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Mazda Developing Next Generation RENESIS Rotary Engine

Next Generation RENESIS (Rotary Engine 16X). Click to enlarge.

Forty years after the introduction of the rotary engine Cosmo Sport in 1967, Mazda is at work on its next-generation rotary powerplant: the direct injection 16X, a 1,600 cc (800 cc x 2) engine with a new trochoid chamber shape aimed at further improving thermal efficiency and boosting torque at all engine speeds.

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).

Shape changes in the new RENESIS. Note the change in shape from the current 13B rotary. Click to enlarge.

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, Mazda was 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, Mazda is simultaneously pursuing higher torque at all engine speeds.

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 homogeneous air-fuel mixture. This in turn leads to substantially improved thermal efficiency and increased torque, and Mazda is actively researching further improvements in efficiency.

The concept Taiki uses the new rotary engine. Click to enlarge.

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.

Mazda Taiki concept. Mazda applied a version of the new RENESIS combined with a dry twin clutch 7-speed power shift in its Taiki concept car, unveiled at the Tokyo Motor Show.



First off I have recently become very interested in the Wankel engine and many misconceptions persist. A higher compresion ratio than 10:1 is certainly possible when the K factor (diameter of the rotor vs. eccentricity) is increased to 8.5-10 as opposed to the typical 7, this is partially what Mazda has done with the 16X and should allow much higher compression, a better shaped combustion chamber via the recess in the rotor not to mention greater mechanical leverage. The remaining challenge is burning all the fuel it inhales and overcoming the trailing quench unburned fuel area. (I have some ideas myself)

The Wankel is by no means inherantly innefficient but it is difficult to get complete combustion and thats why the HC's are high, its unburnt fuel and explains both problems with fuel milage and emmisions.

The Le Mans winning car had much improved BSFC through several design improvements and won partially by virtue of its lower fuel consumption. The wankel actually performs better under highly loaded conditions than a piston engine as previously mentioned.

Consider the fact that Mazda is one small company with a limited budget vs all the major automotive giants research and developement and the 120 year head start for the otto cycle engine and we can see its no comparisson if the tables were turned would the otto cycle engine have a chance? Many of the wankels previouse difficult problems have been resolved or severely diminished and it is by no means fully developed technology.

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