Pistonless rotary engine

From WOI Encyclopedia Italia

This article is about internal combustion engines that do not use conventional pistons. See also rotary engine (disambiguation) for other uses of this term, and rotary engine for the World War I aircraft engines by that name.

A rotary engine is an internal combustion engine that does not use pistons in the way a reciprocating engine does, but instead uses one or more rotors, sometimes called rotary pistons.

Contents 1 Advantages 2 Disadvantages 3 Comparisons 4 External links

The term rotary combustion engine has been suggested as an alternative name for these engines to distinguish them from the obsolete aircraft engines also known as rotary engines. However both continue to be called rotary engines and only the context determines which type is meant. In particular, the only commercial producer of (pistonless) rotary engines as of 2005, Mazda, consistently refers to their Wankel engines as rotary engines.

The basic concept of a (pistonless) rotary engine is to avoid the reciprocating motion of the piston with its inherent vibration and rotational-speed-related mechanical stress. As of 2005 the Wankel engine is the only successful pistonless rotary engine, but many similar concepts have been proposed and are under various stages of development. There are countless other examples of rotary engines varying in rotor design, size and many other categories. Notable examples include:

• The quasiturbine.
• The Sarich orbital engine.
• A rotary engine developed by Texas machinist Frank Turner which was licensed by Malcolm Bricklin for use in place of the V8 powering the Bricklin SV-1 vehicle, but never used.[1]
• The Rand Cam engine [[2]]
• Trochilic engines (in particular the MYT engine developed by Raphial Morgado)

Advantages

All such engines have the potential to improve on the piston engine in the areas of:

• Higher power-to-weight ratios.
• Mechanical simplicity.
• Less vibration.

While typically larger than the piston of an engine of corresponding capacity, a rotor may perform many strokes per revolution. The Wankel produces twelve strokes per revolution of the rotor (four strokes per chamber times three chambers) (although the spindle rotates three times faster than the rotor or three times over the twelve strokes), as opposed to two strokes for each crankshaft rotation of a single-cylinder single acting piston engine, or four strokes for a double-acting cylinder such as found in some steam engines. The quasiturbine and MYT engine deliver sixteen strokes for every rotor (and spindle) revolution.

Disadvantages

In practice, the main problem of the Wankel engine has proven to be the seals, and as of 2005 all proposed designs have some of the same potential weaknesses.

Although in two dimensions the seal system of a Wankel looks to be even simpler than that of a corresponding multi-cylinder piston engine, in three dimensions the reverse is the case. As well as the rotor apex seals evident in the conceptual diagram, the rotor must also seal against the chamber ends. Worse still, these two sets of seals must somehow join at sharp corners at the ends of the apex seals.

An additional problem is that the seals at the Wankel rotor apexes meet the chamber walls at an angle that varies plus and minus ~26 deg; during the cycle, while a piston ring meets the cylinder walls at a constant angle. As well as making the seal design itself more difficult, this means that while multiple rings are easily fitted to a piston, a corresponding approach is impossible with the Wankel apex seals. This limitation is addressed in the Quasiturbine AC design, but the simpler Quasiturbine SC design has the same problem of varying seal angle as the Wankel.

Piston rings are not perfect seals. Each has a gap in fact to allow for expansion. Moreover the sealing at the Wankel apexes is less critical, as leakage is between adjacent chambers on adjacent strokes of the cycle, rather than to the crankcase. However, the less effective sealing of the Wankel is one factor reducing its efficiency, and confining its success mainly to applications such as racing engines and seat belt pretensioners where neither efficiency nor long engine life are major considerations.

Another disadvantage of the Wankel engine in particular is the large surface area of the combustion chamber which reperesents a large heat transfer and quench area, combined with an unfavorably long rather thin stretched combustion space necessitating long flame travel. The combustion is less complete than in e.g. an RPE having a more compact chamber shape with smaller area per chamber volume. The Quasiturbine has similar disadvantages with its concave combustion chamber, and in the AC design the sharp angles of the carriers hamper the propagation of the flame front leading to incomplete combustion.

Comparisons

The simplest design, either proposed or in use, is the Wankel. Its only moving parts are a three-sided rotor turning on a straight spindle; There is neither crankshaft nor camshaft. The rotor is not fixed to the spindle, but turns it by means of an internal gear on the inside of the rotor engaging a smaller conventional gear on the spindle. The rotor is positively located by the spindle and the geometry of the rotor and engine chamber. There is still some vibration, as while the centre of gravity of the spindle does not move, that of the rotor does. The angular momentum and kinetic energy of motion of the rotor also both vary, producing more vibration, see engine balance. A Wankel engine fires three times for every revolution of the rotor, so a single rotor is in some ways equivalent to a six-cylinder reciprocating engine.

However since the output shaft turns faster than the rotor (the ratio is 3:1) effectively at the output shaft there is one "power" stroke per revolution, hence a single rotor-casing combination is the equivalent of a two-cylinder four-stroke (Otto cycle) engine (reciprocating engine).

A two-rotor design has been adopted by Mazda to further reduce vibration, and three- and four-rotor designs have been used in racing, notably the 4-rotor Mazda 26B engine that powered the winning car in the 1991 24 Hours of Le Mans race.

There are various methods of calculating the engine displacement of a Wankel; the Japanese regulations calculating displacements for engine ratings calculate on the basis of the volume displacement of one rotor flank only.

In the most popular Mazda family of engines, the 13B, this consists of two rotors displacing approximately 650 cc (cubic centimeters) each per rotor flank, a total of approximately 1300 cc or 1.3 l (liters). As clarified about in terms of reciprocating engines, this is the equivalent of 2.6 l displacement.

The Sarich orbital engine has a larger number of moving parts than the Wankel. The six-chamber design used for the prototype has, conceptually, eight moving parts within the engine chamber as opposed to two for the Wankel. However it also requires six spark plugs, one per combustion chamber, as opposed to one per rotor for the Wankel (although two are commonly used in practice for performance reasons). The Sarich was developed to the point of being demonstrated running briefly as a bench-test with no load before the design was abandoned.

The Quasiturbine AC design is more complex still than the Sarich. Even with only two wheels per carriage, there are at least nineteen moving parts within the engine chamber including the shaft and differential, and possibly more depending on the design of the differential. In common with the Wankel, the Quasiturbine only requires a single spark plug. A prototype of the Quasiturbine AC design was constructed and turned by an external engine for 40 hours, but ignition was never achieved.

The Quasiturbine SC design is greatly simplified from the AC, but still has at least seven moving parts within the chamber, including the shaft and again possibly more depending on the design of the differential. The SC design has been demonstrated as a steam and pneumatic engine, but as of 2005 not as an internal combustion engine. Prototype steam engines have run for periods of up to a few hours.

The Rand cam engine uses sliding vanes to implement the four stroke cycle. It is primarily being developed by Reg Technology.

The trochilic engines use two interleaved rotors in a cylindric or toroidal stator. The air-fuel mix is aspirated, compressed, ignited and burnt between each rotor's forward and back faces as each rotor advances or retreats relative to the other during operation, varying the volume of the chamber continuously. This principle of operation can be traced back to the 1968 Tschudi engine. In the MYT engine, the rotary pistons are toroid-sections (curved clinders sliding inside the toroidal stator) and connected to either of two inner discs. The main problems of this type of engine is getting a constant rotation on the output shaft from the two oppositely accelerating and decelerating rotors (planetary gears are used on trochilic engines, while the MYT makes use of a more complex connection system using camshafts) and preventing the rotors from turning in the wrong direction. On the other hand, this design does not suffer from the sealing problems of Wankel engine or Quasiturbine, and use very few moving parts (5 in the simpler model of trochilic engine).

External links

• Open Directory: Rotary Engines.
• An illustrated list of rotary engine designs.
• Some illustrations of the Rand Cam Engine
• Animation showing the MYT engine's operation
• Animations showing generalized models of trochilic engines in various configurations

Articles relating to Automobile configurations
Car body style and classification	2 plus 2 | Antique car | Cabrio coach | Cabriolet | City car | Classic car | Compact car | Compact performance car | Compact SUV | Convertible | Coupé | Coupé convertible | Coupe Utility | Crossover SUV | Custom car | Drophead coupe | Fastback | Full-size car | Grand tourer | Hardtop | Hatchback | Hot hatch | Hot rod | Large family car | Leisure activity vehicle | Liftback | Limousine | Luxury car | Microcar | Mid-size car | Mini SUV | Minivan | Multi-purpose vehicle | Muscle car | Notchback | Personal luxury car | Pickup truck | Retractable hardtop | Roadster | Sedan | Saloon | Small family car | Sport compact | Sports car | Sport utility vehicle | Spyder | Station wagon | Estate car | Supermini | Targa top | Taxicab | Touring car | Town car | T-top | Ute | Van | Voiturette
Specialised vehicles	Gyrocar | Flying car. Amphibious vehicle
Fuel technologies	Internal combustion engine | Electric vehicle | Neighborhood electric vehicle | Hybrid vehicle | Battery electric vehicle | Hydrogen vehicle | Fuel cell | Plug-in hybrid electric vehicle | Steam car | Alternative fuel cars | Biodiesel | Gasohol | Ethanol | LPG (Propane) | Homogeneous Charge Compression Ignition | Liquid Nitrogen | Gasoline Direct Injection
Driven wheels	Four-wheel drive | Front-wheel drive | Rear-wheel drive | All-wheel drive | Two-wheel drive
Engine positioning	Front engine | Rear engine | Mid engine
Layout	FF layout | FR layout | MR layout | MF layout | RR layout
Engine configuration	Internal combustion engine | Straight-6 | V engine | Wankel engine | Reciprocating engine | Inline engine | Flat engine | Flathead engine | Diesel engine | Two-stroke cycle | Four-stroke cycle | Pushrod engine | Straight engine | H engine | Turbodiesel | Hybrid vehicle | Rechargeable energy storage system | Electric vehicle | Hydrogen vehicle

Body	Framework	A-pillar | Bumper | Cabrio coach | Chassis | Crumple zone | Body-on-frame | Dagmar bumpers | Fender | Fender skirts | Grille | Hood | Hood scoop | Monocoque construction | Pontoon fenders | Quarter panel | Shaker scoop | Spoiler | Subframe | Tonneau
Doors	Butterfly doors | Gull-wing door | Scissor doors | Suicide door
Glass	Sunroof | Greenhouse | Windshield
Other	Antenna ball | Hood ornament | Japan Black paint | Nerf bar | Truck accessory | Bumper sticker
Exterior Equipment	Lighting	Daytime running lamp | Headlamp | Headlight styling | Hidden headlamps | Retroreflector | Sealed beam | Trafficators | High intensity discharge
	Other	British car number plates | Distance sensor | US and Canadian license plates | Vanity plate | Vehicle registration plate | Windscreen wiper | Windshield washer fluid
Car engine	Air/Fuel	Air filter | Automatic Performance Control | Blowoff valve | Boost | Boost controller | Butterfly valve | Carburetor | Charge cooler | Centrifugal type supercharger | Cold air intake | Engine management system | Engine Control Unit | Forced induction | Front mounted intercooler | Fuel filter | Fuel injection | Fuel pump | Fuel tank | Gasoline direct injection | Indirect injection | Intake | Intercooler | Manifold | Manifold vacuum | Mass flow sensor | Naturally-aspirated engine | Ram-air intake | Scroll-type supercharger | Short ram air intake | Supercharger | Throttle body | Top mounted intercooler | Turbocharger | Turbocharged Direct Injection | Twin-turbo | Variable Length Intake Manifold | Variable geometry turbocharger. Warm air intake
	Exhaust	Catalytic converter | Emissions control devices | Exhaust pipe | Exhaust system | Glasspack | Muffler | Oxygen sensor
	Cooling	Aircooling | Antifreeze | Ethylene glycol | Radiator | Thermostat
	Ignition system	Starter | Car battery | Contact breaker | Distributor | Electrical ballast | Ignition coil | Lead-acid battery | Magneto | Spark-ignition | Spark plug
	Other	Balance shaft | Block heater | Crank. Cam | Camshaft | Connecting rod | Combustion chamber | Crank pin | Crankshaft | Crossflow cylinder head | Crossplane | Desmodromic valve | Engine knocking | Compression ratio | Crank sensor | Cylinder | Cylinder bank | Cylinder block | Cylinder head | Cylinder head porting | Dump valve,Engine balance | Oil filter | Firing order | Freeze plug | Gasket | Head gasket | Hypereutectic piston | Hydrolock | Lean burn | Main bearing | Motor oil | Multi-valve | Oil sludge | Overhead camshaft | Overhead valve | PCV valve | Piston | Piston ring | Pneumatic valve gear | Poppet valve | Power band | Redline | Reverse-flow cylinder head | Rocker arm | Seal | Sleeve valve | Starter ring gear | Synthetic oil | Tappet | Timing belt | Timing mark | Top dead centre | Underdrive pulleys | Valve float | Variable valve timing
Interior equipment	Instruments	Backup camera | Boost gauge | Buzzer | Car computer | Carputer | Check Engine light | Fuel gauge | Global Positioning System | Idiot light | Navigation system | Odometer | Speedometer | Tachometer | Trip computer
	Controls	Bowden cable | Cruise control | Electronic throttle control | Hand brake | Manettino dial | Steering wheel | Throttle | Gear stick
	Motor vehicle theft deterrence	Car alarm | ESITrack | Immobiliser | Klaxon | Vehicle tracking system | VIN etching
	Passenger safety & seating	Airbag | Armrest | Automatic seatbelt | Bench seat | Bucket seat | Child safety lock | Dicky seat | Passive safety | Rumble seat | Seat belt
	Other	Air conditioning | Ancillary power | Car audio | Car phone | Center console | Dashboard | Motorola connector | Power window | Rear-view mirror | TripSense
Powertrain	Wheels and Tires	All-terrain tyre | Bias-ply tire | Contact patch | Custom wheel | Drive wheel | Hubcap | Magnesium alloy wheel | Mud-terrain tyre | Paddle tires | Radial tire | Rostyle wheel | Run flat tires | Schrader valve | Slick tire | Spinner | Tire code | Tread | Treadwear rating | Whitewall tire | Wire wheels
	Transmission	Automatic transmission | Clutch | Continuously variable transmission | Differential | Driveshaft | Electrorheological clutch | Epicyclic gearing | Fluid coupling | Fully-automatic transmission | Gear stick | Gearbox | Hydramatic | Limited slip differential | Locking differential | Manual transmission | Roto Hydramatic | Saxomat | Semi-automatic transmission | Semi-automatic transmission | Super Turbine 300 | Tiptronic Torque converter | Transmission (mechanics) | Transmission Control Unit | Turbo-Hydramatic | Universal joint
	Steering	Ackermann steering geometry | Anti-lock braking system | Camber angle | Car handling | Caster angle | Oversteer | Power steering | Rack and pinion | Toe angle | Torque steering | Understeer
	Suspension	Axle | Beam axle | Coil spring | De Dion tube | Double wishbone | Electronic Stability Control | Hydragas | Hydrolastic | Hydropneumatic suspension | Independent suspension | Kingpin | Leaf spring | Live axle | MacPherson strut | Multi-link suspension | Panhard rod | Semi-trailing arm suspension | Shock absorber | Sway bar | Swing axle | Torsion beam suspension | Transaxle | Trailing arm | Unsprung weight | Watt's linkage | Wishbone suspension
	Brakes	Anti-lock braking system | Disc brake | Drum brake | Hand brake | Hydraulic brake | Inboard brake | Brake lining | Brake fade | Brake fluid | Hydraulic fluid | Brake bleeding | Engine braking | Electronic brakeforce distribution | Regenerative brake

Piston engine configurations
Straight	Single, 2, 3, 4, 5, 6, 8, 9, 10, 12, 14
V	2, 4, 5, 6, 8, 10, 12, 16, 20, 24
Flat	2, 4, 6, 8, 10, 12, 16, H
W	8, 9, 12, 16, 18
Other inline	H, VR, Opposed, U (Square), X
Other	Hemi, Radial, Rotary, Pistonless, Deltic, (Wankel)

Heat engines
Stroke cycles One • Two • Four • Six •
Engine types Gas turbine • Piston • Jet • Rocket engine • Steam engine • Stirling engine • Tschudi• Twingle Rotary • Wankel • Free-piston • Britalus • Coomber • Swing-piston • Orbital • Quasiturbine
Valves Cylinder head porting • D slide • Four-stroke • Manifold • Multi • Piston • Poppet • Sleeve
Piston layouts Single cylinder • Straight • Opposed • Flat • V • W • H • Deltic • Radial • Rocket engine nozzle • Rotary • Stelzer • Controlled Combustion • Bourke
Motion mechanisms Cam • Connecting rod • Coomber rotary • Crank • Crank substitute • Crankshaft • Linkages (Evans • Peaucellier-Lipkin • Sector straight-line • Watt) • Double acting/differential cylinder
Thermodynamic cycle