FEATURE (Continued from Page 7


a gallon of oil destroys the entire amount of ZDDP.


Biographical Profile


Dr. Debasish Mukherjee Date of birth: 27/08/1955


Education: •Graduation with Chemistry Honours in 1976 from Burdwan University.


• Post graduation in pure Chemistry from IIT (Indian Institute of Technology), Kharagpur in 1978.


•Doctorate from IIT Kharagpur in 1985.


Service:


•Worked as a post doctoral fellow in University of Salford, Manchester in 1986-87.


•Worked as a Senior Research Fellow in IIT Kharagpur in sponsored projects from 1987-91.


•Worked in British Oxygen India (BOC India Ltd.) from 1991-98.


• From 1999 to present date working in TIL (Tractors India Ltd, Caterpillar dealer in India) as a manager of oil analysis lab.


Publications:


27 papers have been published. 22 papers are in international journals of repute which include research papers, review articles, teaching modules, articles in international conferences and magazines.


FIG.3.


FIG.3. illustrates how the colour changes when the 15W40 multigrade fresh engine oil (left side) undergoes heavy oxidation (right side, dark colour) within 150 hours.


Consequences of oxidation


With gradual increase of oxidation, following consequences will be observed:


•Plugging of oil filter • Piston deposit formation and ring sticking


• Catalytic effect of metal particles like Cu to speed up the oxidation process


Additives known as metal deactivators (FIG.1) are added to deactivate the catalytic effect and, hence, slow down the oxidation process.


Water contamination


Water in lubricating oil is called the scourge of the machine. Lubricating oil has strong affinity for water. Keeping water content consistently low in oil is a tough challenge experienced by the maintenance professionals. Oil, by nature, is very hygroscopic. Like table salt, it absorbs water from atmosphere. Water enters the oil from the humidity of the air, through fill ports, poor or worn out seals, broken heat exchangers etc.


Three categories of water can be classified when water invades the oil:


• Dissolved water - Water concentration up to 200 ppm in oil is referred to as dissolved water. It exists in the oil as single molecule. The oil looks clear and transparent at this stage.


•Emulsion - When water concentration lies between 200-1000 ppm, oil becomes emulsified with water. It becomes hazy. At this stage, water is suspended in the oil and imparts hazy and cloudy appearance. The oil is then said to be in the emulsified stage. This stage, of course, cannot be detected visually in case of used engine oil because the cloudy appearance is often masked by the black colour of the used oil.


• Free water - When water concentration exceeds 100 ppm, the oil can no longer hold the water molecules. It the settles down at the bottom of the sump. This situation is called free water.


Effect of water contamination


Water concentration of 50 ppm or upto 100 ppm may not create serious problem. However, if the concentration increases unnoticed major problem will occur.


Immediate effect will be on the oil. Viscosity will be lowered. Performance of the oil will be impaired due to inadequate lubricating film thickness. Presence of water along with metal particles can increase the rate of oxidation of the oil by fifty times.


AW additive, ZDDP, reacts with water at high temperature (>80O


8 ISSUE NO. 64 DECEMBER 2004 C). When this happens, the additive is


destroyed. Fast abrasive wear occurs, resulting in metal fatigue. Component life will be subtantially reduced. Researchers have established that one drop of water in


Another wear process occurs when water invades the oil. Water molecules diffuse readily into the reactive surfaces of the microcracks. There it decomposes to release hydrogen and oxygen. Hydrogen atoms being smaller in size, diffuse further into the metal beyond the microcrack causing subsurface crack. This is known as hydrogen embrittlement of steel. Fatigue particles produced in this manner assist wear by generating more particles.


Effect of sulphur and total base number


In India, total sulphur in diesel fuel


(HSD) is 0.25% maximum. When the fuel is burnt, sulphur will also burn in air forming sulphur dioxide and sulphur trioxide. The latter reacts with moisture inside the system to form highly damaging sulphuric acid:


S + O2 = SO2 ; SO2 + O2 = SO3 ; SO3 + H2 O = H2 SO4


If the metal surfaces are exposed to the acid, immediately corrosion reaction will begin and components will be corroded. Ring sticking, valve guide, valve stem corrosion will be the consequences.


To neutralise this acid some base is added as additive (FIG.1.), which is expressed as total base number (TBN), or simply base number (BN). There are two competing reactions:


1. The acid will attack the metal surface 2. The base will attack the acid


Due to stronger affinity of base with acid, the base will consume the acid before the onset of corrosion. However, if the rate of acid formation is too high (due to moisture ingression, extended oil drain interval), then the amount of base might not be enough to consume all the acid. The remaining acid is now ready to do all the damage.


Diesel dilution


When the fuel is atomised and mixed with air subjected to intense pressure, combustion takes place. Situations may arise when whole amount of fuel does not take part in combustion (burning in air) reaction:


Fuel + O2 = CO2 + H2 O + fuel


This unburned fuel along with the combustion products would escape through the piston ring and cylinder wall interface and enters the crankcase lubricating oil. That’s how the lubricating oil is contaminated with diesel and this is what is known as diesel dilution or fuel dilution.


A small amount of diesel dilution is always detected in the used lube oil. This will not pose any threat to the performance of the engine. However, when the diesel dilution becomes significant, there will be a sharp loss of viscosity of the lube oil, making the oil thin. Consequently, this thin oil (low viscosity) cannot produce adequate film thickness between the two metal surfaces. As a result, there will be metal-to-metal contact, increased friction and wear. Also, fuel contamination may substantially impair the performance of the lube oil in the following ways:


Early or premature oxidation - Fuel is more susceptible to oxidation than a lube oil. With the onset of oxidation, the chemically reactive byproducts affect the hydrocarbon part of the lubricant. This sets up the chain reaction and ultimately leads to oxidative failure.


Additives dilution - Fuel contamination allows the additives concentration in the lube oil to be proportionally diluted. Effectiveness of the additives will be reduced.


(To be continued in Part II


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24