Lubricating Oil Functions and Types of Lubrication:
(a) Functions of Lubricating Oil:
Lubricating oil plays a critical role in engine operation by performing several essential functions:
- Reduces Friction: The primary function of lubricating oil is to create a thin film between moving parts, reducing friction and minimizing wear on components. This ensures smooth operation and improves engine efficiency.
- Heat Transfer: Engine operation generates significant heat. Lubricating oil helps transfer heat away from critical components like pistons, rings, and bearings, preventing overheating and potential damage.
- Corrosion Protection: Lubricating oil forms a protective layer on metal surfaces, inhibiting corrosion caused by moisture, combustion byproducts, or acidic contaminants within the engine.
- Sealing and Leak Prevention: In some engines, the lubricating oil film helps to seal clearances between pistons and rings, reducing blow-by of combustion gases and preventing oil leaks.
(b) Types of Lubrication:
(i) Hydrostatic Lubrication:
- Description: Hydrostatic lubrication utilizes an external pressure source, such as a pump, to force oil between the bearing surfaces. This pressurized oil film separates the moving parts completely, preventing metal-to-metal contact.
- Advantages: This method provides a very effective lubrication regime, offering excellent wear protection and minimal friction. It is well-suited for high load applications.
(ii) Boundary Lubrication:
- Description: Boundary lubrication occurs when the lubricating oil film is too thin or the pressure between the bearing surfaces is too high to completely separate them. In this regime, special lubricant additives play a crucial role. These additives form a microscopic protective layer on the metal surfaces, reducing friction and wear even under conditions of partial metal-to-metal contact.
- Disadvantages: Boundary lubrication offers less wear protection compared to hydrostatic lubrication and is more susceptible to friction increases under high loads or extreme temperatures.
(c) Grease as a Lubricant in Plain Bearings:
Advantage:
- Long Service Intervals: Grease has a thicker consistency than oil and can stay in place for longer periods, requiring less frequent re-lubrication compared to oil in plain bearings. This can be beneficial for applications where access to lubrication points is difficult.
Disadvantage:
- Heat Dissipation: Grease generally has a lower heat transfer capacity compared to oil. This can be a disadvantage in high-temperature applications where efficient heat dissipation is crucial for preventing overheating of bearing components.