Cylinder Liner Lubrication in Medium Speed Diesel Engines:
(a) Methods of Cylinder Liner Lubrication:
There are two primary methods for lubricating cylinder liners in medium speed diesel engines:
(i) Forced Lubrication:
- Description: This method utilizes an external pump and dedicated lubrication system to deliver a measured amount of lubricating oil directly to the cylinder liner walls. The oil is typically injected through quills (nozzles) positioned strategically on the cylinder liner.
- Mechanism: The pressurized oil forms a thin film between the piston rings and the cylinder liner, reducing friction and wear during piston movement. Excess oil drains back to the engine sump through designated channels.
- Benefits:
- Precise control over oil delivery allows for optimizing lubrication based on engine load and operating conditions.
- Ensures a consistent oil film for effective wear reduction.
(ii) Splash Lubrication (Dipping System):
- Description: This is a simpler method where the crankcase oil bath serves as the primary source of lubrication. The rotating components like the connecting rods churn the oil in the sump, splashing it onto the cylinder walls.
- Mechanism: As the crankshaft rotates, the connecting rods dip into the oil bath and splash oil upwards, lubricating the cylinder liners and pistons. The excess oil drains back into the sump through gravity.
- Benefits:
- Simpler design with fewer moving parts, resulting in lower maintenance requirements.
- Suitable for engines with less demanding lubrication requirements.
(b) Effects of Lubrication Issues:
(i) Insufficient Lubrication:
Insufficient lubrication due to factors like low oil level, clogged oil passages, or incorrect oil viscosity can lead to several negative consequences:
- Increased Friction and Wear: Without a proper oil film, metal-to-metal contact between the piston rings and liner increases friction, leading to accelerated wear and potential scuffing or scoring of the cylinder liner surface.
- Increased Heat Generation: Friction creates heat, and insufficient lubrication can lead to excessive heat buildup within the cylinder. This can damage pistons, rings, and other engine components.
- Piston Ring Sticking: High temperatures can cause piston rings to stick in their grooves, reducing their sealing effectiveness and leading to compression loss and increased blow-by of combustion gases.
- Potential for Seizures: In extreme cases of insufficient lubrication, complete seizure can occur, where the piston becomes welded to the cylinder liner due to excessive heat and friction, causing catastrophic engine failure.
(ii) Excessive Lubrication:
While insufficient lubrication is a major concern, excessive lubrication can also have detrimental effects:
- Increased Oil Consumption: Excessive oil being delivered to the cylinders can lead to higher oil consumption as more oil is burned in the combustion process.
- Spark Plug Fouling: Excess oil can reach the combustion chamber and foul the spark plugs, hindering proper ignition and engine performance.
- Increased Emissions: Burning excess oil contributes to increased emissions of hydrocarbons and pollutants.
- Degraded Power Output: Oil film buildup on cylinder walls can increase friction and slightly reduce engine power output.
- Environmental Impact: Excessive oil consumption leads to increased oil disposal needs, requiring proper handling and potentially creating environmental concerns.
Maintaining proper lubrication through regular oil changes, using the correct oil viscosity, and monitoring oil levels is crucial for optimal engine performance, longevity, and reduced emissions.