A hypereutectic piston is an internal combustion enginepiston cast using a hypereutectic aluminum alloy with silicon content greater than the eutectic point of 12 weight percent silicon. Most aluminum-silicon casting alloys are hypoeutectic (Si content lower than the eutectic point) and contain relatively fine elemental silicon crystals formed through the eutectic reaction during solidification. In addition to fine silicon crystals, hypereutectic alloys also contain large primary silicon crystals that form before the eutectic reaction, and as a result contain a much higher phase fraction of silicon. Consequently hypereutectic aluminum has a lower coefficient of thermal expansion, which allows engine designers to specify much tighter clearances. The silicon content of these alloys is typically 16-19 weight percent, and above this content the mechanical properties and castability degrade substantially. Special moulds, casting, and cooling techniques are required to obtain uniformly dispersed primary silicon particles throughout the piston material.
Most automotive engines use aluminum pistons that move in an ironcylinder. The average temperature of a piston crown in a gasoline engine during normal operation is typically about 300°C (570°F), and the coolant that runs through the engine block is usually regulated at approximately 90°C (190°F). Aluminum expands more than iron at this temperature range, so for the piston to fit the cylinder properly when at a normal operating temperature, the piston must have a loose fit when cold.
In the 1970s, increasing concern over exhaust pollution caused the U.S. government to form the Environmental Protection Agency (EPA), which began writing and enforcing rules that required automobile manufacturers to introduce changes that made their engines run cleaner. By the late 1980s, automobile exhaust pollution had been noticeably improved, but more stringent regulations forced car manufacturers to adopt the use of electronically controlled fuel injection and hypereutectic pistons. Regarding pistons, it was discovered that when an engine was cold during start-up, a small amount of fuel became trapped between the piston rings [citation needed]. As the engine warmed up, the piston expanded and expelled this small amount of fuel which added to the amount of unburnt hydrocarbons in the exhaust.
By adding silicon to the piston's alloy, the piston expansion was dramatically reduced. This allowed engineers to specify reduced clearance between the piston and the cylinder liner. Silicon itself expands less than aluminum. Another benefit of adding silicon is that the piston becomes harder and is less susceptible to scuffing which can occur when a soft aluminum piston is cold-revved in a relatively dry cylinder on start-up or during abnormally high operating temperatures.
The biggest drawback of adding silicon to pistons is that the piston becomes more brittle as the ratio of silicon to aluminum is increased. This makes the piston more susceptible to cracking if the engine experiences pre-ignition or detonation.
Performance replacement alloys
When auto enthusiasts want to increase the power of the engine, they may add some type of forced induction. By compressing more air and fuel into each intake cycle, the power of the engine can be dramatically increased. This also increases the heat and pressure in the cylinder.
The normal temperature of gasoline engine exhaust is approximately 650°C (1,200°F). This is also approximately the melting point of most aluminum alloys and it is only the constant influx of ambient air that prevents the piston from deforming and failing. Forced induction increases the operating temperatures while "under boost", and if the excess heat is added faster than the engine can shed it, the elevated cylinder temperatures will cause the air and fuel mix to auto-ignite on the compression stroke before the spark event. This is one type of engine knocking that causes a sudden shockwave and pressure spike, which can result in failure of the piston due to shock-induced surface fatigue, which eats away the surface of the piston.
The "4032" performance piston alloy has a silicon content of approximately 11%. This means that it expands less than a piston with no silicon, but since the silicon is fully alloyed on a molecular level (eutectic), the alloy is less brittle and more flexible than a stock hypereutectic "smog" (low compression) piston. These pistons can survive mild detonation with less damage than stock pistons. 4032 and hypereutectic alloys have a low coefficient of thermal expansion, allowing tighter piston to cylinder bore fit at assembly temperature.
The "2618" performance piston alloy has less than 2% silicon, and could be described as hypo (under) eutectic. This alloy is capable of experiencing the most detonation and abuse while suffering the least amount of damage. Pistons made of this alloy are also typically made thicker and heavier because of their most common applications in commercial diesel engines. Both because of the higher than normal temperatures that these pistons experience in their usual application, and the higher coefficient of thermal expansion due to low-silicon content causing greater thermal growth, these pistons require a larger piston to cylinder bore clearance at assembly temperatures. This leads to a condition known as "piston slap" which is when the piston rocks in the cylinder and it causes an audible tapping noise that continues until the engine has warmed to operational temperatures, expanding the piston and reducing piston to cylinder wall clearance.
Forged versus cast
When a piston is cast, the alloy is heated until liquid, then poured into a mold to create the basic shape. After the alloy cools and solidifies it is removed from the mould and the rough casting is machined to its final shape. For applications which require stronger pistons, a forging process is used.
In the forging process, the rough casting is placed in a die set while it is still hot and semi-solid. A hydraulic press is used to place the rough slug under tremendous pressure. This removes any possible porosity, and also pushes the alloy grains together tighter than can be achieved by simple casting alone. The end result is a much stronger material.
Aftermarket performance pistons made from the most common 4032 and 2618 alloys are typically forged.[citation needed]
Compared to both 4032 and 2618 alloy forged pistons, hypereutectic pistons have less strength. Therefore, for performance applications using boost, nitrous oxide, and/or high RPMs, forged pistons (made from either alloy) are preferred. However, hypereutectic pistons experience less thermal expansion than forged pistons. For this reason, hypereutectic pistons can run a tighter piston to cylinder clearance than forged pistons. This makes hypereutectic pistons a better choice for stock engines, where longevity is more important than ultimate performance. Some vehicles do use forged pistons from the factory. Dodge Vipers used forged pistons from 1992-1999 model years, then switched to hypereutectic. The last generation of Vipers(2013-2017) used forged pistons. All Honda S2000s use forged pistons.
The compression ratio is the ratio between the volume of the cylinder and combustion chamber in an internal combustion engine at their maximum and minimum values.
In engineering, the Miller cycle is a thermodynamic cycle used in a type of internal combustion engine. The Miller cycle was patented by Ralph Miller, an American engineer, U.S. Patent 2,817,322 dated Dec 24, 1957. The engine may be two- or four-stroke and may be run on diesel fuel, gases, or dual fuel.
In materials science, a metal matrix composite (MMC) is a composite material with fibers or particles dispersed in a metallic matrix, such as copper, aluminum, or steel. The secondary phase is typically a ceramic or another metal. They are typically classified according to the type of reinforcement: short discontinuous fibers (whiskers), continuous fibers, or particulates. There is some overlap between MMCs and cermets, with the latter typically consisting of less than 20% metal by volume. When at least three materials are present, it is called a hybrid composite. MMCs can have much higher strength-to-weight ratios, stiffness, and ductility than traditional materials, so they are often used in demanding applications. MMCs typically have lower thermal and electrical conductivity and poor resistance to radiation, limiting their use in the very harshest environments.
A four-strokeengine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:
Intake: Also known as induction or suction. This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing a partial vacuum in the cylinder through its downward motion.
Compression: This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.
Combustion: Also known as power or ignition. This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. the compressed air-fuel mixture is ignited by a spark plug or by heat generated by high compression, forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
Exhaust: Also known as outlet. During the exhaust stroke, the piston, once again, returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust port.
In spark ignition internal combustion engines, knocking occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but when one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel-air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive.
Brazing is a metal-joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, with the filler metal having a lower melting point than the adjoining metal.
Aluminium–silicon alloys or Silumin is a general name for a group of lightweight, high-strength aluminium alloys based on an aluminum–silicon system, i.e., Aluminium-silicon alloys (AlSi) that consist predominantly of aluminum - with silicon as the quantitatively most important alloying element. Pure AlSi alloys cannot be hardened, the commonly used alloys AlSiCu and AlSiMg can be hardened. The hardening mechanism corresponds to that of AlCu and AlMgSi. The rarely used wrought alloys in the 4000 series and the predominantly used cast alloys are standardized in the 40000 series. AlSi alloys are by far the most important of all aluminum cast materials. They are suitable for all casting processes and have excellent casting properties. Important areas of application are in car parts, including engine blocks and pistons. In addition, their use as a functional material for high-energy heat storage in electric vehicles is currently being focused on.
The Ford 335 engine family was a group of engines built by the Ford Motor Company between 1969 and 1982. The "335" designation reflected Ford management's decision to produce an engine of that size with room for expansion during its development. This engine family began production in late 1969 with a 351 cu in (5.8 L) engine, commonly called the 351C. It later expanded to include a 400 cu in (6.6 L) engine which used a taller version of the engine block, commonly referred to as a tall deck engine block, a 351 cu in (5.8 L) tall deck variant, called the 351M, and a 302 cu in (4.9 L) engine which was exclusive to Australia.
The 2300 is a 2.3 L; 139.6 cu in (2,287 cc) inline-four engine produced by the Chevrolet division of General Motors for the 1971 to 1977 model years of the Chevrolet Vega and Chevrolet Monza. It featured a die-cast aluminum alloy cylinder block. The high-tech block features an alloy with 17 percent silicon. During the machining process, the cylinders were etched leaving the pure silicon particles exposed providing the piston wear surface, eliminating the need for iron cylinder liners. The block has cast iron main caps and a cast iron crankshaft. The engine's cylinder head is cast iron for lower cost, structural integrity and longer camshaft bearing life. The valvetrain features a direct-acting single overhead camshaft design. The engine block and cylinder heads were cast at Massena Castings Plant in Massena, New York.
In automotive engineering, an exhaust manifold collects the exhaust gases from multiple cylinders into one pipe. The word manifold comes from the Old English word manigfeald and refers to the folding together of multiple inputs and outputs.
The powerplant used in Saturn S-Series automobiles was a straight-4 aluminum piston engine produced by Saturn, a subsidiary of General Motors. The engine was only used in the Saturn S-series line of vehicles from 1991 through 2002. It was available in chain-driven SOHC or DOHC variants.
The Bourke engine was an attempt by Russell Bourke, in the 1920s, to improve the two-stroke internal combustion engine. Despite finishing his design and building several working engines, the onset of World War II, lack of test results, and the poor health of his wife compounded to prevent his engine from ever coming successfully to market. The main claimed virtues of the design are that it has only two moving parts, is lightweight, has two power pulses per revolution, and does not need oil mixed into the fuel.
An aluminium alloy is an alloy in which aluminium (Al) is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon, tin, nickel and zinc. There are two principal classifications, namely casting alloys and wrought alloys, both of which are further subdivided into the categories heat-treatable and non-heat-treatable. About 85% of aluminium is used for wrought products, for example rolled plate, foils and extrusions. Cast aluminium alloys yield cost-effective products due to the low melting point, although they generally have lower tensile strengths than wrought alloys. The most important cast aluminium alloy system is Al–Si, where the high levels of silicon (4–13%) contribute to give good casting characteristics. Aluminium alloys are widely used in engineering structures and components where light weight or corrosion resistance is required.
Engine efficiency of thermal engines is the relationship between the total energy contained in the fuel, and the amount of energy used to perform useful work. There are two classifications of thermal engines-
Internal combustion and
External combustion engines.
Alusil as a hypereutectic aluminium-silicon alloy contains approximately 78% aluminium and 17% silicon. This alloy was theoretically conceived in 1927 by Schweizer & Fehrenbach, of the Badener Metall-Waren-Fabrik, 2a Hermannstraße, Baden-Baden; but practically created only by Lancia in the same year, for its car engines. It was further developed by Reynolds, now Kolbenschmidt. In the United States, Chevrolet was the first to Reynolds A390 in the Chevrolet Vega.
The Hiduminium alloys or R.R. alloys are a series of high-strength, high-temperature aluminium alloys, developed for aircraft use by Rolls-Royce ("RR") before World War II. They were manufactured and later developed by High Duty Alloys Ltd. The name Hi-Du-Minium is derived from that of High Duty Aluminium Alloys.
Y alloy is a nickel-containing aluminium alloy. It was developed by the British National Physical Laboratory during World War I, in an attempt to find an aluminium alloy that would retain its strength at high temperatures.
Eutectic bonding, also referred to as eutectic soldering, describes a wafer bonding technique with an intermediate metal layer that can produce a eutectic system. Those eutectic metals are alloys that transform directly from solid to liquid state, or vice versa from liquid to solid state, at a specific composition and temperature without passing a two-phase equilibrium, i.e. liquid and solid state. The fact that the eutectic temperature can be much lower than the melting temperature of the two or more pure elements can be important in eutectic bonding.
An internal combustion engine is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons, turbine blades, a rotor, or a nozzle. This force moves the component over a distance, transforming chemical energy into kinetic energy which is used to propel, move or power whatever the engine is attached to.
2218 aluminium alloy is an alloy in the wrought aluminium-copper family. It is one of the most complex grades in the 2000 series, with at least 88.4% aluminium by weight. Unlike most other aluminium-copper alloys, 2218 is a high work-ability alloy, with relatively low for 2xxx series alloy yield strength of 255 MPa. Despite being highly alloyed, it have a good corrosion and oxidation resistance due sacrificial anode formed by magnesium inclusions, similar to marine-grade 5xxx series alloys. Although 2218 is wrought alloy, owing to granular structure it can be used in casting and been precisely machined after casting. It is easy to weld, coat, or glue.
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