Fact-checked by Grok 2 weeks ago

Wankel engine

The Wankel engine, also known as the Wankel rotary engine, is an internal combustion engine that employs a three-sided rotor mounted on an eccentric shaft within an epitrochoidal housing to perform the four-stroke cycle of intake, compression, combustion, and exhaust, converting thermal energy into rotational mechanical power without reciprocating pistons.^[1]^[2] The rotor orbits and rotates inside the housing, creating three variable-volume chambers that sequentially execute the Otto cycle, with the eccentric shaft turning three times for each full rotor revolution, delivering one power impulse per shaft rotation.^[3] Key components include the triangular rotor, epitrochoidal chamber walls, apex seals at the rotor tips to maintain gas-tight compartments, side seals on the rotor faces, and corner seals, all of which enable high-speed operation up to 5,000 rpm while eliminating valves through port timing controlled by the rotor's motion.^[2]^[3] Invented by German engineer Felix Wankel, who conceived the basic rotary concept in 1924, the engine underwent significant refinement through collaboration with NSU Motorenwerke, with key patents filed in the 1950s and achieving its first operational prototype in 1957.^[4]^[5] By the 1960s, Japanese automaker Mazda licensed the technology and introduced the world's first production vehicle with a Wankel engine, the 1967 Cosmo Sport featuring a two-rotor design producing 110 horsepower, marking a milestone in automotive application.^[2] The engine's development extended to aviation, with adaptations like the Wright Aeronautical RC2-60 in 1970 powering aircraft such as the Cessna Cardinal and Lockheed Q-Star, demonstrating displacements around 1 liter and outputs of 180-250 horsepower in liquid-cooled configurations weighing approximately 108 kg.^[4] Notable for its compact size—roughly half that of equivalent piston engines—and smooth, vibration-free operation due to only 154 moving parts compared to over 300 in a typical V8, the Wankel engine offers advantages in power-to-weight ratio (up to 1.8 hp per pound) and high-revving capability, making it suitable for applications in automobiles, motorcycles, snowmobiles, and auxiliary power units.^[2] However, challenges including apex seal wear limiting durability to around 100,000 miles, higher fuel consumption from chamber leakage, and elevated hydrocarbon emissions due to incomplete sealing have constrained its widespread adoption, though ongoing research into ceramic components and improved seals aims to address these issues.^[2]^[4] Despite economic and environmental hurdles in the 1970s oil crises, the design's innovative geometry continues to influence rotary engine variants in specialized fields like unmanned aerial vehicles and hybrid systems. As of 2025, companies like Mazda are developing Wankel variants for use as range extenders in electric vehicles.^[6]

History

Invention and early concepts

Felix Wankel, born in 1902 in Lahr, Germany, was a self-taught engineer who developed an early fascination with internal combustion engines during his apprenticeship as a publishing clerk. Without formal engineering training, he established a small laboratory in 1924 to pursue innovative engine designs, initially focusing on rotary mechanisms to replace traditional reciprocating pistons. His early work in the 1920s centered on rotary valve systems for motorcycle engines, aiming to improve efficiency and reduce mechanical complexity.^[7]^[8] Wankel's foundational concepts emerged from these experiments, leading to his first patent in 1929 (DRP 507584) for a pistonless internal combustion engine featuring a rotary valve mechanism that facilitated continuous fluid flow without conventional poppet valves. By the early 1950s, his designs evolved toward a circle-in-circle geometry, where an inner rotor orbited within an outer circular housing to create varying chamber volumes, inspired by principles from pumps and compressors. This configuration sought to enable smooth, uninterrupted rotation, eliminating the inertia losses associated with pistons and crankshafts in conventional engines.^[9]^[10] The seminal advancement came with Wankel's 1957 patent (filed February 4, 1957; US2988008A), which formalized the Wankel cycle using an epitrochoid-shaped housing, a three-apex triangular rotor, and integrated porting for intake, compression, combustion, and exhaust phases. This design maintained the core idea of continuous rotor motion at a 3:2 speed ratio relative to the eccentric shaft, theoretically offering advantages like higher power density, reduced vibration, and fewer moving parts compared to reciprocating engines. Wankel's collaboration with NSU Motorenwerke AG, initiated in 1951, led to refinements of these concepts through early experimental models, culminating in practical development.^[1]^[8]

NSU development and prototypes

NSU Motorenwerke AG initiated development of the Wankel rotary engine in 1951 through a collaboration agreement with inventor Felix Wankel, initially focused on adapting his rotary compressor concepts for engine applications.^[8] NSU engineers advanced the rotor design and overall architecture, transitioning from theoretical models to practical engineering refinements at their Neckarsulm facility.^[11] The milestone first working prototype, designated DKM 54, successfully ran on February 1, 1957, at NSU's research and development department, delivering 20 hp at 3,000 rpm in its single-rotor configuration.^[8] Early testing revealed significant challenges, particularly rapid wear on the apex seals, which limited continuous operation to just 15 hours before requiring maintenance.^[8] These issues highlighted the need for improved sealing materials and geometries, though definitive solutions remained elusive during initial phases. By the early 1960s, NSU progressed to more advanced prototypes, including the KKM series, with experiments in double-rotor setups to enhance power output and supercharging trials to boost performance beyond single-rotor limits.^[2] These efforts built on the DKM 54's foundation, incorporating refinements to housing and rotor dynamics while grappling with persistent apex seal durability problems in endurance tests.^[12] A pivotal public demonstration came in 1963 at the Frankfurt International Motor Show, where NSU unveiled the Spider prototype—a lightweight sports car powered by a single-rotor Wankel engine—marking the technology's transition from laboratory to viable automotive application.^[8]

Licensing and commercialization

In the early 1960s, NSU Motorenwerke AG actively pursued the commercialization of the Wankel rotary engine by licensing the technology to international manufacturers, recognizing its potential beyond in-house production. In 1958, NSU granted a license to the American firm Curtiss-Wright Corporation, which invested approximately $2 million to secure rights for development and production across automotive, aviation, and other applications.^[13] In 1965, NSU extended a licensing agreement to Rolls-Royce in the United Kingdom, which paid for access to the engine design for potential use in aircraft and automotive projects. These early deals marked the beginning of the Wankel's global dissemination, with NSU retaining control over core patents while sharing technical know-how to accelerate adoption. A pivotal agreement came in 1961 when NSU licensed the technology to Toyo Kogyo (later Mazda), following initial reluctance due to the Japanese company's limited resources. The deal, approved by Japan's Ministry of International Trade and Industry, involved an upfront fee of about ¥280 million (equivalent to roughly $780,000 at the time) plus ongoing royalties, enabling Mazda to begin prototyping in collaboration with NSU engineers. Mazda produced its first Wankel engine prototype by 1963, laying the groundwork for future rotary-powered vehicles, though full production would follow later. Other licensees, such as the East German motorcycle manufacturer MZ, also secured rights in 1960 to explore Wankel variants for two-wheeled applications, broadening the engine's experimental footprint. NSU's own entry into production underscored the technology's viability but highlighted adaptation hurdles for licensees. In 1964, NSU launched the Wankel Spider, the world's first series-production car with a rotary engine, featuring a single-rotor KKM unit displacing 498 cc and delivering 50 horsepower. This limited-run convertible, with around 2,375 units built through 1967, served as a proof-of-concept and generated licensing revenue, but international partners like Curtiss-Wright faced engineering challenges in scaling designs, including reconciling NSU's metric specifications with imperial standards prevalent in the U.S. market. These discrepancies complicated component fabrication and testing, contributing to delays in non-German implementations. Despite the influx of licensing fees, NSU grappled with escalating development costs and reliability issues, particularly apex seal wear in early Wankel engines, which eroded profitability. By the late 1960s, financial strains intensified as warranty claims mounted on rotary-equipped models like the 1967 Ro 80 sedan, which used a twin-rotor KKM variant producing 115 horsepower but suffered from premature failures. In 1969, facing insolvency, NSU merged with Volkswagenwerk AG, which acquired the company to gain access to Wankel technology and integrate NSU's operations with Auto Union. This merger effectively ended NSU's independent Wankel production, shifting oversight to Volkswagen while preserving licensing rights for ongoing global use. Mazda's subsequent refinements would prove instrumental in the engine's longevity, though details of their commercial triumphs emerged later.

Design and operation

Core components and geometry

The core of the Wankel engine consists of a triangular rotor housed within an epitrochoidal chamber, driven by an eccentric shaft that converts the rotor's orbital and rotational motion into output torque. The housing profile follows an epitrochoid curve, generated by a point tracing a path as a circle of radius r (the orbiting radius) rolls inside a fixed circle of radius R (the generating radius), with the eccentricity e defining the offset, where typically r = e and R = 2e for a standard 3:1 gear ratio configuration.^[14]^[15] The parametric equations for the housing curve in Cartesian coordinates are:

x = e \cos 3\theta + R \cos \theta

y = e \sin 3\theta + R \sin \theta

where \theta ranges from 0 to $2\pi, yielding the characteristic two-lobed epitrochoid shape that accommodates the rotor's motion while maintaining apex contact.^[14] The rotor is an equilateral triangular prism with curved flanks, its three apexes designed to follow the housing's epitrochoid profile exactly, ensuring constant sealing contact during operation. The apexes are positioned at 120-degree intervals around the rotor's centerline, with the rotor's generating radius R matching that of the housing to align the flanks parallel to the housing curve at contact points.^[14] The rotor's width w spans the housing's axial dimension, forming three variable-volume chambers as it moves. The eccentric shaft serves as both the rotor's journal and the engine's output shaft, featuring an offset lobe of radius e upon which the rotor bearing rides, enabling the combined orbital and rotational motion. To maintain proper phasing, an internal ring gear on the rotor meshes with a fixed gear mounted on the housing, typically in a 2:3 teeth ratio that results in the rotor rotating once for every three revolutions of the eccentric shaft in single-rotor designs; in twin-rotor configurations, the same 3:1 rotation ratio applies per rotor, with the two rotors mounted on phased eccentrics (60 degrees apart) on the shared output shaft for balanced operation.^[14]^[2] Intake and exhaust ports are machined into the housing's epitrochoidal surface, most commonly as peripheral ports located along the major axis for simplicity and flow characteristics, though side ports on the end housings are used in some designs to minimize port overlap. Optional auxiliary intake ports may be added near the primary intake for improved charging at high speeds.^[14]^[15] The engine's geometry defines fixed volume ratios critical to its displacement and compression. The minimum chamber volume V_{\min} occurs at apex-housing contact points, while the maximum intake volume V_i is set by the intake port's trailing edge position; compression volume V_c is the chamber volume at ignition timing, typically yielding compression ratios of 8:1 to 10:1 depending on flank curvature. The total displacement per rotor is given by $2 e R w, with precise volumes derived from the epitrochoid parameters.^[14]

Rotary cycle and sealing

The Wankel engine executes a four-stroke Otto cycle through the orbital motion of a triangular rotor within a trochoid housing, forming three variable-volume combustion chambers that sequentially undergo intake, compression, combustion, and exhaust phases. Unlike reciprocating engines, all phases occur continuously without reciprocating parts, enabling smoother operation. Each chamber completes one full cycle every 1080° of eccentric shaft rotation, equivalent to one rotor revolution.^[16]^[2] Intake begins as a rotor apex uncovers the intake port, allowing the air-fuel mixture to enter the expanding chamber while the opposite apex seals the exhaust port; this phase lasts approximately 360° of shaft rotation, with the chamber volume increasing from minimum to maximum. Compression follows as the rotor continues its motion, narrowing the chamber and raising the pressure until the spark plugs fire near the point of minimum volume, typically at around 10° before the compression peak. Combustion, or the power phase, occurs as the ignited mixture expands the chamber, driving the rotor and producing torque until the exhaust port opens; this expansion converts thermal energy into mechanical work across about 540° of shaft rotation. Exhaust concludes the cycle, with the contracting chamber expelling gases as the rotor apex uncovers the exhaust port, returning the volume toward minimum before the next intake.^[17]^[2] The rotor undergoes combined rotational and orbital motion around the eccentric shaft: it spins on its own axis while orbiting the housing perimeter, tracing an epitrochoid path that maintains contact with the housing surfaces. For every complete rotor orbit (360° rotor rotation), the eccentric shaft completes three full rotations (1080°), during which each of the three chambers experiences one power stroke, yielding three power impulses per rotor revolution—or one per shaft revolution—compared to one per two revolutions in a typical four-stroke piston engine. This motion ensures overlapping phases across chambers, with one always in expansion for continuous torque delivery. Over 360° of shaft rotation, the volumes of the three chambers cyclically vary: one expands for intake, another compresses, and the third expands post-combustion or exhausts, creating a dynamic sequence where total displacement sweeps through approximately one-third of the full cycle per chamber. Visualizations, such as animated diagrams, illustrate this by showing the rotor's wobbling path, with chamber lobes inflating and deflating like a peristaltic pump, highlighting the smooth volume transitions without discrete piston strokes.^[18]^[19] Sealing is critical to isolate the chambers and prevent gas leakage between phases. Apex seals, narrow spring-loaded strips at each rotor tip, maintain contact with the trochoid housing to seal radially against the curved surface. Side seals, positioned in grooves on the rotor's flat faces, press against the engine's side housings to seal axially and contain oil. Corner seals, small segments at the junctions, bridge gaps between apex and side seals, ensuring a continuous barrier around the rotor periphery. These mechanisms accommodate the rotor's complex motion, though they must endure high-speed sliding friction.^[20]^[2] Intake and exhaust ports, machined into the housing periphery or sides, are timed by the rotor's position rather than valves, allowing larger openings and greater intake-exhaust overlap—up to 100° or more in peripheral-port designs—compared to the limited 20-60° overlap in piston engines constrained by valve trains. This facilitates improved scavenging at high speeds, enhancing volumetric efficiency and airflow capacity by promoting fresh charge induction while residual exhaust aids turbine spool-up in turbocharged setups, without the inertia or complexity of poppet valves.^[17]^[21]

Torque delivery and power output

The Wankel engine's torque delivery arises from the tangential force exerted on the rotor flanks during the combustion expansion phase, which spans about 270 degrees of rotor rotation or 90 degrees of output shaft rotation. This relatively short combustion stroke results in torque that peaks early in the RPM range, typically around 3,000–4,000 rpm, followed by a narrow but relatively flat torque band that favors high-revving operation over low-end grunt.^[22] The design enables exceptional RPM capability, with production engines reliably operating up to 8,000 rpm and racing variants exceeding 10,000 rpm, though the overall torque curve remains narrower than that of equivalent reciprocating piston engines due to the continuous but brief power impulses.^[23] Power output in the Wankel engine follows the general form P = \frac{[IMEP](/page/Mean_effective_pressure) \times [V_d](/page/Displacement) \times N \times k}{c}, where P is power, IMEP is indicated mean effective pressure, V_d is total displacement, N is engine speed in RPM, k is a factor for power stroke frequency (1 per shaft revolution per rotor), and c is a constant (typically 5252 for hp units). This yields specific power densities approximately 1.5 times higher than comparable four-stroke piston engines per unit displacement, driven by the rotary's higher achievable RPM and more uniform torque delivery without reciprocating masses.^[24]^[23] In multi-rotor configurations, power scales nearly linearly with the number of rotors, as additional units stack along the shared eccentric shaft, doubling output for a two-rotor setup compared to a single-rotor without proportionally increasing overall engine volume or weight. A three-rotor design further improves rotational balance and smoothness, akin to a V8 or inline-six piston engine, while enhancing total power.^[22] The equivalent displacement V_d for a Wankel engine is defined as V_d = 2 e R w \times n, where n is the number of rotors; this represents the total inducted volume per shaft revolution. For instance, the Mazda 13B two-rotor engine, with an equivalent displacement of 1.3 L, delivers around 130 hp at 6,500 rpm.^[23]

Technical challenges

Materials and durability

The rotor housing in Wankel engines is typically constructed from cast iron or aluminum alloys to balance strength, weight, and heat dissipation requirements. Cast iron housings provide excellent wear resistance and thermal stability, while aluminum variants reduce overall engine weight but necessitate additional treatments for durability. To enhance wear resistance against the sliding contact with rotor apexes, the internal surfaces are often chrome-plated, forming a hard, low-friction layer that minimizes abrasion under high-speed operation.^[10]^[25] The rotor itself is generally made from carbon steel or aluminum, chosen for their machinability and ability to withstand cyclic thermal and mechanical stresses. The apex regions of the rotor, where contact with the housing is most intense, incorporate stainless steel inserts to improve hardness and resistance to wear at elevated temperatures. These material selections help maintain structural integrity during the rotor's orbital and rotational motions.^[26]^[27] The eccentric shaft, which drives the rotor's motion, is forged from high-strength steel, often chrome-molybdenum alloys, to endure torsional loads and fatigue. Internal oil passages and jet cooling systems are integrated to manage heat buildup, ensuring consistent lubrication and preventing overheating in the shaft bearings.^[28] Material compatibility is critical for operational reliability, particularly in managing thermal expansion. The rotor's coefficient of thermal expansion is approximately 11 × 10^{-6}/°C, while the housing's is around 12 × 10^{-6}/°C for cast iron variants, allowing close dimensional matching to preserve clearances under varying temperatures. In aluminum-housed designs, the higher expansion rate of the housing (up to 23 × 10^{-6}/°C) relative to the iron or steel rotor intentionally creates a looser fit when cold, tightening as the engine warms to optimize sealing without seizure.^[26]^[29] Early Wankel engines suffered from limited durability, often requiring overhaul after about 50,000 km due to apex and housing wear. Advancements in chrome plating, ceramic coatings, and material refinements have extended service life to over 150,000 km in modern implementations, with rigorous testing demonstrating endurance beyond 300 hours of continuous operation under load. Seal materials are integrated with these coatings to further enhance longevity, though detailed seal evolution is addressed elsewhere.^[28]^[29]

Sealing systems evolution

The development of sealing systems in the Wankel engine began with the original NSU prototypes in the 1950s, which employed spring-loaded apex seals made of cast iron to maintain contact between the rotor's apexes and the trochoidal housing bore. These seals were designed to slide radially within grooves at each rotor corner, pressed outward by coil springs to compensate for wear and thermal expansion, ensuring gas-tight compartments during the engine's rotary cycle. However, the cast iron material, while durable against detonation, suffered from high friction and rapid wear against the chrome-plated aluminum housings used in early designs like the NSU Spider, leading to frequent leakage and the need for engine teardowns after relatively short operation.^[30] Mazda, licensing the technology in the early 1960s, focused on material innovations to address these shortcomings, introducing aluminum-impregnated carbon apex seals that reduced weight and friction while improving sealing efficiency in production engines like the 1967 Cosmo. In the 1970s, Mazda transitioned to carbon fiber composites such as pyrographite for greater flexibility and longevity. These composite seals, reinforced with high-strength fibers, minimized chipping—a common failure mode in brittle cast iron—and allowed for thinner profiles that lowered inertial loads, contributing to smoother operation in vehicles like the RX-7 series. Later iterations in the 1980s and 1990s incorporated ceramic reinforcements, such as silicon nitride with carbide whiskers, for racing variants, balancing extreme temperature tolerance with reduced wear rates.^[31]^[32]^[33] Face seals, responsible for sealing the rotor's flat sides against the end housings, evolved from simple spring-loaded designs to more sophisticated oil-controlled variants to manage axial leakage and lubrication. In early NSU engines, these side seals consisted of rectangular strips pressed by coil springs, with oil injected via metering ports to form a thin film that both lubricated the contact surfaces and controlled metering to prevent excessive consumption. Mazda refined this by integrating oil control rings—thin, spring-backed barriers that regulated oil flow into the seal grooves—reducing metering rates by up to 50% compared to NSU's approach and mitigating carbon buildup. Alternative labyrinth-type face seals, featuring non-contact grooves that create tortuous paths for gas escape, emerged in specialized applications for the rotor-to-eccentric shaft interface, minimizing wear in high-speed scenarios while avoiding the need for direct contact. These designs prioritized low-friction operation, with oil-controlled springs dominating automotive use for their balance of sealing and cooling.^[33]^[12] The primary leakage paths in Wankel engines are categorized into three types: apex-to-side housing leakage, where gas escapes around the rotor corners due to imperfect apex seal contact; side-to-housing leakage across the rotor faces from axial gaps; and rotor-to-shaft leakage through the eccentric shaft bearings, often via inadequate oil or gas barriers. Apex seal leakage accounts for the majority (approximately 70%) of total blow-by, exacerbated by the seals' complex motion path, while side and shaft paths contribute to efficiency losses through uneven pressure distribution. Innovations like tighter groove tolerances and adaptive spring tensions targeted these paths, progressively reducing volumetric losses from over 10% in early prototypes to under 5% in refined Mazda designs.^[34]^[35] Over time, sealing system evolution markedly improved durability metrics, with early NSU cast iron apex seals lasting only about 10,000 km before significant wear or chipping necessitated replacement, often due to thermal stresses causing seal fragmentation. By the 1980s, Mazda's carbon fiber and ceramic composites extended apex seal life to over 100,000 km in production engines, with failure modes shifting from chipping to gradual abrasion, achievable through better material contributions like fiber reinforcement for impact resistance. These advancements not only enhanced reliability but also supported higher power densities without proportional increases in leakage.^[30]^[31]^[36]

Combustion and efficiency

The combustion process in the Wankel engine is characterized by a uniquely shaped chamber that poses significant challenges to efficient flame propagation. The elongated and narrow geometry of the combustion pocket results in a longer flame travel distance compared to reciprocating piston engines, leading to slower burning rates and incomplete combustion in certain regions.^[29] This design also features a high surface-to-volume ratio, which exacerbates heat losses and promotes flame quenching, particularly at the trailing edges where squish flows generate high velocities but limited turbulence for flame support.^[29] Additionally, the inherent low squish effect in the Wankel configuration—due to the absence of a reciprocating piston—limits the intensification of mixture motion near the spark plug, further hindering rapid and uniform ignition.^[29] Thermal efficiency in the Wankel engine follows the ideal Otto cycle approximation, given by \eta = 1 - (1/r)^{\gamma-1}, where r is the compression ratio and \gamma is the specific heat ratio, but real-world performance is substantially reduced by the aforementioned heat transfer and combustion inefficiencies.^[19] Typical brake thermal efficiencies for conventional Wankel designs range from 25-34%, comparable to equivalent gasoline piston engines, primarily owing to elevated wall heat losses that account for up to 20% of the fuel energy input.^[37] These losses stem from the engine's large wetted surface area and the thin boundary layer in the rotor housing, which conducts heat away more readily during the expansion stroke.^[29] Efforts to improve combustion completeness and efficiency have included stratified charge strategies, which aim to create a richer mixture near the ignition source while maintaining overall lean operation for better fuel-air mixing. In the mid-1960s, Curtiss-Wright explored direct-injection stratified charge configurations in prototype Wankel engines to enhance flame stability and reduce unburned hydrocarbons, achieving gains of up to 10% in combustion efficiency at high loads through improved stratification.^[29] Such approaches, including upstream fuel injection, have demonstrated up to 9% better combustion efficiency at high loads by promoting faster flame kernel development in the elongated chamber.^[29] A notable efficiency penalty arises from the need for oil injection to lubricate the side and apex seals, as the Wankel design lacks traditional piston rings and relies on apex seals sliding against the housing. This practice results in 10-20% of the injected oil burning in the combustion chamber, contributing to higher fuel dilution and reduced thermal efficiency through incomplete combustion of the oil-fuel mixture.^[29] Modern advancements leverage computational fluid dynamics (CFD) modeling to optimize chamber geometry and flow patterns, simulating full-cycle combustion to minimize unburnt pockets and heat losses—for instance, by refining rotor pocket shapes and ignition timing for UAV applications.

Performance characteristics

Displacement equivalence

The displacement of a Wankel engine is determined by the formula V_d = V_h \times N_r, where V_d is the total displacement, V_h is the working volume per rotor (twice the maximum volume enclosed by a single rotor face and the housing), and N_r is the number of rotors. This calculation accounts for the effective swept volume across the engine's geometry, providing a standardized measure for comparison with reciprocating piston engines. For a single-rotor configuration, the displacement is V_h, reflecting the three effective combustion events per eccentric shaft revolution due to the rotor's three faces. In a two-rotor setup, it becomes V_d = 2 \times V_h, as each rotor contributes independently with offset phasing.^[38] This equivalence convention ensures fair assessment of performance potential, as the Wankel produces three power pulses per rotor per eccentric shaft revolution—more frequent than the one power stroke every two revolutions in a four-stroke piston engine. For instance, the Mazda 10A, a two-rotor engine with a working volume per rotor of approximately 491 cc, yields an actual displacement of 982 cc but is rated as a 1.0 L equivalent for regulatory and marketing purposes. Equivalence multipliers vary by context: for example, some jurisdictions and racing bodies (e.g., SCCA) use 1.5× or 2× the conventional displacement to compare with piston engines for taxation, emissions, or classing.^[39] Similarly, the NSU Ro 80's two-rotor design features a working volume per rotor of about 497.5 cc, resulting in 995 cc actual displacement, also denominated as a 1.0 L equivalent.^[40] Regulatory approaches to displacement vary by jurisdiction, influencing taxation and emissions classification. In Japan, engines are taxed based on actual physical volume, which allowed early Mazda rotaries like the 10A to qualify for lower rates by falling under 1.0 L thresholds despite their performance.^[41] In the United States, equivalence factors are applied for performance benchmarking and certain federal standards, often treating Wankel displacement as approximately 1.5–2 times that of a piston engine for comparable output to account for the rotary's higher firing frequency.^[42] This equivalence underscores the Wankel's superior power density, typically around 100 hp per liter of equivalent displacement, versus 70 hp/L for piston engines of the era. The Mazda 10A, for example, delivered about 100–110 hp from its 1.0 L rating, while the NSU Ro 80 achieved 115 hp from the same equivalent size, highlighting the design's efficiency in torque delivery without delving into detailed power derivations.^[43]^[44]

Fuel economy and emissions

The Wankel engine generally demonstrates fuel economy 15-25% inferior to equivalent reciprocating piston engines, stemming from its higher surface-to-volume ratio, which promotes greater heat losses and less efficient combustion processes.^[45] In early applications, such as 1970s Mazda rotary-powered vehicles in the 2750 lb weight class, EPA testing recorded figures as low as 10.6 to 11.0 mpg, reflecting urban driving conditions typical of the era.^[46] By the late 1970s and 1980s, improvements in tuning and thermal management yielded modest gains; for instance, the 1980 Mazda RX-7 achieved EPA ratings of 16 mpg city and 25 mpg highway.^[47] Subsequent models incorporated refinements like lean-burn configurations and better port designs, yet fuel consumption remained a challenge. The 1993 Mazda RX-7, for example, posted an EPA combined rating of 18 mpg, underscoring persistent thirstiness relative to piston counterparts in similar sports car segments.^[48] These metrics highlight how Wankel engines prioritized power density over efficiency, often requiring premium fuel and frequent apex seal maintenance to mitigate oil dilution effects on consumption. Emissions from the Wankel engine are characterized by elevated hydrocarbon (HC) and carbon monoxide (CO) outputs compared to reciprocating engines, largely due to quench zones in the elongated combustion chamber that hinder complete flame quenching and promote unburnt fuel escape—issues rooted in the engine's combustion dynamics.^[49] Without aftertreatment, HC levels could reach several times those of piston engines, while CO emissions were comparably high but NOx remained lower owing to cooler combustion temperatures.^[49] To comply with tightening 1970s regulations like the U.S. Clean Air Act and Japan's Muskie standards, Mazda adapted catalytic converters for the 12A and 13B engines starting around 1974, enabling oxidation of HC and CO by running leaner air-fuel mixtures.^[32] Exhaust gas recirculation (EGR) systems were simultaneously integrated to dilute intake charge and suppress NOx formation, with early implementations on models like the RX-3 achieving certification through combined thermal reactors and catalysts.^[50] These measures reduced raw emissions by up to 80% in controlled tests, though real-world performance varied with seal integrity and load. Regarding greenhouse gases, CO2 emissions per unit of power output align closely with those of piston engines, as both rely on similar stoichiometric combustion of hydrocarbons.^[45] However, the Wankel's higher volumetric fuel consumption translates to elevated CO2 per mile traveled; for instance, a typical 1970s Mazda rotary vehicle emitted approximately 20-30% more CO2 than a piston equivalent over standard drive cycles due to its 10-15 mpg city efficiency.^[46] Regulatory focus on tailpipe pollutants in that era overshadowed CO2, but modern assessments underscore this as a key limitation for broader adoption.

Advantages over reciprocating engines

The Wankel engine offers significant advantages in compactness and weight savings compared to reciprocating piston engines of equivalent power. Due to its rotary design with fewer moving parts and a more streamlined geometry, it achieves a higher power-to-weight ratio, often around 50% lighter for similar output; for instance, Mazda's 12A two-rotor engine weighs approximately 130 kg, while a comparable 2.0-liter V6 piston engine typically exceeds 200 kg.^[51]^[29] This reduced size and mass enable easier packaging in vehicles, contributing to improved overall vehicle dynamics and fuel efficiency through lower inertial loads.^[17] A primary benefit of the Wankel design is its exceptionally smooth operation, stemming from the absence of reciprocating components like pistons and connecting rods, which eliminates the vibrational forces inherent in piston engines.^[52] Instead, the rotor's orbital motion provides continuous rotation, delivering power impulses—three per eccentric shaft revolution for a single rotor (one per face), or six for a two-rotor configuration with offset phasing—resulting in balanced torque delivery without the harshness of linear motion.^[29] This inherent balance leads to lower overall vibration levels, enhancing passenger comfort and reducing wear on engine mounts.^[17] The Wankel engine excels in high-revving performance, capable of redlines exceeding 9,000 rpm in production applications like Mazda's RX series, far surpassing typical piston engine limits of 6,000–7,000 rpm without extensive balancing modifications.^[53] This ability arises from the rotary mechanism's lower reciprocating mass and reduced inertial forces at speed, allowing sustained high RPM for greater power extraction and a responsive, "rev-happy" driving character.^[52] Noise, vibration, and harshness (NVH) characteristics are notably improved in Wankel engines, particularly at idle, where the smooth rotary motion produces a quieter, more refined sound profile than the characteristic rumble of idling piston engines.^[29] This low-NVH quality makes it suitable for luxury and sports vehicle applications, minimizing transmitted vibrations and contributing to a more serene cabin environment.^[17] The valvetrain in a Wankel engine is fundamentally simpler than in reciprocating designs, as it eliminates the need for camshafts, valves, springs, and timing mechanisms; intake and exhaust are managed via ports in the housing, controlled by the rotor's position.^[52] This port-based system reduces mechanical complexity, lowers part count, and decreases potential failure points, while enabling higher airflow at elevated RPMs without valvetrain float issues common in piston engines.^[29]

Disadvantages and mitigations

The Wankel engine's apex seals represent its primary failure mode, as wear at the contact interface with the trochoidal housing leads to gas leakage between combustion chambers, contaminating the intake charge and reducing power output.^[54] This wear arises from high sliding speeds, elevated temperatures, and insufficient lubrication, often resulting in seal chatter or complete breakdown under prolonged operation.^[23] To mitigate this, engineers in the 1980s introduced ceramic materials and coatings for apex seals, enhancing wear resistance through improved hardness and thermal stability while reducing friction losses.^[23] These advancements, tested in NASA programs, allowed seals to achieve durability comparable to piston rings in some applications, extending engine life beyond 100,000 miles in optimized designs.^[2] High oil consumption has long plagued Wankel engines, with early models requiring premixed fuel and oil at rates up to 1 liter per 10,000 kilometers to lubricate seals and maintain compression.^[55] This inefficiency stemmed from the engine's reliance on oil films for sealing the expansive rotor-housing interface, leading to partial combustion of lubricant and increased emissions. In the 1970s, Mazda eliminated premixing by adopting oil metering injection systems directly into the intake ports, reducing consumption by injecting precise amounts only as needed for lubrication.^[55] Further refinements, including oil coolers and synthetic lubricants, stabilized levels to under 0.5 liters per 10,000 kilometers in later iterations.^[2] Torque delivery in the Wankel engine is uneven, with power generated over approximately two-thirds of each crankshaft revolution, creating pulsations that can cause vibrations and stress on drivetrain components.^[2] These fluctuations, more pronounced in single-rotor configurations, arise from the intermittent combustion cycle inherent to the rotary design. Mitigations include heavier flywheels to store and release rotational energy, smoothing output at the cost of added weight, and multi-rotor setups that overlap firing intervals for more consistent torque.^[2] Dual-rotor engines, for instance, reduce pulsations by 50% compared to single-rotor variants, improving drivability in automotive applications.^[2] Heat management poses another challenge, as combustion generates uneven thermal loads, with hotspots near exhaust ports causing housing distortion and accelerated seal wear.^[2] Early air-cooled designs exacerbated this, leading to sealing failures and reduced efficiency. Water-cooled housings became standard by the 1970s, featuring axial-flow coolant passages that direct fluid from high-heat zones to cooler areas, maintaining uniform temperatures across the trochoid surface.^[2] This approach, detailed in patents for circumferential flow systems, improved thermal efficiency by up to 10% and extended component life.^[56] Over time, these mitigations culminated in designs like Mazda's Renesis engine introduced in 2003, which adopted side exhaust ports to eliminate intake-exhaust overlap, enhancing thermal efficiency and reducing fuel consumption by 8-15% over prior models. The side-port configuration also enlarged the intake area by 30%, boosting volumetric efficiency while addressing historical sealing and lubrication issues through refined oil injection and material upgrades. These evolutions demonstrate progressive refinements that have made the Wankel more viable for niche applications despite persistent challenges.

Applications

Automotive implementations

The NSU Ro 80, introduced in 1967, was the first production sedan powered by a twin-rotor Wankel engine, featuring a 995 cc displacement unit producing 115 horsepower. Approximately 37,402 units were produced between 1967 and 1977, but the model suffered from significant reliability issues, particularly with apex seals that often failed before 35,000 miles, leading to frequent engine rebuilds and customer dissatisfaction. These problems contributed to NSU's financial collapse, prompting Volkswagen to acquire the company in 1969; subsequent lawsuits, including a 1975 U.S. federal case by distributor Overseas Motors against Audi NSU and Volkswagen over misrepresented vehicle quality and warranty obligations, further highlighted the engine's durability shortcomings.^[57]^[58]^[59] Mazda pioneered widespread automotive adoption of the Wankel engine with the 1967 Cosmo Sport, a two-door coupe equipped with a 491 cc twin-rotor engine delivering 110 horsepower, of which about 1,176 units were built through 1972. The company expanded its rotary lineup with the RX-7 sports car series, launched in 1978 and produced until 2002, achieving over 811,000 units sold globally across three generations, renowned for its lightweight design and high-revving performance. The RX-8, introduced in 2003 as a four-door sports coupe with a Renesis two-rotor engine, marked Mazda's final mass-market rotary passenger car, with 192,094 units manufactured until production ended in 2012 amid tightening emissions standards.^[60]^[61]^[62] Citroën briefly ventured into Wankel production with the 1973 GS Birotor, a variant of its GS hatchback featuring a twin-rotor engine rated at 106 horsepower, intended to enhance performance while retaining the model's hydropneumatic suspension. Only 847 units were produced before discontinuation in 1975, as the 1973 oil crisis exacerbated the rotary's poor fuel economy—around 15 mpg—and highlighted its high operating costs, leading Citroën to abandon the project.^[63]^[64] Mercedes-Benz explored Wankel technology through the C111 experimental series in the 1970s, with 17 prototypes built between 1969 and 1976, most powered by three- or four-rotor engines producing up to 350 horsepower for high-speed testing. These fiberglass-bodied coupes achieved speeds exceeding 250 mph but never entered production due to unresolved sealing and emissions challenges.^[65]^[66] Other manufacturers conducted limited Wankel trials without committing to production. General Motors licensed the technology in the early 1970s, planning a twin-rotor variant for the Chevrolet Vega subcompact to meet emissions rules, but abandoned the effort in 1974 after prototype testing revealed inadequate fuel efficiency and durability. Ford experimented with a single rotary-powered 1965 Mustang prototype developed by Curtiss-Wright, featuring a 240 cubic-inch twin-rotor engine, though it remained a one-off demonstrator without further development.^[67] In racing, Mazda's Wankel engines achieved their pinnacle with the 787B prototype, which secured victory at the 1991 24 Hours of Le Mans—the only rotary-powered car to win the event—thanks to its reliable four-rotor R26B engine producing over 700 horsepower and superior fuel efficiency under race regulations.^[68]

Motorcycle and small vehicle uses

The Wankel engine's compact design and high power-to-weight ratio made it appealing for motorcycles, where space constraints and the need for smooth, high-revving performance were critical, allowing for lighter frames compared to traditional piston engines.^[69] Early adopters in the 1960s and 1970s experimented with rotary power for two-wheeled vehicles, though challenges like sealing durability and vibration limited widespread adoption.^[70] One of the first production Wankel motorcycles was the Hercules W-2000, introduced in 1974 by the German firm Fichtel & Sachs under license from NSU, featuring a 294 cc single-rotor air-cooled engine producing 20 hp initially, later upgraded to 32 hp.^[69] Approximately 1,500 units were built through 1976, praised for its low vibration and smoothness but hampered by apex seal wear and high maintenance costs.^[69] The engine's transverse mounting contributed to the bike's balanced handling, emphasizing the rotary's suitability for lightweight applications.^[71] Norton, licensing the Wankel in 1967, developed the rotary for motorcycles during the late 1960s and 1970s, culminating in the Commander (also known as the F1) with a 588 cc twin-rotor air-cooled engine.^[70] Early prototypes suffered from torsional vibration that limited engine life to about 5 hours, necessitating a redesign with improved balancing and liquid cooling in later models.^[70] Production from 1983 to 1985 totaled around 500 units, delivering 85 hp and highlighting the engine's potential for high-revving performance in compact chassis, though fuel inefficiency curbed commercial success.^[70] Suzuki entered the market with the RE5 in 1974, the first Japanese production rotary motorcycle, powered by a liquid-cooled 497 cc single-rotor engine producing 62 hp at 6,500 rpm.^[72] Approximately 6,350 units were manufactured through 1976, with a dry weight of 230 kg that made it heavier than contemporaries like the Honda CB750.^[73]^[74] The RE5's smooth power delivery suited urban and highway riding, but overheating issues and complex oil injection systems led to reliability concerns and its discontinuation.^[72] Yamaha showcased the RZ201 prototype at the 1972 Tokyo Motor Show, featuring a water-cooled 660 cc twin-rotor engine equivalent to about 350 cc in piston terms, producing 66 hp.^[75] Intended for the Japanese market in the early 1980s, only a handful of prototypes were built due to sealing and emissions challenges, preventing full production.^[75] The Dutch Van Veen OCR-1000, produced from 1974 to 1978, utilized a liquid-cooled 996 cc twin-rotor Comotor engine derived from Citroën's automotive rotary, delivering 100 hp at 6,500 rpm.^[76] Only 38 units were made, with a claimed top speed of 135 mph, underscoring the Wankel's compactness for high-performance superbikes but limited by high costs and parts availability.^[77]^[76] Beyond motorcycles, Wankel engines saw limited use in small vehicles like personal watercraft and snowmobiles during the 1970s, leveraging their lightweight design for recreational applications. Outboard motors, such as the Sachs Mac-10 introduced in the late 1960s and early 1970s, featured a 10 hp single-rotor unit but achieved only niche production due to sealing wear in marine environments.^[78] Snowmobiles like Arctic Cat's 1971-1972 models used 303 cc Sachs rotaries producing 18-20 hp, while OMC's 35 hp twin-rotor engine powered select 1972-1974 machines, totaling limited runs of a few thousand units before emissions regulations and reliability issues halted further development.^[79]^[80] These applications demonstrated the engine's vibration-free operation in compact, high-maneuverability vehicles but were constrained by fuel economy and durability demands.^[80]

Aviation and other specialized applications

The Wankel engine's compact design and favorable power-to-weight ratio have made it appealing for aviation applications, particularly in light aircraft and homebuilt planes where weight savings are critical. In the 1980s, the Swiss-developed Mistral G-200, a 200-horsepower naturally aspirated rotary engine based on Mazda technology, was employed in experimental and homebuilt aircraft, offering multi-fuel capability including jet fuel or mogas while reducing emissions compared to traditional piston engines.^[81] Similarly, early versions of the Diamond DA20 Katana trainer featured a Diamond-manufactured Wankel rotary engine producing around 80 horsepower, providing smooth operation and low vibration for primary flight training before the model transitioned to piston powerplants.^[82] These implementations highlighted the engine's advantages in aviation, such as simpler installation and quieter performance, though challenges like sealing durability limited widespread adoption. In unmanned aerial vehicles (UAVs), Wankel-derived rotary engines have seen renewed interest due to their high power density and ability to run on heavy fuels like diesel or jet fuel, essential for military and long-endurance missions. The LiquidPiston XTS-210, a 25-horsepower supercharged two-stroke rotary engine weighing 42 pounds (19 kg), represents a modern evolution of Wankel principles with an "inside-out" design that improves efficiency and lubrication; it has been integrated into hybrid-electric UAV prototypes for U.S. military applications in the 2020s, enabling extended range and reduced size.^[83] As of 2025, the engine powers U.S. Army hybrid-electric UAV prototypes and auxiliary power units for mobile command posts, enabling extended endurance and reduced acoustic signatures.^[84] This growth aligns with broader market trends toward rotary power for drones, where compactness supports payload and endurance requirements.^[85] Beyond aviation, Wankel engines have been explored in niche industrial and recreational applications leveraging their lightweight construction. Experimental Soviet rotary engine units from the 1970s, developed under programs like VAZ-311, were tested in various transport prototypes including rail concepts but were ultimately abandoned due to reliability issues and fuel inefficiency.^[86] In go-karts, engines like the Aixro XR-50, a 50-horsepower four-stroke Wankel producing over 100 horsepower per liter, have powered high-performance shifter karts, delivering rapid acceleration without the vibration of piston alternatives.^[87] Prototype chainsaws, such as the Sachs-Dolmar KMS-4 from the 1970s with a 58cc Wankel rotor providing 4.4 horsepower, demonstrated reduced vibration for operator comfort but saw limited production due to high fuel consumption and maintenance needs.^[88] Additionally, Wankel variants appear in conceptual range extender systems for hybrid vehicles and generators, where their quick throttle response and small footprint generate electricity on demand without direct drive.^[89] Regarding safety certifications, select Wankel aviation engines have pursued FAA approvals, with models like the Mistral G-300 advancing toward type certification in the late 2000s for certified aircraft installations, though full approval was not achieved before the program's cessation; experimental category use in homebuilts remains common under FAA supplemental type certificates.

Modern developments

Alternative fuel adaptations

The Wankel engine has been adapted for hydrogen fuel since the 1970s, with Mazda developing prototypes that demonstrated its suitability for hydrogen combustion due to the engine's ability to handle high flame speeds and wide flammability limits of the fuel.^[90] These adaptations often incorporate lean-burn strategies, which enable low NOx emissions by operating at equivalence ratios below 0.5, while achieving higher thermal efficiency compared to gasoline operation.^[91] Recent studies, including large-eddy simulations and experimental evaluations of hydrogen-enriched rotary engines, confirm that hydrogen fueling maintains or improves overall system efficiency without significant losses, even in blends with natural gas.^[92]^[93] Multifuel capabilities in Wankel engines have been explored for military and aviation applications, allowing operation on varied fuels such as diesel and kerosene through port fuel injection systems that accommodate different viscosities and ignition properties.^[94] Curtiss-Wright's RC2-60 series, adapted for aircraft testing in the 1970s, exemplified this versatility by demonstrating reliable performance across fuel types in prototypes designed for general aviation, though fuel economy varied compared to dedicated gasoline setups.^[95] These multifuel designs prioritize robustness in remote or logistical-challenged environments, with injection timing adjustments ensuring stable combustion across hydrocarbons.^[94] Efforts to implement compression ignition in Wankel engines, such as diesel variants developed by Norton in the 1970s, aimed for higher compression ratios around 18:1 to support autoignition, but encountered persistent challenges with apex and side seals under elevated pressures, leading to accelerated wear and leakage. The inherent geometry of the Wankel, with its fixed housing and moving rotor, limits practical compression ratios for diesel operation compared to reciprocating engines, often resulting in incomplete combustion or mechanical failures in experimental units.^[96] Experimental laser ignition systems, tested in Wankel engines during the 2010s, offer improved combustion control by enabling precise plasma formation for ignition, which enhances flame propagation and reduces cycle-to-cycle variability.^[97] These systems have shown potential for NOx emission reductions through optimized timing that minimizes peak temperatures, with initial tests indicating benefits across fuel mixtures including hydrogen blends.^[98]

Range extender and hybrid integrations

The Wankel engine has been adapted as a range extender in hybrid and electric vehicle architectures, functioning as an auxiliary power unit (APU) to generate electricity for battery charging without directly driving the wheels. This series-hybrid configuration leverages the engine's compact design, where a single-rotor variant can produce around 30 kW of output while occupying approximately 50% less volume than an equivalent piston engine, enabling smaller packaging in vehicle platforms.^[99]^[100] Mazda pioneered a modern application with the MX-30 R-EV, a plug-in hybrid SUV launched in Japan in 2020, featuring an 830 cc single-rotor Wankel engine as a generator delivering 55 kW to extend the vehicle's electric range. The system provides an initial battery-only range of about 85 km (WLTP), with the rotary engaging to recharge the 17.8 kWh battery for a total combined range exceeding 600 km, emphasizing the engine's role in addressing EV range anxiety without compromising electric drivetrain efficiency.^[101]^[102] In February 2024, Mazda established a dedicated Rotary Engine Development Group to advance Wankel technology specifically for EV range extenders, signaling a revival amid growing hybrid demand. This initiative explores integrations like a potential MX-5 hybrid, building on the MX-30's success to incorporate the engine in lighter sports car applications for enhanced responsiveness.^[103] Beyond Mazda, LiquidPiston's High Efficiency Hybrid Cycle (HEHC) rotary engine, an evolution of Wankel principles, supports heavy-fuel operations for military hybrid systems, offering compact power generation up to 25 kW in unmanned vehicles and APUs. Earlier efforts include BMW's 1970s prototypes exploring Wankel engines in experimental hybrid setups, though these did not reach production. The Wankel design's benefits in these roles include rapid throttle response, allowing quick activation to maintain EV charging rates during high-demand scenarios.^[104]^[105]^[106] In 2024, LiquidPiston secured a Small Business Innovation Research (SBIR) CATALYST award from the U.S. Army to develop an ultra-compact auxiliary power unit for mobile command posts, building on prior agreements totaling over $9 million for heavy-fueled rotary prototypes.^[84]

Market trends and future prospects

The global Wankel engine market was valued at approximately $47 million in 2023 and is projected to reach $100.4 million by 2033, growing at a compound annual growth rate (CAGR) of around 7.9%.^[107] This expansion is largely propelled by demand in unmanned aerial vehicles (UAVs), which account for a substantial portion of applications due to the engine's compact size and high power-to-weight ratio.^[108] For instance, the UAV-specific Wankel engine segment was valued at $45 million in 2024 and is expected to grow to $85 million by 2033.^[108] Key market drivers include surging demand from drone and military sectors, exemplified by multiple U.S. Department of Defense (DoD) contracts awarded to LiquidPiston for its rotary engine technologies.^[109] Additionally, the revival of Wankel engines as range extenders in electric vehicles (EVs) is gaining traction, particularly through Mazda's MX-30 R-EV model, which integrates a single-rotor Wankel to extend driving range beyond 600 km while addressing battery limitations.^[110] Despite these opportunities, the market faces significant challenges from the accelerating shift toward fully electric vehicles, which is diminishing traditional automotive applications for internal combustion engines like the Wankel.^[111] Stringent emissions regulations, such as evolving EPA greenhouse gas standards for 2027–2032 and EU norms, further favor battery-electric alternatives over rotary designs due to persistent issues with hydrocarbon and NOx emissions in Wankel engines.^[112] Looking ahead, hydrogen-fueled Wankel engines show promise for aviation, with 2025 studies highlighting improved thermal efficiency and reduced emissions compared to conventional fuels.^[113] Experimental analyses indicate that hydrogen combustion in rotary configurations can achieve up to 20.7% higher indicated power in high-altitude operations.^[114] As of November 2025, Mazda's plans for a two-rotor Wankel in a sports car like the Iconic SP concept remain under consideration but face significant financial and prioritization challenges, with no confirmed production timeline despite earlier interest in outputs over 350 hp.^[115]

References

[1]
US2988008A - Rotary piston machines - Google Patents
A rotary mechanism for pumps, fluid motors, combustion engines or the like; said mechanism comprising an outer body having a cavity and an inner body received ...
[2]
[PDF] The Rotary Engine: Principles and Operations - UNI ScholarWorks
Jan 2, 2023 · Abstract. This study will be concerned with tracing the development of the rotary engine and to help prepare a unit.
[3]
[PDF] Wankel engine - CORE
The conventional reciprocating internal combustion engine suffers from several fundamental shortcomings. A major loss of power occurs during the conversion of ...
[4]
Wright Aeronautical (Wankel) RC2-60 Rotary Engine
German engineer Felix Wankel conceived his rotary engine in 1924 and patented it in 1936. It featured a triangular cam connected to the drive shaft.
[5]
Rotary engine inventor Felix Wankel dies | October 9, 1988 | HISTORY
Nov 13, 2009 · The German engineer Felix Wankel, inventor of a rotary engine that will be used in race cars, dies on October 9, 1988, in Lahr, Germany.Missing: taught 1920s<|control11|><|separator|>
[6]
Sporty, beautiful, and innovative: the NSU/Wankel Spider
Sep 27, 2023 · Initially self-taught, Wankel began experimenting with rotary valve control for a motorcycle engine in the late 1920s. In 1934, the first ...Missing: background | Show results with:background
[7]
Resilient Rotary - Automotive Hall of Fame
Nov 4, 2015 · Felix Wankel (1902-1988) received his first patent for a piston-less internal combustion engine in 1929. Wankel, who became fascinated with ...Missing: date | Show results with:date<|control11|><|separator|>
[8]
Engine revolution: Mazda's rotary and its uncertain future - Hagerty
Aug 5, 2020 · Mazda didn't invent the rotary. It was German Felix Wankel who, in the 1920s, drew inspiration from pumps, compressors, and turbines to create an engine ...
[9]
Felix Wankel, father of the rotary engine, is born - Automotive News
Aug 13, 2018 · Wankel received his first patent for a pistonless internal combustion engine in 1929. It proved to be one of many engine developments ahead ...Missing: DE507584 | Show results with:DE507584
[10]
(PDF) Dynamic sealing design for Wankel Engines - ResearchGate
Nov 2, 2019 · Included are descriptions of the various wear test rigs utilized to evaluate apex seal/trochoid coating combinations. Laboratory seal ...<|control11|><|separator|>
[11]
[PDF] 261 C H A P T E R 7 THE WANKEL ROTARY ENGINE 7.1 A ...
Air and combustion gases are transported in the spaces between the rotor and the housing. The rotor rides on an eccentric that is an integral part of a shaft,.
[12]
[PDF] Numerical Investigation of Pressure Losses and its Effect During ...
The radius R of the rotor and the eccentricity e of the output shaft determine the geometry of the rotor housing and flanks. Both are the key design parameters ...
[13]
https://ateupwithmotor.com/model-histories/mazda-rotary-part-1/
[14]
[PDF] Performance and Combustion Characteristics of Direct-In. ection ...
The DISC Wankel engine offers attractive advantages over reciprocating engines. These advantages include higher airflow capacity, higher power-to-weight ratio, ...
[15]
https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=3806&context=icec
[16]
[PDF] Rotary Engine Performance Limits Predicted by a Zero-Dimensional ...
This study shows how well increasing the combustion rate, insulating and turbocharging in- crease brake power and decrease fuel consumption. Several ...
[17]
[PDF] Combustion Engine Seals - NASA Technical Reports Server (NTRS)
The GSnEP for the apex and side seals are plotted as a function of mainshaft speed for the firing engine in Fig. 8. Table 3 l i s t s com- bined values of GSMEP ...<|separator|>
[18]
https://www.sciencedirect.com/science/article/pii/B9780124046160000049
[19]
[PDF] Structure and Working Principles of the Rotary Engine
The rotor has a longer rotation period than the eccentric shaft. The rotor rotates one turn while the eccentric shaft rotates three turns. With the engine ...
[20]
[PDF] An Overview of the NASA Rotary Engine Research Program
This paper presents a brief overview and technical highlights of the research efforts and studies on rotary engines over the last several years at.
[21]
Two-Stroke Wankel Type Rotary Engine: A New Approach ... - MDPI
In order to distinguish the rotary engines from reciprocating engines, considering power output, the related equations are given below. The indicated power per ...Missing: formula | Show results with:formula
[22]
Coating for rotary engine rotor housings and method of making
A method of producing the wear-resistant coating system for a rotor housing is disclosed, comprising preparation of an aluminum casting having a supporting ...
[23]
Technology | AMRP Ltd.
A rotary engine (also known as the Wankel engine or rotary engine) is an internal combustion engine invented in 1954 by the German engineer Felix Wankel.
[24]
US8597006B2 - Apex seal for rotary internal combustion engine
In a particular embodiment, the spring 80 is made of a suitable metal, for example low alloy steel, stainless steel, Ti alloys, and if necessary of a suitable ...
[25]
[PDF] ADIABATIC WANKEL TYPE ROTARY ENGINE PHASE II FINAL ...
Wankel type rotary engine for aircraft applications through the use of adiabatic engine technology. Curtiss-Wright and. John. Deere as part of their. " ...
[26]
None
Summary of each segment:
[27]
Rotary Revolutionary: The NSU Ro80 < Page 3 of 5 < Ate Up With ...
Aug 24, 2012 · The Ro80 was initially slated to use a two-rotor version of the KKM 502 used in the Wankel Spider, but ongoing issues with the Spider's seals ...Missing: double | Show results with:double
[28]
Research overview of rotary engine apex seals - DOAJ
In 1954, Felix Wankel became the first in the world to successfully develop a rotary engine with the cooperation of the NSU. The invention of the rotary engine ...Missing: 1950s | Show results with:1950s
[29]
The History of Mazda's Rotary Engine - AutoSpeed
This type of apex seal resulted from Mazda's independent development work and was proven durable through 1,000 hours of continuous testing. Even after a 100,000 ...
[30]
Sealing the Wankel engine - High Power Media
May 12, 2011 · On Norton race motorcycles fitted with rotor housings made from high-strength, high-silicon aluminium alloy (LM13), a two-piece plain cast-iron ...
[31]
Apex seal bottom pressure prediction and leakage analysis of The ...
The leakage through the apex seals is the main leakage path in the WRE and the apex seal leakage (ASL) accounts for 2/3-3/4 of the total leakage of the WRE [23] ...
[32]
Leakage Flow Analysis for a MEMS Rotary Engine - ResearchGate
There are two inherent leakage paths in rotary engines, which result in blow-by and reduced compression ratio: leakage around the apexes of the rotor and ...
[33]
Why Rotary Apex Seals Fail - Yahoo! Autos
Oct 27, 2025 · Non-turbocharged rotaries can reportedly go 100,000 to 200,000 miles before the apex and other seals wear out to the point of significantly ...
[34]
Enhancing the Efficiency of Rotary Thermal Propulsion Systems
The compression and expansion ratios in a Wankel rotary engine are constrained by its physical shape, which is described using the eccentricity-to-generating ...
[35]
rotary engine displacement ?? - RX7Club.com - Mazda RX7 Forum
Oct 23, 2004 · Each rotor displaces 654 cc per crank revolution. And as you know, the rotor spins at 1/3 the crank speed. So it is 654 cc per face also. Then you get 1308 cc ...Missing: V_d | Show results with:V_d
[36]
Step 1: Choosing an Engine - Rotary Miata
Displacement ; 10A 2-rotor, 982cc ; 12A 2-rotor, 1146cc ; 13B 2-rotor, 1308cc ; 20B 3-rotor, 1962cc.
[37]
Vintage Review: NSU Ro80 – The World's First Rotary Engine Sedan
Nov 24, 2024 · Despite having a combined chamber displacement of only 995 cc (60.7 cu. in.), it boasted 115 PS (113 net hp, to you and me, 130 hp SAE gross) ...
[38]
Mazda RX-85 concept: The second Japanese ever with a Wankel ...
Oct 5, 2024 · In Japan, the installation of the rotary engine allowed buyers to save on road tax since they did not have to pay the higher tax reserved for ...
[39]
[PDF] Freedom Motors, Inc.
The Wankel-type rotary engine, therefore, is considered to have twice the displacement of a four-stroke piston engine of the same nominal displacement. The ...<|separator|>
[40]
RX-Rated: Mazda's Early Rotary Cars, Part 2 - Ate Up With Motor
Nov 24, 2011 · Reclassified yet again in 1973, the RX-2 returned to Bathurst a final time, taking first and second in Class C (2,001 to 3,000 cc displacement), ...
[41]
NSU Ro 80 data and specifications catalogue - Automobile Catalog
Cars were equipped with engines of 995 cc (15000 cui) displacement, delivering 84.5 - 96.2 kW (115 - 131 PS, 113 - 129 hp) of power.
[42]
How to Study Wankel Engine Environmental Compliance?
Aug 26, 2025 · Testing data indicates that unmodified Wankel engines typically produce HC emissions 1.5-2.5 times higher than equivalent displacement piston ...
[43]
Comparative Study of the Fuel Economy Characteristics of Mazda ...
The lowest fuel economy in the 2750 Ib. weight class was achieved by three rotary engine Mazda vehicles: 10.6, 10.8 and ILO^mpg. Exclusive of these three ...Missing: historical | Show results with:historical
[44]
1980 Mazda RX-7 S (man. 4) (model since mid-year 1979 for North ...
1980 Mazda RX-7 S standard and alternative wheel and tire sizes · 185 km/h / 115 mph · 358 km / 222 miles · 16 / 25 (19) mpg (U.S.) · 14.7 / 9.4 (12.4) l/100km.
[45]
Used 1993 Mazda RX-7 MPG & Gas Mileage Data - Edmunds
Rating 4.7 (32) View detailed gas mileage data for the 1993 Mazda RX-7. Use our handy tool ... 18 MPG EPA Combined City/Hwy15 City23 Highway. Cost to Drive. $195/mo. RX-7 ...
[46]
Numerical investigations of combustion and emissions ...
Carbon monoxide (CO) and hydrocarbon (HC) emissions from Wankel engines are much higher than those of reciprocating engines, resulting from narrow and long ...
[47]
Emission Control Systems for Wankel Engines - Patsnap Eureka
01 Catalytic Converters for Wankel Engines. Specialized catalytic converter systems designed specifically for Wankel rotary engines to reduce harmful emissions.
[48]
engine weights - GoMoG
Mazda 12A rotary 275 (85) (w/flywheel, t.reactor, no alt.) Mazda 13A rotary 301 (20) (R130 Lucia - Japan only) (bare) Mazda 13B race 242 ( ...
[49]
Wankel Engines - an overview | ScienceDirect Topics
The Wankel engine uses an oval-shaped housing with a triangular-shaped rotor on an eccentric shaft. The rotary engine is advantageous as it is compact, has ...
[50]
Analyzing the Usage of Wankel Engine Technology in Future ...
Aug 4, 2023 · The results indicate a potential reduction in fuel consumption when utilizing improved Wankel engine designs compared to traditional piston- ...
[51]
[PDF] Analysis of Apex Seal Friction Power Loss in Rotary Engines
An analysis of the frictional losses from the apex seals in a rotary engine was developed. ... failing to comply with a collection of information if it does not ...
[52]
Wankel Rotary Engines – Aren't they unreliable and use excessive oil?
Feb 21, 2018 · Thus the impact on the overall life of the engine and its efficiency has greatly improved. This improved seal performance combined with the ...
[53]
US3964445A - Water cooling system - Wankel engine
A rotary engine employing an improved circumferential flow cooling system is employed to provide an increase in fuel economy and engine efficiency.
[54]
Rotary Revolutionary: The NSU Ro80 < Page 5 of 5 < Ate Up With ...
Aug 24, 2012 · The development and history of the 1967-1977 NSU Ro80 and its Wankel rotary engine.Missing: Hans Mauch
[55]
Rare Rides: A 1974 NSU Ro 80, in Convertible Form
Jan 2, 2020 · Ro 80 was front-wheel drive, powered by a 113-horsepower Wankel engine of 995 cc displacement.
[56]
Overseas Motors, Inc., a Michigan Corporation, Plaintiff-appellant, v ...
This is an action by Overseas Motors, Inc. (Overseas) against Audi NSU Auto Union Aktiengesellschaft (ANAU), Volkswagenwerk Aktiengesellschaft (Volkswagen), ...
[57]
The First Mazda Powered By A Rotary Engine - HotCars
Mar 17, 2025 · The Cosmo Sport's production spanned from 1967 to 1972, during which 1,176 units were built (Mazda). This limited production run was partly due ...
[58]
Mazda RX-7: A Guide To Every Generation | Feature | CarThrottle
Apr 12, 2025 · That contributed to a total production figure of 811,634 RX-7s between 1978 and 2002, per Mazda's UK website.
[59]
https://law.justia.com/cases/federal/appellate-courts/F2/519/119/85717/
[60]
Citroën GS Birotor-1975 - Lane Motor Museum
Introduced at the Frankfurt Auto Show in September, 1973, the Birotor was a bit of a surprise. ... Years of Production: 1973-75. Number Produced: 847. Original ...
[61]
French Deadly Sins (First Batch) – 1973-75 Citroën GS Birotor ...
Dec 22, 2022 · This is the story of the downfall of a giant, full of hubris and shortsightedness akin to General Motors and British Leyland: Citroën and its woeful Wankel- ...
[62]
Experimental car with a Wankel engine. - Mercedes-Benz C 111
The experimental vehicle was powered by a three-rotor Wankel engine and the body was made of fibreglass-reinforced plastic.
[63]
Even After 55 Years, Mercedes' Wankel-Powered C111 Is Still a ...
Oct 9, 2024 · Of the 17 prototypes built, two were pure show cars and four were scrapped; the 13 remaining examples belong to the Mercedes-Benz Museum.
[64]
This is the only rotary-powered Mustang ever built - Hemmings
Oct 21, 2019 · Wankel, an engineer in Germany, designed his rotary engine back in the 1920s, receiving a patent in 1929, but it wasn't until he was employed at ...Missing: experiments | Show results with:experiments
[65]
Mazda 787B That Won Le Mans in 1991 Returned This Year ...
Jun 12, 2023 · The Mazda 787B was the first Japanese car to win Le Mans, taking a hard-fought victory in 1991. After being immediately retired from racing ...
[66]
1976 Hercules W-2000 | The Online Automotive Marketplace
Aug 27, 2024 · Though first envisioned by Felix Wankel as a 17-year-old in 1919 and patented in 1929, the first running engine was not completed until 1957, ...
[67]
Rotary - Norton Owners Club
The rotary engine develops its maximum power at about 7000 rpm, hence it is necessary to fit a speed reduction gearbox to the front of the unit.
[68]
Fichtel & Sachs | The Online Automotive Marketplace - Hemmings
Mar 26, 2024 · As one of the earliest licensees of the Wankel rotary engine patents, F&S produced the first rotary-powered motorcycle with the Hercules W-2000 ...
[69]
1975 Suzuki RE-5 Rotary Motorcycle
Apr 22, 2011 · 1975 Suzuki RE-5. Claimed power: 62hp @ 6.500rpm ; Top speed: 105mph ; Engine: 497cc liquid-cooled single rotor Wankel rotary engine ; Weight (dry): ...
[70]
1974 Suzuki RE5 Rotary - Motorcycle Specs
Suzuki RE5 Rotary ; Ground Clearance. 170 mm / 6.7 in ; Dry Weight. 230 kg / 507 lbs ; Wet Weight. 252 kg / 556 lbs ; Fuel Capacity. 16.8 Litres / 4.4 US gal / 3.7 ...Missing: 1974-1976 | Show results with:1974-1976
[71]
Suzuki Tried To Steal Mazda's Thunder With A Rotary Motorcycle
Jun 12, 2025 · Suzuki RE5 Production Stats · Years in production: 1974-1976 · Total produced: ~6,350 · Original MSRP: $2,945 ...<|separator|>
[72]
Yamaha Rz 201 Wankel | Cycle World | FEB 1973
Feb 1, 1973 · The 68-bhp Yamaha will be both smooth and a capable performer. It combines the 59.4 in. wheelbase and girth of a touring machine with the power potential and ...Missing: 1980s production displacement equivalent
[73]
Rotary Revival: Van Veen OCR 1000 - Motorcycle Classics
Dec 19, 2017 · Transverse-mounted twin-rotor Wankel rotary with wet sump oil-cooled rotors and water-cooled casing, 2 x 498cc swept volume trochoidal chambers.Missing: 1978 | Show results with:1978
[74]
https://www.hotcars.com/suzuki-steal-mazdas-rotary-motorcycle/
[75]
Mac 10 Wankel antique outboards, mopeds, cars - Oddjob Motors
The Mac-10 Sachs Wankel outboard was available from the late 1960's through the early 70's. It was a joint German & Italian effort.
[76]
2-Strokes and 4-Strokes and Rotaries, Oh My! - Snowmobile.com
Aug 13, 2015 · The patented idea for a rotary engine design was awarded in 1929 to Felix Wankel, a German engineer. In the 1970s the Wankel concept of a ...Missing: limited | Show results with:limited
[77]
wankel rotary engines | SnoWest Magazine
As it turned out, the OMC snowmobile rotary engine ended up being the only Wankel engine ever manufactured in the U.S., and as such has some historical merit.
[78]
More Mistral Magic - Kitplanes Magazine
Oct 23, 2014 · The Mistral engine, based on a Mazda Wankel, is less polluting, uses jet fuel or mogas, has a 200/300 hp option, and is easy to install. It has ...Missing: applications | Show results with:applications
[79]
The Diamond Aircraft Story Continues to Evolve - FLYING Magazine
Dec 10, 2023 · ... Diamond—DV20 Katana, powered by a Diamond Wankel engine. It made only a minor splash when a Rotax 912-powered DA20-A1 version was produced ...
[80]
XTS-210 ENGINE - LiquidPiston
The XTS-210 is a 25 horsepower, two-stroke, supercharged, liquid-cooled 210cc X-Engine variant currently under development that reduces size and weight by ...
[81]
LiquidPiston Evolves the Rotary - Inside Unmanned Systems
Jun 5, 2023 · The largest but still compact type—the XTS-210—“is “a liquid-cooled, two-stroke supercharged variant. On the two-stroke, both sides of the ...
[82]
Join the Wankel Party - Driven to Write
Sep 6, 2022 · The resulting first Russian Wankel that appeared in 1978, known as the VAZ-311, was a single-rotor engine which delivered 71bhp. The first batch ...Missing: train | Show results with:train
[83]
Aixro XR-50 Rotary Karting Engine w/ Standard - RENNtech
The XR-50 is a 4-stroke rotary engine working on the Wankel principle and consequently has no oscillating masses due to an eccentric shaft and rotor turning.
[84]
Yanmar Diesel's Rotary Engine Chain Saw 760642 - SAE International
Jan 31, 1976 · A new chain saw powered by rotary engine has been developed with a view to prevent the current injuries due to vibration from chain saws.
[85]
Game-changing rotary engine muscles a go-kart - New Atlas
Jun 15, 2016 · The engine being used in the video to power the go-kart is a four-stroke 70cc gasoline version that produces about 3.5 horsepower (2.2 kW) at ...
[86]
[PDF] Combustion Chamber Design Effect on The Rotary Engine ...
A single rotor Wankel engine does two complete cycles within two revolutions of the eccentric shaft. A single cylinder piston requires two crankshaft ...<|control11|><|separator|>
[87]
Effect of ignition pattern on combustion characteristics in a hydrogen ...
Hydrogen is considered the optimal solution for achieving high efficiency and low emissions in Wankel rotary engines (WREs). This paper aims to reveal the ...Missing: adaptation | Show results with:adaptation
[88]
Enhancing the Efficiency of Rotary Thermal Propulsion Systems
Feb 12, 2024 · The rotor in a Wankel engine takes the form of a Reuleaux triangle [23] and rotates around an eccentric output shaft inside a trochoidal housing ...Missing: coefficient | Show results with:coefficient
[89]
(PDF) Evaluation of a Rotary Engine Adapted for Power Generation ...
Measured engine system efficiency was not impacted by the addition of hydrogen. Mixing performance tests for the injectors showed that the fuel and air were ...
[90]
[PDF] Multi-Fuel Rotary Engine for General Aviation Aircraft
Presently under a new NASA contract, Curtiss-Wright will design and build a single rotor test engine to evaluate the various technologies needed for an advanced ...Missing: kerosene | Show results with:kerosene
[91]
[PDF] advanced rotary engine studies - NASA Technical Reports Server
Both engines proved their multi-fuel capabilities, but neither could match the fuel economy of our carbureted. RC2-60U5 automotive prototype engine of the same.Missing: kerosene | Show results with:kerosene<|separator|>
[92]
Wankel engine - MotorWiki
Apr 8, 2023 · Eventually, in 1951, Wankel began working at German firm NSU Motorenwerke to design a rotary compressor as a supercharger for NSU's motorcycle ...
[93]
First tests of laser ignition in Wankel engine - IOP Science
Laser ignition has been found possible and quite beneficial for both types of engines and different fuel mixtures; in terms of NOx emission reduction especially ...
[94]
First tests of laser ignition in Wankel engine - ResearchGate
Feb 17, 2021 · Laser ignition has been found possible and quite beneficial for both types of engines and different fuel mixtures; in terms of NOx emission ...
[95]
revisiting Ethanol 2021 - RX7Club.com - Mazda RX7 Forum
Mar 18, 2021 · Most know that you get diminished additional benefit past 40% (by volume). this is an interesting consideration to me as less % ethanol, less internal issues.
[96]
Ethanol Swap : r/RX8 - Reddit
Jan 7, 2022 · You will need to choose whether to retune the stock ECU to run exclusively an ethonal blend tune (E-50, E-60, E-75, E-80, E-85, E-100) and ...Does Ethanol blended petrol going to harm engine and reduce ...E85/premix : r/RX8 - RedditMore results from www.reddit.comMissing: Wankel tweaks
[97]
Mazda Plots Wankel-powered Range Extenders, HCCI Mild Hybrids
Feb 24, 2025 · Mazda illustrates how its compact 330-cc single-rotor rotary engine (shaded blue here) compares in size to a piston engine of equivalent power.
[98]
[PDF] Compact, Lightweight, High Efficiency Rotary Engine for Generator ...
Aug 9, 2018 · This engine aims to fit in a 10” box, with a weight of less than 40 lb, and could efficiently charge a battery to extend the range of an ...
[99]
Mazda rotary engine returns (for Japan) as EV range extender in MX ...
Oct 12, 2020 · The rotary range extender will be used in the Japanese-market MX-30 crossover beginning in 2022, according to a Japanese-language video posted ...Missing: specs | Show results with:specs
[100]
Mazda MX-30 R-EV SUV
The beautifully designed Mazda MX-30 R-EV is a unique plug-in hybrid that combines the excitement of electric driving with the convenience of a petrol engine.
[101]
Mazda CEO Reveals Long-Awaited Rotary Engine Revival - Forbes
Jan 27, 2025 · President Masahiro Moro revealed that 'on February 1, we will launch the Rotary Engine Development Group'.
[102]
LiquidPiston | Reinventing the Rotary Engine
We patented a new rotary engine that delivers up to 10X more power, 30% more efficient than traditional piston engines, and a perfect fit for ...Xts-210 engine · About us · Careers · Invest in LiquidPiston
[103]
Army innovation programs propel LiquidPiston's rotary engine ...
May 15, 2025 · LiquidPiston is developing a new class of hybrid power solutions, and a new engine program based on its HEXE platform. The firm collaborates ...Missing: HEHC Wankel
[104]
Six rotary-engined cars you didn't know about | Axon's Automotive ...
Mar 24, 2023 · The C111 was a series of experimental gullwing GTs, serving as a very public test-bed for Wankel rotary engine technology and initially planned ...
[105]
Wankel Engines Market to Reach $100.4 Million, Globally, by 2033 ...
Oct 4, 2024 · According to the report, the wankel engines market was valued at $47.0 million in 2023, and is estimated to reach $100.4 million by 2033, ...
[106]
UAV Wankel Engines Market Size, Growth, Share, & Analysis Report ...
The UAV Wankel engines market was valued at approximately USD 45 million in 2024 and is projected to reach around USD 85 million by 2033, with a compound annual ...
[107]
Our Rotary Engine Press Releases - LiquidPiston
LiquidPiston signs $1M agreement with DARPA to develop fuel-efficient, lightweight, heavy-fueled, rotary combustion engine technologies for the US military.Missing: Wankel | Show results with:Wankel
[108]
U.S. Army Taps LiquidPiston to Build Ultra-Compact Mobile
Aug 27, 2025 · LiquidPiston has begun developing an ultra-compact auxiliary power unit (APU) for mobile command posts under U.S. Army's SBIR CATALYST ...Missing: Wankel | Show results with:Wankel
[109]
Range Extenders in Electric Vehicles: Range Without Regrets - Felss
Aug 5, 2025 · Mazda MX-30 R-EV (2023): Compact crossover with Wankel engine as a range extender. Electric range: 85 km, total over 600 km. The combustion ...
[110]
Automakers Urge EPA to Revise Greenhouse Gas Standards Amid ...
Sep 24, 2025 · Automakers say current EPA GHG standards for 2027–2032 are unachievable due to slowing EV demand, charging gaps, and loss of federal incentives.
[111]
United Kingdom Wankel Engines Market: Key Highlights
Oct 1, 2025 · Regulatory & Environmental Challenges: Stringent UK and EU emission standards pose significant hurdles for Wankel engine commercialization.
[112]
A review of recent advances in hydrogen fueled Wankel engines for ...
May 1, 2025 · This review comprehensively analyzes experimental and CFD studies of hydrogen-fueled Wankel rotary engines (HWREs), comparing their performance and emissions ...
[113]
Performance Analysis of a Hydrogen-Doped High-Efficiency Hybrid ...
Oct 26, 2022 · A single-zone model of a hydrogen-doped high-efficiency hybrid cycle rotary engine that considers high-altitude environments was proposed.