Automakers explore gas-saving technology

Daimler calls its version the DiesOtto. During startup and under full load, the engine uses a spark plug to ignite the gasoline/air mixture, as in a conventional gasoline engine. At low and medium engine speeds, within one engine stroke, the motor automatically switches to a mode similar to that of a diesel, in which it ignites the gasoline-air mixture by compressing it.

Mercedes claims that its DiesOtto motor minimizes nitrogen oxide emissions because the compression ignition takes place at relatively low temperatures (unlike a conventional diesel) and thus generates only small amounts of nitrogen oxides. As a result, the exhaust gas treatment requires nothing more than a standard three-way catalytic converter, rather than the sophisticated controls needed for a pure diesel.

Daimler has a 1.8-liter V-4 DiesOtto in its F 700 show car, a full-sized luxury sedan. This little motor — which bristles with other advanced technology, such as two sequential turbochargers, variable valve timing and variable compression ratio — bangs out 238 hp. A hybrid electric motor adds another 20 hp.

Probably the toughest part of the DiesOtto development is managing the transition between spark- and compression-ignition and making it smooth and transparent to the driver. In all likelihood, this idea is still several years away (at best) from being in a production vehicle.

Two-stroke, four-stroke
An even more radical long shot is an internal combustion engine that switches between two- and four-stroke operations. Most consumers associate two-stroke with chain saws, grass trimmers and smelly exhaust, but this technology also found its way into a few automobiles, such as Saabs in the 1950s and the unloved East German Trabant. Now, a consortium led by Ricardo of the U.K. — and including Ford Motor, Denso, Ma2T4, Brunel University in the U.K. and the University of London — is investigating such an engine.

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The camless engine
Over the past two decades, automakers have adopted variable-valve technology, in which various mechanical systems vary the lift and duration of valves opening and closing for intake and exhaust in order to maximize power and efficiency and minimize exhaust emissions. This technology in one form or another is widespread in modern automobiles.

The next big breakthrough could be the camless engine, a motor that does away with the conventional camshaft to operate the engine valves and replace them with electromechanical or hydraulic-powered values.

The lure of the camless motor? A significant reduction in internal friction from powering a crankshaft and associated belts, gears, etc., as well as precise control of valve timing. French auto parts supplier Valeo claims this technology could deliver 20 percent gains in fuel efficiency, emissions reduction and low-end torque. According to Valeo, this technology could appear in a production motor in the near future.

The challenge is designing a camless system so that a possible failure of the valves is not catastrophic to the engine; other issues are reliability, noise and vibration.

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