Avoiding the problems of the Wankel engine

The Wankel rotary engine was hailed as ‘revolutionary’ during the late 1950s and early 1960s and its subsequent failure has caused most ICE engineers to pre-judge the R6 eco-engine in the same light. Despite its own radical architecture, the Wankel engine utilised a traditional 4-stroke Otto cycle. The best Wankel engines are only about 30% efficient due to a combination of low compression ratio (~9:1) and inefficient combustion due to the very shallow elongated combustion chamber. Wankel engines also have significant issues with overheating, seal wear, high emissions and noise.

The R6 eco-engine can operate at much higher compression ratios due its HCCI combustion strategy which inhibits pre-ignition and due to the architecture of its two inter-locking rotors which switch instantly from compression to expansion, avoiding potential damage from detonation/ engine knock. The R6 eco-engine combustion chamber is hemispheroid in shape which promotes complete combustion of the fuel-air mixture.

The R6 eco-engine uses ferrous bonding, abradable thermal barrier coatings and non-contact labyrinth sealing similar to a turbine. The peripheral sealing surfaces of the rotors are large and the side surfaces have a series of grooves etched into them. At pressures of >100bar and rotational speeds of 2,000 – 4,000 rpm there is not enough time for more than a small percentage of blow-by losses. This is not detrimental since it contributes to the engine internal EGR, for ultra-low emissions.

Although like the Wankel engine, the R6 eco-engine has a ‘hot’ side and a ‘cold’ side, the R6 eco-engine utilises low pressure intake air scavenging of the combustion and expansion chambers and water injection evaporative cooling of internal exhaust gas recirculation. Therefore, the two sides of the engine are much better thermally balanced. Since there is no contact of mechanical seals, the R6 eco-engine does not suffer from seal wear and should be exceptionally durable and low maintenance. Since the R6 eco-engine combustion geometry has a much lower surface area to volume ratio, utilises HCCI combustion and does not burn lubrication oil, emissions should be dramatically lower than for a Wankel engine. Due to the R6 eco-engine’s over expansion, exhaust pressure and temperature are significantly lower, dramatically reducing noise.