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Engine systems
Published in Tom Denton, Automobile Mechanical and Electrical Systems, 2018
It is important that the closed cylinder is sealed properly to maintain the appropriate pressures in the cylinder during the working cycle. Any losses in pressure would significantly reduce the efficiency of the engine. To seal the piston and bore, piston rings are fitted into radial groves near the top of the piston and provide a gas-tight seal between the moving piston and the cylinder bore. When the cylinder volume is reduced during the compression stroke, the trapped gas is compressed and the amount of compression is known as the compression ratio. Compressing the charge before combustion allows more oxygen or fuel/oxygen in the cylinder than would otherwise have been available without compression and this improves combustion efficiency. Most spark ignition engines have a compression ratio of 8:1 to 10:1. This means that the cylinder volume reduces by eight or ten times during the compression stroke (Fig. 2.19).
Friction, Lubrication, and Wear
Published in John B. Heywood, Eran Sher, The Two-Stroke Cycle Engine, 2017
The function of the piston rings is to seal off the piston, which is the movable part of the combustion chamber, and control the amount of lubricant on the cylinder liner. In addition, a substantial part of the heat transferred from the hot in-cylinder gases to the piston passes through the rings to the cooled cylinder liner. The passage of combustion gases from the combustion chamber into the crankcase must be kept below a tolerable small amount (of order 1%), because increased blowby overheats the piston and rings and the lubrication conditions on the cylinder liner are disturbed. The sealing of the piston to prevent gas blowby is done primarily by the top or compression ring. No less important is the creation of a barrier that prevents unacceptable amounts of oil passing into the combustion chamber from the crankcase. The load-bearing surfaces of the piston, rings, and cylinder must be supplied with a quantity of lubricating oil that is as small as possible but also provides adequate lubrication under all operating conditions. This is essentially the task of the oil scraper rings.23
Metrology as an Identification Tool for Worn-Out Air-Cooled Diesel Engine
Published in Salah H. R. Ali, Automotive Engine Metrology, 2017
Air-cooled diesel engines, for instance, are commonly used in heavy-duty transport fleet applications due to their high performance, efficiency, and low fuel consumption. The surface contact problems between cylinders and pistons through their rings are vital to the engine performance within the adverse operating conditions of high pressure, temperature rise, and high relative velocity of the contacting surfaces [2–4]. Fine finish and surface treatment together with proper geometrical and dimensional tolerances standards implementation are required in order to ensure good sealing between the cylinder wall and the piston rings, good load carrying capacity, good lubrication conditions, less friction, suitable wear resistance, low translated vibration levels, high engine efficiency, and longer service life span [5,6]. The main function of the piston rings assembly is to provide a good dynamic sealing between the combustion chamber and the crankcase during compression and power strokes. Reasonable sealing minimizes power loss due to charge escape from the combustion chamber within suitable ring expansion gap and limited friction force. For long sealing service life, friction and wear between piston rings and the cylinder wall have to be properly controlled [7,8]. They are controlled by the lubrication of the interface with dry lubrication of cylinder bore material composition besides an oil film thick enough to separate the asperities of piston rings and the cylinder surface [3–7]. The friction loss varies according to the piston velocity between the top dead center (TDC) and the bottom dead center (BDC), where the oil film thickness depends on the instantaneous relative velocity of the piston ring, which varies from zero at TDC and BDC to the maximum in the middle section. This means that wear conditions will vary along the piston ring traveling distance, from mild to severe [9].
Thermal and experimental analyses of thermal barrier coated pistons
Published in International Journal of Modelling and Simulation, 2023
Krishna Kumar Pandey, Murugan S.
Piston rings are used to seal the combustion chamber to reduce the leakage of the fresh charge from the chamber to the oil sink. In addition, they are used to maintain cylinder pressure. The oil ring provides proper lubrication between the piston and liner. The bond coat is 0.15 `mm thick. The top coatings are offered in three different thicknesses; 0.3 mm, 0.6 mm, and 0.9 mm. The bond coat is applied to the piston substrate. The top coat is applied over the bond coat. The bond coat is attached to the piston substrate with a bond joint. It is ensured that there is good bonding between the two coats. In the ANSYS Workbench, the materials (aluminum alloy, nickel aluminide (NiAl), YSZ, and YSZ+CeO2) are first selected. The drawing is imported from SOLIDWORKS, and meshing is done on the coated piston. Different boundary conditions are applied to the coated piston, and results are obtained. The flowchart of the methodology adopted is depicted in Figure 3. The thermal analysis is done for the YSZ coated piston and YSZ+CeO2 coated piston.
Thermal and static analysis of engine piston rings
Published in International Journal of Ambient Energy, 2022
E. Gopi, M. Saleem, Sri Chandan, Arun Nema
Nowadays, the demand for energy released and storage of energy has increased in the automobile industry and aerospace industries (Singh and Sharma 2014). To reduce the cost and weight of material, the automobile and aerospace components are manufactured by composites. To prevent and reduce the wear and friction in combustion engines, gases from combustion is by-passed and friction is kept to a minimum (Munyao et al. 2013) at each ring around it. The piston ring maintains gas compression between the cylinder wall and piston. It seals the cylinder and compression gas is generated (Fang et al.2017) at ignition. If leaks occur between the cylinder and piston, the engine cannot have sufficient power. Piston rings maintain necessary lubricating oil film between the cylinder and the piston to avoid friction. Ignition occurs in the engine after the combustion process, the temperature (Zhang, Li, and Xu 2013) reaches a maximum and leads to damage of the engine. Piston rings are used to release the temperature built up in the engine (Parthiban et al. 2015). Piston rings are used to move the piston easily up and down without any disturbance. Piston rings are usually made of some metals and coated with different coating techniques (Georgiev and Roldan Dk 2013), Some engines have several rings made of cast iron and it is approximately made of 2–6 rings and each ring has different functions (Sathish Kumar 2016).
Tribological solutions for engine piston ring surfaces: an overview on the materials and manufacturing
Published in Materials and Manufacturing Processes, 2020
Rita Ferreira, Jorge Martins, Óscar Carvalho, Luis Sobral, Sandra Carvalho, Filipe Silva
Until a decade ago, most of the piston rings used a heat-treated low-alloyed nodular cast iron as the structural material.[62] Other coatings[63] or composite materials using an aluminum alloy matrix[64] have been proposed, but without success for commercial implementation. The high modulus of elasticity and high bending strength of nodular cast iron fulfilled the mechanical requirements for the ring. The requirements for reduced ring friction led to slimmer widths and the subsequent increase in combustion pressure imposed a radical change in the structural materials, with high chromium alloyed steels being the norm (of 300 and 400 series groups of stainless steel). Its improved fatigue strength, greater durability and superior wear resistance supported that change. To further increase their mechanical strength and their wear resistance, different surface treatments were applied to the structural material. Surface treatments such as nitriding are commonly used to increase surface hardness through a phase transformation of the near-surface region, creating a diffusion layer. This process is still being used by some manufacturers.[65–67]