Seminar Report On Rotary Engine y6v36

InTRODUCTION The Rotary engine is a type of internal combustion engine which uses a rotor to convert pressure into a rotating motion instead of using reciprocating pistons. Its four-stroke cycle is generally generated in a space between the inside of an oval-like epitrochoid-shaped housing and a roughly triangular rotor (hypotrochoid). This design delivers smooth high-rpm power from a compact, lightweight engine. The engine was invented by German engineer Felix Wankel. He began its development in the early 1950s at NSU Motorenwerke AG (NSU) before completing a working, running prototype in 1957. NSU then subsequently licensed the concept to other companies across the globe, who added more efforts and improvements in the 1950s and 1960s. Because of its compact, lightweight design, Wankel rotary engines have been installed in a variety of vehicles and devices such as automobiles and racing cars, aircraft, go-karts, personal water crafts and auxiliary power units. In a piston engine, the same volume of space (the cylinder) alternately does four different jobs -- intake, compression, combustion and exhaust. A rotary engine does these same four jobs, but each one happens in its own part of the housing. It's kind of like having a dedicated cylinder for each of the four jobs, with the piston moving continually from one to the next. The rotary engine (originally conceived and developed by Dr. Felix Wankel) is sometimes called a Wankel engine.

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History: In 1951, Wankel began development of the engine at NSU (NSU Motorenwerke AG), where he first conceived his rotary engine in 1954 (DKM 54, Drehkolbenmotor) and later the KKM 57 (the Wankel rotary engine, Kreiskolbenmotor) in 1957. The first working prototype DKM 54 was running on February 1, 1957 at the NSU research and development department Versuchsabteilung TX. Considerable effort went into deg rotary engines in the 1950s and 1960s. They were of particular interest because they were smooth and quiet running, and because of the reliability resulting from their simplicity. In the United States, in 1959 under license from NSU, Curtiss-Wright pioneered minor improvements in the basic engine design. In Britain, in the 1960s, Rolls Royce Motor Car Division at Crewe, Cheshire, pioneered a twostage diesel version of the Wankel engine Also in Britain Norton Motorcycles developed a Wankel rotary engine for motorcycles, which was included in their Commander and F1; Suzuki also made a production motorcycle with a Wankel engine, the RE-5. In 1971 and 1972 Arctic Cat produced snowmobiles powered by 303 cc Wankel rotary engines manufactured by Sachs in . John Deere Inc, in the U.S., designed a version that was capable of using a variety of fuels. The design was proposed as the power source for several U.S. Marine combat vehicles in the late 1980s. After occasional use in automobiles, for instance by NSU with their Ro 80 model, Citroën with the M35, and GS Birotor using engines produced by Co motor, as well as abortive attempts by General Motors and Mercedes-Benz to design Wankel-engine automobiles, the most extensive automotive use of the Wankel engine has been by the Japanese company Mazda. After years of development, Mazda's first Wankel engined car was the 1967 Mazda Cosmo. The company normally used two-rotor designs, but received considerable attention with their 1991 Eunos Cosmo, which used a twinturbo three-rotor engine. In 2003, Mazda introduced the RENESIS engine with the new RX-8. The RENESIS engine relocated the ports for exhaust and intake from the periphery of the rotary housing to the sides, allowing for larger overall ports, better airflow, and further power gains. The RENESIS is capable of delivering 238 horsepower (177 kW) from its 1.3 L displacement with better fuel economy, reliability, and environmental friendliness than any other Mazda rotary engine in history.

Naming: Since its introduction in the NSU Motorenwerke AG (NSU) and Mazda cars of the 1960s, the engine has been commonly referred to as the rotary engine, a name which has also been applied to several completely different engine designs.

The Parts of a Rotary Engine: A rotary engine has an ignition system and a fuel-delivery system that are similar to the ones on piston engines. If you've never seen the inside of a rotary engine, be prepared for a surprise, because you won't recognize much. 1.

Rotor:

The rotor has three convex faces, each of which acts like a piston. Each face of the rotor has a pocket in it, which increases the displacement of the engine, allowing more space for air/fuel mixture. At the apex of each face is a metal blade that forms a seal to the outside of the combustion chamber. There are also metal rings on each side of the rotor that seal to the sides of the combustion chamber.

[Rotor]

The rotor has a set of internal gear teeth cut into the center of one side. These teeth mate with a gear that is fixed to the housing. This gear mating determines the path and direction the rotor takes through the housing. 2.

Housing: The housing is roughly oval in shape (it's actually an epitrochoid).The shape of the combustion chamber is designed so that the three tips of the rotor will always stay in with the wall of the chamber, forming three sealed volumes of gas. Each part of the housing is dedicated to one part of the combustion process.

The four sections are: • • • •

Intake Compression Combustion Exhaust

The intake and exhaust ports are located in the housing. There are no valves in these ports. The exhaust port connects directly to the exhaust, and the intake port connects directly to the throttle. 3.

[Housing]

Shaft: The output shaft has round lobes mounted eccentrically, meaning that they are offset from the centerline of the shaft. Each rotor fits over one of these lobes. The lobe acts sort of like the crankshaft in a piston engine. As the rotor follows its path around the housing, it pushes on the lobes. Since the lobes are mounted eccentric to the output shaft, the force that the rotor applies to the lobes creates torque in the shaft, causing it to spin.

[Output Shaft; Note the eccentric lobes.] Now let's take a look at how these parts are assembled and how it produces power.

Principles of a Rotary Engine: Like a piston engine, the rotary engine uses the pressure created when a combination of air and fuel is burned. In a piston engine, that pressure is contained in the cylinders and forces pistons to move back and forth. The connecting rods and crankshaft convert the reciprocating motion of the pistons into rotational motion that can be used to power a car. The rotor follows a path that looks like something you'd create with a Spiro graph. This path keeps each of the three peaks of the rotor in with the housing, creating three separate volumes of gas. As the rotor moves around the chamber, each of the three volumes of gas alternately expands and contracts. It is this expansion and contraction that draws air and fuel into the engine,

compresses it and makes useful power as the gases expand, and then expels the exhaust.

How it works: The "A" marks one of the three apexes of the rotor. The "B" marks the eccentric shaft and the white portion is the lobe of the eccentric shaft. The shaft turns three times for each rotation of the rotor around the lobe and once for each orbital revolution around the eccentric shaft. In the Wankel engine, the four strokes of a typical Otto cycle occur in the space between a rotor, which is roughly triangular, and the inside of housing. In the basic single-rotor Wankel engine, the oval-like epitrochoid-shaped housing surrounds a three-sided rotor (similar to a Reuleaux triangle, a three-pointed curve of constant width, but with the middle of each side a bit more flattened). The central drive shaft, also called an eccentric shaft or E-shaft, es through the center of the rotor and is ed by bearings. The rotor both rotates around an offset lobe (crank) on the E-shaft and makes orbital revolutions around the central shaft. Seals at the corners of the rotor seal against the periphery of the housing, dividing it into three moving combustion chambers. Fixed gears mounted on each side of the housing engage with ring gears attached to the rotor to ensure the proper orientation as the rotor moves. The best way to visualize the action of the engine in the animation at left is to look not at the rotor itself, but the cavity created between it and the housing. The Wankel engine is actually a variable-volume progressing-cavity system. Thus there are 3 cavities per housing, all repeating the same cycle. As the rotor rotates and orbitally revolves, each side of the rotor gets closer and farther from the wall of the housing, compressing and expanding the combustion chamber similarly to the strokes of a piston in a reciprocating engine. The power vector of the combustion stage goes through the center of the offset lobe. While a four-stroke piston engine makes one combustion stroke per cylinder for every two rotations of the crankshaft (that is, one half power stroke per crankshaft rotation per cylinder), each combustion chamber in the Wankel generates one combustion stroke per each driveshaft rotation, i.e. one power stroke per rotor orbital revolution and three power strokes per rotor rotation. Thus, power output of a Wankel engine is generally higher than that of a four-stroke piston engine of similar engine displacement in a similar state of tune and higher than that of a four-stroke piston engine of similar physical dimensions and weight. Wankel engines also generally have a much higher redline than a reciprocating engine of similar size since the strokes are completed with a rotary motion as opposed to a reciprocating engine which must use connecting rods and a crankshaft to convert reciprocating motion into rotary motion.National agencies that tax automobiles according to displacement and

regulatory bodies in automobile racing variously consider the Wankel engine to be equivalent to a four-stroke engine of 1.5 to 2 times the displacement; some racing regulatory agencies ban it altogether.

Rotary Engine Power: Rotary engines use the four-stroke combustion cycle, which is the same cycle that four-stroke piston engines use. But in a rotary engine, this is accomplished in a completely different way. The heart of a rotary engine is the rotor. This is roughly the equivalent of the pistons in a piston engine. The rotor is mounted on a large circular lobe on the output shaft. This lobe is offset from the centerline of the shaft and acts like the crank handle on a winch, giving the rotor the leverage it needs to turn the output shaft. As the rotor orbits inside the housing, it pushes the lobe around in tight circles, turning three times for every one revolution of the rotor. As the rotor moves through the housing, the three chambers created by the rotor change size. This size change produces a pumping action. Let's go through each of the four strokes of the engine looking at one face of the rotor.

Intake: The intake phase of the cycle starts when the tip of the rotor es the intake port. At the moment when the intake port is exposed to the chamber, the volume of that chamber is close to its minimum. As the rotor moves past the intake port, the volume of the chamber expands, drawing air/fuel mixture into the chamber. When the peak of the rotor es the intake port, that chamber is sealed off and compression begins.

Compression: As the rotor continues motion around the housing, the volume of the chamber gets smaller and the air/fuel mixture gets compressed. By the time the face of the rotor has made it around to the spark plugs, the volume of the chamber is again close to its minimum. This is when combustion starts.

Combustion: Most rotary engines have two spark plugs. The combustion chamber is long, so the flame would spread too slowly if there were only one plug. When the spark plugs ignite the air/fuel mixture, pressure quickly builds, forcing the rotor to move. The pressure of combustion forces the rotor to move in the direction that makes the chamber grow in volume. The

combustion gases continue to expand, moving the rotor and creating power, until the peak of the rotor es the exhaust port.

Exhaust: Once the peak of the rotor es the exhaust port, the high-pressure combustion gases are free to flow out the exhaust. As the rotor continues to move, the chamber starts to contract, forcing the remaining exhaust out of the port. By the time the volume of the chamber is nearing its minimum, the peak of the rotor es the intake port and the whole cycle starts again. The neat thing about the rotary engine is that each of the three faces of the rotor is always working on one part of the cycle -- in one complete revolution of the rotor; there will be three combustion strokes. But , the output shaft spins three times for every complete revolution of the rotor, which means that there is one combustion stroke for each revolution of the output shaft. 

[The Wankel cycle: Intake (blue), Compression (green), Ignition (red), Exhaust (yellow)]

Differences and Challenges: There are several defining characteristics that differentiate a rotary engine from a typical piston engine.

Fewer_moving_parts: The rotary engine has far fewer moving parts than a comparable four stroke piston engine. A two-rotor rotary engine has three main moving parts: the two rotors and the output shaft. Even the simplest four-cylinder piston engine has at least 40 moving parts, including pistons, connecting rods, camshaft, valves, valve springs, rockers, timing belt, timing gears and crankshaft. This minimization of moving parts can translate into better reliability from a rotary engine. This is why some aircraft manufacturers (including the maker of Sky car) prefer rotary engines to piston engines. 

Smoother: All the parts in a rotary engine spin continuously in one direction, rather than violently changing directions like the pistons in a conventional engine do. Rotary engines are internally balanced with spinning counterweights that are phased to cancel out any vibrations. The power delivery in a rotary engine is also smoother. Because each combustion event lasts through 90 degrees of the rotor's rotation, and the output shaft spins three revolutions for each revolution of the rotor, each combustion event lasts through 270 degrees of the output shaft's rotation. This means that a single-rotor engine delivers power for three-quarters of each revolution of the output shaft. Compare this to a single-cylinder piston engine, in which combustion occurs during 180 degrees out of every two revolutions, or only a quarter of each revolution of the crankshaft (the output shaft of a piston engine). 

Slower: Since the rotors spin at one-third the speed of the output shaft, the main moving parts of the engine move slower than the parts in a piston engine. This also helps with reliability. 

Materials used: Wankel engine is constructed with an iron rotor within a housing made of aluminum, which has greater thermal expansion. Unlike a piston engine, where the cylinder is cooled by the incoming charge after being heated by combustion, Wankel rotor housings are constantly heated on one side and cooled on the other, leading to high local temperatures and unequal thermal expansion. While this places high demands on the materials used, the simplicity of the Wankel makes it easier to use alternative materials like exotic alloys and ceramics. With water cooling in a radial or axial flow direction, with the hot water from the hot bow heating the cold bow, the thermal expansion remains tolerable.

Sealing: Early engine designs had a high incidence of sealing loss, both between the rotor and the housing and also between the various pieces making up the

housing. Also, in earlier model Wankel engines carbon particles could become trapped between the seal and the casing, jamming the engine and requiring a partial rebuild. Modern Wankel engines have not had these problems for many years. Further sealing problems arise from the uneven thermal distribution within the housings causing distortion and loss of sealing and compression. This thermal distortion also causes uneven wear between the apex seal and the rotor housing, quite evident on higher mileage engines. Attempts have been made to normalize the temperature of the housings, minimizing the distortion, with different coolant circulation patterns and housing wall thicknesses.

Fuel consumption and hydrocarbon emissions: Just as the shape of the Wankel combustion chamber prevents preignition; it also leads to incomplete combustion of the air-fuel charge, with the remaining unburned hydrocarbons released into the exhaust. While manufacturers of piston-engine cars were turning to expensive catalytic converters to completely oxidize the unburned hydrocarbons, Mazda was able to avoid this cost by enriching the air/fuel mixture and increasing the amount of unburned hydrocarbons in the exhaust to actually complete combustion in a 'thermal reactor' (an enlarged open chamber in the exhaust manifold) without the need for a catalytic converter, thereby producing a clean exhaust at the cost of some extra fuel consumption. The exhaust ports, which in earlier Mazda rotaries were located in the rotor housings, were moved to the sides of the combustion chamber. This approach allowed Mazda to eliminate overlap between intake and exhaust port openings, while simultaneously increasing exhaust port area.

Advantages:  Wankel engines have several major advantages over reciprocating piston designs, in addition to having higher output for similar displacement and physical size. It is simple and has fewer moving parts.  The rotor is geared directly to the output shaft, there is no need for connecting rods, a conventional crankshaft, crankshaft balance weights, etc  Smoother flow of power but also the ability to produce more power by running at higher rpm.  Fuel of very low octane number can be used without pre ignition or knock.  It’s substantial safety benefit makes it useful in aircraft  There is no valve operation.  The engine is constructed with an iron rotor within a housing made of aluminum, which has greater thermal expansion. This ensures that even a severely overheated Wankel engine cannot seize.

 It has smaller frontal area than a piston engine of equivalent power. The simplicity of design and smaller size of the Wankel engine also allows for savings in construction costs, compared to piston engines of comparable power output.

Disadvantages: The fuel-air mixture cannot be pre-stored as there is no intake valve. Time available for fuel to be injected into a Wankel engine is significantly shorter. More complicated fuel injection technologies are required. In of fuel economy, Wankel engines are generally less efficient than four stroke piston engines Sealing loss is high. The compression ratio is lower. This lowers the thermal efficiency and thus the fuel economy. It is difficult to expand the engine to more than two rotors. There can be more carbon monoxide and unburned hydrocarbons in a Wankel's exhaust stream. Wankel engines are very sensitive to misfires since the engine will lose momentum from the lost stroke and get slammed back into movement from the next chamber firing. Care of the ignition system is of utmost importance to avoid the problem.

Applications: Used in aircraft. Racing car. For mini, micro, and micro-mini engine designs. The most exotic use of the Wankel design is in the seat belt pre-tensioner system of some Mercedes-Benz.  Go-karts, personal water craft and auxiliary power units for aircraft.    

CONTENTS:  INTRODUCTION  HISTORY  THE PARTS OF A ROTARY ENGINE  WORKING PRINCIPLE  DIFFERENCES AND CHALLENGES  MATERIALS USED  SEALING  FUEL CONSUMPTION & EMISSION  ADVANTAGES  DISADVANTAGES  APPLICATIONS  REFERENCES

REFERENCES: www.wikipedia.com www.praxair.com www.linde group.com www.vorras.com msn Encarta  www.google.com