In a wall-guided system, the stream of fuel hits the piston floor, forming a cloud of fuel and air that moves toward the spark plug (top). In spray-guided gasoline direct injection, a hollow cone of fuel forms at the injection nozzle. This cloud of fuel and air remains stable up until the precise moment when it needs to ignite (bottom).

The Direct Hybrid uses DaimlerChrylser’s second-generation spray-guided gasoline direct injection (GDI) technology in a 3.5-liter, 4-valve V6 with fully variable valve timing.

For the spray-guided combustion process, the engineers developed a special piezo injection valve and a fuel system with a high pressure of 200 bar. A special injection nozzle that opens to the outside and is activated at ultra-high speeds by a piezo crystal ensures the stability of the injection spray—one of the critical aspects of the process.

The key is in the control of the fuel spray and the extremely rapid timing of the piezo nozzle, which allow the formation of a fuel-air mixture with the ideal flammability. The thermodynamic efficiency improves markedly and enables low fuel consumption with better engine performance.

With the spray-guided direct injection process, the Direct Hybrid 3.5-liter V6 generates an output of 215 kW (292 hp) at 6,000 rpm. Its maximum torque of 365 Nm is already accessible at 2,400 rpm and remains available over a broad range of engine speeds up to 5,000 rpm.

The exhaust treatment for this layered direct injection process takes place in the double-stream exhaust system. A NO_xtrap system for reducing the nitrogen oxides is also used, in addition to the two bulkhead catalytic converters and controlled recirculation of exhaust gas in each branch. The results meet both current EU 4 exhaust emissions standards and the forthcoming EURO 5 limit.

A 6-kW electric motor is installed between the engine and the 7G-TRONIC automatic transmission’s converter. Depending on the driving situation, it functions as a starter or a generator, and provides a tractive boost on startup—up to 250 Nm—at other points during operation.

The combination of motor and engine boosts the maximum available torque to 395 Nm and makes the vehicle’s starting characteristics powerful.

The mild Direct Hybrid consumes 8.3 liters of gasoline per 100 km (34 mpg US). Compared with its predecessor model, the S 350 V6 (W 220), the power has been increased by 19% and the consumption cut by 25%.

Regenerative braking recharges the lithium-ion storage system. Mercedes-Benz is also investigating supercapacitors. (The new BMW X3 hybrid concept uses supercapacitors as its energy storage system. (Earlier post.)

The Bluetec diesel hybrid uses the same electric motor and energy management systems, but combined with a 3.0-liter V6 diesel, a variant of the 320 CDI, that delivers 173 kW (235 hp) of output and a maximum torque of 540 Nm that is already available at between 1,600 and 2,400 rpm.

Combined power for the diesel hybrid is 179 kW (243 hp) and combined torque is 575 Nm. Fuel consumption is 7.7 l/100km (36.7 mpg US)—a fuel savings of 20% for comparable power and torque.

The Bluetec SCR system requires a separate urea (AdBlue) tank to hold the exhaust additive. This reacts with the nitrogen oxides in the catalytic converter to form ammonia (NH₃) as an intermediate product which then is converted into the water and nitrogen.

The hybrid uses a 22-liter tank built into the spare-wheel well of the S Class. Average AdBlue consumption is around 0.1 liter per 100 kilometers. Should the supply run out before the next service, a signal in the instrument cluster warns the driver to visit a service station in plenty of time. This tank is therefore sufficient for the driving distance between two service intervals and the service personnel simply fill the tank up automatically when the car goes in for its next service.

DaimlerChrysler also emphasized its ongoing development work on the two-mode hybrid powertrain with GM (and now BMW), reiterating that it would concentrate developing applications of this powertrain for luxury-class cars with rear-wheel and all-wheel drive.

The company also stressed, however, the potential for natural gas, Gas-to-Liquid synthetic fuels, and Biomass-to-Liquid fuels as part of a portfolio of solutions.