Viscosity is a measure of the internal fluid friction or resistance of
oil to flow, which tends to oppose any dynamic change in the fluid motion. As the
temperature of oil increases, its viscosity decreases, and it is therefore able
to flow more readily. It is also important for the flow of oil through
pipelines, injector nozzles, and orifice. The lower the viscosity of the oil,
the easier it is to pump and atomize and achieve finer droplets.
Viscosity is the
most important property of biofuel since it affects the operation of fuel
injection equipment, particularly at low temperatures when the increase in
viscosity affects the fluidity of the fuel. Biodiesel has a viscosity close to
that of diesel fuels. High viscosity leads to poorer atomization of the fuel
spray and less accurate operation of the fuel injectors.
Vegetable oils are extremely viscous with viscosities 10 to 20 times
greater than that of D2 fuel. The viscosity of oil can be lowered by blending
it with pure ethanol. To reduce the high viscosity of vegetable oils, microemulsions
with immiscible liquids such as methanol and ethanol and ionic or non-ionic
amphiphiles have been studied. Short engine performances of both ionic and
non-ionic microemulsions of ethanol in soybean oil are nearly as good as that
of D2 fuel. All microemulsions with butanol, hexanol, and octanol meet the
maximum viscosity requirement for D2 fuel. 2-octanol ia an effective amphiphile
in the micellar solubilization of methanol in triolein and soybean oil.
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