FEATURE ISSUE NO. 64 DECEMBER 2004 Degradation (or failure) of lubricating oil


As the oil ages it breaks down. This happens because the lubricating oil inside the machine is exposed to a very hostile environment: heat, air, moisture and other contaminants. We must try to understand the following concepts thoroughly in order to have a deep insight into the fate of the used oil under such conditions:


Soot


Soot consists almost entirely of carbon particles, 98% by weight of carbon. These are very tiny particles, average particle size being about 0.04 micron (1 micron= 10-6 meter). They have strong tendency to agglomerate (cluster together).


Soot is formed during combustion process and enters the crankcase with the combustion gas blowby. Soot is caused by the following parameters:


High fuel-air ratio - If the airflow is less (restricted or plugged air filter) or incorrect mixture setting. Let us take the following example:


When a hydrocarbon (fuel can be considered as a mixture of hydrocarbons) is burnt in air (oxygen), it forms carbon dioxide and moisture:


CH4 + 2O2 = CO2 combustion)


When the air supply is insufficient, then carbon monoxide instead of carbon dioxide will be formed:


CH4 + 3/2O2 combustion)


When the air supply is still insufficient, carbon particles (soot) instead of carbon monoxide will be formed: CH4


+ O2 combustion)


1. Compression - Conditions when there is low compression, poor or incomplete combustion occurs. Soot generation rate is increased.


2. Excessive idling - Excessive low speed during operation or extended periods of at-rest are found to build up more soot


3. Lugging - Operating the engine in too high a gear or in excessive high load are also responsible for increased soot formation


Effects of high soot content


1. Fine soot particles in the oil will increase the viscosity of the oil


2. These particles will block the oil flow passage, causing lubrication starvation


3. Dispersant and AW additives will gradually become less and less effective


4. Gradual increase in component wear will be observed


In an automotive engine, soot will always be formed due to process inefficiency (thermo- dynamically, no machine performs with 100% efficiency). So long as soot particles are away from each other, there is no harm to the engine components. Dispersant addit- ives keep the soot particles away from each other. They envelope the soot particles in a single layer preventing them to cluster together. Under high soot load conditions this dispersancy is lost. Consequently, soot particles cluster together forming large particles, become heavy and finally deposit onto the machine surface.


The above statements have been substantiated from the oil analysis test results shown in FIG.2. The blue line curve shows


(Continued on Page 8 = C + 2H2 0 (Fuel:air:: 1:1, incomplete = CO + 2H2 0 (Fuel:air:: 1:1.5, incomplete + 2H2 0 (Fuel:air :: 1:2, complete


the original data, variation of iron content with soot load. The thick red line shows the best-fit curve with the original curve. The correlation coefficient R2 refers to the correlation between the two curves. Mathematically, under best- fit conditions, R2 becomes equal to 1. The relation between the two parameters can be expressed by a 4-degree polynomial equation generated from the graph. Under this condition only, the correlation coefficient becomes maximum, i.e., 1. Finally, it boils down to the fact that if soot content of any engine can be measured accurately, it is possible to predict the amount of iron particles generated due to wearing of components using this polynomial relationship. This is valid under conditions when dirt ingression, oxidation, corrosion and other contaminants ingression are well within control.


Oxidation


Perhaps the simplest case of oxidation is rusting of iron. Rusting occurs when iron is exposed to atmospheric air. Oxygen along with moisture in air attacks iron and rust (iron oxides) is formed on the surface of the metal. The situation is somewhat similar in case of lubricating oil inside the machine. It is exposed to air and moisture. When these chemicals attack the oil, the oil thickens and loses its lubricating properties.


Causes of oxidation


• Presence of air in the system is primarily responsible for oxidation of the oil. In an air-depleted atmosphere, oxidation can never start.


• It is well known that temperature has a pronounced effect on any chemical reaction. Ten degree rise in temperature will double the rate of oxidation.


• If the reaction time is increased by extending the oil drain interval, then also oxidation will increase.


• Depletion of antioxidant additives will increase the rate of oxidation.


• Metal particles like Cu, Fe, Pb act as catalysts in speeding up the oxidation reaction


Physical and chemical properties of the oil starts changing significantly with the onset of oxidation:


• Colour becomes darker and darker • Odor becomes acidic and pungent


•Viscosity of the oil increases due to oxidative thickening


• Acidity of the oil increases due to formation of organic and inorganic acids from their precursors


• Insoluble precipitate and sludge formation occurs DISPUTES


From 1 October 2004, all employers and employees must follow a new 3 step process in the event of dismissal, disciplinary action or grievance in the workplace.


Put it in Writing


Employees must put the reasons for grievance in writing to their employer. Similarly, an employer must put in writing to an employee the reasons why disciplinary action or dismissal is being considered.


Meet and Discuss


A face-to-face meeting must be arranged between employer and employee. Both parties must be given time to consider the other’s complaint prior to the meeting. After the meeting an employer must inform the employee of their decision and advise on an employee’s right to appeal.


Appeal


If required an Appeal meeting must be held, after which the employer must notify the employee of the final decision.


A copy of this publication can be obtained from the DTI publication help-line quoting URN 04/1651


LINK


Tel: 020 7215 5000 www.dti.gov.uk/resolvingdisputes


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