The old motor roars back

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: valves instead of pushrods operated by a camshaft. As each valve can be operated independent of any other, all sorts of tricks become possible, including shutting down cylinders and switching temporarily from the traditional four-stroke Otto cycle (as developed by Nicolaus Otto, a German engineer in 1876) to a type of Atkinson cycle (an ultra-lean system invented as a rival in 1882 by James Atkinson, a British engineer, but which suffered from a lack of power). The Toyota Prius already uses a form of Atkinson cycle for the petrol engine that operates alongside an electric motor in its hybrid system.

Valeo reckons that on average their e-Valve system can cut fuel consumption and CO2 emissions in a car by up to 20%. It could also be used to make three- and two-cylinder engines that run efficiently and smoothly. These tiny engines could power small cars directly, combine with electric motors in hybrids or work as ‘get-you-home’ engines or range-extending generators in plug-in electric cars.

Fiat is investing heavily in smaller engines with its new valve-control system, Multiair. This uses hydraulics and electronics to optimise valve settings. When combined with a turbocharger (a supercharger driven by exhaust gases), Fiat engineers talk of producing a ‘downsized’ two-cylinder engine that performs like a bigger four-cylinder one, but with fuel savings of some 20%. Fiat is expected to start using Multiair engines in its cars in a year or so.

Using a combination of variable valve-control, fuel injection and turbocharging, Daimler is developing an entirely new type of engine. It can switch between operating as a petrol engine, with agility and power, to operating as a diesel, with economy and torque. The DiesOtto engine, as Daimler has called it, starts as a petrol engine with spark plugs igniting the mixture of fuel and air in its cylinders, and remains as a petrol engine when high performance is needed. But at low and medium speeds the engine switches into diesel mode, in which the fuel is ignited by compression and heat alone. A 1.8-litre four-cylinder test version of DiesOtto fitted to a prototype Mercedes S-class saloon produced plenty of power, but also returned an average fuel consumption of 5.3 litres per 100 km (equivalent in America to 44.4 mpg)—extremely good for a such a big car. The vehicle’s emissions were also lower.