and toluene without compensation for instrumental response). Higher resolution values are possible, since the greater optical path lengths of the FT-Raman are achievable before the instrumental physical effects appear. The robust and highly flexible FT-Raman prototype proposed for the spectral analysis, consisting mainly of a Michelson interferometer and a self-designed photon counter, is able to deliver high resolution and precise Raman spectra with 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 a λ=632.8 nm Helium-Neon laser (HeNe laser), which is used at the spectrum evaluation.