Two-stroke engine

The first commercial two-stroke engine involving cylinder compression is attributed to Scottish engineer Dugald Clerk, who patented his design in 1881.^[1] However, unlike most later two-stroke engines, his had 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.^[2][3] 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.^[4]

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.

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Scotland

Scotland

Scotland is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a 96-mile (154-kilometre) border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the north and west, the North Sea to the northeast and east, and the Irish Sea to the south. It also contains more than 790 islands, principally in the archipelagos of the Hebrides and the Northern Isles. Most of the population, including the capital Edinburgh, is concentrated in the Central Belt—the plain between the Scottish Highlands and the Southern Uplands—in the Scottish Lowlands.

Dugald Clerk

Dugald Clerk

Sir Dugald Clerk KBE, LLD FRS was a Scottish engineer who designed the world's first successful two-stroke engine in 1878 and patented it in England in 1881. He was a graduate of Anderson's University in Glasgow, and Yorkshire College, Leeds. He formed the intellectual property firm with George Croydon Marks, called Marks & Clerk. He was knighted on 24 August 1917.

Crankcase

Crankcase

In a piston engine, the crankcase is the housing that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block.

Joseph Day (inventor)

Joseph Day (inventor)

Joseph Day is a little-known English engineer who developed the extremely widely used crankcase-compression two-stroke petrol engine, as used for small engines from lawnmowers to mopeds and small motorcycles. He trained as an engineer at the Crystal Palace School of Engineering at Crystal Palace in London, began work at Stothert & Pitt in Bath, and in 1889 designed the crankcase-compression two-stroke engine as it is widely known today, the Valve-less Two-Stroke Engine. In 1878 he started his own business, an iron foundry making cranes, mortar mills and compressors amongst other things.

Germany

Germany

Germany, officially the Federal Republic of Germany, is a country in Central Europe. It is the second-most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated between the Baltic and North seas to the north, and the Alps to the south; it covers an area of 357,022 square kilometres (137,847 sq mi), with a population of around 84 million within its 16 constituent states. Germany borders Denmark to the north, Poland and the Czech Republic to the east, Austria and Switzerland to the south, and France, Luxembourg, Belgium, and the Netherlands to the west. The nation's capital and most populous city is Berlin and its main financial centre is Frankfurt; the largest urban area is the Ruhr.

Alfred Angas Scott

Alfred Angas Scott

Alfred Angas Scott (1875–1923) was a British motorcycle designer, inventor and founder of the Scott Motorcycle Company. A prolific inventor, he took out over 50 patents between 1897 and 1920, mostly concerning two-stroke engines and road vehicles. Scott was a keen potholer and the second president of the Gritstone club. In July 1923 Scott travelled back to Bradford in his open Scott Sociable wearing wet potholing clothes and contracted pneumonia from which he died.

Motorcycle

Motorcycle

A motorcycle is a two or three-wheeled motor vehicle steered by a handlebar from a saddle-style seat.

Gasoline

Gasoline

Gasoline or petrol is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. On average, U.S. refineries produce, from a barrel of crude oil, about 19 to 20 gallons of gasoline; 11 to 13 gallons of distillate fuel ; and 3 to 4 gallons of jet fuel. The product ratio depends on the processing in an oil refinery and the crude oil assay. A barrel of oil is defined as holding 42 US gallons, which is about 159 liters or 35 imperial gallons.

Diesel fuel

Diesel fuel

Diesel fuel, also called diesel oil or historically heavy oil, is any liquid fuel specifically designed for use in a diesel engine, a type of internal combustion engine in which fuel ignition takes place without a spark as a result of compression of the inlet air and then injection of fuel. Therefore, diesel fuel needs good compression ignition characteristics.

Marine propulsion

Marine propulsion

Marine propulsion is the mechanism or system used to generate thrust to move a watercraft through water. While paddles and sails are still used on some smaller boats, most modern ships are propelled by mechanical systems consisting of an electric motor or internal combustion engine driving a propeller, or less frequently, in pump-jets, an impeller. Marine engineering is the discipline concerned with the engineering design process of marine propulsion systems.

Locomotive

Locomotive

A locomotive or engine is a rail transport vehicle that provides the motive power for a train. If a locomotive is capable of carrying a payload, it is usually rather referred to as a multiple unit, motor coach, railcar or power car; the use of these self-propelled vehicles is increasingly common for passenger trains, but rare for freight.

Diesel generator

Diesel generator

A diesel generator (DG) is the combination of a diesel engine with an electric generator to generate electrical energy. This is a specific case of engine generator. A diesel compression-ignition engine is usually designed to run on diesel fuel, but some types are adapted for other liquid fuels or natural gas.

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 32:1. 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, and can achieve higher thermodynamic efficiency.

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Total-loss oiling system

Total-loss oiling system

A total-loss oiling system is an engine lubrication system whereby oil is introduced into the engine, and then either burned or ejected overboard. Now rare in four-stroke engines, total loss oiling is still used in many two-stroke engines.

NOx

NOx

In atmospheric chemistry, NOx is shorthand for nitric oxide and nitrogen dioxide, the nitrogen oxides that are most relevant for air pollution. These gases contribute to the formation of smog and acid rain, as well as affecting tropospheric ozone.

Sump

Sump

A sump is a low space that collects often undesirable liquids such as water or chemicals. A sump can also be an infiltration basin used to manage surface runoff water and recharge underground aquifers. Sump can also refer to an area in a cave where an underground flow of water exits the cave into the earth.

1966 Saab Sport

A two-stroke minibike

Lateral view of a two-stroke Forty series British Seagull outboard engine, the serial number dates it to 1954/1955

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.

A number of mainstream automobile manufacturers have used two-stroke engines in the past, including the Swedish Saab and German manufacturers DKW, Auto-Union, VEB Sachsenring Automobilwerke Zwickau, VEB Automobilwerk Eisenach, and VEB Fahrzeug- und Jagdwaffenwerk „Ernst Thälmann. The Japanese manufacturers Suzuki and Subaru did the same in the 1970s.^[5] Production of two-stroke cars ended in the 1980s in the West, due to increasingly stringent regulation of air pollution.^[6] 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, small on- and off-road motorcycles, mopeds, scooters, 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,^[7] for instance, ceased selling two-stroke off-road motorcycles in the United States in 2007, 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.

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Saab Sport

Saab Sport

The Saab Sport is an automobile from Saab, launched in 1962 as a replacement for the Saab GT750. It used the same body shell as the Saab 96, with slight modifications and with a different interior configuration and equipment. From the outside it could be differentiated from a standard 96 by the twin chrome stripes along the lower part of the sides.

British Seagull

British Seagull

The British Seagull was a British manufacturer of two-stroke outboard engines in Poole, Dorset from the late 1930s until the mid-1990s. Although their "Classic" engines were for decades an exemplar of rugged simplicity and reliability, the company eventually failed when customer tastes changed and as tighter emissions regulations took effect. Production of complete engines stopped in 1996, and another company bought the rights to the brand in 1999. Spare parts continue to be produced for existing engines.

Power-to-weight ratio

Power-to-weight ratio

Power-to-weight ratio is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measurement of actual performance of any engine or power source. It is also used as a measurement of performance of a vehicle as a whole, with the engine's power output being divided by the weight of the vehicle, to give a metric that is independent of the vehicle's size. Power-to-weight is often quoted by manufacturers at the peak value, but the actual value may vary in use and variations will affect performance.

Sump

Sump

A sump is a low space that collects often undesirable liquids such as water or chemicals. A sump can also be an infiltration basin used to manage surface runoff water and recharge underground aquifers. Sump can also refer to an area in a cave where an underground flow of water exits the cave into the earth.

Saab Automobile

Saab Automobile

Saab Automobile AB was a car manufacturer that was founded in Sweden in 1945 when its parent company, Saab AB, began a project to design a small automobile. The first production model, the Saab 92, was launched in 1949. In 1968 the parent company merged with Scania-Vabis, and ten years later the Saab 900 was launched, in time becoming Saab's best-selling model. In the mid-1980s the new Saab 9000 model also appeared.

DKW

DKW

DKW was a German car- and motorcycle-marque. DKW was one of the four companies that formed Auto Union in 1932 and thus became an ancestor of the modern-day Audi company.

Simson (company)

Simson (company)

Simson was a German company which produced firearms, automobiles, bicycles and motorcycles, and mopeds. Under the Third Reich, the factory was taken from the Jewish Simson family, and was renamed several times under Nazi and later Communist control. The Simson name was reintroduced as a brand name for mopeds produced at the factory in the former German Democratic Republic (GDR). Simson mopeds were then produced in Suhl (Germany) until 2002.

Suzuki

Suzuki

Suzuki Motor Corporation is a Japanese multinational corporation headquartered in Minami-ku, Hamamatsu, Japan. Suzuki manufactures automobiles, motorcycles, all-terrain vehicles (ATVs), outboard marine engines, wheelchairs and a variety of other small internal combustion engines. In 2016, Suzuki was the eleventh biggest automaker by production worldwide. Suzuki has over 45,000 employees and has 35 production facilities in 23 countries, and 133 distributors in 192 countries. The worldwide sales volume of automobiles is the world's tenth largest, while domestic sales volume is the third largest in the country.

Subaru

Subaru

Subaru (スバル) is the automobile manufacturing division of Japanese transportation conglomerate Subaru Corporation, the twenty-first largest automaker by production worldwide in 2017.

Clean Air Act (United States)

Clean Air Act (United States)

The Clean Air Act (CAA) is the United States' primary federal air quality law, intended to reduce and control air pollution nationwide. Initially enacted in 1963 and amended many times since, it is one of the United States' first and most influential modern environmental laws.

Eastern Bloc

Eastern Bloc

The Eastern Bloc, also known as the Communist Bloc, the Socialist Bloc, and the Soviet Bloc, was the group of socialist states of Central and Eastern Europe, East Asia, Southeast Asia, Africa, and Latin America under the influence of the Soviet Union that existed during the Cold War (1947–1991). These states followed the ideology of Marxism–Leninism, in opposition to the capitalist Western Bloc. The Eastern Bloc was often called the Second World, whereas the term "First World" referred to the Western Bloc and "Third World" referred to the non-aligned countries that were mainly in Africa, Asia, and Latin America but notably also included former pre-1948 Soviet ally Yugoslavia, which was located in Europe.

Outboard motor

Outboard motor

An outboard motor is a propulsion system for boats, consisting of a self-contained unit that includes engine, gearbox and propeller or jet drive, designed to be affixed to the outside of the transom. They are the most common motorised method of propelling small watercraft. As well as providing propulsion, outboards provide steering control, as they are designed to pivot over their mountings and thus control the direction of thrust. The skeg also acts as a rudder when the engine is not running. Unlike inboard motors, outboard motors can be easily removed for storage or repairs.

Two-stroke motorbike with an expansion chamber exhaust system that increases the cylinder charge

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-controlled inlet port

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 1970s, 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. However, a mechanical limit exists to the width of a single exhaust port, at about 62% of the bore diameter for reasonable piston ring life. Beyond this, the piston 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. Intake duration is between 120 and 160°. 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.^[8] 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.

Reed inlet valve

A Cox Babe Bee 0.049 in³ (0.80 cm³) reed valve engine, disassembled, uses glow-plug ignition. Its mass is 64 g.

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.

Rotary inlet valve

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.

Cross-flow scavenging

Deflector piston with cross-flow scavenging

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.^[9] The deflector increases the piston's weight and exposed surface area, and the fact that it makes piston cooling and achieving an effective combustion chamber shape more difficult is why this design has been largely superseded by uniflow scavenging after the 1960s, especially for motorcycles, but for smaller or slower engines using direct injection, the deflector piston can still be an acceptable approach.

Loop scavenging

The two-stroke cycle

1. Top dead center (TDC)
2. Bottom dead center (BDC)

  A: Intake/scavenging

  B: Exhaust

  C: Compression

  D: Expansion (power)

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. The fuel/air mixture strikes the cylinder head, then follows the curvature of the combustion chamber, and then is deflected downward.

This not only prevents the fuel/air mixture from traveling directly out the exhaust port, but also creates a swirling turbulence which improves combustion efficiency, power, and economy. Usually, a piston deflector is not required, so this approach has a distinct advantage over the cross-flow scheme (above).

Often referred to as "Schnuerle" (or "Schnürle") loop scavenging after Adolf Schnürle, the German inventor of an early form in the mid-1920s, it became widely adopted in that country during the 1930s and spread further afield after World War II.

Loop scavenging is the most common type of fuel/air mixture transfer used on modern two-stroke engines. 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 1960s 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 750- and 850-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.

The 750-cc standard engine produced 36 to 42 hp, depending on the model year. The Monte Carlo Rally variant, 750-cc (with a filled crankshaft for higher base compression), generated 65 hp. An 850-cc version was available in the 1966 SAAB Sport (a standard trim model in comparison to the deluxe trim of the Monte Carlo). Base compression comprises a portion of the overall compression ratio of a two-stroke engine. Work published at SAE in 2012 points that loop scavenging is under every circumstance more efficient than cross-flow scavenging.

Uniflow scavenging

Uniflow scavenging

The uniflow two-stroke cycle

1. Top dead center (TDC)
2. Bottom dead center (BDC)

  A: Intake (effective scavenging, 135°–225°; necessarily symmetric about BDC; Diesel injection is usually initiated at 4° before TDC)

  B: Exhaust

  C: Compression

  D: Expansion (power)

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. The valved arrangement is common in on-road, off-road, and stationary two-stroke engines (Detroit Diesel), certain small marine two-stroke engines (Gray Marine), certain railroad two-stroke diesel locomotives (Electro-Motive Diesel) and large marine two-stroke main propulsion engines (Wärtsilä). 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 205 and Napier Deltic.^[10] The once-popular split-single design falls into this class, being effectively a folded uniflow. With advanced-angle exhaust timing, uniflow engines can be supercharged with a crankshaft-driven (piston^[11] or Roots) blower.

Stepped piston engine

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.

The upper section of the piston still relies on total-loss lubrication, but the other engine parts are sump lubricated with cleanliness and reliability benefits. The mass of the piston is only about 20% more than a loop-scavenged engine's piston because skirt thicknesses can be less. ^[12]

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Cylinder (engine)

Cylinder (engine)

In a reciprocating engine, the cylinder is the space in which a piston travels.

Piston

Piston

A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. In a pump, the function is reversed and force is transferred from the crankshaft to the piston for the purpose of compressing or ejecting the fluid in the cylinder. In some engines, the piston also acts as a valve by covering and uncovering ports in the cylinder.

Crankcase

Crankcase

In a piston engine, the crankcase is the housing that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block.

Reed valve

Reed valve

Reed valves are a type of check valve which restrict the flow of fluids to a single direction, opening and closing under changing pressure on each face. Modern versions often consist of flexible metal or composite materials.

Cox Models

Cox Models

Cox Models, a former division of Estes Industries of Penrose, Colorado, was a multimillion-dollar hobby company, is one of the hobby industry's oldest companies and is noted for its production of miniature model internal-combustion engines.

Check valve

Check valve

A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid to flow through it in only one direction.

Crankshaft

Crankshaft

A crankshaft is a mechanical component used in a piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating shaft containing one or more crankpins, that are driven by the pistons via the connecting rods.

Rotary valve

Rotary valve

A rotary valve is a type of valve in which the rotation of a passage or passages in a transverse plug regulates the flow of liquid or gas through the attached pipes. The common stopcock is the simplest form of rotary valve. Rotary valves have been applied in numerous applications, including:Changing the pitch of brass instruments. Controlling the steam and exhaust ports of steam engines, most notably in the Corliss steam engine. Periodically reversing the flow of air and fuel across the open hearth furnace. Loading sample on chromatography columns. Certain types of two-stroke and four-stroke engines. Most hydraulic automotive power steering control valves.

Exhaust gas

Exhaust gas

Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline (petrol), diesel fuel, fuel oil, biodiesel blends, or coal. According to the type of engine, it is discharged into the atmosphere through an exhaust pipe, flue gas stack, or propelling nozzle. It often disperses downwind in a pattern called an exhaust plume.

Cylinder head

Cylinder head

In an internal combustion engine, the cylinder head sits above the cylinders and forms the roof of the combustion chamber. In sidevalve engines, the head is a simple sheet of metal; whereas in more modern overhead valve and overhead camshaft engines, the cylinder head is a more complicated block often containing inlet and exhaust passages, coolant passages, valves, camshafts, spark plugs and fuel injectors. Most straight engines have a single cylinder head shared by all of the cylinders and most V engines have two cylinder heads.

Detroit Diesel

Detroit Diesel

Detroit Diesel Corporation (DDC) is an American diesel engine manufacturer headquartered in Detroit, Michigan. It is a subsidiary of Daimler Truck North America, which is itself a wholly owned subsidiary of the multinational Daimler Truck AG. The company manufactures heavy-duty engines and chassis components for the on-highway and vocational commercial truck markets. Detroit Diesel has built more than 5 million engines since 1938, more than 1 million of which are still in operation worldwide. Detroit Diesel's product line includes engines, axles, transmissions, and a Virtual Technician service.

Gray Marine 6-71 Diesel Engine

Gray Marine 6-71 Diesel Engine

The 6-71 Gray Marine Diesel Engine is a marinized version of the General Motors Detroit Diesel 6-71 engine produced by the Gray Marine Motor Company. It was used in landing craft during World War II and is used today in private boats and training facilities.

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.A.V.E, Yamaha YPVS, Honda RC-Valve, Kawasaki K.I.P.S., Cagiva C.T.S., or Suzuki AETC systems, or by altering the volume of the exhaust, which changes the resonant frequency of the expansion chamber, such as the Suzuki SAEC and Honda V-TACS system. 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.

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Two-stroke power valve system

Two-stroke power valve system

The two-stroke power valve system is an improvement to a conventional two-stroke engine that gives a high power output over a wider RPM range.

Rotax

Rotax

Rotax is the brand name for a range of internal combustion engines developed and manufactured by the Austrian company BRP-Rotax GmbH & Co KG, in turn owned by the Canadian Bombardier Recreational Products.

Yamaha Corporation

Yamaha Corporation

Yamaha Corporation is a Japanese multinational corporation and conglomerate with a very wide range of products and services. It is one of the constituents of Nikkei 225 and is the world's largest musical instrument manufacturing company. The former motorcycle division was established in 1955 as Yamaha Motor Co., Ltd., which started as an affiliated company but later became independent, although Yamaha Corporation is still a major shareholder.

Honda

Honda

Honda Motor Co., Ltd. is a Japanese public multinational conglomerate manufacturer of automobiles, motorcycles, and power equipment, headquartered in Minato, Tokyo, Japan.

Kawasaki Heavy Industries Motorcycle & Engine

Kawasaki Heavy Industries Motorcycle & Engine

Kawasaki Heavy Industries Motorcycle & Engine Company (川崎重工業モーターサイクル&エンジンカンパニー) is a division of Kawasaki Heavy Industries that produces motorcycles, ATVs, utility vehicles, jet ski personal watercraft, and general-purpose petrol engines. Before the 2011 fiscal year it was called Consumer Products & Machinery. Its slogan is "Let the good times roll!"

Cagiva

Cagiva

Cagiva is an Italian motorcycle manufacturer. It was founded in 1950 by Giovanni Castiglioni in Varese, originally producing small metal components. Giovanni's sons, Claudio and Gianfranco Castiglioni, went into the motorcycle industry in 1978. The name is a portmanteau derived from the founder's name 'Giovanni Castiglioni' and the founding location, i.e. CAstiglioni GIovanni VArese.

Suzuki

Suzuki

Suzuki Motor Corporation is a Japanese multinational corporation headquartered in Minami-ku, Hamamatsu, Japan. Suzuki manufactures automobiles, motorcycles, all-terrain vehicles (ATVs), outboard marine engines, wheelchairs and a variety of other small internal combustion engines. In 2016, Suzuki was the eleventh biggest automaker by production worldwide. Suzuki has over 45,000 employees and has 35 production facilities in 23 countries, and 133 distributors in 192 countries. The worldwide sales volume of automobiles is the world's tenth largest, while domestic sales volume is the third largest in the country.

Expansion chamber

Expansion chamber

On a two-stroke engine, an expansion chamber or tuned pipe is a tuned exhaust system used to enhance its power output by improving its volumetric efficiency.

Direct injection has considerable advantages in two-stroke engines. In carburetted two-strokes, a major problem is a portion of the fuel/air mixture going directly out, unburned, through the exhaust port, and direct injection effectively eliminates this problem. Two systems are in use, low-pressure air-assisted injection and high-pressure injection.

Since the fuel does not pass through the crankcase, a separate source of lubrication is needed.

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Brons two-stroke V8 diesel engine driving an N.V. Heemaf generator

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.

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Two-stroke diesel engine

Two-stroke diesel engine

A two-stroke diesel engine is a diesel engine that uses compression ignition in a two-stroke combustion cycle. It was invented by Hugo Güldner in 1899.

Brons

Brons

Brons, named after Jan Brons, was a Dutch engine manufacturer in Appingedam that existed from 1907 to 2004. The company made more than 4000 engines for large machines such as ships, tractors, and busses. The company is notable for its early stationary industrial motors and ship engines, but also for an early 1899 prototype light omnibus called "The Brons".

Schnuerle porting

Schnuerle porting

Schnuerle porting is a system to improve efficiency of a valveless two-stroke engine by giving better scavenging. The intake and exhaust ports cut in the cylinder wall are shaped to give a more efficient transfer of intake and exhaust gases.

Poppet valve

Poppet valve

A poppet valve is a valve typically used to control the timing and quantity of gas or vapor flow into an engine.

Forced induction

Forced induction

In an internal combustion engine, forced induction is where turbocharging or supercharging is used to increase the density of the intake air. Engines without forced induction are classified as naturally aspirated.

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Many two-stroke engines use their crankcase to pressurize the air-fuel mixture before transfer to the cylinder. Unlike four-stroke engines, they cannot be lubricated by oil contained in the crankcase and sump: lubricating oil would be swept up and burnt with the fuel. Fuels supplied to two-stroke engines are mixed with oil so that it can coat the cylinders and bearing surfaces along its path. The ratio of gasoline to oil ranges from 25:1 to 50:1 by volume.

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 1970s, 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.^[13] Ultimately, oil injection is still the same as premixed gasoline in that the oil is burnt in the combustion chamber (albeit not as completely as premix) and the gas is still mixed with the oil, although not as thoroughly as in premix. This method requires extra mechanical parts to pump the oil from the separate tank, to the carburetor or throttle body. In applications where performance, simplicity, and/or dry weight are significant considerations, the premix lubrication method is almost always used. For example, a two-stroke engine in a motocross bike pays major consideration to performance, simplicity, and weight. Chainsaws and brush cutters must be as lightweight as possible to reduce user fatigue and hazard.

Crankcase compression two-stroke engines suffer oil starvation if rotated at speed with the throttle closed. Motorcycles descending long hills and perhaps when decelerating gradually from high speed by changing down through the gears are examples. Two-stroke cars (such as those that were popular in Eastern Europe in the mid-20th century) were usually fitted with freewheel mechanisms in the powertrain, allowing the engine to idle when the throttle was closed and requiring using brakes to slow down.

Large two-stroke engines, including diesels, normally use a sump lubrication system similar to four-stroke engines. The cylinder must be pressurized, but this is not done from the crankcase, but by an ancillary Roots-type blower or a specialized turbocharger (usually a turbo-compressor system) which has a "locked" compressor for starting (and during which it is powered by the engine's crankshaft), but which is "unlocked" for running (and during which it is powered by the engine's exhaust gases flowing through the turbine).

Discover more about Lubrication related topics

Crankcase

Crankcase

In a piston engine, the crankcase is the housing that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block.

Automatic lubrication

Automatic lubrication

Automatic lubrication refers to a lubrication system on a two-stroke engine, in which the oil is automatically mixed with fuel and manual oil-fuel pre-mixing is not necessary. The oil is contained in a reservoir that connects to a small oil pump in the engine, which needs to be periodically refilled.

Freewheel

Freewheel

In mechanical or automotive engineering, a freewheel or overrunning clutch is a device in a transmission that disengages the driveshaft from the driven shaft when the driven shaft rotates faster than the driveshaft. An overdrive is sometimes mistakenly called a freewheel, but is otherwise unrelated.

API-TC

API-TC

API TC is a certification for two-stroke oils, awarded by the American Petroleum Institute. It is given after the product passes through stringent tests that determine the level of detergent performance, dispersion, and anti-oxidation. It is the only remaining, not revoked classification of the API Two-Cycle motor oil specifications. Being a very old standard itself, most currently produced 2T lubricants meet its specifications, even the lowest quality ones; current high-quality oils exceed them.

For the purpose of this discussion, it is convenient to think in motorcycle terms, where the exhaust pipe faces into the cooling air stream, and the crankshaft commonly spins in the same axis and direction as do the wheels i.e. "forward". Some of the considerations discussed here apply to four-stroke engines (which cannot reverse their direction of rotation without considerable modification), almost all of which spin forward, too. It is also useful to note that the "front" and "back" faces of the piston are - respectively - the exhaust port and intake port sides of it, and are not to do with the top or bottom of the piston.

Regular gasoline two-stroke engines can run backward for short periods and under light load with little problem, and this has been used to provide a reversing facility in microcars, such as the Messerschmitt KR200, that lacked reverse gearing. Where the vehicle has electric starting, the motor is turned off and restarted backward by turning the key in the opposite direction. Two-stroke golf carts have used a similar system. Traditional flywheel magnetos (using contact-breaker points, but no external coil) worked equally well in reverse because the cam controlling the points is symmetrical, breaking contact before top dead center equally well whether running forward or backward. Reed-valve engines run backward just as well as piston-controlled porting, though rotary valve engines have asymmetrical inlet timing and do not run very well.

Serious disadvantages exist for running many engines backward under load for any length of time, and some of these reasons are general, applying equally to both two-stroke and four-stroke engines. This disadvantage is accepted in most cases where cost, weight, and size are major considerations. The problem comes about because in "forward" running, the major thrust face of the piston is on the back face of the cylinder, which in a two-stroke particularly, is the coolest and best-lubricated part. The forward face of the piston in a trunk engine is less well-suited to be the major thrust face, since it covers and uncovers the exhaust port in the cylinder, the hottest part of the engine, where piston lubrication is at its most marginal. The front face of the piston is also more vulnerable since the exhaust port, the largest in the engine, is in the front wall of the cylinder. Piston skirts and rings risk being extruded into this port, so having them pressing hardest on the opposite wall (where there are only the transfer ports in a crossflow engine) is always best and support is good. In some engines, the small end is offset to reduce thrust in the intended rotational direction and the forward face of the piston has been made thinner and lighter to compensate, but when running backward, this weaker forward face suffers increased mechanical stress it was not designed to resist.^[14] This can be avoided by the use of crossheads and also using thrust bearings to isolate the engine from end loads.

Large two-stroke ship diesels are sometimes made to be reversible. Like four-stroke ship engines (some of which are also reversible), they use mechanically operated valves, so require additional camshaft mechanisms. These engines use crossheads to eliminate sidethrust on the piston and isolate the under-piston space from the crankcase.

On top of other considerations, the oil pump of a modern two-stroke may not work in reverse, in which case the engine suffers oil starvation within a short time. Running a motorcycle engine backward is relatively easy to initiate, and in rare cases, can be triggered by a back-fire. It is not advisable.

Model airplane engines with reed valves can be mounted in either tractor or pusher configuration without needing to change the propeller. These motors are compression ignition, so no ignition timing issues and little difference between running forward and running backward are seen.

Discover more about Two-stroke reversibility related topics

Microcar

Microcar

Microcar is a term often used for the smallest size of cars, with three or four wheels and often an engine smaller than 700 cc (43 cu in). Specific types of microcars include bubble cars, cycle cars, invacar, quadricycles and voiturettes. Microcars are often covered by separate regulations to normal cars, having relaxed requirements for registration and licensing.

Messerschmitt KR200

Messerschmitt KR200

The Messerschmitt KR200, or Kabinenroller, is a three-wheeled bubble car designed by the aircraft engineer Fritz Fend and produced in the factory of the German aircraft manufacturer Messerschmitt from 1955 until 1964.

Golf cart

Golf cart

A golf cart is a small motorized vehicle designed originally to carry two golfers and their golf clubs around a golf course with less effort than walking. Over time, variants were introduced that were capable of carrying more passengers, had additional utility features, or were certified as a street legal low-speed vehicle.

Ignition magneto

Ignition magneto

An ignition magneto is an older type of ignition system used in spark-ignition engines. It uses a magneto and a transformer to make pulses of high voltage for the spark plugs. The older term "high-tension" means "high-voltage".

Dead centre (engineering)

Dead centre (engineering)

In a reciprocating engine, the dead centre is the position of a piston in which it is either farthest from, or nearest to, the crankshaft. The former is known as Top Dead Centre (TDC) while the latter is known as Bottom Dead Centre (BDC).

Crosshead

Crosshead

In mechanical engineering, a crosshead is a mechanical joint used as part of the slider-crank linkages of long reciprocating engines and reciprocating compressors to eliminate sideways force on the piston. Also, the crosshead enables the connecting rod to freely move outside the cylinder. Because of the very small bore-to-stroke ratio on such engines, the connecting rod would hit the cylinder walls and block the engine from rotating if the piston was attached directly to the connecting rod like on trunk engines. Therefore, the longitudinal dimension of the crosshead must be matched to the stroke of the engine.

Thrust bearing

Thrust bearing

A thrust bearing is a particular type of rotary bearing. Like other bearings they permanently rotate between parts, but they are designed to support a predominantly axial load.