Combustibles ambientalmente sostenibles: caracterización termofísica de biogasolinas y biodieseles formulados a partir de biobutanol

Abstract

Shortage of easily accessible fossil fuels makes the implementation of biofuels in the automotive field a priority. There are several possibilities to provide oxygenated additives from renewable sources to develop new generation of biofuels. In this context the knowledge of the thermophysical properties of such new fuels is of paramount necessity in particular to design the appropriate engines injectors. This study focuses on the thermodynamic characterization of new blends involving two alcohols, 1-butanol (usually considered as a second generation biofuel) and 2-butanol, with four reference hydrocarbons (each one from a representative group that constitutes a gasoline) and two biodiesels obtained from wasted vegetable oils. The properties of each one as a pure component and their mixtures with butanol have been studied. The selected experimental techniques used were a vibrating tube automated densimeter to measure the densities with an uncertainty of ± 0.2% at temperatures up to 423 K and pressures up to 140 MPa, and an original automated flow calorimeter to accurately measure isobaric heat capacities in the temperature range from 273 K to 333 K and in the pressure range from 0.1 MPa to 25 MPa with a ± 0.5% estimated uncertainty. Additionally, a scanning transitiometer allowed to directly determining the isobaric thermal expansion with a ±2% estimated uncertainty, through temperature scans in the range from 273 K to 423 K and pressure scans up to 170 MPa. From densities and heat capacities as primary data measured over extended temperature and pressure ranges other important thermophysical properties can be obtained by derivation, like the isobaric thermal expansion and the isothermal compressibility. As a matter of fact, obtaining with good precision the three properties, molar volumes from densities, heat capacities and isobaric thermal expansions, using three independent experimental techniques present the great advantage to calculate the Joule-Thomson coefficient, which direct experimental measurement is rather cumbersome. Actually, the present data on Joule-Thomson coefficient are among the first to be obtained on liquid fuels. They are essential to correctly tune the new generation of automotive engines injectors in order to properly control the isenthalpic injection/combustion. In particular this coefficient is essential as regards the crucial temperature inversion curve for a given fluid, which it is the temperature at which becomes zero.