Tvåtaktare baktänder
Svar för DEN DANSAS I TVÅTAKT i korsord, pilord och 2 andra möjliga svar. Bland svaren hittar du här den bästa Snoan med 5 bokstäver, genom att klicka på det eller på andra ord kan du hitta liknande ord och synonymer som kan hjälpa dig i ditt korsord. A two-stroke or two-stroke cycle engine is a type of internal combustion engine that completes a power cycle with two strokes of the piston one up and one down movement in one revolution of the crankshaft.
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A four-stroke engine requires four strokes of the piston to complete a power cycle, in two crankshaft revolutions. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust or scavenging functions occurring at the same time. Two-stroke engines often have a higher power-to-weight ratio than a four-stroke engine, since their power stroke occurs twice as often.
Two-stroke engines can also have fewer moving parts , and thus be cheaper to manufacture and weigh less. In countries and regions with stringent emissions regulation, two-stroke engines have been phased out in automotive and motorcycle uses. In regions where regulations are less stringent, small displacement two-stroke engines remain popular in mopeds and motorcycles. The first commercial two-stroke engine involving cylinder compression is attributed to Scottish engineer Dugald Clerk , who patented his design in The crankcase -scavenged engine, employing the area below the piston as a charging pump, is generally credited to Englishman Joseph Day.
The first truly practical two-stroke engine is attributed to Yorkshireman Alfred Angas Scott , who started producing twin-cylinder water-cooled motorcycles in Two-stroke gasoline engines with electrical spark ignition are particularly useful in lightweight or portable applications such as chainsaws and motorcycles. However, when weight and size are not an issue, the cycle's potential for high thermodynamic efficiency makes it ideal for diesel compression ignition engines operating in large, weight-insensitive applications, such as marine propulsion , railway locomotives , and electricity generation.
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In a two-stroke engine, the exhaust gases transfer less heat to the cooling system than a four-stroke, which means more energy to drive the piston, and if present, a turbocharger. Crankcase-compression two-stroke engines, such as common small gasoline-powered engines, are lubricated by a petroil mixture in a total-loss system. Oil is mixed in with their petrol fuel beforehand, in a fuel-to-oil ratio of around This oil then forms emissions, either by being burned in the engine or as droplets in the exhaust, historically resulting in more exhaust emissions, particularly hydrocarbons, than four-stroke engines of comparable power output.
The combined opening time of the intake and exhaust ports in some two-stroke designs can also allow some amount of unburned fuel vapors to exit in the exhaust stream. The high combustion temperatures of small, air-cooled engines may also produce NO x emissions. Two-stroke gasoline engines are preferred when mechanical simplicity, light weight, and high power-to-weight ratio are design priorities. By mixing oil with fuel, they can operate in any orientation as the oil reservoir does not depend on gravity.
The Japanese manufacturers Suzuki and Subaru did the same in the s. Two-stroke engines are still found in a variety of small propulsion applications, such as outboard motors , small on- and off-road motorcycles , mopeds , scooters , motorized bicycles , tuk-tuks , snowmobiles , go-karts , ultralight and model airplanes. Particularly in developed countries, pollution regulations have meant that their use for many of these applications is being phased out.
Honda , [ 8 ] for instance, ceased selling two-stroke off-road motorcycles in the United States in , after abandoning road-going models considerably earlier. Due to their high power-to-weight ratio and ability to be used in any orientation, two-stroke engines are common in handheld outdoor power tools including leaf blowers , chainsaws , and string trimmers. Two-stroke diesel engines are found mostly in large industrial and marine applications, as well as some trucks and heavy machinery.
Although the principles remain the same, the mechanical details of various two-stroke engines differ depending on the type. The design types vary according to the method of introducing the charge to the cylinder, the method of scavenging the cylinder exchanging burnt exhaust for fresh mixture and the method of exhausting the cylinder. Piston port is the simplest of the designs and the most common in small two-stroke engines.
All functions are controlled solely by the piston covering and uncovering the ports as it moves up and down in the cylinder. In the s, Yamaha worked out some basic principles for this system. They found that, in general, widening an exhaust port increases the power by the same amount as raising the port, but the power band does not narrow as it does when the port is raised. Beyond this, the piston rings bulge into the exhaust port and wear quickly.
Intake duration is between and °. Transfer port time is set at a minimum of 26°. The strong, low-pressure pulse of a racing two-stroke expansion chamber can drop the pressure to -7 psi when the piston is at bottom dead center, and the transfer ports nearly wide open. One of the reasons for high fuel consumption in two-strokes is that some of the incoming pressurized fuel-air mixture is forced across the top of the piston, where it has a cooling action, and straight out the exhaust pipe.
An expansion chamber with a strong reverse pulse stops this outgoing flow. A fundamental difference from typical four-stroke engines is that the two-stroke's crankcase is sealed and forms part of the induction process in gasoline and hot-bulb engines. Diesel two-strokes often add a Roots blower or piston pump for scavenging. The reed valve is a simple but highly effective form of check valve commonly fitted in the intake tract of the piston-controlled port.
It allows asymmetric intake of the fuel charge, improving power and economy, while widening the power band. Such valves are widely used in motorcycle, ATV, and marine outboard engines. The intake pathway is opened and closed by a rotating member.