There are different ways of doing the pistons and they all aims to achieve the lighter piston with least friction. Some of these are explained as follows:
Cast piston is used for light-duty. The cast surface tells us this piston won't stand up to extremes of temperature and rpm because the molecular structure isn't as tight as it is with hypereutectic and forged pistons.
Die-cast pistons are made by pouring molten aluminium into a mould. Then, the piston is machined into a finished product.
Hypereutectic pistons are little more than a die-cast slug with a high silicone content. This makes the surfaces harder and shinier. It also changes the expansion properties, allowing you to run tighter piston-to-cylinder-wall clearances. You can run a hypereutectic piston a lot harder than you can a cast unit. The high-silicone content gives the hypereutectic a forged appearance. Note the huge valve relief for those Cleveland intake valves.
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Forged pistons are more involved, and, certainly, more expensive to make. Instead of a simple mould, we need a giant press, which rams the aluminium into a complex mould under high pressure. Machining forged pistons is no small feat. It is both time consuming and expensive. The forged piston advantage is greater strength, harder surfaces, more predictable expansion properties, and virtually no porosity. Another advantage to forged pistons is the ability to make them lighter and with less skirt. We can do this because forged pistons are stronger. We can machine more meat out of them without suffering structural losses. Forged pistons have a distinctive look, with an extra-hard surface and machining marks. These are what you go with when high rpm and high heat are expected. If you're running nitrous or supercharging, they're mandatory.
Piston technology has come a long way. Computer-aided design and CNC machining technology has made it possible to make custom pistons for just about any application you can think of. With this technology has come lighter pistons with less skirt that offer less friction.
Piston design and shape greatly effect how an engine performs. When pistons are too heavy, we lose power. Design in too much skirt, and we lose power through excessive friction. Too little skirt, and the piston becomes unstable. Shoehorn in too much displacement, push the wrist pin into the ring grooves, and you have a formula for piston failure because this exerts too much heat on the pin and boss.
In the dreamy world of piston science, we dream of the perfect piston--the piston that creates very little friction (drag), weighs very little, carries just the right amount of oil up the cylinder walls, and provides a perfect cylinder seal. In the real world, it is nearly impossible to achieve all of these elements at once.
A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more
reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types. The main types are:
The internal combustion engine, used extensively in motor vehicles,
The steam engine, the mainstay of the Industrial Revolution,
The niche application Stirling engine.
The current problem is that there are two pistons with failure; the author here is doing analysis and investigation on the tow pistons trying to find the root causes for this problem and how to avoid this to happen again next time. Those tow pistons are parts in a marine diesel engine made by a German company called MAN Diesel & Turbo. MAN Diesel & Turbo is one of the world's leading suppliers in its various fields. From pleasure yacht engines to four-stroke engines for giant container ships, from emergency power unitsÂ to turnkey diesel power plants, from single compressors and turbines to complete machine trains for various industrial applications. The engine for the piston is a marine engine with product number L20/27.
In theory, diesel engines are internal combusÂtion engines designed to convert the chemical energy available in fuel into mechanical energy. This mechanical energy moves pistons up and down inside cylinders. The pistons are connected to a crankshaft, and the up-and-down motion of the pistons, known as linear motion, creates the rotary motion needed to turn the wheels of a car forward.
Diesel engines covert fuel into energy through a series of small explosions or combustions.
explosions happen In a diesel engine; the air is compressed first, and then the fuel is injected. Because air heats up when it's compressed, the fuel ignites.
The diesel engine uses a four-stroke combustion cycle .
The four strokes are:
Stroke 1 of 4 "Suck": Intake stroke On the intake or induction stroke of the piston , the piston descends from the top of the cylinder to the bottom of the cylinder, reducing the pressure inside the cylinder. A mixture of fuel and air is forced by atmospheric (or greater) pressure into the cylinder through the intake port. The intake valve(s) then close. - The intake valve opens up, letting in air and moving the piston down. Â
Stroke 2 of 4 "Squeeze" Compression stroke: With both intake and exhaust valves closed, the piston returns to the top of the cylinder compressing the fuel-air mixture. This is known as the compression stroke. -- The piston moves back up and compresses the air.
Stroke 3 of 4 "Bang" Combustion stroke: While the piston is at or close to Top Dead Center, the compressed airââ‚¬"fuel mixture is ignited, usually by a spark plug (for a gasoline or Otto cycle engine) or by the heat and pressure of compression (for a diesel cycle or compression ignition engine). The resulting massive pressure from the combustion of the compressed fuel-air mixture drives the piston back down toward bottom dead center with tremendous force. This is known as the power stroke, which is the main source of the engine's torque and power. -- As the piston reaches the top, fuel is injected at just the right moment and ignited, forcing the piston back down.
Stroke 4 of 4 "Blow" Exhaust stroke: During the exhaust stroke, the piston once again returns to
top dead center while the exhaust valve is open. This action evacuates the products of combustion from the cylinder by pushing the spent fuel-air mixture through the exhaust valve(s). -- The piston moves back to the top, pushing out the exhaust created from the combustion out of the exhaust valve.
Remember that the diesel engine has no spark plug, that it intakes air and compresses it, and that it then injects the fuel directly into the combustion chamber (direct injection). It is the heat of the compressed air that lights the fuel in a diesel engine. In the next section, we'll examine the diesel injection process.
Medium-alkaline lube oils have proven to be suitable for lubricating the power train, the cylinders, the turbocharger and, if the facility is provided, for the cooling of the pistons. Such medium-alkaline lube oils contain additives which, amongst other things, provide them with a higher neutralization capability than is the case with blended (HD) oils.
The basic oil (medium-alkaline lube oil = basic oil + additives) must be a narrow distillation cut and must be refined according to modern methods. Bright stocks, if contained, must neither adversely affect the thermal nor the oxidation stability of the basic oil
Medium-alkaline lube oil
The basic oil with additives have been mixed (medium-alkaline lube oil) must demonstrate the following characteristics:
The additives must be dissolved in the oil and must be of such a composition tat an absolute minimum of ash remains as residue after combustion, even if temporary operated on distillate fuel. That ash must be soft. If this prerequisite id not complied with, increased deposits are to be expected in the combustion chamber especially at the outlet valves and in the inlet housing of the turbochargers. Hard additive ash promotes pitting on the valve seats, as well as burnt-out valves and increased mechanical wear.
Additives must not cause clogging of the filter elements, neither in their active nor in their exhausted state.
The cleaning capacity must be so high that coke and tar-like residues occurring when fuel is combusted must not build-up.
The dispersing capacity must selected such that commercially available lube oil cleaning equipment can remove the combustion deposits from the used oil, i.e. the used oil must possess good separation and filtration properties.
The neutralization capacity (ASTM-D2896) must be so high that the acidic products which emanate during combustion are neutralized by the lube oil consumption of the engine. The reaction time of the additives must be matched to the process in the combustion chamber.
The tendency to evaporate must be as low as possible, otherwise the oil consumption is adversely affected.
The lube oil must not form a stable emulsion with water. < 40 ml emulsion as per ASTM-D1401.
The lube oil must not contain agents to improve viscosity index.
The fresh oil must be free from water and other contaminants.
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