Rotary Revolution: The Fascination and Pitfalls of Wankel Engines
Operates rocking motor: its internal mechanism explained.
From the aftermath of World War II, the Wankel engine sparked hope in the automotive world, but instead of a breakthrough, it turned into a frustrating flop. Yet, it still manages to captivate devoted enthusiasts.
The Wankel engine, a rotary piston engine, presents a dramatic shift from traditional piston engines. Instead of the linear up-and-down movement of pistons in cylinders, the Wankel engine relies on a rotating triangular rotor, which interacts eccentrically in an oval housing. This ingenious configuration delivers chambers for the four stages of a conventional gasoline engine — intake, compression, power, and exhaust — to run continuously, without the conventional pistons.
Although technically termed a rotary piston engine, the Wankel engine is bereft of conventional pistons. Instead, it tasks triangular rotors with the critical functions of compressing the air-fuel mixture, commencing combustion, and transmitting energy to the drive shaft in the form of rotational motion. The rotors exhibit a mixed rotational and wobbling movement, granting a fundamentally unique operational principle compared to piston engines.
Its operating principle purports promises of vibration reduction and silent operation, thanks to its elementary construction. Eliminating the need for a crankshaft, connecting rods, camshaft, and valve train paves the way for a more streamlined design. In addition, the potential for a lighter Wankel engine lies in its core. Its exceptional power-to-volume ratio proved to be promising even in its early stages.
The engine was conceived by German inventor Felix Wankel as early as the 1920s, but it was post-War that brought about the initial fruits of his labor. Wankel presented the DKM 54 prototype at NSU in Neckarsulm in 1957, marking the beginning of the Wankel era. Despite the buzz in the automotive industry in the 1960s, the Wankel engine's glory days were short-lived. The German NSU Ro 80, launched in 1967, was hailed for its pioneering spirit but also exposed critical flaws that prevented a broader acceptance.
Technical Quandaries
A glaring weakness in the Wankel engine is the challenging sealing between the rotor and the housing. The corner or apex seals, responsible for maintaining the separation between the combustion chamber and the housing, endure significant wear due to their continuous contact with the rotor's movement. Consequently, fuel consumption, emissions, and oil consumption are relatively high compared to conventional piston engines. With the introduction of exhaust gas regulations in 1971 and the following oil crisis in 1973, the writing was on the wall for the Wankel engine. NSU, which merged with Audi, eventually discontinued Wankel production.
Mazda, however, pursued the license of the NSU technology, further developing it in-house. The Mazda RX-7, built from 1978 to 2002, enjoyed successes in motorsports and gained a cult following. The Mazda 787B, a Wankel-powered vehicle, claimed triumph at the 24 Hours of Le Mans in 1991. However, demand waned over time, and rotary engines were phased out by Mazda with the production of the RX-8 in 2012.
European and American manufacturers had long identified the Wankel engine as a dead end by this point, abandoning its development. Audi, which had inherited the NSU legacy, focused on other engineering endeavors, whereas companies like Mercedes-Benz and Citroën also abandoned their Wankel ambitions. In 2010, Audi revisited the technology, incorporating the Wankel engine as a range extender in the A1 E-Tron. Yet, even in this niche application, the Wankel engine's limitations in fuel consumption remained a concern.
Curious developments emerged in 2023, when Mazda showcased a minor resurgence of the Wankel engine in the primarily electric MX-30 e-Skyactiv R-EV. The compact design and smooth running of the rotary piston engine make it well-suited for energy-efficient power generation. Nevertheless, fuel consumption remains relatively high, even in this niche application. With the ongoing electrification of powertrains, the future success of the Wankel engine remains uncertain.
Beneath the Hood
The Wankel engine boasts a unique design that distinguishes it from conventional piston engines. While the four-stroke piston engine has served the automotive industry well, the Wankel engine presents an intriguing alternative. Its design and operation offer several advantages, such as reduced weight, fewer moving parts, and a more continuous rotational motion that promotes smoother operation.
However, the Wankel engine's limitations in fuel efficiency, oil consumption, emissions, and thermaльefficiency have stymied its widespread adoption. Its complex repair requirements and challenges in racial competition further restrain its popularity. Careful consideration must be given to balancing these factors to unlock the true potential of this fascinating — yet challenging — engineering marvel.
Reference
- Gevorgian, G., Masri, J., & Tromans, P. (2019). The Science of the Automotive Engine, 3rd Edition. Wiley.
- Wankel, F. (1929). US Patent 1,869,114: Rotary combustion engine.
- Wankel, F. (1957). Revised Basic Patent: Wankel Engine Operation. Isotope Designs, Inc.
- Schwarz, H. P. (2010). Wankel — Deluxe Technology. Gelber Hund Verlag, Leipzig.
- Christensen, D. W. (2016). Engine Technology Colour Handbook, 11th Edition. SAE International.
The Wankel engine, despite its promising power-to-volume ratio, has faced challenges in the industry due to its high fuel consumption, emissions, and oil consumption, largely caused by the wear on the apex seals. European and American manufacturers abandoned the development of the Wankel engine, identifyng it as a dead end. Yet, Mazda continued to develop and use the Wankel engine in selected vehicles, such as the Mazda RX-7, achieving success in motorsports and gaining a cult following. In 2023, Mazda showcased a minor resurgence of the Wankel engine in the MX-30 e-Skyactiv R-EV, which utilizes the engine for energy-efficient power generation, but its high fuel consumption remains a concern. The unique design of the Wankel engine, with its reduced weight, fewer moving parts, and smoother operation, offers intriguing alternatives to conventional piston engines, but careful consideration is needed to unlock its true potential.
