DIESOTTO: Gasoline engine with diesel DNA

 

The F 700’s drive system combines the low-emissions of gasoline engines with the fuel economy of diesel systems. To achieve this, development engineers linked several proven technologies with a new combustion process. The first thing they did was to downsize the engine by reducing its displacement and number of cylinders. The resulting drop in output in the 1.8-liter unit was more than offset by two sequential turbochargers that go into action quickly and deliver high torque.

A further key component is a gasoline direct injection system that utilizes extremely precise piezo injectors and ensures a homogeneous low-fuel mixture in the cylinder that cuts fuel consumption by around ten percent. There’s also a two-stage valve train assembly and a variable crankshaft drive that enable continuously variable adjustments to opening intervals and compression ratios.

The all-new controlled auto ignition system brings the diesel principle to the gasoline engine. During starting and full load operation, the fuel/air mixture is ignited by a spark plug as in conventional SI engines. However, controlled auto ignition occurs under the partial load conditions (low and medium engine speeds) that are most common in driving. Because such partial load operation occurs at relatively low temperatures, only small amounts of nitrogen oxides form as a result — which is why exhaust gas treatment in the DIESOTTO requires nothing more than a standard three-way catalytic converter.

The F 700 also includes a hybrid module that supports the gasoline engine. To this end, a disk-shaped starter-generator is integrated into the housing for the 7G-TRONIC automatic transmission. This high-torque unit assists the engine by acting as an electric motor during initial acceleration and in stop-and-go traffic. When the vehicle brakes and rolls, the starter-generator recovers energy, which it stores in a high-voltage battery and uses the next time the vehicle accelerates. Daimler engineers also developed an extremely efficient engine-control system to ensure that the individual sub-systems would together form an effective drive concept.

The maximum output of the DIESOTTO engine in the F 700 is 175 kW (238 hp); the starter-generator contributes an additional 15 kW (20 hp). The maximum torque is 400 Nm, and the F 700 accelerates from 0 to 100 kilometers per hour in 7.5 seconds. As far as top speed is concerned, the vehicle is limited to 200 kilometers per hour, while the NEDC fuel consumption is 5.3 liters per 100 kilometers, which corresponds to CO2 emissions of only 127 grams per kilometer.