Tokyo Auto Show - Sept. 17, 2007
Mazda will show off next generation Rotary Engine technology, including a larger rotary, the first time the actual displacement of a 2 rotor engine will have changed since 1974 if it makes production. The last time a production engine increased was with the introduction of the 13b in the RX-4 and REPU in 1974. The engine will also be the first time the other dimensions of the rotor will have changed since the 13a in the 1971. The 13a was the engine that powered the front-wheel-drive Japanese only Luce.

The car shown is said to have clues from the Kabura and Ryuga, as well as other Mazda DNA. It will be the first all new Mazda Rotary Coupe since the third-generation RX-7 launched in 1991. The car is said to have a particularly distinctive exterior design, with lightweight, compact and high-output next generation RENESIS(2) rotary engine. It will epitomize Mazda's spirit of sports car, as the RX-7 won popularity among the customers since its 1978 launch. The last RX-7 model (FD3S) ended a 10 year production run in August 2002, and is sometimes still regarded as the pinnacle of Mazda Engineering and Design.

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Next Generation RENESIS (Rotary Engine 16X)
Mazda is celebrating 40 years of rotary engine development since the introduction of the rotary engine Cosmo Sport in 1967. To mark the occasion, we have begun development of the direct injection 16X, a 1600 cc (800 cc x 2) powerplant with a new trochoid chamber shape aimed at further improving thermal efficiency and boosting torque at all engine speeds. The 16X is made possible through the experience and technology gained with RENESIS, a unit featuring side exhaust ports and other features that greatly advanced the rotary engine.

All-round change of dimensions
With the next-generation RENESIS, Mazda has changed the cocoon shape of the trochoid rotor housing. This marks a further evolution of the basic structure of the engine which began with an early period of over seven years spent researching the optimum trochoid shape, from the introduction of the first 10A (491cc x 2) in 1967, followed by the 13A (655cc x 2), 12A (573cc x 2) and the current 13B (654cc x 2). This shape change is brought about by reducing the rotor housing width and housing thickness while increasing the trochoid outline, resulting in a displacement increase to 800 cc x 2. But despite this dimensional increase, we were able to keep the engine itself essentially as compact and lightweight as the current RENESIS.

As for its specific shape, increasing the trochoid radius and eccentricity and reducing rotor housing width achieved a longer stroke, thereby shrinking the combustion chamber aspect ratio. Due to this modification, the surface area-to-volume ratio of the combustion chamber decreases, enabling a reduction in cooling losses. Also, since the very tight space in the combustion chamber is reduced, flame growth is promoted and the engine exhibits faster combustion and better fuel economy. As well as improving fuel economy-an essential part of environmental performance-we are simultaneously pursuing higher torque at all engine speeds.

Direct injection technology
The next-generation RENESIS is the first gasoline rotary engine developed to use direct fuel injection. The system inherits the basic design concept of the hydrogen rotary engine, injecting gasoline in a high-pressure spray during the intake cycle, promoting atomization and vaporization of fuel and the formation of a stable air-fuel mixture. The latent heat of fuel vaporization lowers the temperature of the air-fuel mixture, thus raising the engine’s charging efficiency. At the same time, it reduces fuel adhesion to the chamber wall, which has been a problem of the conventional port injection system, while promoting a more homogenous air-fuel mixture. This in turn leads to substantially improved thermal efficiency and increased torque, and Mazda is actively researching further improvements in efficiency.

Aluminum side housing
In developing the new engine, Mazda engineers have dramatically improved both power output and environmental efficiency. They have also contributed to further increases in fuel-economy and driving performance by lightening the vehicle weight. By keeping the engine’s exterior dimensions about the same as the current RENESIS, which allows more of the vehicle’s volume to be devoted to passenger space, and by using an aluminum side housing aiming at lighter weight than the current RENESIS along with various other measures, Mazda continues to advance the merits of the compact and lightweight rotary engine.