Volkswagen is planning to release a Golf capable of an incredible 2.8 litres per 100km, with emissions of just 75g/km, by 2020.
Planned EU regulations would require an automaker's entire range of passenger vehicles to average 95g/km by then - and that's forcing European automakers to consider some radical fuel-efficiency solutions.
VW's ultra-green fuel-sipper will be released as part of the Golf 8 line-up; it will probably be badged as a blue-e-motion derivative and will include much of the technology featured in the new XL1 concept.
It'll have an 800cc parallel-twin-turbodiesel, derived from the current 1.6-litre, four-cylinder TDI and developing only 35kW, permanently coupled to a 19kW electric motor, as in Honda's hybrids, and driving a seven-speed double-clutch gearbox.
It won’t be able to run on battery power alone because the battery will be too small to power the car for more than a few seconds; the role of the electric motor will be to boost standing starts and for brief periods of hard acceleration, and to recover energy under braking.
The engine will have an alloy block and plasma-coated bores, as per the XL1, with a balance shaft to sort out the inherently unbalanced twin-cylinder layout - all of which is well-established motorcycle technology but hasn't been used in a diesel application before.
It will probably also have the XL1's “pulse starting” feature, that spins the engine up to idle speed for the re-start, making the stop-start cycle practically undetectable.
Sources at VW say improved combustion technology and new materials will increase power density while using less fuel - but that's not going to be enough to get it under the magic three-litre barrier.
It'll also need significant friction reduction and aerodynamic improvement as well as a big weight loss. Sound-deadening material in the shell will be replaced by “white noise” sound cancellation working through the car's audio system and carbon fibre-reinforced composites could be used for the bonnet and roof panels.