WHAT IS INFARED ANALYSIS? What is Infrared Analysis? Infrared (IR or FTIR) analysis has been employed as an analytical technique for monitoring the condition of used lubricating oils for many years. It is an effective diagnostic tool used to identify equipment problems and their causes, for optimizing oil change intervals and in evaluating the chemical degradation of the lubricant. Lubricating oil molecules molecules are made up of atoms linked to each other by chemical bonds. When a beam of infrared light contacts these molecules, this light is absorbed by the chemical bonds causing them to vibrate with the same frequency as that of the infrared light. The amount of infrared light absorbed is recorded as an infrared spectrum. Infrared Analysis is not concerned with the detection of specific elements such as copper or iron, but rather with the groupings and specific combinations of Carbon, Oxygen, Hydrogen, Nitrogen and Sulphur. These combinations or groups, known as functional groups, commonly appear in oil as Oxidation, Nitration, Soot, Water and Sulfation products. Each of these functional groups absorbs a specific wavelength of light. The amount of infrared light being absorbed at specific wavelengths by the sample is therefore a measure of the concentration of these various functional groups. The concentration is normally expressed as an index number except for soot and water, which is expressed as a percentage. The interpretation of IR analysis is usually based on the trending of results, with a significant deviation deviation from the normal trend signaling problems before the maximum allowable limits (MAL) are reached. IR analysis also measures the presence of additives and other parameters such as fuel, and contamination from water and glycol. CONTAMINANTS AND THEIR IDENTIFICATION
The following six parameters are usually monitored using IR analysis, depending on the compartment analytical test package. •
Sulfation
•
Nitration
•
Oxidation
•
Soot
•
Glycol
•
Water
Oxidation, nitration and sulfation monitor degradation of an oil’s service life for industrial lubricants and diesel engine oils. The test results are a relative value and are best used as a trending tool Test results for oxidation, nitration and sulfation are generally not used solely as a condemning parameter. Test results should be compared with other test results such as increases in acid number or viscosity or decrease in base number. SULFATION NUMBER
Sulphur compounds are generally found in many crude oils. Although environmental regulations have significantly decreased the levels of sulphur in commercial diesel fuel, sulphur contamination can still be found in some diesel fuels. Sulfation may also result from the oxidation of sulphur present in the base oil. Sulphur in diesel fuel combines with oxygen during the combustion process to form oxides of sulphur, such as sulfur trioxide, which escape into the
lubrication system around piston rings. These compounds tend to build up over time and form highly corrosive acids, which are quite harmful to the metallic components in the system. A sudden increase in the sulfation index could be due to the depletion of oil additives, and may also indicate ring failures and ignition problems. Other possible reasons for high sulfation are: -
Crankcase blow-by Water present in the crankcase Incorrect operating conditions Poor combustion
An increase in sulfation generally correlates with a decrease in Base Number in crankcase oils. NITRATION NUMBER
Nitration products can develop in all engines, however it is a major consideration in natural gas engines. The nitration process begins in the combustion chamber, where oxides of nitrogen (from air) are formed by heat and pressure. Subsequent reactions with oil and fuel results in the formation of nitration compounds in the lubricant. These compounds cause oil thickening and cause the build-up of varnish or lacquer deposits, which may interfere with lubrication. A high nitration value may also indicate incorrect spark timing. Nitration is also influenced by: -
Incorrect air/fuel ratios Improper ignition timing Crankcase blow-by and mixture with exhaust gases Low operating temperatures
Increases in nitration should correlate to increase in acid number, viscosity, oxidation number, and decrease in base number. OXIDATION NUMBER
Oxidation is a chemical reaction between oxygen and oil, just as rusting is a reaction between oxygen and iron. As oxidation increases, the oil begins to lose its lubricating properties and forms resins, varnishes or sludge. The most noticeable change is the thickening of the oil i.e. an increase in viscosity. The rate of oxidation in hydraulic, transmission or diesel engine oils usually depends on the length of time the oil is in use and the operating temperature of the compartment. Various other factors may also contribute to this state; some of these are listed below: -
High operating temperatures (overheating) Aeration in oil (exposure to air) Presence of contaminants such as ethylene glycol etc Extended oil change intervals
Increases in oxidation number should correlate to increase in acid number, viscosity, nitration number, and decrease in base number. SOOT
Soot particles primarily result from the incomplete combustion of fuel. These particles remain too small to be filtered as long as sufficient dispersants are present in the oil. When the dispersant levels begin to deplete, the particles combine very quickly to clog filters and passageways and contribute to engine wear. Assessing soot levels is therefore important to determine the combustion efficiency of an engine.
Soot is influenced by: -
Blow-by Fuel setting Air inlet restriction Incorrect ignition timing Engine operation (lugging etc)
GLYCOL
The presence of water and glycol indicates a leak from the cooling system, which needs to be determined accurately and quickly, as a coolant leak can cause rapid sludging and aging of oil. The presence of ethylene glycol in the oil not only causes the oil to thicken but may also act as a catalyst to promote oxidation. A significant presence of Glycol may interfere with the quantification of water on the infrared spectrum but the reverse is not true. For more information regarding the use of IR analysis or for general oil analysis enquiries, please contact your nearest ALS Tribology laboratory.
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