Oxidation, Nitration, TBN and TAN numbers explained
Dirthog28,
Oxidation (evidence of lubrication breakdown). The causes of oxidation are: overheating, over-extended oil drain intervals, improper oil type, combustion by-products, blow-by and coolant leaks. A lower oxidation number is good, a higher number is indicating that the oil is breaking down. Conventional oils are typically flagged excessive or condemned at 30 and synthetics lubricants at 50.
Oxidation occurs when lubricating oil undergoes a chemical change under the influence of high operating temperatures or while operating over extended drain service intervals. This can create acids which cause corrosion, increase viscosity and deplete additives. The process is accelerated by heat, metal catalysts and the presence of water, acids or solid contaminants. Oxidation can also cause filter plugging, lacquer build up, sludge deposits, overheating and increased wear. Oxidation is measured by an FTIR scan. The effects of a high oxidation number are: Shortened equipment life, lacquer deposits, oil filter plugging, increased oil viscosity, corrosion of metal parts, increased operating expenses, increased wear and shortened equipment life.
Nitration occurs during the fuel combustion process when combustion by-products mix with the engine oil. This occurs during normal engine operation but is also a result of abnormal blow-by. The products of nitration are highly acidic. Their effects include accelerated oxidation, oil thickening, corrosion, increased wear and poor engine performance. Nitration is measured by infrared analysis or FTIR. Other indicators that may suggest abnormal nitration
levels are a rapid reduction in the oil’s reserve alkalinity (Total Base Number). The effects of a high nitration number are: Accelerated oxidation, increased exhaust emissions, acidic by-products formed, increased cylinder and valve train wear, oil thickening, combustion are deposits and increased TAN.
Total Base Number (TBN) depending upon the application, different oils have different blends of additives designed to maintain the oil’s lubricating properties and protect equipment. Base (alkaline) additives are present in automotive engine oils to neutralize acidic by-products of combustion. New oils start out with the strongest TBN they can possess, depending upon the base oil and the additive chemistry used to make them. Over its service life, a motor oil will lose its ability to neutralize acids. Measuring the TBN strength of the oil is very important when extending oil drain intervals, as the TBN value indicates the capability of the additives to protect the engine from acidic corrosion. The standard test for measuring an engine oil’s acid neutralizing strength, or Total Base Number, is the ASTM-D 4739 Reserve Alkalinity Test. TBN is expressed using a value number, which decreases as nitration and oxidation values rise over the service life of the oil. Because an oil’s characteristics are interdependent, TBN depletion reflects other characteristics of the engine oil that are out of acceptable range. This may indicate that the oil’s service life has ended and the oil should be changed. The effects of a low TBN number are: Increased TAN, oil degradation, increased wear, corrosion of metal parts.
Total Acid Number (TAN) Is the lubricants acid content. Causes of a high TAN number are: High sulfer fuel, overheating, excessive blow-by, over-extended oil drains, improper oil type. The effects of a high TAN number are: corrosion of metallic components, increased oxidation, oil degradation, oil thickening and additive depletion.
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