Mazda Wankel engine


The Mazda Wankel engines are a family of Wankel rotary combustion car engines produced by Mazda.
Wankel engines were invented in 1950s by Felix Wankel, a German engineer. Over the years, displacement has been increased and turbocharging has been added. Mazda rotary engines have a reputation for being relatively small and powerful at the expense of poor fuel efficiency. The engines became popular with kit car builders, hot rodders and in light aircraft because of their light weight, compact size, tuning potential and inherently high power-to-weight ratio—as is true for all Wankel-type engines.
Since the end of production of the Mazda RX-8 in 2012, the engine was produced only for single seater racing, with the one-make Star Mazda Championship being contested with a Wankel engine until 2017; the series' transition to using a Mazda-branded piston engine in 2018 temporarily ended the production of the engine. In 2023, Mazda reintroduced the engine as a generator for the 2023 MX-30 e-Skyactiv R-EV plug-in hybrid.

Displacement

s can be classified by their geometric size in terms of radius and depth, and offset. These metrics function similarly to the bore and stroke measurements of a piston engine. The displacement of rotor can be calculated as
Note that this only counts a single face of each rotor as the entire rotor's displacement, because with the eccentric shaft – crankshaft – spinning at three times the rate of the rotor, only one power stroke is created per output revolution, thus only one face of the rotor is actually working per "crankshaft" revolution, roughly equivalent to a 2-stroke engine of similar displacement to a single rotor face. Nearly all Mazda production Wankel engines share a single rotor radius,, with a crankshaft offset. The only engine to diverge from this formula was the rare 13A, which used a rotor radius and crankshaft offsetoffset, and [|8C] which is based on 13A but with a larger 76 mm depth.
As Wankel engines became commonplace in motorsport, the problem of correctly representing their displacement for the purposes of competition arose. Rather than force participants who drove vehicles with piston engines, who were the majority, to halve their quoted displacement, most racing organizations decided to double the quoted displacement of Wankel engines.
The key for comparing the displacement between the 4-cycle engine and the rotary engine is in studying the number of rotations for a thermodynamic cycle to occur. For a 4-cycle engine to complete a thermodynamic cycle, the engine must rotate two complete revolutions of the crankshaft, or 720°. By contrast, in a Wankel engine, the engine rotor rotates at one-third the speed of the crankshaft. Each rotation of the engine will bring two faces through the combustion cycle. This said, it takes three complete revolutions of the crankshaft, or 1080°, to complete the entire thermodynamic cycle. To get a relatable number to compare to a 4-stroke engine, compare the events that occur in two rotations of a two-rotor engine. For every 360° of rotation, two faces of the engine complete a combustion cycle. Thus, for two whole rotations, four faces will complete their cycle. If the displacement per face is, then four faces can be seen as equivalent to.
Extrapolating to the case of where three whole rotations is a complete thermodynamic cycle of the engine with a total of six faces completing a cycle, per face for six faces yields.

40A

Mazda's first prototype Wankel was the 40A, a single-rotor engine very much like the NSU KKM400. Although never produced in volume, the 40A was a valuable testbed for Mazda engineers, and quickly demonstrated two serious challenges to the feasibility of the design: "chatter marks" in the housing, and heavy oil consumption. The chatter marks, nicknamed "devil's fingernails", were caused by the tip-seal vibrating at its natural frequency. The oil consumption problem was addressed with heat-resistant rubber oil seals at the sides of the rotors. This early engine had a rotor radius of, an offset of, and a depth of.

L8A

The very first Mazda Cosmo prototype used a L8A two-rotor Wankel. The engine and car were both shown at the 1963 Tokyo Motor Show. Hollow cast iron apex seals reduced vibration by changing their resonance frequency and thus eliminated chatter marks. It used dry-sump lubrication. Rotor radius was up from the 40A to, but depth dropped to.
One-, three-, and four-rotor derivatives of the L8A were also created for experimentation.

10A

The 10A series was Mazda's first production Wankel, appearing in 1965. It was a two-rotor design, with each chamber displacing so two chambers would displace ; the series name reflects this value. These engines featured the mainstream rotor dimensions with a depth.
The rotor housing was made of sand-cast aluminium plated with chrome, while the aluminium sides were sprayed with molten carbon steel for strength. Cast iron was used for the rotors themselves, and their eccentric shafts were of expensive chrome-molybdenum steel. The addition of aluminium/carbon apex seals addressed the chatter mark problem.

[|0810]

The first 10A engine was the 0810, used in the Series I Cosmo from May 1965 to July 1968. These cars, and their revolutionary engine, were often called L10A models. Gross output was at 7000 rpm and at 3500 rpm, but both numbers were probably optimistic.
The 10A featured twin side intake ports per rotor, each fed by one of four carburetor barrels. Only one port per rotor was used under low loads for added fuel economy. A single peripheral exhaust port routed hot gas through the coolest parts of the housing, and engine coolant flowed axially rather than the radial flow used by NSU. A bit of oil was mixed with the intake charge for lubrication.
The 0810 was modified for the racing Cosmos used at Nürburgring. These engines had both side- and peripheral-located intake ports switched with a butterfly valve for low- and high-RPM use
Applications:
The improved 0813 engine appeared in July 1968 in the Series II/L10B Cosmo. Its construction was very similar to the 0810.
Japanese-spec gross output was at 7000 rpm and at 3500 rpm. The use of less-expensive components increased the mass of the engine from.
Applications:
The final member of the 10A family was the 1971 0866. This variant featured a cast-iron thermal reactor to reduce exhaust emissions and re-tuned exhaust ports. The new approach to reducing emissions was partly a result of Japanese Government emission control legislation in 1968, with implementation starting in 1975. Mazda called their technology REAPS. The die-cast rotor housing was now coated with a new process: The new Transplant Coating Process featured sprayed-on steel which is then coated with chrome. Gross output was at 7000 rpm and at 3500 rpm.
Applications:
Mazda began development on a single rotor engine displacing, and was designed for kei car use in the upcoming Mazda Chantez but was never placed into production. It was a slimmed down derivative of the 10A engine as fitted to the R100. A prototype engine is on display at the Mazda Museum in Hiroshima, Japan.

13A

The 13A was designed especially for front-wheel drive applications. It was a two-rotor design, with each chamber displacing so two chambers would displace ; continuing earlier practice, the series name reflects this value. This was the only production Mazda Wankel with different rotor dimensions: Radius was and offset was, but depth remained the same as the 10A at. Another major difference from the previous engines was the integrated water-cooled oil cooler.
The 13A was used only in the 1969–1972 R130 Luce, where it produced and. The next Luce was rear-wheel drive and Mazda would not make a front-wheel drive rotary vehicle until the development of the 8C for use in the 2021 Mazda MX-30, which is used to power an electric motor spinning the front axle.
Applications:
The 12A is an "elongated" version of the 10A: the rotor radius was the same, but the depth was increased by to. It continued the two-rotor design; with the depth increase each chamber displaced so two chambers would displace. The 12A series was produced for 15 years, from May 1970 through 1985. In 1974, a 12A became the first engine built outside of western Europe or the U.S. to finish the 24 hours of Le Mans.
In 1974, a new process was used to harden the rotor housing. The Sheet-metal Insert Process used a sheet of steel much like a conventional piston engine cylinder liner with a chrome plated surface. The side housing coating was also changed to eliminate the troublesome sprayed metal. The new "REST" process created such a strong housing, the old carbon seals could be abandoned in favour of conventional cast iron.
Early 12A engines also feature a thermal reactor, similar to the 0866 10A, and some use an exhaust port insert to reduce exhaust noise. A lean-burn version was introduced in 1979 and 1980 which substituted a more-conventional catalytic converter for this "afterburner". A major modification of the 12A architecture was the 6PI which featured variable induction ports.
Applications:
  • 1970–1972 Mazda R100
  • 1970–1974 Mazda RX-2, and
  • 1972–1974 Mazda RX-3, and
  • 1972–1974 Mazda RX-4
  • 1972–1980 Mazda Luce
  • 1978–1985 Mazda RX-7,
  • Aero Design DG-1 racing aircraft used two Mazda RX-3 engines, each driving a propeller—one at the front, the other at the rear of the aircraft.
  • Richter Ric Jet 4 experimental aircraft
  • Lean-burn
  • * 1979–1985 Mazda RX-7
  • * 1980–1985 Mazda RX-7
  • 6PI
  • * 1981–1985 Mazda Luce
  • * 1981–1985 Mazda Cosmo