Hybrid concept car achieves record fuel economy

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Volkswagen has built a concept diesel-electric hybrid that achieves a fuel economy of 313 miles per gallon, a record for such vehicles.

Unveiled at the Qatar motor show this week, the XL1 has actually been in development for around 10 years and could go into low-volume production, according to Angus Fitton, product affairs manager at Volkswagen.

‘The concept has evolved, so it’s a mixture of making clean-sheet design and setting out to make the car as efficient as possible,’ he told The Engineer.

Indeed, back in 2002 Volkswagen released the rather spartan ‘VW one-litre’ concept which used a single-cylinder 8.5bhp diesel engine to achieve a fuel economy milestone of one litre per 100km (or 285mpg).

‘In many ways it was a crude vehicle to drive, but it did demonstrate that if you took vehicle efficiency to extremes, this is what you could achieve. Many of the lessons learnt in that car made it into, for example, Bluemotion models.’

The concept was taken further in 2009 with the quicker and more practical ‘VW L1’, which had a two-cylinder TDI diesel hybrid engine – although fuel economy dropped to 189mpg.

Now, the XL1 hybrid combines practicality with a fuel economy of 313mpg (0.9 litres per 100km) and a CO2 emissions value of 24g/km.

The car can be driven for 22 miles (35km) on its 27bhp electric motor before the 48bhp diesel engine takes over. The battery is charged from a conventional household electric outlet, although it can also be regenerated through energy recovery from braking.

Streamlining and weight were also major considerations – the body was constructed from carbon-fibre-reinforced polymer parts (CFRP) using a unique process called advanced Resin Transfer Moulding (aRTM), developed and patented by Volkswagen. The teardrop-shaped monoque achieves drag coefficient of Cd 0.186.

‘Every element of the car is designed to be highly efficient, from the chassis, to the aerodynamics, to the engine, everything has been designed to reduce loading on the engine and to therefore maximise economy and lower emissions,’ said Fitton.