25 Jul 07 10:13
Mercedes DiesOtto engine
Mercedes has revealed details of the DiesOtto engine designed to use the best features of petrol and diesel technology in a planet-friendly new package.
Still at the concept stage, it's a turbocharged 1.8-litre four-cylinder petrol engine that, says Mercedes, would be suitable for use in the S-Class. It could make 235bhp and 295lb-ft of torque, and return an mpg figure in the high 40s. That's the same power as the S320 diesel (but less torque), with more torque (but less power) than an S350 petrol, and better fuel economy than either.
'Our next goal will now be to make the gasoline engine as economical as a diesel. All the preconditions for this are provided by our DiesOtto concept, which incorporates the foremost strengths of both the gasoline engine and diesel engine,' said Professor Herbert Kohler, DaimlerChrysler's chief environmental officer. He said the DiesOtto could do for petrol engines what ultra-clean Bluetec technology - which arrives in Europe later this year after a successful US debut - has done for diesels.
When starting or when being used hard, the DiesOtto's fuel-air mixture is ignited by a spark plug in the conventional way. But at low and medium engine speeds the spark plug is unnecessary, as the engine is able to achieve diesel-style automatic ignition, resulting in lower nitrogen oxide emissions.
The engine has not only variable valve control but also a variable compression ratio. In some cases, an integrated starter-generator will be fitted, similar in principle to that used on the Smart mhd.
More details about the DiesOtto are expected to be revealed next month at the Frankfurt Motor Show.
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