The Wankel Rotary Engine
Dr. Felin Wankel was
born on August 13, 1902 in Swabia, Germany. He was interested in the idea of
rotary engine. He did not invent the first rotary engine but invent the basic
design of rotary engine that led to the eventual development of the first successful
rotary engine. The first rotary engine was tested at NSU, Germany in 1957.
The engine has a three
lobe rotor which is driven eccentrically in a casing in such a way that there
are three separate volume trapped between the rotor and the casing. The three
volumes perform induction, compression, combustion, expansion and exhaust
process in sequence and this design therefore has a good power/volume ratio. Sealing,
seal wear and heat transfer were of the same initial development problems of
the Wrankel engine. These problems have now largely been solved.
The Working of Wankel Rotary Engine
Breathing is through ports
so that valves and valve operating mechanism is not needed. As the rotor apexes
pass around the walls, the volume enclosed between the bore and the rotor flank
varies in a sinusoidal manner and executes the four phases. This entrapped
volume expands when the apex passes over the intake port, thereby, drawing in
the fuel-air mixture. As the rotor turns further, this rotor is isolated from
the intake port and compressed. Then it passes over a recessed spark plug and
enlarges again during the expansion phase, thereby, absorbing the power
produced by the combustion. Finally when the apex passes the exhaust port in
the opposite end of combustion chamber, exhaust phase is executed and one thermodynamic
cycle is completed. At the same other
chambers follow exactly the same sequence, though with some phase difference.
Features of the rotary engine (Rotary Engine vs. Piston Engine)
As compared with the
reciprocating engine, the rotary engine has the following basic features:
1.
There are
no reciprocating parts. Thus the problems of unbalance caused by the inertia of
the reciprocating parts and complicated engine vibration is eliminated. In rotary
engines vibration is very low because it is possible to perfectly balance the
engine by using the balancing weights.
Also,
since the rotary engine does not require a cranking mechanism, it has the
advantages of the smooth motion, less mechanical loss, simple construction and
compactness.
2.
There is
no separate intake-exhaust valve mechanism. In a reciprocating engine
intake-exhaust valve mechanism generates mechanical noise by opening and
closing of the valves, and valves themselves obstruct air flow. Further, due to
inertia of the valve mechanism, the valves are unable to fully follow the
motion of the cam at high revolutions. This results in variations in effective
valve timings of the engine.
In a
rotary engine, the rotor directly opens and closes the intake and exhaust
ports, eliminating the valve mechanism; hence, correct timing for opening and
closing can be maintained even at high speeds.
3.
The time
for one stroke is 270 degrees in terms of the rotating angle of the output
shaft, and there is one explosion for one rotation of the output shaft.
The long intake stroke means that the volumetric
efficiency becomes higher even at the high speed range, and reduces the torque
drop. Also, the long expansion stroke is advantageous from the point of torque
fluctuations. In a rotary engine that has two rotors, the expansion stroke
overlaps so the torque fluctuation is as low as in the case of a six-cylinder
reciprocating engine. 
