A new analytical method based on midband infrared spectroscopy in the 4,000-400 cm-1 wavenumber region has been developed that allows for rapid and reliable measurement of several pertinent fuel properties simultaneously. The method may be automated and, by using commercially available Fourier transform infrared (FTIR) equipment, would be eminently suitable for laboratory and field applications.
Preliminary studies show that midband infrared spectroscopic data may be calibrated to determine those fuel properties that are due to chemical structural features that give rise to active infrared resonance bands. The measured fuel property values must relate linearly to spectral intensities, that is, they must obey Beer's law. In this study, the initially selected fuel properties were aromatic hydrocarbon-, benzene-, and MTBE contents, carbon-to-hydrogen ratio, heat of combustion, cetane index, refractive index, viscosity, and density. Good correlations were found between FTIR and nuclear magnetic resonance (NMR) data, and between FTIR and cetane number, as measured in the constant volume combustion apparatus (CVCA). NMR data may be considered definitive in chemical structural arguments. Since the FTTR data correlate well with both the fundamental NMR and the CVCA-determined cetane number data, by inference, the correlations elevate the fundamental credibility of the CVCA data as well.
Usefulness of the method is discussed for middle distillate fuels (DF-2, JP-5, JP-8, Jet A, and Jet A-1), for gasolines, and for natural gas.