**2. Tribological improvement of machine components in marine diesel engines**

Many ship owners demanded from marine engine manufacturers to execute various technological modifications to increase the engine efficiency and to extend the life time of machine components. One of methods to accomplish these demands is to improve the tribological characteristics of machine components in the marine engines. In the Section 2, tribological improvement of machine components such as cylinder liners, fuel injection pumps, and bearings are explained. In addition, it includes the contents of lacquering that causes the tribological problems and the contents of machine condition diagnosis using the lubricant analysis.

#### **2.1 Cylinder liner**

The cylinder liners are a hollow cylinder shell which acts as the enclosure in which the combustion takes place. They have enough strength under the fluid pressure due to combustion and high-level stress induced in them. The cylinder liners are a cylindrical part to be fitted into an engine block to form a cylinder, and they are called "cylinder sleeve" in some countries.

They have main functions such as formation of sliding surface, heat transfer and compression gas sealing. The cylinder liners are served as the inner wall of a cylinder, and forms a sliding surface for the piston rings in order to reduce wear of piston, piston ring and oil consumption while supplying the lubricant in the clearance. The cylinder liners receive combustion heat through the piston and piston rings, and transmit the heat to the coolant. The cylinder liners are responsible to tolerate the combustion pressure, the contact with piston and piston rings while guiding the piston [5]. When the lubrication characteristics between the cylinder liner and the piston are poor, wear occurs on the lubricating surfaces, and scuffing phenomena also appear in severe cases.

#### *Tribology in Marine Diesel Engines DOI: http://dx.doi.org/10.5772/intechopen.100547*

Since there are few failure dates, it is difficult to estimate the reliability of the cylinder liners and ad hoc reliability tests are prohibitively expensive. Therefore, the liners are subjected to rigorous maintenance in order to reduce the frequency of failures while in operation. Both wear degradation and thermal cracking are the leading causes of failure of cylinder liners [6]. The significant number of abrasive particles on the piston surface generated by intensive combustion of fuel and lubricant deterioration is the primary wear process in this location [6]. A fatigue process caused by repetitive thermal shocks results in thermal cracking of the liner. As a result of insufficient chemical treatment, a thermal shock is generated by a fast temperature shift of the cooling fluid that laps the liner's exterior surface. Furthermore, this shock is typically exacerbated by scale and corrosion in the cooling water spaces [6].

The cylinder liner-piston ring system is one of the major contributors for the mechanical losses in marine diesel engines [7]. Lubrication of cylinder liner is very important for any marine diesel engines because it controls the wear and enhance the life of the engine. In general, lubrication performs three purposes. First, it prevents metal-to-metal contact between the cylinder liner and piston rings by creating an oil layer. Second, it neutralizes sulfuric acid and controls corrosion caused by detergent. Third, it cleans the cylinder liner, especially the piston ring pack, and prevents failures and corrosion due to neutralization residues and fuel combustion. So, several researches related to lubricant of cylinder liners are performed. Measurement of iron ppm in the cylinder drain oil was used to assess the degree of cylinder wear. Moreover, the role of alkaline additive in protecting surface of the metal from the acid was estimated in cylinder liner. That is, linear wear rates were estimated as a function of sulfur contents in fuel, feed rate and alkalinity of lubricant [8].

Surface texture of the cylinder liner identified as one of the significant factors that improve the tribological properties of marine diesel engine with regard to wear, oil consumption, fuel efficiency, lubrication oil (wear particle concentration). Surface texture is one of technical methods which alter a material's surface by modifying its texture and roughness. Various surface texturing methods employed such as laser surface texturing (LST), pulsed air arc treatment, electropolishing, reactive ion etching (RIE), photochemical machining, maskless electro chemical texturing, microcomputer numerical control (CNC) texturing. Among the different surface texturing techniques, LST is one of the most widely used non-contact type method and **Figure 1** show the cylinder liner with surface texturing. The effect of partially LST is evaluated through testing of marine diesel engines. The ellipse patterns oriented at the sliding direction contributed the most to reduce the friction coefficient [7].

**Figure 1.** *Surface textured cylinder liner.*

Generally, the honing applied to inner wall of the cylinder liners as shown in **Figure 2**. The function of the honing to hold a satisfactory amount of lubricant oil and reduce friction. The honing process is applied to get surfaces with good functions for the ring or liner contact. The honing tool is comprised of a number of honing stones, which are similar to grinding wheel [9]. The surface of honed cylinder liner is characterized by a negative skewness, Rsk (Ssk) and kurtosis, Rku (Sku) values higher than 3. The honing is comprised of smooth wear resistant plateaus with deep valley, which have the effect of oil reservoirs and traps for wear particles [10]. Moreover, the selection of honing machine depends on the honing process (vertical or horizontal honing), honing angle, depth of honing, bore diameter, stroke length. The processing condition of honing should be selected according to engine's output, engine type, and engine manufacturer recommendation.
