Exercise 29. Make up your own story about the engines according to the fol-

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THE WANKEL ENGINE
The most successful rotary engine is the Wankel engine. German engi-
neer Felix Wankel first conceived his rotary engine in 1924 and finally received 
a patent for it in 1929. He worked through the 1940s to improve the design. 
Considerable effort went into designing rotary engines in the 1950s and 1960s. 
They were of particular interest because they were running smoothly and qui-
etly, and because of the reliability resulting from their simplicity. The Com-
pany NSU, where Wankel worked at that time, then licensed the concept to 
companies around the world, which continued to improve the design. Among 
the manufacturers signing licensing agreements to develop Wankel engines 
were the automobile companies of Europe, America, Japan, Russia, and other 
countries.
The Wankel engine is a type of an internal combustion engine in which the 
four strokes of a typical Otto cycle occur in the space between a three-sided 
symmetric rotor and the inside of a housing. 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. In the basic single-rotor Wankel en-
gine, the oval-like epitrochoid-shaped housing surrounds a rotor which is tri-
angular with bow-shaped flanks. It has a disk that looks like a triangle with 
bulging sides rotating inside a cylinder shaped like a figure eight with a thick 
waist. Intake and exhaust are through ports in the flat sides of the cylinder. The 
spaces between the sides of the disk and the walls of the cylinder form com-
bustion pockets. During a single rotation of the disk, each pocket alternately 
grows smaller, then larger because of the contoured outline of the cylinder. 
This provides compression and expansion. The engine runs on a four-stroke 
cycle. The expansion phase of the Wankel cycle is much longer than that of 
the Otto cycle. 
The Wankel engines have some advantages. They are considered to be 
simpler and contain far fewer moving parts. For instance, they have no valves 
or complex valve trains. Moreover, since the rotor is geared directly to the 
output shaft, there is no need for connecting rods, a conventional crankshaft, 
crankshaft balance weights, etc. The elimination of these parts makes a Wankel 
engine not only much lighter, but it also completely eliminates the reciprocat-
ing mass of a piston engine with its internal strain and inherent vibration due 
to repeated acceleration and deceleration, producing not only a smoother flow 
of power but also the ability to produce more power by running at higher rpm. 
Though the Wankel engine has about 50% fewer parts and about a third the 
bulk and weight of a reciprocating engine, its main advantage is that advanced 
pollution control devices are easier to design for it than for the conventional 
piston engine. Besides, higher engine speeds are made possible by rotating in-

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stead of reciprocating motion, but this advantage is partially offset by the lack 
of torque at low speeds, leading to greater fuel consumption. Moreover, the 
shape of the Wankel combustion chamber and the turbulence induced by the 
moving rotor prevent localized hot spots from forming, thereby allowing the 
use of fuel of very low octane number without preignition or detonation, a par-
ticular advantage for hydrogen cars. 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.
The Wankel engine has also some disadvantages. The design of the Wan-
kel engine requires numerous sliding seals and a housing that is typically built 
as a sandwich of cast iron and aluminum pieces that expand and contract by 
different degrees when exposed to heating and cooling cycles in use. These 
elements led to a very high incidence of loss of sealing, both between the rotor 
and the housing and also between the various pieces making up the housing. 
Besides, 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. One more disadvantage of 
the Wankel engine is the difficulty of expanding the engine to more than two 
rotors. The complex shapes of the rotor, housing, and output shaft and the way 
they fit together requires that engines with more than two rotors use an output 
shaft made of several sections assembled during the assembly of the rest of the 
engine. While this technique has been used successfully in Wankel powered 
racing cars, it negates a great deal of the relative simplicity and lower cost of 
the Wankel engine construction.
Because of their compact, lightweight design, Wankel rotary engines have 
been installed in a variety of vehicles and devices such as automobiles and rac-
ing cars, aircraft, go-karts, personal water craft, and auxiliary power units. The 
simplicity of the Wankel makes it ideal for macro, mini, micro, and micro-
mini engine designs.

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