Figure 1: Parts of the Rotary engine
Figure 2: Combustion cycle of the
Rotary engine
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Dr. Ing. Felix Heinrich Wankel (1902-1988) Inventor and Developer of the Practical
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You don't have to look too hard to notice that the functions of the intake, compression, power and exhaust strokes are present in the Wankel as one of its rotors goes through a single revolution.
And because the Wankel does all this in one revolution, not in two complete turns as happens in most other car engines, it's also reminiscent of the two-stroke engines you're apt to find in your lawn mower or your boat's outboard motor. In fact, the Wankel sounds very much like these conventional twostrokers as it runs.
What's more, there's nothing really unusual about the operating hardware that works with the rotary engine. It's fed by either a carburetor or a fuel injection system, depending upon emissions requirements in demand at the time it was built. It fires the fuel-air mixture by means of spark plugs. It gets rid of burned gases through an exhaust system. And it propels the car by means of a rotating output shaft and a conventional powertrain, just like other automotive engines.
LETS TAKE A LOOK INSIDE
Now that we've somewhat diffused the mystery of the rotary engine, let's look inside one and discover what makes it tick. Here's what we'll see.
Figure I puts us squarely in front of the heart of the engine's interior, looking rearward. The bulgy triangle-shaped part with a geared hole in its center is one of the rotors that are standard in every current Mazda Wankel engine.
As the rotor turns clockwise (in the illustration) within its housing, the smaller gear that mates with the rotor gear is pulled along by the rotor gear teeth, also in a clockwise direction. And because it's attached firmly to the output shaft, rotation of that smaller gear turns the shaft. This is how the Wankel sends rotating power (or torque, to give it thecorrect name) to turn shafts, gears, U-joints and what-have-you on it’s way to the driving wheels of the car.
In addition to the rotor and the output shaft, the rotary engine's key components in the power-production fonnula are the spark plugs and the intake and exhaust ports. We've already covered how altering the size and/or shape of the ports can significantly increase horsepower
SO WHERE'S THE ACTION?
Okay, now we're going to fire up this powerplant and see what happens in slow motion. We'll begin the show by looking at the illustration "A" of Figure 2.
Notice that the rotor flank (the almost-flat side of the rotor) at the left side of illustration "A" is starting to create a working chamber with the inside curved wall of the housing. This chamber is taking in a charge of the fuel-air mixture from the open intake port in response to the increasing volume as the rotor turns clockwise.
While the rotor continues to turn in illustration "B", the expanding chamber draws in still more of the fuel-air mixture until at "C" the trailing edge of the rotor closes off the intake port to seal the fuel-air mixture in the chamber.
Continued clockwise rotation as the rotor moves toward Top Dead Center creates compression.
At D the spark plugs fire. Two spark plugs are used for each rotor to help assure proper combustion and reduce emissions within the Wankel's long, thin combustion area.
Expansion of the burning fuel-air mixture, as shown in "F", creates pressure in this chamber, forcing the rotor to turn. Rotation of the rotor causes it to transmit torque to the eccentric shaft. This (expanding charge) principle is the same for all internal combustion engines.
At "G", the leading apex seal passes the exhaust port and burnt gasses escape out the port and through the car's exhaust system.
At "H", the last remnants of the exhaust gases are being carried by their own momentum out the exhaust port even as the leading apex seal is uncovering the intake port to accept another fuel-air charge. In practice, this technique is the same as providing a slight amount of valve overlap for more efficient scavenging of exhaust gases with a reciprocating piston engine. And as with a piston engine, the resulting dilution of the fuel-air mixture helps to keep emission levels of unburned hydrocarbons and oxides of nitrogen under control.
STILL MORE?
Now let's pick up a point that fell by the wayside in our necessarily brief overview. Perhaps you may have noticed that some illustrations in this series are almost deadringers for others in the sequence of events. No, we didn't get lazy with the illustrations. The reason for this is that there were two more chambers sharing the rotor and housing with the chamber we were watching. In turn, these two rotor chambers were going through the same steps as the one we watched, only later. While the first chamber was pushing out exhaust gases, for example, the fuel-air mixture with the second chamber was being ignited and the third chamber was getting a fresh charge of fuel and air.
In effect, each rotor acts like three pistons of a conventional reciprocating engine. With the two-rotor Wankel that's a Mazda standard, it's like having a conventional six under the hood. And you know how smoothly they can run.
Figure 1: Parts of the Rotary engine
Figure 2: Combustion cycle of the
Rotary engine
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