LABORATORY WORK № 8
Determınıng the viscosıty-temperature properties of engıne oil.
1. Contents of the work:
1) Preparation and testing of a laboratory apparatus for determining the
kinematic viscosity of a petroleum product;
2) Carry out kinematic viscosity tests on viscosity of engine oil;
3) Processing of results.
2 Equipment and instruments.
Samples of engine oil, thermometer, thermostat, capillary
viscometers, technical ethyl alcohol, distilled water, calculator.
General information.
Viscosity is the main parameter of engine oils. It is used to mark
oils. The viscosity of the engine oil at operating temperatures in the
engine determines the quality of lubrication and wear of friction parts.
The viscosity of engine oil varies depending on the temperature:
the viscosity decreases as the temperature rises. The intensity of the
change in viscosity as the temperature changes is not the same for
different engine oils. The nature of the viscosity-temperature curve is
assessed by the viscosity index (VI).
The viscosity index describes the change in viscosity of oils
depending on the temperature, i.e. the smoothness of the viscositytemperature curve of the oil.
The viscosity of high index engine oils changes only slightly
with changes in temperature, whereas the viscosity of low index oils
changes considerably.
The viscosity index of oils is assessed in conventional units. It is
determined by comparing the viscosity curve of the tested oil with
similar curves of two reference oils. One has a very steep curve, the
viscosity index is taken as 100, the other has a steep curve, the viscosity
index is taken as 0. The viscosity of the reference oil and the test oil are
identical at 1000°C.
Engine oils with a higher viscosity index have better performance
properties. Engine oils with a higher viscosity index have viscosity
additives added to them.
Thickened oils are oils that contain a viscosity additive. A low
viscosity mineral oil is characterised by a gentle curve. Viscosity
additives (polyisobutylenes and polyalkylmethacrylates) are added to
this oil.
A thickened engine oil is obtained, whose viscosity at 100 0C is
increased by adding a viscosity additive, and whose viscosity at 0 0C is
approximately the same as that of a low-viscosity, non-thickened
mineral oil.
This results in a thickened oil with a low viscosity-temperature
curve and a high viscosity index.
Thickened oils have good viscosity-temperature properties and
fluidity at low temperatures, contribute to easy and rapid engine starting
in cold weather, produce little soot and ensure minimal power loss due
to friction, which leads to fuel economy.
To calculate the viscosity index, determine the kinematic viscosity
of the tested engine oil at 40 and 100 0C.
Processing of results. The viscosity index IV is calculated according to the
formulas
𝐼𝑉 =
𝐼𝑉 =
𝑉−𝑉1
𝑉−𝑉2
𝑉−𝑉1
𝑉−𝑉3
100;
100;
(1)
(2)
where :
v- kinematic viscosity of oil at 40 0C with viscosity index equal to 0,
Having the same kinematic viscosity at 100°C as the tested oil
the tested oil, mm2/s (cSt);
v1 - kinematic viscosity of the tested oil at 40 0C, mm2/s (cSt);
v2 - kinematic viscosity of the tested oil at 40 0C and viscosity index
is 100, having the same kinematic viscosity at 100 0C of the oil tested
at 400°C and the viscosity index of the oil tested at 400°C.
Viscosity, mm2/s (cSt), has the same kinematic viscosity at 1000C as
the tested oil,
v3= v-v2
These formulas are used to calculate the IV if the kinematic viscosity
of the oil at 100 0C is in the range 2...70mm2/s(cSt).
The values of v and v3 are taken from Table 10. If v and v3 are not
stated in the table for the kinematic viscosity of the tested engine oil but
lie within the range of the values given, v and v 3 shall be calculated by
linear interpolation.
The engine oil viscosity index shall be rounded to a whole number.
Calculation accuracy at 95% confidence level shall be in accordance
with Table 3.
If the measured value of the kinematic viscosity of the test oil is not
specified for accuracy in Table 3, but the values are in the range of the
values given, they shall be calculated by linear interpolation.
Calculation example .As a result of the tests carried out, it was
found that the viscosity of the tested engine oil at 40 0C is 61.58mm2/s
(cSt) and at 1000C is 8mm2/s (cSt).
Use Table 1 in the appendix to find v=100, v 3 = 40.4 mm2/s (cSt).
The data obtained are substituted into equation 1.
IV =[(100-61,58):40,4]100=95,1
The viscosity index is rounded to a whole number: IV=95.
Use the table to find repeatability and reproducibility for a kinematic
viscosity of 8mm2/s (cSt):
IV=0 repeatability1.9 reproducibility 3.7.
IV=100 repeatability1.1 reproducibility 2.2.
From these data, interpolation for IV=95 gives a repeatability of 1.14, a
reproducibility of 2.28.
Kinematic
viscosity at
100°C,mm2/s
(cSt)
4
6
8
15
30
Table 1
To determine the viscosity index
Accuracy
IV=0
IV=100
Repeatability Reproducibili
Repeatability Reproducibili
ty
ty
2,4
2,1
1,9
1,5
1,2
4,8
4,2
3,7
3,0
2,5
1,7
1,3
1,1
0,7
0,4
3,4
2,6
2,2
1,4
0,9