A rotary engine is even less efficient than a piston internal combustion engine, so its use powering the range extending generator is a bit surprising. But, it's only 254cc. Very impressive fuel consumption figure of 1.9 litres/100 kilometres is quoted, but as one of the commenters notes, a fuel capacity of 12 litres & a range of 250 km on a tank is 4.8 litres/100km [12/(250/100)] on fuel.
Some very impressive figures were claimed for the Chevrolet Volt, before the official figures of 6.4 l/100km (combined city & highway) on petrol were released.
Having said the above, it must be said that actual fuel use for a range extended vehicle can be very low if it is mainly used for short journeys & charged frequently.
