It’s been 40 years since Mazda introduced the first rotary engine in the Mazda Cosmo Sport in 1967. This year, Mazda puts another marker on the history of the Mazda rotary engine with the RENESIS 16X, the successor to the 13B-MSP in the Mazda RX8.
The new 16X rotary engine uses new trochoid-shaped chambers aimed at improving thermal efficiency and increasing torque across all engine speeds. Mazda has been continuously researching the best shape for the trochoid chambers ever since the first 10A rotary in 1967, followed by the 13A, 12A and now the 13B.
The new trochoid chamber has had its rotor housing width and thickness reduced while the trochoid outline has been increased, resulting in a displacement increase to 800cc per rotor – this means a 1.6 litre displacement as the engine’s 16X name indicates. This is despite exterior dimensions of the engine being about the same as the current 13B.
The trochoid shape has had its radius and eccentricity increased. Stroke has also been increased, this means better torque. Due to the change in shape, not only is an increase in displacement achieved but the surface area-to-volume ratio of the combustion chamber is reduced, enabling a reduction in cooling losses. Flame growth is also promoted. The engine uses side housings made of aluminium, and this together with other weight reduction methods make the new 16X lighter than the 13B.
The 16X rotary engine is also the first gasoline rotary engine to use direct injection. This was developed from the hyrogen injection system used in the hydrogen rotary engine. Gasoline is injected via a high pressure spray during the intake cycle. This spray also tends to reduce fuel adhesion to the chamber wall, promoting a more homogenous air-fuel mixture. This results in better torque and thermal efficiency. Power and fuel economy is expected to be 20% better than the technologies in the 13B can achieve.
A concept version of this engine is installed in the Mazda Taiki Concept, and in that car it drives the rear wheels through a 7-speed dry twin clutch gearbox.