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A combustion system is a device or apparatus that utilizes the process of

combustion to generate heat or energy. Combustion is a chemical reaction
between a fuel and an oxidizer, typically oxygen from the air, that releases
energy in the form of heat and light.
Combustion systems are essential in various applications, including:
 Power generation: In power plants, combustion systems are used to
burn fuels like coal, natural gas, or oil to generate electricity.
 Heating and cooling: Furnaces, boilers, and water heaters rely on
combustion to provide heat for homes, buildings, and industrial processes
 Transportation: Internal combustion engines in vehicles use combustion
to convert fuel into mechanical energy that propels the vehicle.
 Industrial processes: Combustion systems are used in various
industries, such as steelmaking, cement production, and glass
manufacturing, to provide the necessary heat for processing materials.

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Cylinder
 Function: A cylinder is the hollow tube within an engine where the piston
moves up and down. It provides a sealed environment for the combustion
process.
Piston Rings
 Function: Piston rings are metal bands that fit into grooves on the piston.
They serve two critical purposes:
o Sealing: They create a tight seal between the piston and the
cylinder wall, preventing combustion gases from escaping into the
crankcase and oil from entering the combustion chamber.
o Heat transfer: They help transfer heat from the piston to the
cylinder wall, aiding in engine cooling.
Types: There are typically three types of piston rings on a piston:
 Compression rings: These are located at the top of the piston and are
responsible for sealing the combustion chamber. They are usually made
from cast iron or steel.
 Oil control rings: These are located at the bottom of the piston and
control the amount of oil that reaches the cylinder wall. They are often
made from cast iron with an oil-resistant coating.
 Scraper rings: These are sometimes used in addition to the oil control
rings to further scrape excess oil from the cylinder wall.
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Piston ring materials are selected based on runnability and the conditions that
the piston rings have to work under. Good elasticity and corrosion resistance are
just as important as a high resistance to damage under extreme operating
conditions. Grey cast iron is still the main material used to manufacture piston
rings today. From a tribological perspective, grey cast iron and the graphite
deposits in the joint offer extremely good emergency running properties (dry
lubrication via graphite). These are particularly important if the lubrication via
engine oil is no longer guaranteed or the lubricating film is already destroyed.
Graphite veins within the ring structure also act as an oil reservoir and, here to,
serve to combat the destruction of the lubricating film under adverse operating
conditions. The following materials are used as grey cast iron materials
• Cast iron with lamellar graphite structure (lamellar graphite cast iron), annealed
and non-annealed
• Cast iron with nodular graphite structure (nodular cast iron), annealed and non-
annealed
Chrome steel with martensitic microstructure and spring steel are used as steel.
To increase the wear resistance, the surfaces are hardened. This usually takes
place via nitriding*.
* In specialist language, nitriding refers to the supply of nitrogen and is a process
for hardening steel. Nitriding is usually carried out at temperatures between 500
and 520°C with treatment times of 1 to 100 hours. Nitrogen is diffused onto the
workpiece surface to form an extremely hard, superficial compound layer of iron
nitride. Depending on the treatment time, this can have a thickness between 10–
30 µm. Common methods include salt bath nitriding (e.g. crankshafts), gas
nitriding (with piston rings) and plasma nitriding.
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The sliding lands or sliding surfaces of piston rings can be coated to improve the
tribological* characteristics. The focus here is on increasing the wear resistance
and ensuring the lubrication and sealing under extreme conditions. The coating
material must work harmoniously with the materials of the piston ring and the
cylinder wall, as well as with the lubricant. The use of surface coatings is
therefore widely spread on piston rings. The rings of series engines are often
coated with chrome, molybdenum and ferrous oxide.
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Characteristics
• High durability (wear resistant)
• Hard, non-sensitive surface
• Reduced cylinder wear (approx. 50% compared with uncoated piston rings)
• Good resistance against burn marks
• Lower emergency running properties than with molybdenum coatings
• Good wear resistance provides: a longer running-in time than with unreinforced
piston rings, steel rail oil control rings or U-flex oil control rings
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These coatings consist of a galvanised chromium layer with a network of cracks,
into which firmly anchored hard materials are embedded. Ceramic (CC) or
microdiamonds (DC) are used as the integrated material.
Characteristics
• Minimal frictional loss due to extremely smooth surface
• Maximum wear resistance and high durability due to embedded hard materials
• Good burn mark resistance
• Low wear on the layer of the piston ring, with consistently low cylinder wear
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PVD stands for “Physical Vapour Deposition”, a vacuum-based coating procedure,
where hard material layers (CrN – chrome(III)-nitride) are applied directly on the
piston ring surface via vapour deposition.
Characteristics
• Frictional loses are minimized due to an extremely smooth surface.
• Extremely high wear resistance is achieved with an ultra-thin and dense layer
structure with a high hardness level.
• Due to the high wear resistance, the ring contour is retained over a longer
service life. With a PVD-coated oil control ring, for example, the ring tension can
be reduced further, resulting in significant friction advantages.