Wankel(Rotary) Engine Seminar Report
Ø Abstract:
Introduction
A rotary engine is an internal combustion engine, like the engine in your car, but it works in a completely different way than the conventional piston engine.
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, or Wankel rotary engine.
Ø WORKING
In the Wankel engine, the four strokes of a typical Otto cycle engine are arranged sequentially around an oval, unlike the reciprocating motion of a piston engine. In the basic single rotor Wankel engine, a single oval (technically a trochoid) housing surrounds a three-sided rotor (a Reuleaux triangle) which turns and moves within the housing. The sides of the rotor seal against the sides of the housing, and the corners of the rotor seal against the inner periphery of the housing, dividing it into three combustion chambers.
The Wankel cycle: Intake (blue), Compression (green), Ignition (red), Exhaust (yellow)
As the rotor turns, its motion and shape and the shape of the housing cause each side of the rotor to get closer and farther from the wall of the housing, compressing and
expanding the combustion chamber similarly to the "strokes" in a reciprocating engine. However, whereas a normal four stroke cycle engine produces one combustion stroke per cylinder for every two revolutions, i.e. one half power stroke per revolution per cylinder, each combustion chamber of each rotor in the Wankel generates one combustion 'stroke' per revolution, i.e. three power strokes per rotor revolution. Since the Wankel output shaft is geared to spin at three times the rotor speed, this becomes one combustion 'stroke' per output shaft revolution per rotor, twice as many as the four-stroke piston engine, and similar to the output of a two stroke cycle engine. Thus, power output of a Wankel engine is generally higher than that of a four-stroke engine of similar engine displacement in a similar state of tune, and higher than an engine of similar physical dimensions. In international sports car racing the FIA considers a Wankel engine to be equivalent to a four-stroke engine of twice the displacement; other racing series seem to have settled on 1.8 times the displacement. The Wankel engine is quite different from a more recent concept called the Quasiturbine.
Advantages:
v 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.
v The rotor is geared directly to the output shaft, there is no need for connecting rods, a conventional crankshaft, crankshaft balance weights, etc
v Smoother flow of power but also the ability to produce more power by running at higher rpm.
v Fuel of very low octane number can be used without pre ignition or knock.
v It’s substantial safety benefit makes it useful in aircraft
v There is no valve operation.
v 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.
v 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:
v The fuel-air mixture cannot be pre-stored as there is no intake valve.
v Time available for fuel to be injected into a Wankel engine is significantly shorter.
v More complicated fuel injection technologies are required.
v In terms of fuel economy, Wankel engines are generally less efficient than four stroke piston engines
v Sealing loss is high.
v The compression ratio is lower. This lowers the thermal efficiency and thus the fuel economy.
v It is difficult to expand the engine to more than two rotors.
v There can be more carbon monoxide and unburned hydrocarbons in a Wankel's exhaust stream.
v 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:
Ø Used in aircraft. Racing car.
Ø For mini, micro, and micro-mini engine designs.
Ø The most exotic use of the Wankel design is in the seat belt pre-tensioner system of some Mercedes-Benz.
Ø Go-karts, personal water craft and auxiliary power units for aircraft .
3