4/17/2021 0 Comments 2 Stroke Engine
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.This is in contrast to a four-stroke engine, which requires four strokes of the piston to complete a power cycle during 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.
Compared to four-stroke engines, two-stroke engines have a greatly reduced number of moving parts. The crankcase -scavenged engine, employing the area below the piston as a charging pump, is generally credited to Englishman Joseph Day. On 31 December 1879, German inventor Karl Benz produced a two-stroke gas engine, for which he received a patent in 1880 in Germany. The first truly practical two-stroke engine is attributed to Yorkshireman Alfred Angas Scott, who started producing twin-cylinder water-cooled motorcycles in 1908. However, when weight and size are not an issue, the cycles 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. 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. Oil is mixed in with their petrol fuel beforehand, in a ratio of around 40:1. This oil then forms emissions, either by being burned in the engine or as droplets in the exhaust, 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. With the traditional lubrication technique of mixing oil into the fuel, they also have the advantage of working in any orientation, as the oil reservoir is not dependent on gravity; this is an essential property for hand-held power tools such as chainsaws. The Japanese manufacturers Suzuki and Subaru did the same in the 1970s. Production of two-stroke cars ended in the 1980s in the West, due to increasingly stringent regulation of air pollution. Eastern Bloc countries continued until around 1991, with the Trabant and Wartburg in East Germany. Two-stroke engines are still found in a variety of small propulsion applications, such as outboard motors, high-performance, small-capacity motorcycles, mopeds, dirt bikes, underbones, scooters, tuk-tuks, snowmobiles, karts, ultralight airplanes, and model airplanes and other model vehicles. They are also common in power tools used outdoors, such as lawn mowers, chainsaws, and weed-wackers. 2 Stroke Engine Trial And MarineTherefore, the cycle has historically also been used in large diesel engines, mostly large industrial and marine engines, as well as some trucks and heavy machinery. Several experimental designs are intended for automobile use; for instance, Lotus of Norfolk, UK, had in 2008 a prototype direct-injection, two-stroke engine intended for alcohol fuels called the Omnivore, 7 8 which it is demonstrating in a version of the Exige. 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. All functions are controlled solely by the piston covering and uncovering the ports as it moves up and down in the cylinder. In the 1970s, Yamaha worked out some basic principles for this system. ![]() However, a mechanical limit exists to the width of a single exhaust port, at about 62 of the bore diameter for reasonable ring life. Beyond this, the rings bulge into the exhaust port and wear quickly. A maximum 70 of bore width is possible in racing engines, where rings are changed every few races.
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