Tribologie O

Octane number (ON)
This is a dimension value for the anti-knock properties of petrol; it describes the behaviour of fuel during combustion in the engine. For the combustion process to operate normally, it is essential for the fuel to have adequate anti-knock properties - see anti-knock resistance. Reference fuels are: n-heptane with ON = 0 and Iso octane with ON = 100, determined in DIN 51 756 P 1 to P 6.
 

Oil coal or oil coke
Hard deposits like coal or coke in cylinders and piston ring grooves of internal combustion engines, etc. Occurs in recirculating oils if the oil has aged, and also as a result of the ingress of contaminants and thermal loading.
 

Oil separation
It is possible that small amounts of oil may separate from lubricating greases if it is stored for a long time or if it operates at higher operating temperatures. This is normal and of no significance. However, it is not acceptable for larger amounts of oil to separate out (what is termed bleeding). DIN 51 817 sets out conditions of oil separation under static conditions.
 

Oils
A distinction is made between the source, manufacture and the chemical structure:
a) Animal and vegetable oils: these are esters or fatty acids

b) Mineral oils, which - depending on their structure - are composed of paraffins (alkanes)
naphthenes (cycloalkanes) or aromats

c) Synthetic oils, such as silicone oils, polyglycols, ester compounds, etc.
 

Olefins (alkenes)
Unsaturated hydrocarbons (n or Iso alkenes), which have one or more hydrocarbon double bonds (alkadienes, dienes, trienes, etc.); These are produced during cracking processes; as a result of double bonds they have a tendency to oxidise and polymerise (formation of resin and residues); their names are characterised by "ene" endings, e.g. ethenes, propenes, butenes.

Olein
Oleic acid, active ingredient for certain lubricating purposes, improvement in adhesion, e.g. for metalworking oils.
 

Oleoresins
Organic oxygen and/or sulphur compounds which are found in dissolved form in petroleum products; generally have strong dyeing effect; oil resins are absorbed in silica gel or bleaching earth.
 

OMC
Outboard Marine Corporation; manufacturer of spark-ignition engines for 2- and 4-stroke outboard motors, chain saws, etc.; the OMC specifications specifically set out requirements for two-stroke engine oils.
 

OPEC
Organisation of the Petroleum Exporting Countries.
 

Oxidation
Oxidation is a combustion process; oxygen is attached to certain elements or molecules. Thickening, varnishing, polymers, corrosive-acting radicals, etc. occur in the case of hydrocarbons.
 

Oxidation inhibitors
(Antioxidants – AO) dialkylzinc dithiophosphates; compounds of nitrogen, phosphorus and sulphur (amines, phenoles in combination with zinc, tin, barium, calcium, etc.). They prevent or control the oxidation of oil and the formation of sludge, varnishing and corrosive compounds. They thus limit or retard the increase in viscosity of the lubricating oil.