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The viscosity of liquid petroleum products depends on
their boiling temperatures. The higher the boiling point of the
fraction, the greater its viscosity. Among the various
hydrocarbons, the least viscosity is paraffin, the largest -
aromatic hydrocarbons.
The kinematics viscosity of petroleum products is
determined by glass capillary viscosimeters of type VPG. The
essence of the method for determining the kinematic viscosity
of these viscometers is to measure the leakage time of a certain
volume of the investigated liquid through the capillary under
the action of gravity. For diesel fuels, the kinematic viscosity at
temperature is determined 20 С.
Fuel of very high viscosity may cause interruptions in
its supply to the pump due to resistance due to flow through the
supply system through filters and nozzle openings. When
spraying such fuel in the combustion chamber, droplets of large
diameter are formed which do not completely evaporate and
burn. Residues of unburned fuel can penetrate through the gap
between the piston rings and the walls of the combustion
chamber in the crankcase and dilute the oil. This leads to over-
consumption of fuel and oil, shortage of power, shortening
service life of the oil, increase in the pressure of the cylinder-
piston group, increase in smoke and toxicity of the exhaust
gases.
With a decrease in the viscosity of fuel, the lubrication
of precision pairs of the fuel pump of high pressure deteriorates
and there is a penetration of fuel due to the non-condensation
between the plunger and the sleeve. During the sputtering of
such a fuel, small droplets are formed that have a small supply
of kinetic energy. Fuel is unevenly mixed with air, burns
directly near the injectors, the volume of the combustion
chamber is not fully utilized, resulting in overheating and

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