Hello, readers! This post explores the Wankel Engine, covering its working, types, advantages, and a comparison between Rotary and Piston Engines.
Engines are widely utilized across the globe and have become an essential component in all vehicles. Various types of engines exist to meet the diverse needs of different applications.
The Wankel engine, a renowned type of internal combustion engine, generates power through a rotating rotor. This article provides insights into the workings of Wankel engines, their types, components, and applications.
What is the Wankel Rotary Engine & it’s History
The Wankel rotary engine, conceived by German engineer Felix Heinrich Wankel in 1954 as an alternative to traditional engines, gained initial acclaim for its smooth operation and power density. However, challenges such as high fuel consumption and technical vulnerabilities hindered widespread adoption over the years.
In 2021, Mazda renewed interest in the Wankel engine with a revamped version in their MX-30 model, signaling a comeback for this technology. Mazda has a history of supporting Wankel engines, notably in the RX-8 until 2012.
The rotary piston design of the Wankel engine offers distinct advantages, though it faced difficulties in gaining broad acceptance. This article explores the history of Wankel engines, tracing back to Felix Wankel’s initial designs and subsequent improvements by engineer Hanns Dieter Paschke in 1957. In the 1960s, major automakers like Ford, Toyota, Mercedes-Benz, Porsche, Rolls-Royce, and Mazda embraced Wankel engines, with the NSU Ro 80, powered by a Wankel engine, earning the title of the first German “Car of the Year” in 1968.
Despite early success, challenges like the apex compression problem arose. Mazda addressed these issues, employing rotary engines in their RX series sports cars until 2012, achieving recognition at the 1991 24 Hours of Le Mans with a car powered by the 4-rotor Mazda 26B engine.
In subsequent decades, Wankel rotary engines found applications in motorcycles, racing cars, airplanes, small ships, and power generators, showcasing their versatility. Ongoing developments in Wankel technology aim to align these engines with future demands for low-emission, climate-neutral, reliable, and affordable energy supply.
Parts of Wankel Rotary Engine
- Rotor: Three convex faces with pockets for air/fuel mixture, metal blades, and rings for sealing, and internal gear teeth determining its path.
- Housing: Epitrochoid shape maintaining constant contact with rotor tips, integrating intake and exhaust ports directly for Intake, Compression, Combustion, and Exhaust stages.
- Output Shaft: Eccentrically mounted lobes, acting like a crankshaft, generating torque during rotation.
- Assembly Layers: End layers with seals and bearings, housing rotor-containing sections. Rotor housing layer with an oval shape and exhaust ports. Central piece with intake ports, separating and smoothing the outer surfaces of the rotors.
- Coolant Circulation: Passages surrounding components for effective cooling.
- Intake and Exhaust Ports: Integrated directly into the housing, eliminating the need for valves.
- Internal Gear: A large gear in the center of each rotor determines its orbit, engaging with a smaller fixed gear on the engine housing.
A Wankel rotary engine, distinct from conventional designs, has components like the rotor, which operates like pistons, featuring three convex faces with pockets for the air/fuel mixture. Metal blades and rings on the rotor create seals in the combustion chamber. The rotor engages with internal gear teeth, determining its path in the housing.
The housing, an epitrochoid shape, maintains constant contact with the rotor’s tips, creating sealed gas volumes for distinct combustion stages: Intake, Compression, Combustion, and Exhaust. The housing integrates intake and exhaust ports directly, eliminating the need for valves.
The output shaft, with eccentrically mounted lobes, acts like a crankshaft, generating torque as the rotor exerts force during rotation.
Assembly occurs in layers, with end layers housing seals and bearings, enclosing rotor-containing sections. The rotor housing and central piece with intake ports are layered inward. Each rotor’s center has a large internal gear determining its orbit.
This setup provides a clear understanding of how the engine harnesses power.
Working of Wankel Rotary Engine
Rotary engines operate on the familiar four-stroke combustion cycle, similar to four-stroke piston engines. However, the execution in a rotary engine is distinctly different.
The pivotal element of a rotary engine is the rotor, comparable to the pistons in a piston engine. Mounted on a large circular lobe offset from the output shaft’s centerline, the rotor is akin to a crank handle on a winch, providing leverage to turn the output shaft. As the rotor orbits within the housing, it propels the lobe in tight circles, completing three rotations for every revolution of the rotor.
During the rotor’s movement through the housing, the three chambers it creates undergo size changes, generating a pumping action. Examining each face of the rotor in the context of the four strokes of the engine reveals the following:
- The intake phase initiates as the rotor’s tip passes the intake port.
- The chamber’s volume expands as the rotor moves past the intake port, drawing in the air/fuel mixture.
- Continuing its motion, the rotor reduces the chamber’s volume, compressing the air/fuel mixture.
- Compression peaks around the rotor’s face at the spark plugs.
- Rotary engines typically feature two spark plugs in the elongated combustion chamber.
- Ignition of the air/fuel mixture by the spark plugs induces pressure, compelling rotor movement.
- The expanding combustion gases move the rotor, generating power until the rotor’s peak reaches the exhaust port.
- Once the rotor’s peak passes the exhaust port, high-pressure combustion gases exit through the exhaust.
- As the rotor continues, the chamber contracts, expelling the remaining exhaust.
- The cycle restarts as the rotor’s peak passes the intake port.
An intriguing aspect of the rotary engine is that each of the rotor’s three faces is continually engaged in one part of the cycle. In a complete rotor revolution, three combustion strokes occur. Notably, the output shaft completes three rotations for every rotor revolution, ensuring one combustion stroke per output shaft revolution.
Why is the Wankel Engine Uncommon?
The rarity of Wankel engines today can be attributed to several factors:
Low Thermal Efficiency
- The Wankel engine’s elongated and irregular combustion chamber contributes to its lower thermal efficiency compared to reciprocating engines. This design often leads to unburned fuel escaping through the tailpipe.
- The engine design inherently causes oil burning. The intake manifold incorporates squirters and an injector that directly pumps oil into the burner, resulting in increased emissions of harmful substances, which is environmentally undesirable.
Rotor Sealing Challenges
- Rotor sealing in a rotary engine becomes challenging when there are significant temperature variations around the rotor. This challenge elevates the engine’s emission rate. The simultaneous occurrence of suction and burning processes in different parts of the engine housing contributes to varying temperatures, with the top being cooler than the bottom.
High Emission Rate
- Wankel rotary engines suffer from a lack of popularity due to their elevated emission rate. Difficulties in sealing, inherent oil combustion, and inefficient combustion contribute to engines that fail to meet current fuel economy or emissions standards.
Poor Fuel Economy
- In comparison to reciprocating engines, Wankel engines exhibit higher fuel consumption, leading to increased fuel prices. This factor further diminishes their appeal in the automotive landscape.
Advantages of Rotary Wankel Engine
- Compact Size and Lightweight: The Wankel rotary engine is smaller, lighter, and more compact than reciprocating engines.
- Cost-Effective Construction: Cheaper and simpler construction for mass production due to the absence of many working parts like connecting rods, crankshafts, and valve mechanisms.
- Easy Balancing: Balancing is simpler as it lacks reciprocating parts, resulting in road tests confirming minimal vibrations.
- High Volumetric Efficiency: The Wankel engine boasts very high volumetric efficiency, often exceeding 100%.
- Increased Power-to-Weight Ratio: Considerably higher power output per kilogram of the engine.
- Lower Running Costs: The Wankel engine requires a lower running cost compared to reciprocating engines.
- No Need for Overdrive: Due to its high speed, the Wankel engine does not require over-drive.
Disadvantages of Rotary Wankel Engine
- The engine consumes more fuel at low speeds and uses increased oil per B.H.P.
- It operates at lower torque speeds.
- The braking effect of the engine is significantly reduced.
- Due to the very high engine speed, a reduction of speed in the transmission is necessary.
- The use of a transistorized ignition has addressed historical ignition troubles, eliminating the need for periodic spark plug changes.
- The sealing problem, a historical obstacle in Wankel rotary engine development, has largely been resolved.
- Proximity of the inlet and exhaust ports may lead to potential cylinder distortion.
- Designing the exhaust manifold and silencer is challenging due to very high exhaust gas temperatures, nearly 1600°F.
Uses of Rotary Wankel Engine
- Mazda pioneered the construction of the first Wankel engine with the Mazda 12A engine.
- Its specific design aims to create a light, reliable, and relatively powerful engine tailored for aircraft use.
- Wankel engines are favored by motorcycle manufacturers owing to their small size and appealing power-to-weight ratio.
- The compact size and high power-to-weight ratio of the Wankel engine suggest its potential use in electric vehicles to provide supplementary power when battery levels are low.
- Smaller Wankel engines are increasingly finding applications in various fields, including auxiliary power units for go-karts and personal watercraft.
- The simplicity of the Wankel engine renders it suitable for mini, micro, and micro-mini engine designs.
In conclsuion, this exploration of the Wankel Engine comprehensively covers its operational principles, types, advantages, and a comparison with Piston Engines. While engines remain vital globally, the Wankel engine, featuring a rotating rotor, is scrutinized, including its history, challenges, and diverse applications.
The Wankel engine’s distinctive attributes, such as compact size, high power-to-weight ratio, and simplicity, render it adaptable for airplanes, electric vehicles, and miniature engine designs. Despite facing challenges like thermal efficiency and oil consumption, ongoing innovations strive to position Wankel engines as efficient, low-emission energy solutions for the future.