15 Highly Unusual Engine Designs You Need To Know About
Engines power our world, but not all of them follow the standard playbook. From rotating triangles to spinning discs, some inventors threw conventional wisdom out the window and created mechanical marvels that defy expectations.
These strange powerplants might not all have become mainstream successes, but they showcase human creativity and engineering genius at its best.
1. Wankel Rotary Engine
Triangles spinning in oval chambers! Mazda’s famous rotary engine ditched traditional pistons for a three-sided rotor that creates all four strokes while spinning continuously.
This weird wonder produces remarkable power for its size but gulps fuel like a thirsty marathon runner. Despite its quirks, the Wankel rotary earned cult status in the RX-7 and RX-8 sports cars.
2. Adams-Farwell Rotary Engine
Backward thinking that actually worked! Unlike conventional engines where pistons drive a crankshaft, this 1904 oddity featured a stationary crankshaft with cylinders that rotated around it like a mechanical merry-go-round.
Powering early automobiles, these spinning powerplants doubled as their own cooling fans. The entire engine block spun at high speed, creating a gyroscopic effect that must have made cornering interesting!
3. Quasiturbine Engine
Four-hinged rhomboid seals perform a hypnotic dance inside this Canadian creation. The Quasiturbine combines rotary and piston principles into something entirely unique, with four moving parts tracing a perfect oval path.
Invented by the Saint-Hilaire family, this mechanical marvel promises higher efficiency than traditional engines. Its continuous combustion process theoretically delivers more power with fewer moving parts and reduced emissions.
4. Duke Axial Engine
Pistons arranged like bullets in a revolver cylinder! The Duke engine places its cylinders parallel to the crankshaft instead of perpendicular, creating a compact powerhouse.
A swashplate mechanism converts the pistons’ linear motion into rotation. Formula 1 engineers have eyed this Australian invention for its potential advantages in aerodynamics and weight distribution, though it remains largely experimental.
5. Opposed Piston Engine
Double the pistons, double the fun! These mechanical oddities feature two pistons sharing a single cylinder, moving toward each other during compression and away during power strokes.
Without cylinder heads, opposed piston engines boast excellent thermal efficiency. Fairbanks Morse used them in submarines, while Junkers powered WWII German aircraft with them. Modern startups like Achates Power are reviving this design for its efficiency potential.
6. Sleeve Valve Engine
Sliding metal sleeves replaced conventional valves in these whisper-quiet powerplants. Inside each cylinder, a metal sleeve with precisely cut ports moved up and down or rotated to control intake and exhaust timing.
Rolls-Royce and Napier built legendary aircraft engines using sleeve valves during WWII. Their smooth operation and resistance to wear at high temperatures made them ideal for warplanes, despite being more complex to manufacture.
7. Orbital Engine (Two-Stroke)
Squirting fuel directly into the combustion chamber transformed the dirty two-stroke! Australian engineer Ralph Sarich developed this system that sprays a precise air-fuel mixture at the exact moment needed.
Unlike traditional carbureted two-strokes that waste fuel, the Orbital engine achieves remarkable efficiency and cleanliness. This technology found its way into marine outboards and light aircraft, proving that sometimes innovation means reinventing rather than replacing.
8. Deltic Engine
Three crankshafts arranged in a triangle powered British locomotives and naval vessels! The Deltic’s cylinders formed a delta shape (hence the name), with opposed pistons meeting in the middle of each cylinder.
Napier developed this monstrous two-stroke diesel in the 1940s. With no cylinder heads and 18 cylinders arranged in three banks, the Deltic packed remarkable power density for its era, though it sounded like nothing else on Earth.
9. Swing-Piston Engine
Pistons that swing rather than slide! These peculiar powerplants use pivoting “pistons” that sweep through a toroidal (donut-shaped) chamber.
The motion resembles a metronome more than a conventional engine. Japanese manufacturer Matsushita briefly produced these for portable generators.
Their simple design with few moving parts offered excellent reliability, though power output remained modest compared to traditional alternatives.
10. Radial Engine
Cylinders arranged like spokes on a wheel defined aviation’s golden age! Radial engines placed cylinders in a star pattern around the crankshaft, creating distinctive round powerplants that dominated aircraft design for decades.
Their excellent power-to-weight ratio made them perfect for early flight. The odd number of cylinders (typically 5, 7, or 9 per row) ensured smooth firing intervals. Some massive examples used in WWII bombers featured multiple rows with up to 28 cylinders!
11. Gnome Rotary Engine
In WWI fighters like the Sopwith Camel, the entire cylinder block spun with the propeller around a fixed crankshaft.
Acting as its own flywheel, it enhanced maneuverability but demanded nerve, with pilots cutting ignition to adjust speed mid-flight.
12. Commer TS3 Engine
Horizontal pistons, driven by rocker arms, powered 1950s British trucks. This three-cylinder, two-stroke diesel’s “rocker and scissor” mechanism cut parts and boosted torque.
Its “whoosh-whoosh” exhaust, dubbed “Knocker,” faded due to maintenance woes despite fuel savings.
13. Atkinson Cycle Engine
Unequal strokes create efficiency magic! James Atkinson’s 1882 invention used linkages to create a power stroke longer than the compression stroke—a thermodynamic advantage that sacrifices some power for efficiency.
Modern hybrid vehicles like the Toyota Prius use a modified Atkinson cycle. The original design featured complex mechanical linkages, while today’s versions use valve timing to achieve the same effect, delivering excellent fuel economy at steady speeds.
14. Revetec Engine
Scissor gears replace the crankshaft in this Australian innovation! The Revetec uses counter-rotating cams that push against rollers to convert piston motion directly into rotation.
This unique design eliminates connecting rods and conventional crankshafts entirely. Claimed benefits include reduced friction, improved thermal efficiency, and more compact packaging.
Despite decades of development, the Revetec remains primarily experimental, though its principles continue to intrigue automotive engineers.
15. Cam Engine
Pistons push directly against a curved track! These unconventional powerplants replace the crankshaft with a specially shaped cam or swashplate that converts linear motion to rotation more directly.
Axial cam engines arrange their cylinders parallel to the output shaft. Duke Engines and the Dynacam system represent modern implementations of this concept.
Theoretical advantages include reduced friction, fewer parts, and more compact packaging than traditional crankshaft designs.