Current and future injector designs for diesel engines
approach
pressures of greater than 100 MPa. However, the high-pressure physical
properties, such as viscosity, of biodiesel blends with diesel fuel
are nearly absent in the literature. This study focuses on the viscosity
of biodiesel, diesel, and several biodiesel blends from 283.15 to
373.15 K and pressures up to 131 MPa. Soybean biodiesel (B100) and
ultra-low-sulfur diesel (ULSD, B0) were combined to form biodiesel/diesel
blends: B5, B10, B20, B40, B60, and B80. The viscosity of the samples
increases linearly with the pressure until approximately 35 MPa, followed
by a higher order response to pressure. The biodiesel blends with
low biodiesel content (B5, B10, and B20) had very similar viscosities
to ULSD. The normalized viscosity increased with a decreasing temperature
and a decreasing biodiesel blend fraction. The viscosity of the various
blends increased above the ambient pressure viscosity ranging from
164% at 373.15 K to 547% at 283.15 K at the highest pressure of 131
MPa. The biodiesel and some biodiesel blend samples at 283.15 K experienced
pressure-induced cloud points (solid–liquid equilibrium) from
70 to 131 MPa. The Tait–Litovitz equation was found to correlate
the biodiesel and diesel data with an absolute average relative deviation
(AARD) of less than 1% over the large range of both temperature and
pressure, and Kay’s mixing rule predicted the viscosity of
the biodiesel blends with an AARD of 1.75%.