How a Rotary Engine Works, Step by Step

A rotary (Wankel) engine makes power by orbiting a triangular rotor inside an oval-like housing, creating three moving combustion chambers that sequentially perform intake, compression, ignition/expansion, and exhaust; an eccentric shaft converts this orbital motion into smooth rotation, delivering one power stroke per output-shaft revolution per rotor. Below is a detailed, step-by-step look at how the cycle unfolds and how the major parts coordinate to produce power.

What Is a Rotary (Wankel) Engine?

Unlike a piston engine with cylinders and reciprocating pistons, a Wankel rotary engine uses a roughly triangular rotor that turns and orbits within an epitrochoid-shaped housing. Each rotor face forms a combustion chamber whose volume changes as the rotor moves. Port openings in the housing manage when air-fuel enters and exhaust exits, while a pair of spark plugs ignite the charge for efficient burn. The result is a compact, high-revving engine with few moving parts and a notably smooth power delivery.

The Essential Parts and What They Do

To understand the step-by-step operation, it helps to know the core components and how they interact to create, seal, and time the combustion process.

• Rotor: A three-sided (Reuleaux-like) rotor with combustion faces that form chambers against the housing.
• Housing (epitrochoid): The precisely shaped cavity where the rotor orbits; contains intake and exhaust ports.
• Eccentric shaft: The output shaft with offset lobes that the rotor orbits around, converting orbital motion into rotation.
• Synchronizing gears: An internal gear on the rotor meshes with a fixed gear in the housing, keeping the rotor oriented and enforcing the 3:1 speed relationship (the eccentric shaft spins three times for each rotor revolution).
• Seals: Apex seals at the rotor tips plus side and corner seals maintain gas-tight chambers as the rotor sweeps the housing.
• Spark plugs: Typically two per rotor face (leading and trailing) to ignite the elongated chamber efficiently.
• Ports: Intake and exhaust openings in the housing (or side plates) that act like valve timing without using camshafts.
• Lubrication and cooling systems: Metered oil to seals and bearings, coolant passages in the housing, and oil cooling for the rotor.

Together, these parts create three separate, moving combustion chambers per rotor and coordinate their timing so each chamber completes the four phases of the Otto cycle as the engine turns.

Step-by-Step: One Full Cycle Inside a Rotary Engine Chamber

Each rotor face undergoes a four-phase cycle as it passes the intake and exhaust ports. Because the rotor has three faces and spins at one-third the eccentric shaft speed, the engine delivers a steady stream of power pulses. The sequence below describes the process for a single chamber.

1. Intake: As a chamber’s leading apex passes the intake port, the chamber volume is increasing. The low pressure draws in the air-fuel mixture (or just air in direct-injected designs). The apex and side seals maintain separation from the other two chambers.
2. Port closure and trapping: Continued rotor motion carries the chamber past the intake port, which closes off. The charge is now trapped, ready for compression.
3. Compression: The chamber volume decreases as the rotor moves toward the “spark zone.” Pressure and temperature rise, preparing the mixture for ignition.
4. Ignition and expansion (power): The leading spark plug fires, followed shortly by the trailing plug to complete the burn across the elongated chamber. Expanding gases push on the rotor face, generating torque on the eccentric shaft.
5. Exhaust: As the chamber approaches the exhaust port, the port opens and hot gases flow out under pressure, then are scavenged as the chamber volume continues changing.
6. Reset and repeat: The rotor continues to orbit. Each of the three faces repeats this sequence in turn. Due to the 3:1 kinematic relationship, each rotor produces one power stroke per output-shaft revolution; a two-rotor engine produces two power strokes per output-shaft revolution, aiding smoothness.

This continuous procession of staggered cycles across the rotor’s three faces yields near-overlapping power events, which contributes to the engine’s distinctive smooth feel and high-revving character.

Timing, Motion, and Power Delivery

Several kinematic and timing features make the rotary engine behave differently from a piston engine in sound, smoothness, and responsiveness.

• 3:1 speed relationship: The eccentric shaft spins three times for each rotor revolution; the gears synchronize orientation rather than transmit power.
• Port timing instead of valves: Intake and exhaust open/close based on rotor position relative to fixed ports, shaping torque, power, and emissions.
• Smooth power pulses: With one power stroke per shaft revolution per rotor and no reciprocating masses stopping and starting, vibration is low.
• High redline potential: Fewer moving parts and low reciprocating inertia support high rotational speeds, though heat and sealing must be managed.

These characteristics explain why rotaries feel linear and eager to rev, while also highlighting why port design and cooling are so critical.

Sealing, Lubrication, and Cooling

The rotor must maintain three separate chambers while sliding along the housing at high speed and temperature; that demands careful sealing, lubrication, and thermal control.

• Apex, side, and corner seals: Spring-loaded and oil-wetted, they maintain gas tightness across the housing and side plates.
• Oil metering/injection: Small amounts of engine oil are injected (often into the intake or directly onto the rotor/housing) to lubricate seals and reduce wear, resulting in some normal oil consumption.
• Cooling: Water jackets in the housing manage combustion heat; rotor cavities circulate oil to carry heat away from the rotor itself.
• Materials and coatings: Housing surface treatments and carefully chosen seal alloys reduce wear and friction under high thermal loads.

Because sealing is fundamental to efficiency and durability, proper oiling and temperature control are central to rotary engine design and care.

Intake and Exhaust Port Strategies

Port shape and placement strongly influence drivability, power, and emissions. Engineers and tuners choose different layouts for different goals.

• Side intake ports: Common on street engines for smoother idle, better low-speed torque, and emissions compliance.
• Peripheral intake ports: Larger, high-flow openings for racing or high-rpm use, trading low-speed manners and emissions for top-end power.
• Exhaust port shaping: Controls blowdown and overlap with intake timing, affecting torque curve and catalyst performance.

These choices define the engine’s character—civil and efficient, or peaky and powerful—by tailoring how the cycle breathes.

Advantages and Trade-offs

Rotary engines offer unique benefits deriving from their geometry and simplicity, alongside well-known compromises that shape their use cases.

• Advantages: Compact size and weight, few moving parts, smooth operation, high specific power potential, and excellent balance at high rpm.
• Trade-offs: Higher fuel consumption and emissions (due to chamber shape and sealing losses), oil consumption by design, hot exhaust, and sensitivity of seals and housings to heat and lubrication quality.

These strengths and weaknesses explain why rotaries thrive in some roles but are less common as mainstream automotive powerplants today.

Where You’ll Find Rotary Engines Today

While no longer common as primary car engines, rotaries persist where their compactness, smoothness, and power density shine.

• Range extenders: Mazda’s MX-30 R-EV (launched 2023 in select markets) uses a single-rotor engine as a compact generator.
• Aerospace and UAVs: Small rotaries power drones and light aircraft where weight and vibration are critical.
• Alternative fuels and research: Ongoing development explores hydrogen- and LPG-fueled rotaries for cleaner operation.

These applications leverage the rotary’s size and smoothness while mitigating emissions and efficiency concerns through hybridization or specialized duty cycles.

Summary

A Wankel rotary engine creates three moving combustion chambers with a triangular rotor inside an epitrochoid housing. As the rotor orbits, each chamber sequentially performs intake, compression, ignition/expansion, and exhaust, with the eccentric shaft converting this motion into rotation. The synchronized 3:1 kinematics yield one power stroke per shaft revolution per rotor, producing smooth, high-revving power from a compact package—balanced against challenges in sealing, fuel efficiency, emissions, and heat management.

How do rotary engines make so much power?

Rotary engines produce significant power for their size because they achieve more power strokes per engine revolution compared to a traditional four-stroke piston engine, have fewer moving parts, and can operate at higher RPMs. Their compact design, high power-to-weight ratio, and smooth, vibration-free operation also contribute to their reputation for high performance in vehicles like sports cars.
 
This video explains the differences between rotary and piston engines: 48sCar ThrottleYouTube · Nov 10, 2017
More Power Strokes 

• Continuous Power Generation: Opens in new tabUnlike a four-stroke piston engine, where a power stroke only occurs once every two crankshaft revolutions, a rotary engine’s rotor performs intake, compression, combustion, and exhaust processes continuously. 
• Higher Power Density: Opens in new tabThis results in a more frequent application of power to the output shaft, meaning a rotary engine delivers more power relative to its displacement and size. 

Fewer and Smoother Moving Parts 

• Reduced Reciprocating Mass: Opens in new tabRotary engines lack the heavy, up-and-down motion (reciprocating mass) of pistons, which dramatically reduces internal friction and vibrations. 
• Higher RPMs: Opens in new tabThis smoother, balanced design allows rotary engines to spin at higher speeds, further contributing to their powerful output. 

Compactness and High Power-to-Weight Ratio 

• Smaller Footprint: With fewer components, a rotary engine can be made significantly smaller and lighter than a comparable piston engine. 
• Improved Vehicle Dynamics: This high power-to-weight ratio allows engineers to design more agile and performance-focused vehicles by placing the engine lower and further back in the chassis, improving weight distribution. 

Why were rotary engines banned?

The rotary has never been explicitly banned, the alignment to F1 was the only reason it wasn’t allowed, much like many of the piston engines that had been racing at the time were no longer allowed.

What is the rotary engine in simple terms?

The rotary engine is an early type of internal combustion engine, usually designed with an odd number of cylinders per row in a radial configuration. The engine’s crankshaft remained stationary in operation, while the entire crankcase and its attached cylinders rotated around it as a unit.

What is the biggest problem with rotary engines?

First, they are neither efficient nor clean to run due to limitations in the chambers and rotors giving relatively poor gas mileage and poor emissions. Additionally there have always been problems with the rotor seals wearing prematurely reducing engine longevity and increasing oil burn.