How does a rotary engine work

The rotary engine was designed and developed by the German engineer Dr. Felix Wankel in 1957. Unlike a typical internal combustion engine that uses pistons that move up and down in a reciprocating motion, rotary engines utilize a triangular-shaped rotor that orbits in elliptical circles. So how does this revolutionary engine work?

Rotary engines are compact by design and a twin-rotor 1.3L engine is around the size of a beer keg, which is minute by automotive standards. Despite its diminutive size, engine volume is more than doubled when compared to a similarly sized piston engine, as the triangular-shaped rotor forms three separate moving combustion chambers as it moves around in its orbit.

The major parts comprising a rotary engine are as follows:

Rotor Triangular shaped component which is the equivalent to the piston. Most street-driven rotary cars use a twin-rotor engine while racing versions use triple rotor engines.

Rotor Housing €“ This is the housing that the rotor fits into and its thickness is equal to that of the rotor. The unusual shape of the inner wall of the rotor housing (which the three corners of the rotor run along) is called the peritrochoid curve.

Apex Seals €“ At each corner of the triangular-shaped rotor is an apex seal. These seals are used to separate the three moving chambers created by the orbiting rotor.

Eccentric Shaft This is the equivalent of the crankshaft in a piston engine and is driven by the rotor as a result of combustion.

Side Housings €“ These are the housings located on the extreme ends of the twin-rotor engine.

Intermediate Housing This is the housing located in between the two rotor housings in a twin-rotor engine.

Despite these unusual components, rotary engines are very efficient in the production of power via a four-stage process that occurs in each of the three separate chambers. The unusual interior shape of the rotor housing, created by the peritrochoid curve, causes the volume within these three moving chambers to change during a complete orbit of the rotor. For simplicity, let’s focus on one of these chambers as it completes one revolution within the rotor housing.

Intake Phase The intake phase occurs when the leading tip of the chamber first uncovers the intake ports. During this phase, the volume with the chamber is designed to increase, which causes a fuel and air mixture to be drawn into the chamber from the intake system and fuel injectors. This phase ends when the flank tip of the chamber covers up the intake port.

Compression Phase As the rotor continues to revolve, the peritrochoid curve causes the volume of the chamber to be reduced, which in turn compresses the fuel and air mixture to a pre-determined point.

Power Phase At a certain compression level, when the fuel and air mixture reaches its peak compression, spark plugs ignite this mixture, causing combustion to occur. The gases within the chamber expand rapidly as a result, and the power produced from this then pushes against the side of the rotor causing it to continue its orbit. The rotor then imparts torque to the eccentric shaft that it orbits around. The eccentric shaft turns three times for every complete revolution of the rotor as this power phase occurs once in each of the three separate chambers.

Exhaust Phase €“ After combustion, when the leading tip of the chamber first uncovers the exhaust port, this phase begins. Its purpose is to expel the spent gases to the exhaust system, clearing the chamber before this process starts over again.

This is essentially how a rotary engine works and produces power. These engines are used solely in the automotive industry today by the Japanese manufacturer Mazda. Rotary engines have also found their way to marine and aviation engines.

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