Surrogates for Fuel Property Modeling in Alternative Fuel Blends

Alternatives to petroleum based fuels are essential for the future transportation industry. For a fuel to be a viable replacement for a petroleum fuel it must meet a number of specifications. The prediction of fuel properties for blends of alternative and petroleum fuels is becoming increasingly important. This work considers the compatibility of potential alternative fuels with petroleum diesel and jet fuels, with a focus on property prediction and the development of surrogates for the prediction of multiple properties. Important cold flow properties addressed in this presentation include cloud point and pour point temperatures. Important engine performance-related properties addressed include the cetane number, boiling curve, and liquid phase compressibility. Modeling is performed using surrogates which represent the overall classes and distribution of components found in these fuels.

The temperature at which solids first form in a fuel mixture is referred to as the cloud point temperature. Cloud point measurements are presented for additives in two test diesel blends and a jet fuel. The behavior of potential fuel additives is found to relate more to the oxygen containing functional group rather than extent of branching or size of the alkane groups. Additive functionalities studied include, diesters, esters, ketones, alcohols, ethers, and alkanes. Long chain ester components were also tested. Experimental results are interpreted with thermodynamic models using fuel surrogates.

The cetane number of a fuel is a measure of the ignition delay after injection in a compression-ignition engine. Engines are tuned to have peak performance using fuels within a certain range of cetane numbers. Measured cetane numbers of blended fuels are modeled using composition-specific blending numbers based on the functionality class of the fuel constituents. This presentation will include brief comments on the compressibility of fuels and fuel blends.

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