Rotary Engine

History of Rotary

Engineering History
The Advanced Rotary Engine
Turbo and Dynamic Superchargers

The Cosmo RE Turbo, which went on sale in 1982, was the world's first rotary engine car equipped with a turbocharger. The Type 12A turbo engine was also the world’s first rotary engine that came with an electronically controlled fuel injection system.

The rotary engine, which is inherently resistant to knocking, is better suited to turbochargers. Due to its unique characteristics of a stronger exhaust pulse caused by the near-instantaneous opening of the exhaust port, and a short and smoothly shaped manifold, the rotary engine’s exhaust system has more energy to drive the turbocharger turbine compared with the reciprocating engine.

The Cosmo RE Turbo was the fastest commercial vehicle available in Japan at that time and it clearly demonstrated the attractiveness of the rotary engine. Shortly after came the debut of the "Impact-Turbo," developed exclusively for the rotary engine and delivering even further improvements in engine response and output.

The "Dynamic Supercharging" system was adopted in 1983 for the naturally aspirated (NA) Type 13B rotary engine. This system used the pressure wave arising from the phase difference between the two rotors as an intake pulse to force air into the combustion chamber at the optimal moment. In short, this system delivered supercharging effects without the aide of a turbo or supercharger.

Equipped with this dynamic supercharging system, and with the six-port induction system (three intake ports for each rotor) and a dual injector system with two fuel injectors per chamber, the type 13B rotary engine achieved significant output increases regardless of the speed range. The dynamic supercharging system was further improved in 1985 through changes to the surge tank configuration.

Twin-Scroll Turbo

To improve the driving performance of the turbo rotary engine, the second generation Savanna RX-7 came with the Type 13B engine linked to a Twin-Scroll Turbo to minimize turbo lag. Exhaust gas supplied to the Twin-Scroll Turbo was divided in two, a large scroll and a small scroll, which allowed the turbine to be powered step-wise. With this configuration, the single turbocharger acted as a variable turbo and was sufficiently effective at both low and high rpm.

Second generation Savanna RX-7
Second generation Savanna RX-7

In 1989, the Twin-Scroll Turbo evolved into the Twin-Independent-Scroll Turbo, which had a more simplified configuration. When this new turbocharger was coupled with other improvements in the engine, it provided more outstanding low-speed torque and improved responsiveness.

Since 1983, Mazda has used a dual fuel injector system which features two injectors in each rotor chamber. Generally speaking, a small nozzle is more desirable at low speeds as it can atomize fuel more effectively for more stable combustion, while a large nozzle is better at high speeds as it can provide larger volumes of fuel to boost performance. Mazda’s electronically controlled fuel injection system was developed to control the supply of fuel to these nozzles over a wide range of engine operations. For the dual-rotor 13B-REW and the Triple-rotor 20B-REW rotary engines, both put into mass production in 1990, the dual injectors were further evolved into air-mixture injectors, which achieved more than double the degree of fuel atomization.

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Related information

Dynamic Supercharging System

Dynamic Supercharging System
This system used neither turbo nor supercharger, but filling efficiency could be drastically increased over the conventional design, by utilizing pressure waves generated inside the intake tracts by the sudden opening and closing of the ports.

Twin-Scroll Turbo System

Twin-Scroll Turbo System
This system helps reduce the turbo-lag, a traditional drawback of the turbo-charged engine. The duct leading the exhaust gas to the turbine was split into two passages, one of which was closed by a valve to accelerate exhaust gas flow at low speeds.

How a Rotary Engine Works

Watch an easy-to-understand animated explanation of how a rotary engine works.