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. In the previous article, we discussed different types of Internal Combustion engines (ICE). In this article, we will mainly be discussed to Wankel engine.

What is a Wankel Engine?

A Wankel engine is a type of IC rotary engine that uses the rotary motion of a triangular rotor mounted in an elliptical chamber to transform the thermal energy into rotary motion without using the traditional reciprocating piston. The Wankel engine is also known as a rotary engine because it has all the rotating parts.

Compared to piston engines, the Wankel rotary engines have low weight, small in size, and compact in design. In contrast, a piston engine has a reciprocating piston that moves upward and downward inside the cylinder.

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

wankel engine

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 to the conventional reciprocating engine.
  • An engineer Hanns Dieter Paschke was 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 the 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) had 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 rotary motor 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.

These engines have high output power as compared to four-stroke petrol engines with comparable engine movement.

Wankel Engine Working

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

A Wankel engine has 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 casing. There is an air pocket or air inlet on each side of the rotor to allow more gas into the casing. 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 installs at the casing 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 or Casing

The casing is the most important part of the engine. It is also known as an engine body.  The elliptical design of the casing helps to maximize the engine’s displacement as the rotor rotates. During the rotation of the rotor, the edges of the rotor are in constant contact with the inward wall of the casing.

When the rotor rotates in the casing, 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 casing wall. External passages allow coolant and oils to flow by the system to maintain system temperature and integrity.

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 and exhaust gases to eject gases 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.

Fuel Economy and Emissions rate of a Wankel Rotary Engine

When a rotary engine burns gasoline, it has many emissions and efficiency issues.  Compared to 0.6 mm hydrogen, the petrol ignites more slowly and has a slower flame propagation speed, and has a longer extinguishing distance with a 2 mm compression cycle. Due to these factors, the engine consumes more fuel, and engine efficiency reduces.

When the Wankel rotary engine uses gasoline, the gap (on the compression cycle) between the casing and the rotor becomes very tight while this gap is wide enough for hydrogen. The engine requires this narrow gap for compression.

When engines use petrol instead of diesel fuel, the remaining petrol expels into the atmosphere via an exhaust valve. But this problem doesn’t appear when the engine uses hydrogen as a fuel. This is because the entire fuel mixture is burned inside the combustion chamber, which has very low emissions and fuel efficiency also improves up to 23%.

The Wankel engine’s combustion chamber design is more resistant to pre-ignition functioning on lower octane gasoline than a similar piston engine.

The design of the combustion chamber can cause inadequate burning of the air-fuel mixture when using gasoline. Due to this incomplete burning, it releases a large amount of unburned hydrocarbons in the exhaust.

Though the combustion temperature of the Wankel rotary engine is less than other engines, and early engines also have exhaust gas recirculation (EGR). Therefore, exhaust gas emission from the Wankel engines is relatively low.

The rotary engine in a vehicle can run at high speed. This is due to the high eccentricity of the rotor, longer suction ducts, and early opening of the suction valve increase torque at low speed—the position and design of the rotor recess affect fuel consumption rate and emissions.

The fuel consumption rate and emissions results depend on the design of the combustion recess, which determines through the spark plug position inside the chamber of an engine.

Read Also: Different types of EC Engines

Why is Wankel Engine so rare?

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

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 the reciprocating engines. This often results in unburned fuel exiting the tailpipe.

2) Burn Baby Burn

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 casing. This shows that the top of the engine casing 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) Fuel Economy

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

Advantages and Disadvantages of Rotary Engine

The Wankel rotary 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 and connecting rods etc. The removal of these components makes the Wankel engine lighter.
  • These have a wide range of speeds.
  • They can also burn high octane number fuel without knocking.
  • These engines have multiple safety advantages that make them useful in aircraft.
  • Sump fuel pollution doesn’t appear on some Wankel engines, which means there is no need for fuel change.
  • 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.
  • More straightforward to pack in limited engine areas than a piston engine.
  • These engines don’t need reciprocating parts.
  • A Wankel rotary engine has a higher rpm ratio as compared to a reciprocating engine.
  • These engines don’t produce high noise while working.
  • Because Wankel engine has very low moving components, therefore, its manufacturing price is low.
  • These engines are quite than piston engines.
  • The high speed of these engines gives superior adaptability.
  • These are best appropriate for using hydrogen fuels.

Disadvantages of Wankel Engines

  • High Sealing Loss: This is also a minor concern since the Wankel engine housing has slightly different temperatures in each separate chamber segment. The various substance expansion coefficients contribute to imperfect screening. Therefore, these engines have high sealing loss. 
  • Lifting of the Apex seal: 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 apex seal and housing may develop in the event of centrifugal force and gas pressure imbalances.
  • High rate of emissions: Because unburned fuel is in the exhaust flux as fuel is used, emissions standards are difficult to fulfill. Direct fuel injection into the engine combustion chamber will solve this problem.
  • Low fuel economy of petrol fuel: This is formed due to moving combustion chamber, which contributes to poor combustion and good pressure at part load and low rpm. This leads to unburned fuel joining the exhaust flux; fuel not used to produce electricity is lost.
  • Sometimes, the Wankel rotary engine has gas mileage and oil burning problems.
  • The air-fuel mixture can’t be pre-stored because this engine has no inlet port.
  • These engines require a complex fuel injection technology.
  • These engines have a low compression ratio. Due to this reason, they have low fuel economy and thermal efficiency.
  • In the exhaust stream of the Wankel engine, there may be high unburned hydrocarbons and carbon monoxide emissions. 
  • 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.

Wankel Engine Applications

  • Tiny Wankel engines are used in applications such as go-karts, personal water vessels, and aircraft auxiliary power units.
  • Some people have used the Wankel engines in vehicle models, which were mostly in use since 1970. Even with a big muffler, the whole kit only weighs 13.4 oz (380 grams).
  • The versatility of the Wankel engines makes them suitable for designs with small, micro, and micro-mini applications.
  • These engines use in aircraft.
  • These engines use in the Mazda cars.
  • Small Wankel engines are also used in motorcycles.
  • These types of engines also use in boats.

What is the difference between a Piston engine and a 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.

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.
  • Fuel consumption: The Wankel engine has a thin and long combustion chamber driven by the rotor. This slows down the combustion of the fuel. The engine tried to solve this problem with double spark plugs (start and end). 
  • Emission: In the case of a rotary engine, both unburned fuel and combustion oil cause terrible emissions. 

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

These types of engines do not burn very cleanly and, as a result, have high levels of emissions. Rotary engines also have high wear compared to piston engines and can’t last as long as piston engines.

The other thing about them is they are terrible engines for people that drive short distances.

The Wankel engines are also used for vehicles/machines turning at high rpm for long periods like airplanes. This is because the peak power is found at these high rpms, and they all have a lack of torque, making it very fuel-consuming to get up to that high powerband.

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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