Characterization and Discrimination of Aircrafts and Runways Winter Maintenance Anti-Icing Fluids

Aircrafts and runways de-icing operations with anti-icing fluids are still the most commonly used methods. In the specific case of aircrafts, they do contain glycols. Nevertheless, since two decades now, major environmental concerns are raised, along with important associated costs. Furthermore, once applied either on aircrafts or on runways, these fluids are diluted because of water brought from adverse weather conditions (rain, snow, icy conditions), conducting to increasing the freezing point from a subzero level to 0°C. The characterization of the freezing points of these fluids is indeed crucial for safety reasons. For years now, Raman spectroscopy is used for the characterization of these fluids, specifically the freezing point. But the presence of dyes did perturb the usual spectroscopic characterization. Three fluids, from their pure commercial form to highly diluted rate, were then studied by means of Raman spectroscopy at a new laser wavelength, and with the support of multivariate data analysis (MDA). Each fluid belonged to a specific type of aircraft anti-icing fluid (I, II and IV). The discrimination of the fluids between each other was obtained. Spectroscopic data was organized through MDA in such a way that neither the presence of a dye nor the dilution would allow any confusion. The identification of the evolution of freezing temperatures with dilution was elaborated, with their rapid increase as dilution increased too. MDA allowed also the elaboration of prediction models, and such tool conducted to the forecast of concentration in anti-icing, or of its freezing temperature on the basis of the Raman signature of the considered fluid, with a given degree of confidence.