By Andrew Noakes
First drive
16 June 2008 17:16
Advanced engineering wrapped in ‘aquatic’ styling made the Mercedes F700 concept car one of the stars of the Frankfurt motor show in September 2007, and CAR has been itching to put its technologies to the test ever since.
Flip-over, cork-faced seats and a navigation system run by a virtual assistant called Gloria are novel enough, but we’re really here to find out about the revolutionary DiesOtto engine and Pre-Scan suspension.
What’s so clever about the Mercedes F700’s engine, then?
Mercedes calls it DiesOtto because it combines elements of diesel and petrol (Otto cycle) engines. Centrepiece of the DiesOtto concept is a new combustion system called Homogeneous Charge Compression Ignition (HCCI), which several manufacturers are now developing. It uses carefully controlled in-cylinder temperature and pressure conditions to ignite the air/fuel mixture without a spark.
The result is very clean, efficient combustion, but the drawback is that HCCI struggles to work over a wide range of engine speed and load. So for cold starts and full-throttle acceleration, DiesOtto switches back to spark-ignition mode.
So is the F700 a green special, or does it fly too?
With twin sequential turbochargers and a capacity of just 1.8 litres, the F700 DiesOtto generates 238hp. An electric motor adds another 20hp and boosts total torque to 295lb ft. As a result, the S-class-sized F700 has S350 performance.
Thanks to the efficiency of the engine, plus an urban start/stop function and regenerative braking, it returns up to 53mpg. Highly impressive for a big limo like this.
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