Difference Between 2stroke And 4stroke Engine Pdf

difference between 2stroke and 4stroke engine pdf

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Two-Stroke Engines: Defining Their Purpose

A two-stroke or two-cycle engine is a type of internal combustion engine that completes a power cycle with two strokes up and down movements of the piston during only one crankshaft revolution.

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. Two-stroke engines often have a high power-to-weight ratio , power being available in a narrow range of rotational speeds called the " power band ". Compared to four-stroke engines, two-stroke engines have a greatly reduced number of moving parts.

The first commercial two-stroke engine involving in- 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. 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 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. However, with direct fuel injection and a sump -based lubrication system, a modern two-stroke engine can produce air pollution no worse than a four-stroke, [ citation needed ] and can achieve higher thermodynamic efficiency.

Two-stroke petrol 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. This is an essential property for hand-held power tools. 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 , tuk-tuks , snowmobiles , go-karts , ultralight and model airplanes. They are also common in outdoor power tools such as lawn mowers , 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 rings bulge into the exhaust port and wear quickly. 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. 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 track 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.

A familiar type sometimes seen on small motorcycles is a slotted disk attached to the crankshaft , which covers and uncovers an opening in the end of the crankcase, allowing charge to enter during one portion of the cycle called a disc valve.

Another form of rotary inlet valve used on two-stroke engines employs two cylindrical members with suitable cutouts arranged to rotate one within the other - the inlet pipe having passage to the crankcase only when the two cutouts coincide. The crankshaft itself may form one of the members, as in most glow-plug model engines. In another version, the crank disc is arranged to be a close-clearance fit in the crankcase, and is provided with a cutout that lines up with an inlet passage in the crankcase wall at the appropriate time, as in Vespa motor scooters.

The advantage of a rotary valve is that it enables the two-stroke engine's intake timing to be asymmetrical, which is not possible with piston-port type engines. The piston-port type engine's intake timing opens and closes before and after top dead center at the same crank angle, making it symmetrical, whereas the rotary valve allows the opening to begin and close earlier.

Rotary valve engines can be tailored to deliver power over a wider speed range or higher power over a narrower speed range than either a piston-port or reed-valve engine. Where a portion of the rotary valve is a portion of the crankcase itself, of particular importance, no wear should be allowed to take place. In a cross-flow engine, the transfer and exhaust ports are on opposite sides of the cylinder, and a deflector on the top of the piston directs the fresh intake charge into the upper part of the cylinder, pushing the residual exhaust gas down the other side of the deflector and out the exhaust port.

This method of scavenging uses carefully shaped and positioned transfer ports to direct the flow of fresh mixture toward the combustion chamber as it enters the cylinder. Usually, a piston deflector is not required, so this approach has a distinct advantage over the cross-flow scheme above. Suzuki was one of the first manufacturers outside of Europe to adopt loop-scavenged, two-stroke engines.

This operational feature was used in conjunction with the expansion chamber exhaust developed by German motorcycle manufacturer, MZ, and Walter Kaaden. Loop scavenging, disc valves, and expansion chambers worked in a highly coordinated way to significantly increase the power output of two-stroke engines, particularly from the Japanese manufacturers Suzuki, Yamaha, and Kawasaki.

Suzuki and Yamaha enjoyed success in Grand Prix motorcycle racing in the s due in no small way to the increased power afforded by loop scavenging. An additional benefit of loop scavenging was the piston could be made nearly flat or slightly domed, which allowed the piston to be appreciably lighter and stronger, and consequently to tolerate higher engine speeds.

The "flat top" piston also has better thermal properties and is less prone to uneven heating, expansion, piston seizures, dimensional changes, and compression losses. SAAB built and cc three-cylinder engines based on a DKW design that proved reasonably successful employing loop charging. The original SAAB 92 had a two-cylinder engine of comparatively low efficiency. At cruising speed, reflected-wave, exhaust-port blocking occurred at too low a frequency. Using the asymmetrical three-port exhaust manifold employed in the identical DKW engine improved fuel economy.

Base compression comprises a portion of the overall compression ratio of a two-stroke engine. Work published at SAE in points that loop scavenging is under every circumstance more efficient than cross-flow scavenging. In a uniflow engine, the mixture, or "charge air" in the case of a diesel, enters at one end of the cylinder controlled by the piston and the exhaust exits at the other end controlled by an exhaust valve or piston.

The scavenging gas-flow is, therefore, in one direction only, hence the name uniflow. Ported types are represented by the opposed piston design in which two pistons are in each cylinder, working in opposite directions such as the Junkers Jumo and Napier Deltic. With advanced-angle exhaust timing, uniflow engines can be supercharged with a crankshaft-driven piston [10] or Roots blower. The piston of this engine is "top-hat"-shaped; the upper section forms the regular cylinder, and the lower section performs a scavenging function.

The units run in pairs, with the lower half of one piston charging an adjacent combustion chamber. This system is still partially dependent on total-loss lubrication for the upper part of the piston , the other parts being sump lubricated with cleanliness and reliability benefits. Many modern two-stroke engines employ a power-valve system. The valves are normally in or around the exhaust ports. They work in one of two ways; either they alter the exhaust port by closing off the top part of the port, which alters port timing, such as Rotax R.

The result is an engine with better low-speed power without sacrificing high-speed power. However, as power valves are in the hot gas flow, they need regular maintenance to perform well. Direct injection has considerable advantages in two-stroke engines. Two systems are in use, low-pressure air-assisted injection and high-pressure injection. Diesel engines rely solely on the heat of compression for ignition.

In the case of Schnuerle-ported and loop-scavenged engines, intake and exhaust happen via piston-controlled ports. A uniflow diesel engine takes in air via scavenge ports , and exhaust gases exit through an overhead poppet valve.

Two-stroke diesels are all scavenged by forced induction. Some designs use a mechanically driven Roots blower, whilst marine diesel engines normally use exhaust-driven turbochargers, with electrically driven auxiliary blowers for low-speed operation when exhaust turbochargers are unable to deliver enough air. Marine two-stroke diesel engines directly coupled to the propeller are able to start and run in either direction as required. The fuel injection and valve timing are mechanically readjusted by using a different set of cams on the camshaft.

Thus, the engine can be run in reverse to move the vessel backwards. Two-stroke engines use their crankcase to pressurize the air:fuel mixture before transfer to the cylinder.

They cannot be lubricated by oil contained in the crankcase and sump per practice with four-stroke engines because the crankcase is being used to pump the mixture into the cylinder; standard lubricating oil would be swept up and burnt with the fuel. Fuels supplied to two-stroke engines are often mixed with oil so that it can coat the cylinders and bearing surfaces along its path. The ratio of gas to oil is set by the engine manufacturer but ranges from to per volume unit.

Oil remaining in the mixture is burnt with the fuel and results in a familiar blue smoke and odor. Two-stroke oils, which became available in the s, are specifically designed to mix with petrol and be burnt with minimal unburnt oil or ash.

This led to a marked reduction in spark plug fouling, which had previously been a problem in two-stroke engines. Other two-stroke engines might pump lubrication from a separate tank of two-stroke oil.

The supply of this oil is controlled by the throttle position and engine speed. Examples are found in Yamaha's PW80 Pee-wee , and many two-stroke snowmobiles. The technology is referred to as auto-lube. This is still a total-loss system with the oil being burnt the same as in the premix system. Given that the oil is not properly mixed with the fuel when burned in the combustion chamber, it provides slightly more efficient lubrication.

This lubrication method eliminates the user's need to mix the gasoline at every refill, makes the motor much less susceptible to atmospheric conditions ambient temperature, elevation , and ensures proper engine lubrication, with less oil at light loads such as idle and more oil at high loads full throttle. Some companies, such as Bombardier, had some oil-pump designs have no oil injected at idle to reduce smoke levels, as the loading on the engine parts was light enough to not require additional lubrication beyond the low levels that the fuel provides.

Six-stroke engine

Linda Benedict. Small power tools, like this trimmer, run on 2-stroke engines, which offer more power for their weight than 4-stroke engines. Most small, hand-carried lawn and garden tools such as string trimmers and chainsaws use 2-stroke engines, while larger machines such as lawn and garden tractors use 4-stroke engines. Lawn mowers are available with either type of engine. Dick Parish explains the differences and why 2-stroke engines are more commonly used on small tools. The engineer says that every reciprocating internal combustion engine operates through a "cycle" of five functions — intake, compression, ignition, combustion and exhaust.

A two-stroke or two-cycle engine is a type of internal combustion engine that completes a power cycle with two strokes up and down movements of the piston during only one crankshaft revolution. 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. Two-stroke engines often have a high power-to-weight ratio , power being available in a narrow range of rotational speeds called the " power band ". Compared to four-stroke engines, two-stroke engines have a greatly reduced number of moving parts. The first commercial two-stroke engine involving in- cylinder compression is attributed to Scottish engineer Dugald Clerk , who patented his design in

Hey, how are you? Assuming you are good! As we all know the there are two types of engines although there are various kinds of engines are available however these are some popular engines we are talking about one is four-stroke another one is two-stroke. We call an engine 2-stroke when the four successive strokes, i. Suction, Compression, Power, and Exhaust are completed in 1 revolution of the crankshaft, which means in the degree rotation of a crankshaft all the successive strokes are completed. And again we call an engine 4-stroke when the same successive strokes Suction, Compression, Power, and Exhaust are completed in the 2-revolution of the crankshaft. I will suggest you to reading those articles too.


The 4-stroke engine requires heavy flywheel. The 2-stroke engine requires lighter flywheel. whereas in the 2-stroke engine has Inlet and exhaust ports are present. Charges (Air and fuel mixtures) or only Air directly enter into the cylinder.


2-Stroke And 4-Stroke Engines – Whats The Difference?

Revs Your Heart — Explore the world of Yamaha motorcycles. Fuel for a 2-stroke engine has a small amount of oil mixed into it. No intake or exhaust valves are used and instead, small holes called scavenging ports in the cylinder wall are used for drawing in air and expelling exhaust. Because combustion takes place with each revolution of the crankshaft with a 2-stroke, this format puts out more power than a 4-stroke engine and the power has more instantaneous delivery. This are some reasons why 2-stroke engines have a long history of use on many different types of motorcycles.

A four-stroke also four-cycle engine 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:. Nicolaus August Otto was a traveling salesman for a grocery concern. In his travels, he encountered the internal combustion engine built in Paris by Belgian expatriate Jean Joseph Etienne Lenoir.

When deciding on the ideal motorcycle to purchase or use, one of the questions to ask yourself is: what kind of engine do I want? What are the differences between a two-stroke engine and a four-stroke engine, and which is better? To simplify things, typically motorcycles with two-stroke engines are no longer produced, as they do not comply with the environmental laws of many countries and are not allowed to be driven in cities, and the debate between the two kinds of engines is more applicable to off-road vehicles, such as dirt bikes. A four-stroke engine, as the name suggests, has a piston that goes through four strokes or two crankshaft revolutions to complete one full cycle; the intake, compression, power and exhaust stroke.

What is the difference between a 2-stroke and a 4-stroke motorcycle engine?

Two stroke engine

The term six-stroke engine has been applied to a number of alternative internal combustion engine designs that attempt to improve on traditional two-stroke and four-stroke engines. These engines can be divided into two groups based on the number of pistons that contribute to the six strokes. The pistons in this type of six-stroke engine go up and down three times for each injection of fuel.

A 4-stroke engine is a type of small internal combustion engine that uses four different piston strokes to complete one operating cycle. During this cycle, the crankshaft rotates twice while the piston goes up and down twice to fire the spark plug. Small engines get fuel and air through the carburetor. The carburetor then combines the fuel and air for combustion. During the intake stroke, the intake valve between the combustion chamber and the carburetor opens, which allows atmospheric pressure to push the fuel-air mixture into the cylinder as the piston moves downward.

As the name implies, the two stroke engine only requires two piston movements one cycle in order to generate power. There is a valve for the intake stroke that opens and closes due to changing pressures. In addition, due to its frequent contact with moving components, the fuel is mixed with oil to add lubrication, allowing smoother strokes. The thermal efficiency of these gasoline engines will vary depending on the model and design of the vehicle. Compared to four stroke engines , two strokes are lighter, more efficient, have the ability to use lower-grade fuel, and more cost-efficient. However, they lack the maneuverability possible in four stroke engines and require more lubrication. This makes two stroke engines ideal for ships need to carry a lot of cargo [2] , motorcycles, and lawn mowers—whereas a four stroke would be ideal for automobiles like cars and trucks.


COMPARISON BETWEEN TWO STROKE AND FOUR STROKE ENGINES. Four stroke engine. Two stroke engine. 1. One power stroke for every two revolutions.


What Are the Different Parts of a 4-Stroke Engine?

Automotive engines have transformed over the years, but two main gasoline powered combustion engine designs remain: the 2-stroke and the 4-stroke. How do they work, and which is better? Read on to learn the answers! In order to understand how these two engines are different, you first need to become familiar with the basics.

 Не несет ответственности? - Глаза Стратмора расширились от изумления.  - Некто шантажирует АНБ и через несколько дней умирает - и мы не несем ответственности. Готов поспорить на любую сумму, что у партнера Танкадо будет иное мнение.

Difference Between Four-stroke and Two-stroke Engine [With PDF]

 Шифры, - задумчиво сказал Беккер - Откуда ты знаешь, с чего начинать. То есть… как ты их вскрываешь.

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