Examination of physical properties of fuels and mixtures with alternative fuels

ABSTRACT.;EXAMINATION OF PHYSICAL PROPERTIES OF FUELS AND MIXTURES WITH ALTERNATIVE FUELS.;By.;Anne Lauren Lown.;The diversity of alternative fuels is increasing due to new second generation biofuels. By modeling alternative fuels and fuel mixtures, types of fuels can be selected based on their properties, without producing and testing large batches. A number of potential alternative fuels have been tested and modeled to determine their impact when blended with traditional diesel and jet fuels. The properties evaluated include cloud point and pour point temperature, cetane number, distillation curve, and speed of sound. This work represents a novel approach to evaluating the properties of alternative fuels and their mixtures with petroleum fuels.;Low temperature properties were evaluated for twelve potential biofuel compounds in mixtures with three diesel fuels and one jet fuel. Functional groups tested included diesters, esters, ketones, and ethers, and alkanes were used for comparison. Alkanes, ethers, esters, and ketones with a low melting point temperature were found to decrease the fuel cloud point temperature. Diesters added to fuels display an upper critical solution temperature, and multiple methods were used to confirm the presence of liquid-liquid immiscibility. These behaviors are independent of chain length and branching, as long as the melting point temperature of the additive is not significantly higher than the cloud point temperature of the fuel.;Physical properties were estimated for several potential fuel additive molecules using group contribution methods. Quantum chemical calculations were used for ideal gas heat capacities.;Fuel surrogates for three petroleum based fuels and six alternative fuels were developed. The cloud point temperature, distillation curve, cetane number, and average molecular weight for different fuel surrogates were simultaneously represented. The proposed surrogates use the experimental mass fractions of paraffins, and the experimental concentrations of mono- and di-aromatics, isoparaffins, and naphthenics. The surrogates represent both low and high temperature properties better than most surrogates in the literature.;Three different methods were developed to predict the cetane number of alternative fuels and their mixtures with JP-8, a military jet fuel. The same six alternative fuels were distilled, as well as blended with JP-8, and the cetane numbers measured. The Ghosh and Jaffe model represented the neat fuels with pseudocomponents to predict the cetane numbers of blends. This model worked well for the neat fuels, but the mixture behavior was predicted with incorrect curvature. The second and third methods used near infrared (NIR) and Fourier transform infrared (FTIR) spectroscopy to correlate the cetane number. The correlation provides prediction of the cetane numbers of the blends based on spectral measurements. Both the FTIR and NIR correlations are able to predict mixture cetane numbers within experimental error, but the NIR model was found to be the most reliable of all three methods.;Finally, the SAFT-BACK and ESD equations of state were used to model the density and speed of sound for hydrocarbons at elevated pressures. The SAFT-BACK equation was found to be more accurate, and the model was extended to predicting the speed of sound. Mixtures of hydrocarbons were also predicted, but the SAFT-BACK is limited in capability for representing compressed alkanes heavier than octane.