Article Preview
TopIntroduction
The sealing of combustion gas in an internal combustion (IC) engine is an essential requirement to obtain high-performance. An ideal piston ring needs to be designed to perform simultaneous sealing and sliding action without significant failures like wear or blow-by. Improper sealing may lead to gas blow-by or excessive cylinder liner wear. It is important to improve the wear resistance of ring through the coating, which can prevent it from rapid decay. Before discussing the coating strength, it is essential to understand the function of piston rings. The piston rings were first introduced in the reciprocating engine by (Ramsbottom, 2009) who showed how the friction is reduced and gas blow-by is restricted due to its implementation. In practice, mainly three types of piston rings - which are widely used in automotive - are compression ring, scraper/wiper ring, and oil control ring.
The efficiency of IC engines is reduced due to frictional losses out of piston ring and cylinder liner co-action. According to (Buyukkaya and Cerit,2007) investigation, about 33% of the total heat is transferred to the cylinder wall via piston and then via piston ring. Therefore, to reduce friction loss and thermal fatigue - as a mode of failure–efficient engine cooling and better fuel economy are required. The main function of the rings is to seal the combustion chamber to minimize loss of power. This is achieved through proper lubrication and faster heat transfer through piston ring and cylinder wall. Generally, three or, minimum, two rings are necessary on most piston-cylinder systems. Usually, rings need to be loosely fitted to allow the expansion at elevated temperatures. However thermal deformation, with low clearance, may lead to welding - due to high friction - of rings with cylinder causing serious damage. On the other hand, if high clearance is provided then blow-by will occur thereby reducing the efficiency (Cerit,2011).
Generally, rings mostly are made of cast iron and usually coated with chromium and molybdenum to enhance the resistance against thermal deformation. The main problem with the piston ring as mentioned earlier is wear, due to which engine is required to be disassembled after standard 100,000 miles run of a vehicle for ring replacement. Such disassemble activities affect and lead to misalignment of the other engine components and reduce engine life. Therefore, to increase the lifetime of engine, different types of coating materials, which have high wear resistance, have been applied on rings and the results showed improvement of the ring durability and thereby reducing frequent engine maintenance.
To examine the reliability and level of improvement in which the coating process will add to engine performance, researchers relied for a long time on the experimentally obtained results. However, in the last decade, developing new numerical methods and simulations on coating strength have widely been applied by researchers to examine the performance of the coated materials. Finite element analysis (FEA) is effectively used in the design analysis of structural and mechanical elements. It has been used to analyze modes of failure, the effect of coating and up-gradation of existing designs, identifying ideal coating materials that provide the highest life and performance.
Buyukkaya and (Buyukkaya and Cerit,2007) used the 3D ANSYS method to analyze the thermal behavior of ceramic coating on four types of rings. The results showed that Al-Si and steel coated rings provide an increase of 48% and 35% in thermal conductivity respectively. Moreover, a partially coated piston ring with a ceramic coat improved the thermomechanical properties. (Cerit,2011) found that a bond coat thickness of 1.0 mm of NiCrAl, reduces the normal stress and increases the shear stress. While a 4.0 mm coat thickness of the same type of material helps to elevate the surface temperature to the order of 82oC (Sliwa et al, 2016) used FEA to simulate the stress distribution of components through PVD/CVD coating. They used Multilayer coatings of Ti/Ti (C, N)/CrN, Ti/Ti (C, N)/ (Ti, Al) N, Ti/ (Ti, Si) N/ (Ti, Si) N, and Ti/DLC/DLC on surface of magnesium alloy. The simulated ANSYS results and experimentally determined x-ray diffraction pattern showed high similarities in this investigation.