The oil refinery nearest to Prague is in Kolín, at a distance of about 65 km. We therefore decided to obtain information about car oils at the Fuel and Lubricant Research Institute in Prague 10. Until 1993 the institute carried out development of new oils. The formulation and complex tests of one oil type cost a minimum of 10 million Czech Crowns. This is too expensive and the development was therefore discontinued. At present, the institute performs conventional tests and concentrates more on fuel testing. Nevertheless, we found there experts well versed in the problems of car oils, who were willing to explain things to us.
The importance of engine oils for car operation is such that the oils are considered a car construction element.
What are the current requirements for quality oils?
- good lubricating ability under all conditions
- extension of the engine life time
- extension of the oil replacement intervals
- reduction of pollutant emissions (since lead substance have lubricating effects, the changeover to unleaded gasolines necessitated the formulation of new oil types)
The development of new engines and new oils thus obviously has to proceed in close collaboration of engine and oil manufacturers.
Engine oil = oil base + additives
Oil base is either oil raffinate or synthetic oil, or their mixture.
The development is oriented to fully synthetic oils, which are high quality
but are very expensive. They are based on poly-alpha olefines (PAO) or
dicarbonic acid esters. The Czech Republic is well prepared for the production
of PAO because Spolana Neratovice produces sufficient amounts of quality
linear alpha olefines (LAO) whose oligomerisation yields PAO.
Production of oil raffinates
Distillation of crude oil under atmospheric pressure separates fuel
components, giving rise to an atmospheric residue containing oil fractions,
paraffin and asphalt. Vacuum distillation of the atmospheric residue yields
several oil fractions and a vacuum residue containing heavy oils and asphalt.
The vacuum residue can be used to obtain oils by extraction with liquefied
propane.
Oil distillates are refined either by furfural extraction (extraction of aromatics and heterocyclic compounds) or a high-pressure hydrogenation (undesirable components are not removed but are chemically converted - aromatics provide cycloalkanes or alkanes, heteroatoms are then removed in the form of H2S, H2O and NH3). The next step is deparaffination by cooling - the separated paraffin crystals are filtered off. The oil refining is completed by adsorption.
Oil additives
- polymethacrylates - polymers of methacrylic acid esters CH2
= C - COOR
|
CH3
- polyisobutylenes
- copolymers of ethylene and propylene
- styrene diene copolymers (styrene, isoprene)
2. Dispersion agents - are used for preventing the formation
of deposits on pistons and of "cold sludge". Their molecules contain hydrocarbon
chains with polar groups.
3. Detergents - are used to prevent the formation of
high-temperature deposits and for suppression of corrosion.
They include, e.g., alkyl salicylates, and calcium or magnesium alkyl
phenolates with the so-called alkaline reserve (i.e. surplus of Ca and
Mg carbonates). This reserve is important for neutralisation of organic
acids formed by oxidation of oils by oxygen at higher temperatures.
4. High-pressure and anti-abrasion additives - by reacting
with the metal surface they form protective film on component parts exposed
to heat stress. They are usually zinc salts of dithiophosphates.
5. Antioxidants and anti-corrosives - this function is fulfilled by the above components. Small amounts of other substances are sometimes added.
6. Congealing point depressants - prevent the separation of paraffin crystals (for instance the deparaffination is carried out to - 15 oC while depressant-containing oil can be used down to - 30 oC). The compounds used for the purpose are polymethacrylates.
7. Friction modifiers - about 1 %. They include, e.g., various metal soaps, esters or amines, which form thin adhesive films on metal surfaces.
8. Antifoam agents - silicon oils of the methylsiloxane type in a concentration of 0.001 - 0.0001 %.
Oil testing
In the Institute´s laboratories we saw a number of tests, e.g. viscosimetry,
foaming ability and foam stability tests, inflammation point measurement,
and assay of heavy metal by the AAS method. In our school laboratory, we
measured the inflammation point and also performed viscosity measurement
by using the Ubbelohde viscometer.
Inflammation point
it is the lowest temperature at which the oil forms a sufficient amount
of vapours for inflammation to occur. The oil is electrically heated in
the ceramic crucible. A thermometer is immersed in the oil. A small flame
travels over the oil surface. The temperature is recorded at a point when
the vapours ignite but are again extinguished when the flame is removed.
Our oil sample had an inflammation temperature of 187 oC.
Viscosity
is a very important property of lubrication oils. In engine oils it
is necessary that the oil should fulfil its function at very low temperatures
(in engines standing idle during wintertime) as well as at the highest
engine working temperatures. This implies that the oil viscosity should
change as little as possible with changing temperature. The table gives
comparison of dynamic viscosity for the so-called single-stage oil (for
the summer season) and an all-season oil.
Today, all-season oils are almost exclusively used.
| Temperature (oC) |
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| Single-stage | viscosity |
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| All-season | (mPa.s) |
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Viscosity measurement
Viscosity is measured by glass Ubbelohde viscometers. The measured
parameter is the time necessary for the passage of a given fluid volume
through a capillary. The time t is multiplied by a viscometer constant
k (given in mm2 .s-2) to obtain the cinematic
viscosity n in mm2 .s-1.
The constant is given by the manufacturer, but it has to be verified by using a fluid with known viscosity. The viscometer has to be placed vertically in a thermostat. When calculating the dynamic viscosity h it is necessary to know the density of the fluid r at the given temperature
We measured the viscosity in the school laboratory with less viscous fluids because our viscometers were suitable only for the viscosity range of 0 to 10 mm2 .s-1.
We found out that, for oils, the manufacturers give in addition a so-called viscosity index (VI). This is a dimensionless quantity which reflects the temperature dependence of viscosity, and is determined by comparing the given oil with two other oils one of which has a large and the other a low viscosity temperature dependence, yet both have the same viscosity at 100 oC.
The higher the VI value, the lower the temperature dependence of the oil viscosity. Quality oils have VI in the range of 130 - 145.
Transmission oils
These oils are composed of an oil base and of special additives increasing
the resistance to high pressures, or other adjuvants (antioxidants, anti-corrosives,
and friction modifiers). Their viscosity indexes are lower than those of
engine oils are.
Plastic lubricants
These oils are used for lubricating bearings and journals. The oil
base is made denser by adding lithium, calcium, sodium or aluminium soaps
derived from different fatty acids.
Used oils - a dangerous waste
Despite all efforts of the manufacturers to extend the oil replacement
intervals, vast amounts of this waste are produced worldwide (an estimate
runs to tens of millions of tonnes annually).
The simplest method for re-valuation of used oils is their combustion in cement factories, similar to that used for used tyres. The cement works furnaces have sufficiently high temperature to prevent the formation of very toxic substances such as CO, HCN, dioxins, furans, etc.
Another, far more complicated and expensive method is recycling in refineries or in smaller mobile devices at the collection sites. The best process appears to be the extraction of polymeric additives, which are then used as bitumen fillers, and subsequent distillation, which yields again utilizable lubrication and heating oils. In the future, recycling has to prevail over combustion.
In the Czech Republic, several companies are engaged in oil recycling. The setting up of an oil collection network presents problems.
