The Wankel Rotary Engine


    Please refer to my post about the 4-stroke piston engine first here if you don’t know much about engines.

     The rotary engine is a type of internal combustion engine, also featuring 4 different strokes, but instead of using pistons they use rotors.  It was first created by a Mr. Felix Wankel in the 50s.  Thus we name it the “Wankel engine”, or the “Wankel rotary engine” due to a different kind of engine also dubbed the “rotary engine”.

     Since we’re still dealing with internal combustion, the idea is basically the same.  Compress fuel mixed in with air, then ignite it to create a small explosion to power our car.  A piston engine does it with a reciprocating piston which in turn turns the crankshaft.  For every 4 strokes of the piston, we get one cycle.  But for a rotary, we’re dealing with something different.  Take a look here:


     Definately different huh?  How does it work?  Well, the three end points of the rotor are always touching the oval (epitrochoid) rotor housing.  With that in mind, the rotor is constantly “rotating” around this housing.  See how the rotor divides the housing into 3 different sections?  Each section is basically its own “piston” since the rotor will constantly move the air/fuel or exhaust gases with it as it rotates.  The “top left” section will always be for the intake stroke, while the “top right” section will be for compression.  The “bottom right” is for combustion, and finally the “bottom left” section is for the exhaust stroke.  Still confused?  Here it is in action (click the image if it doesn’t animate):


     Starting with the intake stroke, we fill up an opened up volume in the rotor housing with air/fuel.  The rotor then turns, and compresses that air against the “right” side of the rotor housing, where we’ll get the ignition with the spark plugs and the combustion.  After that is done and it pushes the rotor along with the energy, the rotor then once again pushes the exhaust air out of the rotor housing through the exhaust port.  For rotaries, we refer to the intake opening as the “intake port” and the exhaust opening as the “exhaust port”. 

     So the rotor basically “pushes” one volume of gas all the way from the intake stroke to the exhaust stroke.  Notice how even while one secion is being compressed, the other 2 sections are also working.  This is what allows such a small displacement motor to push out so much power.  Its efficient due this structure.  While a piston engine takes 4 strokes to turn its crankshaft once, for every 4 strokes of the rotor, we get 2 turns of the crankshaft.  Also, since our rotor is moving around the crankshaft (output shaft in rotary terms), there is less vibration allowing for smoother revving.  Notice how there are no valve for the intake and the exhaust, since the motor does all the work.  Air is constantly being moved around the rotor housing, from the intake phase all the way to the exhaust.  Also, notice there are two spark plugs since the volume of the compressed air/fuel is quite long due to the rotor and rotor housing shape.

     What are the pro’s of a rotary engine over a piston engine?  First, there are alot less moving parts meaning its simpler.  Less parts = less mass which equals a lighter engine.  Also, all the rotors are moving in one direction in a constact fluid motion as opposed to the piston engine where the pistons move both up and down perpendicular to the crankshaft.

     The con’s are that the engine is thirsty.  It consumes alot of fuel to keep the air/fuel from prematurely combusting (also known as detonation or knocking).  It’s also harder to meet emissions laws with a rotary and production prices are more expensive due to its lack of popularity.  Also, rotarys aren’t known to be the most reliable engines around.  Their weakness are the edges of the rotors where it means the rotor housing.

     Next I’ll explain a diesel engine, and how its different from a normal piston engine.  Stay tuned.


1 Response to “The Wankel Rotary Engine”

  1. 1 The Wankel Rotary Engine Trackback on March 28, 2009 at 11:50 pm

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