Friction is a necessary evil and it opposes the relative movement between any two objects which leads to loss of energy and hence wastage. Since there are lots of moving parts in any engine including marine diesel engines, there needs to be a method to take care of the same. Friction cannot be eliminated completely but can be reduced by applying appropriate lubrication techniques which we will see in this article.
The main object of lubrication is to separate moving metallic parts by inserting a layer of fluid between them in the form of a thin film which reduces friction. Before going on to study the actual mechanism of lubrication system in a marine diesel engine, let us first see which all parts of the engine need lubrication. It requires just an elementary knowledge of the engine construction and a little forethought to imagine which all parts are moving relative to each other and hence require lubrication.
There are mainly four types of motions present in a marine engine and hence the lubrication can be provided based on the type of motion. These types are as follows.
- There is purely rotational motion between certain components and these include the bearings of various parts such as the camshaft, crankshaft and so forth.
- There is purely sliding motion between components such as the piston ring/cylinders, crosshead guide
- There is oscillatory motion between parts such as the rocker arms
- There is very small point or line type friction in certain parts such as meshing gear teeth, chain and sprocket wheels and so forth.
Types of Fluid Lubrication
Whenever a layer of lubrication fluid exists between two surfaces it has to be under one of the following conditions.
- When there is a continuous thick film of lubricant between the moving surfaces without any break, it is referred to as perfect or thick film lubrication.
- When the layer is just a few molecules thick the lubrication is said to be boundary lubrication
- When the layer is imperfect and the two objects in relative motion are in partial contact, the lubrication is known as imperfect lubrication or partial film lubrication.
We have cleared the basic concept of lubrication in this article and will further proceed to study the exact mechanisms of lubrication used in various types of moving parts in marine engines in the subsequent articles.