What Is Wankel Engine? | How does a Rotary Engine work?

Engines are most commonly used all over the world. They have become an important part of all vehicles. There are different types of engines according to the need of different applications. The Wankel engine is one of the most famous types of internal combustion engines. It uses a rotary rotor to generate power. This article properly describes the Wankel engine working, types, parts, and applications.

What is a Wankel Engine?

A Wankel engine is a type of IC engine that uses the rotary motion of a triangular rotor mounted in an elliptical chamber to transform the fuel’s thermal energy into rotary motion. The Wankel engine is also known as a rotary engine because it has all the rotating parts.

This type of engine doesn’t contain any reciprocating components. The Wankel rotary engines have low weight and a more compact design than the piston engines.

The Wankel engine contains a triangular rotor instead of a piston engine. This rotor rotates inside the housing. This housing has an oval design. The rotor has three sides, each of which works as a piston as it rotates around the housing.

When the rotor rotates, the housing produces various volumes of space, causing compression and expansion of the air-fuel mixture.

The Wankel rotary engine produces less vibration and more even torque than the piston engine. 

wankel engine

The Wankel engines are most commonly used in different applications, including motorcycles, automobiles, and aviation. However, the use of these engines is reduced in recent years due to stricter emissions regulations and environmental concerns.

History of Wankel Engine

  • In 1924Felix Heinrich Wankel made a small laboratory and started developing and researching his dream engine that could rotate, suck, compress, burn, and exhaust. 
  • In 1951, NSU Motorenwerke AG started the development of the Wankel engine. 
  • In 1957, the engineer Felix Heinrich Wankel designed the first Wankel rotary engine as a substitute for the conventional reciprocating engine.
  • An engineer Hanns Dieter Paschke developed the second KKM motor by following some technological changes and improved the technology of the Wankel engine. 
  • The Wankel rotary engine was unveiled for the first time to the specialists and press at the 1960 German Engineering Union conference in Munich.
  • In the 1960s, due to the simplicity, excellent strength-to-weight ratio, smooth operation, and very high working efficiency of rotary engines, they were on everyone’s lips in the car and motorcycle industry. 
  • In August 1967, the NSU Motorenwerke AG gained considerable publicity for the very new NSU Ro 80, which had a 115-hour Wankel engine with two rotors. It was the first German car in 1968 to be chosen as the “Car of the Year”.
  • Due to the excellent features of the Wankel engine, many major car manufacturers (Ford, Toyota, Mercedes-Benz, Porsche, Rolls-Royce, and Mazda) signed Wankel rotary engine production license agreements over the next decade among them.

Rotary Engine Design

A rotary engine works on the principle of the otto-cycle. Unlike the reciprocal action of a piston engine, the 4 strokes of the standard Otto-cycle engine are organized in series around an elliptical rotor in the Wankel engine.

A Wankel engine has one rotor and a single elliptical box circle to a triangular rotor (a three-side of the Reuleaux) that rotates and travels in the box. The side of the rotor seal is connected to three combustion chambers on the side of the housing and the corners of the rotor seal on the main box perimeter.

As the rotor spins, the rotation and the shape of the housing push the rotor closer to the housing wall and the engine combustion chamber closer and farther down the “strokes” of a reciprocal piston. But these 4-stroke engines produce a combustion stroke after two revolutions of the piston inside the cylinder.

rotary engine design

The combustion chambers of the Wankel engine produce one “combustion stroke” during each turn. As the Wankel power shaft spins at three times to the rotor rpm, it becomes one ‘stroke’ of combustion per rotor output shaft rotation, twice as many times as the four-stroke piston engine and equivalent to that of a two-stroke cycle engine.

Wankel Engine Working

A Wankel rotary engine is a famous type of internal combustion engine that works on the basic principle of the otto-cycle.

A Wankel engine has a four-stroke and works according to the following way:

  1. Suction
  2. Compression
  3. Combustion
  4. Exhaust
wankel engine working
Wankel Engine Working

1) Intake or Suction Stroke: –

  • As the rotor’s tip goes through the inlet port, fresh air begins to enter the first cylinder, as shown in the above diagram.
  • The 1st cylinder continues to draw fresh air until the 2nd tip of the rotor reaches the inlet port and shuts it.
  • After this process, the intake port closes, and the fresh fuel-air mixture traps in the first cylinder for compression and combustion.

2) Compression: –

  • After the completion of the intake stroke, the compression stroke of the trapped air-fuel mixture starts.
  • As the rotor starts rotating, the gap between corner 1 to corner 2 of the first cylinder (as shown in the above diagram) reduces due to that the volume of the mixture reduces, and compression of the mixture occurs.
  • As the air-fuel mixture is compressed according to the requirements, it is sent for the combustion process.

3) Combustion: –

  • As the mixture of the first cylinder (between 1 to 2 corners) is compressed according to the requirement, a spark plug introduces a spark inside the cylinder, which ignites the air-fuel mixture.
  • Due to the ignition, the mixture is converted into high temperature and pressure gases. The energy of the combusted mixture forces the rotor to move forward. This process continues until the 1st corner passes by the exhaust port.

4) Exhaust: –

  • When corner 1 touches the exhaust or discharge port, the high-pressure burning gases are discharged from the engine.
  • After discharging exhaust gases, the exhaust port closes, and again the whole cycle repeats.

For a better understanding, watch the following video:

Read Also: Working of Stirling Engine

Wankel Rotary Engine Parts

A rotary engine may have a complicated design, but it doesn’t have as many moving parts or components as a piston engine. Below, we look at the essential components of a Wankel rotary engine to give you a better sense of how things work.

The rotary engine has the following major parts:

  1. Rotor
  2. Spark Plug
  3. Output Shaft
  4. Casing
  5. Intake & Exhaust Ports

rotary engine components

1) Rotor

A rotor is a triangular concave part that provides a tight seal when pushed against the engine housing. There is an air pocket or air inlet on each side of the rotor that allows more gas to enter the housing. These inlets or pockets efficiently increase the displacement rate of the Wankel engine. 

The rotor rotates on several gears that are connected to the shaft. This shaft is located at the housing center. The gears permit the rotor edges to rotate in such a way that they always make contact with the casing, maintaining three separate combustion bags.

2) Housing 

The housing is one of the most important parts of the Wankel engine. It is also known as an engine body. The elliptical design of the housing helps to maximize the engine’s displacement as the rotor rotates. During the rotation of the rotor, the edges of the rotor make constant contact with the inward wall of the housing.

When the rotor rotates in the housing, each air pocket passes through four parts of the combustion cycle:

  1. Suction to Compression
  2. Combustion to exhaust

A fuel injector and spark plug are inserted directly into the combustion chamber via the housing wall. External passages allow coolant and oils to flow by the system to maintain the temperature and integrity of the engine’s rotating parts.

The housing also acts as a protector for the internal parts of the engine. It saves the internal parts from any type of damage due to the fall of any external load on the engine.  

Read Also: Types of Reciprocating Engines

3) Output Shaft

The output shaft transmits the energy produced due to compression and combustion to the transmission system to drive the wheel of the vehicle. It is equipped with a round lob that touches the rotor and turns the shaft.

4) Intake & Exhaust Ports

The intake port allows the fresh mixture to enter a combustion chamber. The exhaust gases are expelled via an outlet or exhaust port.

5) Spark Plug

A spark plug is a part of the engine used to transfer electric current from an ignition system into the combustion chamber of an SI engine to burn a compressed air-fuel mixture with an electrical spark. It has a threaded metal housing that is electrically isolated from the central electrode by a ceramic insulator.

This plug connects with the ignition coil, which generates high voltage. When current moves through the coil, a voltage generates between the side electrode and the central electrode.

When the voltage exceeds the dielectric strength of the gas, the gas ionizes. The ionized gas works as a conductor that permits the current to flow through the room.

Read More: Bad Spark Plug Symptoms and Causes

Why is Wankel Engine so rare?

Nowadays, Wankel engines are not very common because of the following main reasons:

  • Low thermal efficiency
  • Burn oil
  • Rotor seal
  • Higher emission rate
  • Poor fuel economy
1) Low Thermal Efficiency

The combustion chamber of the rotary Wankel engine has a long and unique shape. Therefore, it has low thermal efficiency than reciprocating engines. This often results in unburned fuel exiting the tailpipe.

2) Burn Oil

Due to the design, these engines burn oil. The intake manifold of this engine has squirters and also an injector that injects oil directly into the burner. Therefore, the rider has to check the oil level regularly for the proper lubrication of the rotor. Due to this, more bad stuff comes out of the exhaust. The environment doesn’t like bad stuff.

3) Rotor Sealing

The rotor sealing of the rotary engine is a challenge when the temperature around the rotor fluctuates massively. This problem also increases the emission rate of the engine.

Keep in mind that the suction and burning process occurs at the same time but at different places within the engine housing. This shows that the top of the engine housing has a relatively low temperature than the bottom of the housing.  

4) High Emission Rate

The rotary Wankel engines are not famous because of their high emission rate. The combination of sealing challenges, inherent oil combustion, and inefficient combustion results in uncompetitive engines by current fuel economy or emissions standards. 

5) Poor Fuel Economy

Wankel engines have high fuel consumption than reciprocating engines. Due to high fuel consumption, the fuel cost also increases.

Advantages and Disadvantages of Rotary Engines

The rotary Wankel engine has the following major advantages and disadvantages: 

Advantages of Wankel Engines

  • These types of engines have a simple design.
  • A rotary engine has no valve for operation.
  • These engines don’t require crankshafts, pistons, connecting rods, etc. The removal of these components makes the Wankel engine lighter.
  • They have the ability to burn high-octane number fuel without knocking.
  • These engines have multiple safety advantages that make them useful in aircraft.
  • They have a high power output than their size. This makes them best suitable for use in motorcycles, aircraft, and other applications where weight is the most important factor.
  • A Wankel engine doesn’t have knocking problems. The knocking problems occur due to incomplete burning of the air-fuel mixture.
  • These engines have a significantly higher power/weight ratio than a column motor.
  • Wankel engines have smooth and quiet operation.
  • A Wankel rotary engine has a higher rpm ratio as compared to a reciprocating engine.
  • They are less expensive than reciprocating engines.
  • They are more compact than piston engines of similar power output.
  • Wankel engines have the ability to spin at high RPMs without experiencing the same level of stress and wear as a reciprocating engine.
  • These engines generate less vibration compared to reciprocating engines, which makes them more comfortable for passengers in vehicles such as boats and airplanes

Disadvantages of Wankel Engines

  • Centrifugal force forces the apex seal on the engine surface of the bodies to create a firm seal. In the light-load activity, gaps between the apex seal and housing may develop in the event of centrifugal force and gas pressure imbalances.
  • They consume high fuel than piston engines.
  • They have poor emissions performance.
  • The air-fuel mixture can’t be pre-stored because this engine has no inlet port.
  • These engines have complex fuel injection technology.
  • These engines have a low compression ratio. Due to this reason, they have low fuel economy and thermal efficiency.
  • They have less torque output compared to reciprocating engines of similar size and power output.
  • Wankel engines tend to be more expensive to manufacture than reciprocating engines.
  • The rotary engine is very prone to misfire, as the loss of stroke causes the engine to lose momentum and then start moving again the next time the combustion chamber is fired. Maintenance of an ignition system is essential to avoid this problem.
  • They have lower fuel efficiency than piston engines.

Rotary Wankel Engine Applications

  • Automotive: The Wankel engines are most commonly used in different cars over the years, most notably in the RX-8 sports cars and Mazda RX-7.
  • Industrial: These engines are used in different industrial applications, such as pumps and generators. Its compact size and high-power output make it the best suitable for these types of applications.
  • Marine: The rotary Wankel engines are used in different marine applications, such as personal watercraft and boats. The high-power output and compact size of these engines make them best suitable for these types of applications.
  • Aviation: They power different small aircraft, such as the Brantly B-2 helicopter and the RotorWay helicopter.
  • Racing: They are employed in different racing applications, such as hill climbing and drag racing. The high-power output and high-revving nature of these engines make them ideal for these types of competitions.

Difference between Piston Engine and Wankel Engine

Wankel EnginePiston Engine
It has a rotary rotor which is used to convert the thermal energy into rotatory motion.It has a reciprocating piston that moves up and down for the conversion of thermal energy into mechanical energy.
A Wankel rotary engine has a lightweight than a piston engine.A piston engine is heavy than a Wankel engine.
These engines have smaller sizes.These have a large size.
They burn more fuel.They burn less fuel than Wankel engines.
They produce less power than piston engines on the same fuel quantity.They produce high horsepower.
Wankel engines produce more emissions.These engines produce fewer emissions.
They have a smaller number of moving parts than piston pumps.They have many moving parts.
It has a smooth working.It doesn’t have a smooth operation like the Wankel engine.
Wankel engine has a compression ratio from 9:1 to 11:1.Piston engine has a compression ratio from 8:1 to 12:1.
They are capable of high RPMs and smoother power delivery.These have the ability to generate high torque at low RPMs.

FAQ Section

Who invented the Wankel engine?

In 1957, the engineer Felix Heinrich Wankel designed the first Wankel engine.

Why is a rotary engine known as a Wankel engine?

The Wankel was invented by Felix Heinrich Wankel. Therefore, it is known as the Wankel engine due to the name of its founder.

Why are rotary engines so powerful?

Because of their revolutionary movement, rotary engines have less operating vibration than piston engines. This allows the Wankel engine to be set so that it runs faster and can generate more power. 

What cars have a Wankel engine?

The Wankel engines can be found in the following cars mode:

  • 1969 Citroen M3
  • 1970 Mazda RX-500 concept
  • 1973 Citroen GS Birotor
  • 1970 Mercedes-Benz C111-II
  • 1975 Mazda Roadpacer AP
  • 1973 Chevrolet Corvette XP897 GT concept
  • 1974 Mazda Parkway RE13 Rotary 26 Superdeluxe
  • 2003 Mazda RX-8 Hydrogen RE

Why did the Wankel engine fail?

The Wankel engine fails due to the following reasons:

  • The Wankel engines have gas mileage and oil-burning issues.
  • They need complex fuel injection technology.
  • These engines have a low compression ratio. Due to this reason, they have poor fuel economy and low thermal efficiency.
  • In a rotary engine, both unburned fuel and combustion oil cause terrible emissions. 
  • They have lower fuel efficiency than reciprocating engines.

What are the parts of the Wankel Engine?

The Wankel Engine has the following parts:

  1. Rotor
  2. Intake & Exhaust Ports
  3. Spark plug
  4. Output shaft
  5. Housing
  6. Combustion chamber

Is a Wankel engine 4 stroke or 2 stroke?

The Wankel engine is a 4-stroke engine, similar to a traditional piston engine. The combustion process in a Wankel engine occurs over four strokes of the rotor, which are intake, compression, power, and exhaust, just like in a piston engine. So, while the Wankel engine has a different design than a piston engine, it still operates on the same 4-stroke cycle.

Read More
  1. Different types of Engines
  2. Different Types of Internal Combustion (IC) Engine 
  3. Types of External Combustion Engines
  4. Types of Heat Engines
  5. Working of Rankine Cycle
  6. Working of Otto Cycle

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