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Mercedes announced about a month ago that they would be showing off their new DiesOtto engine in a new concept car at the Frankfurt Motor Show. As a refresher, the DiesOtto (Diesel + Otto cycles) is an HCCI/spark ignition combination engine. It's basically the same as the GM HCCI prototype we drove in an Opel Vectra and Saturn Aura recently. The 1.8L four cylinder engine has an output of 238hp and 295ft-lb and is rated at 44.4 mpg (US) in the F700.
The F700 that contains this very efficient new engine is a full size luxury sedan of which we have our first tease in the photo above. From what can be seen in the photo it looks like the F700 has a long hood/short rear deck profile, an odd choice for a car with such a small engine. Regardless we'll probably see elements of this design in future Mercedes models, perhaps the new E-Class next year?