Volume 7, Issue 3 (March 2010)
Standard Reference Data for the Thermophysical Properties of Biofuels
The thermophysical properties of biofuels are required for the efficient design of their chemical processing, distribution, and utilization. We provide a review of biofuel properties research at the National Institute of Standards and Technology (NIST). We are expanding two Standard Reference Databases to include biofuels. The ThermoData Engine will collect and evaluate all published property data on biofuel components. The NIST Reference Fluid Thermodynamic and Transport Properties database is a calculational database providing properties of biofuel components and blends based on thermodynamic and transport models. The property models in the databases implement an equation of state approach based on well defined reference fluids. Complex mixtures, including blends of biofuels with conventional fuels, are modeled as “surrogate blends,” i.e., a blend of perhaps a dozen components that captures the essential characteristics of a complex fuel. Surrogate blends are formulated from a “suite” of well-characterized pure compounds. Property measurements for the pure compounds in the surrogate suite include but are not limited to density, speed of sound, and viscosity. We have also carried out measurements on actual biofuel samples. A recent extension of the distillation curve that we have developed at NIST is proving very valuable in characterizing fuels. This “advanced distillation curve method” provides much more quantitative information than the traditional method, including chemical characterization of the different “cuts” as the distillation proceeds. We present examples of our measurements and models completed to date and outline future plans.