The development of the rotary engine began with the German inventor Felix Wankel. A man without an engineering degree, or even a driver’s license, wrote automobile history and has taken his place alongside other automotive engineers like Nicolaus August Otto, Carl Benz, Gottlieb Daimler, Wilhelm Maybach and Rudolf Diesel.

Wankel was fascinated his entire life with machines, even though he did not possess a technical education. He was never an abstract thinker, but an inventor who had a different view of, and kept a certain distance to, mathematics. “I don’t like the formulas,” he said. Despite this, he is recognized as the father of the rotary engine.

No one formulated Wankel’s importance to the automotive industry better than Kenichi Yamamoto, Director of Research and Development, and later Chairman of the Mazda Motor Corporation. “The automotive world lost one of its greatest thinkers,“ Yamamoto said upon hearing of the death of Felix Wankel on October 9, 1988. On that day, Mazda Motor Corporation announced that it would continue to develop engines without valves and connecting rods according to the Wankel principle. Mazda kept its word and, since first starting to work on Wankel’s engine in 1961, has built over 1.8 million rotary engines—most of them for the Mazda RX-7.

Today Mazda is the only major carmaker to continue the legacy of Felix Wankel’s rotary engine concept with the latest rotary engine, RENESIS, under the bonnet of the Mazda RX-8. Constructed with twin-rotors it is available in two power versions. The entry level engine produces 192ps of power and the flagship engine 231ps, making RENESIS the most powerful non-turbo Mazda rotary engine.

How The Rotary Engine Works

The rotary engine functions in a way that is fundamentally different than conventional internal combustion engines. The piston is in fact a rotor that spins in the centre of a housing that is shaped like an oval pinched slightly in the middle. The rotor has a set of internal gear teeth cut into the centre of one side. These teeth mate with a gear that is fixed to the housing. This gear mating determines the path and direction the rotor takes through the housing.

The eccentric shaft is turned by the rotors in a way similar to a handle turning a winch. With every 360-degree turn of the rotor, the output shaft turns three times. The rotor itself is triangular shaped, and its three points are in constant contact with the housing wall through an apex seal. The shape of the housing ensures that the rotor’s centre point forms a closed circle with every complete turn. The three flanks of the rotor combined with the inner surface of the housing form three working chambers, whose volume constantly changes during a single turn of the rotor. This architecture makes a traditional crankshaft and valves unnecessary. The only moving parts are the rotary piston itself and the eccentric shaft. These characteristics mean that a rotary engine is lighter and more compact than a traditional reciprocating engine.

While a normal four-cycle piston engine needs four cycles to facilitate two turns of the crankshaft, rotary engines achieve all four cycles with only one turn of the rotor. The rotor itself produces the power of the rotary engine and applies it to the eccentric shaft, which fulfils a function comparable to the crankshaft of a traditional piston engine.

The Unique Characteristics of a Rotary Engine

Rotary engines with more than a single rotor are characterized by their extreme operating smoothness and low vibration. With a twin-rotor engine the lobes of the eccentric shaft are placed 180 degrees in relation to each other, which ensures an almost perfect balance of mass. A twin-rotor engine operates more smoothly than a six-cylinder piston engine with hardly any vibrations at all. The rotary engine is also characterized by its uncomplicated architecture, with a minimum on components, which means less weight and a compact size. The extremely compact size of Mazda RX-8’s rotary engine allowed engineers to place it more towards the centre of the vehicle, in a front-midship layout, which meant a 50/50 weight distribution over the front and rear axle. This guarantees excellent handling characteristics.

RENESIS: Rotation Instead of Translation

The name RENESIS stands for “rotary engine (RE) genesis” and is representative of a revolutionary approach to rotary engine technology at Mazda. RENESIS is an elegant combination of high performance potential, on the one hand, and acceptable fuel consumption and low emissions on the other.

Starting point for RENESIS development was the MSP-RE (Multi-Side-Port Rotary Engine), first shown in the concept sports car RX-01 at the Tokyo Motor Show in 1995. Four years later, a refined version of the engine was presented at the 1999 Tokyo Motor Show in the concept vehicle RX- EVOLV. RENESIS as it is now being launched in the new Mazda RX-8, is the final production version of these concept engines, and the product of several years of unbroken development.

RENESIS developers were give three clear goals. The new engine should produce roughly the same power as the twin-turbo 13B engine of the Mazda RX-7, but at the same time use less fuel and produce a minimum amount of emissions. Mazda developers achieved these goals. The result of their effort is RENESIS, a twin-rotor, water-cooled engine with two chambers, each with 654 cm³ volume capacity. RENESIS comes in two power versions. The 192ps reaches maximum torque of 220 Nm at 5,000 rpm. The 192ps version’s torque curve climbs quickly, then flattens out to a high plateau-like shape, which means there is plenty of power available over a wide speed range. In fact, 80 percent of peak torque is available at 2.500 rpm with the last 20 percent prior to peak torque at 5.000 rpm achieved gradually — not in a sudden jump of torque — over a wide speed range. This characteristic makes everyday driving enjoyable and has definite advantages for city driving.

The 231ps achieves maximum torque of 211 Nm at 5,500 rpm. These figures show how the 231ps version of RENESIS has been modified to be more performance oriented. It develops its power at higher engine speeds. For this reason, the 231ps version has a maximum engine speed of 9,000 rpm, clearly higher than the 192ps version, which reaches maximum engine speed at 7,500 rpm.