The Best Tutorial on Lubrication & System of Marine and Industrial Diesel Engine

Lubrication of Marine Diesel Engine

In this post Lubrication of Marine Diesel Engine we will discuss in detail regarding the Lubricating oils used in marine Diesel Engines. This post will be a very useful guide of the marine and captive diesel Power plant Engineers.

What is Lubrication

The Definition of Lubrication minimizes the friction between frictions, minimizing material between rubbing surfaces of parts having relative motion. In other terms, lubrication is the solution to energy wastage reduction and deterioration of components/parts. Maintenance of mechanical equipment at their optimum efficiency and extended mechanical life is achieved by reducing the wear

Friction

Definition of friction is the force interposed between two contacting surfaces of two bodies and resistance of motion of one body relative to the other. Friction causes deterioration of the surfaces that rub against each other; this is called vernacular wear. The other significant effect of friction is the wastage of energy which is spent in overcoming the friction. Continued operation of a machine in such a state will fail machinery.

Friction is a major headache for the Maintenance engineers since it causes equipment breakdown and continuous replacement of worn-out parts.

The essential tasks of lubricating oil

1. Reduction of wear in all revolving and sliding surfaces within the engine by abbreviating the friction.
2. Decrease in temperature rise by Cooling of under crown and piston ring area
3. Cleaning and flushing of pollutants
4. Retention of jolts and blows between bearings and other moving components.
5. Providing a sealing between piston rings and cylinder liner walls to diminish the infiltration of gases from combustion chamber to crankcase.
6. Increased life of machinery
7. Reduction in downtime
8. Reduces the interruption of machinery operation
9. Lower the maintenance cost by reducing the spares consumption

The Main Components of lubricating Oil

1. Gear-driven or multi-lobed rotor type Lube Oil circulating pump.
2. Pressure Relief valve to manage the constant pressure in the system
3. Lubricating oil filters combo of full flow and partial flow type.
4. Thermostatic valve
5. A shell type of Plate type heat exchanger between the feed pump and the filters.

Before the Engine, the Lube oil discharge pressure is maintained between 0.5 to 2 bar in slow-speed engines and up to 5 bar in high-speed engines.

In dry sump-type Engines, two pumps are installed. Lubricating Oil after circulation flows down by gravity to the engine crankcase pan. The first Pump, known as the scavenging Pump, deports the Oil to a tank independent of the Engine. The second Pump, known as the pressure pump, takes suction from this tank and distributes the Oil through the thermostatic valve, heat exchangers, and filters to the engine lubrication points.

Another arrangement is called a wet sump. In a wet sump system, lubricating Oil after lubrication falls with gravity in the crankcase known as a sump. The Pump draws the lubricating Oil from the sump and distributes the high-pressure Oil through the thermostatic valve, heat exchangers, and filters to the engine lubrication points.

Types of Maintenance

The maintenance department looks after the following two types of maintenance

1. Corrective maintenance
2. Preventive maintenance

Corrective maintenance

Corrective maintenance is encompassed during any failure or damage in a machine. This policy is generally adopted in smaller industries where production flow is not affected due to such damages.

Preventive maintenance

Preventive Lubrication Oil Maintenance is the most critical aspect of preventative maintenance. Preventive maintenance aims to achieve the maximum performance of machinery without problem or damage, which would disrupt the production flow

Types of Lubrication (Lubrication of Marine Diesel Engine)

• Boundary Lubrication
• Hydrodynamic Lubrication.
• Hydrostatic Lubrication
• Extreme pressure lubrication

Boundary Lubrication

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In this state of Lubrication, the thickness of the oil film is so small that oiliness becomes the predominant factor. This lubrication condition could be said to exist in some top-end bearing guides.

Hydrodynamic Lubrication

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in this state of Lubrication, the bearing surfaces are entirely separated by an oil layer. The oil film wholly takes the load; the film thickness is more significant at the inlet and remains steady up to the bearing center, and becomes zero at the outlet. This form of lubricates most suitable for the journal bearings where wedge formation takes place.

Hydrostatic Lubrication

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In Hydrostatic Lubrication metal surfaces are separated by optimum oil film but the oil pressure is supplied at pressure from an external source. Hydrostatic lubrication is dependant on oil clearance between surfaces and oil inlet pressure.

Example of such lubrication is wrist pin and cross head pin bearing.

Extreme pressure lubrication

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Due to theattainment of high local temperature by virtue of high pressure and speed between two sliding surfaces, lubrication fails to stick around the moving surfaces.

To overcome such conditions special additives are added to mineral oils. This type of lubrication is known as extreme pressure lubrication. Added additives form a durable film which can withstand high loads and temperatures.

Factors affecting Hydrodynamic Lubrication

1. Relative surfaces speed
2. Bearing clearances
3. Pressure on bearing (per unit area )

Relative surface speed

The higher relative speed is proportional to the greater tendency toward Hydrodynamic Lubrication.

Increasing the diameter of a crankpin/ journal and retaining the rotational speed will increase the relative speed.

Bearing clearances

– in case of too large clearance knocking will cause. This impulsive loading will increase the pressure between the surfaces and cause boundary lubrication if the clearance is too small; overheating of oil causes the boundary lubrication and will result in a seizure.

Pressure on bearing (per unit area

high load/pressure can lead to boundary lubrication. If the peak pressures are high in cylinders of a diesel engine due to the wrong fuel injection timing or other reasons, bearing pressure will increase.

Lubricating Oil Characteristics (Lubrication of Marine Diesel Engine)

1. Viscosity
2. Viscosity Index
3. Pour Point
4. Flash Point
5. The Fire point
6. Total Acid Number or TAN
7. Total Base Number or TBN Total Base
8. Detergency and dispersancy
9. Cold filter filling point
10. Demulsification number

Viscosity

Viscosity of the oil is directly proportional to the hydrodynamic lubrication tendency. The temperature will be increased due to insufficient oil circulation to remove the heat generated in a bearing. This condition could be caused by too little clearance and/inadequate supply of oil.

Viscosity results are recorded in the following three ways

1. Normal

2. High

3. Low

Investigate the High and Low Viscosity results to ascertain the cause and should undertake immediate maintenance.

Causes of abnormal Viscosity

• Oxidation
• Overextended oil change period
• Oil contamination by water
• Oil mixed with various grades of lubricants.
• Contaminated with anti-freeze
• Break down of additives
• Blow-by
• Wrong use of lubricant.

Maintenance action

• Check working temperature
• Check Air-fuel ratio
• Check for polluted new oil
• Check for high soot density
• Check for the grade of oil used
• Check for dilution by fuel
• Check for the equipment operations assessment
• Asses the oil change intervals
• Check for idling period of engine
• Check for the water contamination
• Replace/ repair the defective seal
• Change oil and filters
• Ensure the use of correct grade oil

Observation in abnormal changes of viscosity is severe, and takes immediate action for the maintenance.

Viscosity Index

Viscosity index is the numerical expression of the average slope of the viscosity — temperature curve of a lubricating oil between 400 C to 1000 C.

Higher the viscosity index lowers the rate at which viscosity decreases with increase of temperature.

Pour Point

Pour point is the temperature below which lubricating oil will lose its flow attributes. The lubricating oil will flow above the pour point temperature under standard conditions. Above the pour point temperature lubricating oil flow with gravity.

Pour point is influenced by presence of waxes..

Flash Point

Flash point is defined as the minimum temperature at which the lubricating oil gives off adequate vapor to ignite momentarily when a flame of specified standard dimension brought near the surface of oil for a prescribed rate in an apparatus of specified dimensions.

The Fire point

The Fire point of oil is the lowest temperature vapor of oil burn continuously for at least five seconds when the standard flame is brought near the surface of the oil.

All the above factors are essential in choosing the oil for the Engine. In addition, flashpoint should be reasonably higher than the working temperature of an engine.

Average Flash Point of different fluids used in machines.

• Lube Oil = 220°C
• Diesel Oil = 65°C
• Petrol = -20°C
• 70cSt Fuel Oil = 71°C.
• Paraffin = 40°C

Total Acid Number or TAN

The Total Acid Number is an assessment of acidity, which is decided by the measure of Potassium hydroxide in mg required to neutralize the acids in one gram of oil. In this process, quantities depletion, acidic pollution, and lubricating oil deterioration by oxidation are estimated.

TAN analysis is a quality analysis of crude oil and is referred to as a standard in Lubricating oil composition quality monitoring. This analysis is also used as an assessment of Lubricating oil deterioration.

The Total Acid Number value illustrates the probabilities of Corrosion issues. Therefore, TAN analysis is a must to monitor and conserve the equipment. Tan analysis assesses both the weak organic acids and solid inorganic acids commenced in lubricating oil.

Higher TAN indicates the danger of component failure. An increase in TAN is symbolic of lubricating oil oxidation due to prolonged use of oil/ higher operating temperatures.

Total Base Number or TBN Total Base

This is about the measure of acid, indicated in terms of the correspondent figure of mg. Of potassium hydroxide needed to neutralize all essential components available in 1 gram of specimen.

TBN determines control of acid effectiveness during the combustion process. Higher TBN reduces acid corrosion by suspending wear, causing contaminants.

The Total Base number is a property related to the Machine oils. It is oil’s capability to nullify acid. Therefore, the higher the TBN value, the more the lube oil power negates the acid effects in lubricating oils.

The amount of TBN in new oils is found in the range of 5.0 to 15, depending upon the producer and the desired use. During the continuous use of oil, it gets polluted with acids resulting in a reduction of TBN value. Values lower than 3 TBN are considered dangerous and highly recommended for a replacement for the excellent fitness of the engine.

The low-quality fuel with higher sulphur contents is the chief reason for TBN depletion. Initially, in the engine operation, this sulphur turns into sulphurous acid, and with the prolonged continuation of the process, it gets converted into sulphuric acid. Overheating and prolonged oil replacement could cause oxidation.

Detergency and dispersancy

additives expedite the cleanliness of the mechanical parts in a machine. However, due to the omission of detergency and dispesancy in the combustion chamber, the lubricating oil accumulates are inhibited by detergent powder. The origin of deposits found in the engine is due to the following reasons.

Engine usages

2. Condition of combustion

3. Lubricating oil temperature

4. Temperature of coolant

5. Sealing of rings

These deposits will shorten the engine life exceedingly if the accumulated deposits are not withdrawn during the oil change.

Detergents assist in reducing the quantity of formed deposits and their easy extraction. The additives will pass on different detergent properties to oil depending upon the source of their orientation as high or low temperature.

Fuel combustion produces low-temperature deposits, and the detergent will keep them suspended in the oil. Conversely, an oxidized fraction of oil is the cause of high-temperature deposits. The detergents will not only keep the sediments suspended but will also stop the growth from orientation itself.

Cold filter filling point

The temperature at which crystallization of wax takes place is the cold filter filling point. There is no implication of this characteristic during the engine’s regular operation

Demulsification number

The time ( in seconds) needed for the oil to separate from water under the condition of emulsification.

Combustion products in the lubricating oil are accelerated since the emulsification permits the water particles for the following undesirable reasons.

Lubricants will undergo degradation.

2. Will undergo Mechanical failures

3. Will result in Rust and corrosion

4. Foaming will be taking place.

General Guide Lines for the essential components (Lubrication of Marine Diesel Engine)

A) Oil Testing. Oil testing is executed to authenticate the quality of oil supplied. In service, testing is performed to resolve the condition of oil. The test result will justify the type of oil maintenance needed, treatment, additives, and replacement in partial or complete quantity.

A single test result will never lead to a justified conclusion.

1. The test result certificate must be available during the receipt of the oil supply. If the certificate is not available, then the oil sample needs to be tested before the use of oil. However, it is good practice to get the sample tested for the new lot to cross-check and verify oil purity as per the specified data.

2. The sample report will predict the oil change or conditioning duration as per the engine manufacturer’s recommendation.

a) The oil sample must be analyzed regularly. The running hours since the last oil maintenance should be recorded in the logbook by the engine operator. The operator should maintain the accurate history of each engine separately.

b) Results of oil analysis will indicate the following predictions.

1. Running the engine at no load:- Excessive carbon growth will occur in Engine Lube oil due to the increased acid under overcooled conditions. This phenomenon wills pre-pone the oil change intervals.
2. Every engine should sample lube oil in a clean sample bottle. Should take the sample to be taken during the engine operation at average operating temperatures.
3. Measure viscosity with the help of Visage.
4. Monitor soot and residues using blotter test
5. Monitor contaminants by centrifuge method.
6. Measure the detergence capacity

I hope the Article will be useful to the readers.