A two-stroke engine is an internal combustion engine that completes the process cycle in one revolution of the crankshaft (an up stroke and a down stroke of the piston, compared to twice that number for a four-stroke engine). This is accomplished by using the end of the combustion stroke and the beginning of the compression stroke to perform simultaneously the intake and exhaust (or scavenging) functions. In this way, two-stroke engines often provide high specific power, at least in a narrow range of rotational speeds. The functions of some or all of the valves required by a four-stroke engine are usually served in a two-stroke engine by ports that are opened and closed by the motion of the piston(s), greatly reducing the number of moving parts. Gasoline (spark ignition) versions are particularly useful in lightweight (portable) applications, such as chainsaws, and the concept is also used in diesel compression ignition engines in large and weight insensitive applications, such as ships and locomotives.
The first commercial two-stroke engine involving in-cylinder compression is attributed to Scottish engineer Dugald Clerk, who in 1881 patented his design, his engine having a separate charging cylinder. The crankcase-scavenged engine, employing the area below the piston as a charging pump, is generally credited to Englishman Joseph Day.
Applications
The first commercial two-stroke engine involving in-cylinder compression is attributed to Scottish engineer Dugald Clerk, who in 1881 patented his design, his engine having a separate charging cylinder. The crankcase-scavenged engine, employing the area below the piston as a charging pump, is generally credited to Englishman Joseph Day.
Applications
A two-stroke minibike
The two-stroke engine was very popular throughout the 20th century in motorcycles and small-engined devices, such as chainsaws and outboard motors, and was also used in some cars, a few tractors and many ships. Part of their appeal was their simple design (and resulting low cost) and often high power-to weight ratio. Because of the lower cost to rebuild and maintain, the two stroke engine was incredibly popular in the dirt bike and motocross industry for many years, until recently when the EPA required the industry to switch to four-stroke engines because they emit less pollution than two stroke engines. Many designs use total-loss lubrication, with the oil being burned in the combustion chamber, causing "blue smoke" and other types of exhaust pollution. This is a major reason for two-stroke engines being replaced by four-stroke engines in many applications.
Two-stroke engines continue to be commonly used in high-power, handheld applications such as string trimmers andchainsaws. The light overall weight, and light-weight spinning parts give important operational and even safety advantages. For example, only a two-stroke engine that uses a gasoline-oil mixture can power a chainsaw operating in any position.
These engines are still used for small, portable, or specialized machine applications such as outboard motors, high-performance, small-capacitymotorcycles, mopeds, underbones, scooters, tuk-tuks, snowmobiles, karts, ultralights, model airplanes (and other model vehicles) and lawnmowers. The two-stroke cycle is used in many diesel engines, most notably large industrial and marine engines, as well as some trucks and heavy machinery.
A number of mainstream automobile manufacturers have used two-stroke engines in the past, including the Swedish Saab and German manufacturersDKW and Auto-Union. The Japanese manufacturer Suzuki did the same in the 1970s.[1] Production of two-stroke cars ended in the 1980s in the West, but Eastern Bloc countries continued until around 1991, with the Trabant and Wartburg in East Germany. Lotus of Norfolk, UK, has a prototype direct-injection two-stroke engine intended for alcohol fuels called the Omnivore[2][3] which it is demonstrating in a version of the Exige.
[edit]Different two-stroke design types
A two-stroke engine, in this case with a tuned expansion pipe illustrates the effect of a reflected pressure wave on the fuel charge. This feature is essential for maximum charge pressure (volumetric efficiency) and fuel efficiency. It is used on most high-performance engine designs.
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.
The two-stroke engine was very popular throughout the 20th century in motorcycles and small-engined devices, such as chainsaws and outboard motors, and was also used in some cars, a few tractors and many ships. Part of their appeal was their simple design (and resulting low cost) and often high power-to weight ratio. Because of the lower cost to rebuild and maintain, the two stroke engine was incredibly popular in the dirt bike and motocross industry for many years, until recently when the EPA required the industry to switch to four-stroke engines because they emit less pollution than two stroke engines. Many designs use total-loss lubrication, with the oil being burned in the combustion chamber, causing "blue smoke" and other types of exhaust pollution. This is a major reason for two-stroke engines being replaced by four-stroke engines in many applications.
Two-stroke engines continue to be commonly used in high-power, handheld applications such as string trimmers andchainsaws. The light overall weight, and light-weight spinning parts give important operational and even safety advantages. For example, only a two-stroke engine that uses a gasoline-oil mixture can power a chainsaw operating in any position.
These engines are still used for small, portable, or specialized machine applications such as outboard motors, high-performance, small-capacitymotorcycles, mopeds, underbones, scooters, tuk-tuks, snowmobiles, karts, ultralights, model airplanes (and other model vehicles) and lawnmowers. The two-stroke cycle is used in many diesel engines, most notably large industrial and marine engines, as well as some trucks and heavy machinery.
A number of mainstream automobile manufacturers have used two-stroke engines in the past, including the Swedish Saab and German manufacturersDKW and Auto-Union. The Japanese manufacturer Suzuki did the same in the 1970s.[1] Production of two-stroke cars ended in the 1980s in the West, but Eastern Bloc countries continued until around 1991, with the Trabant and Wartburg in East Germany. Lotus of Norfolk, UK, has a prototype direct-injection two-stroke engine intended for alcohol fuels called the Omnivore[2][3] which it is demonstrating in a version of the Exige.
[edit]Different two-stroke design types
A two-stroke engine, in this case with a tuned expansion pipe illustrates the effect of a reflected pressure wave on the fuel charge. This feature is essential for maximum charge pressure (volumetric efficiency) and fuel efficiency. It is used on most high-performance engine designs.
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.
No comments:
Post a Comment