Lightweight construction as a factor in exemplary diesel driving pleasure

The choice of materials, technical design, fuel injection and engine management system of the V6 diesel engine reflect the state of the art.

Mercedes-Benz has developed an aluminium crankcase with cast-in grey iron cylinder liners for this unit, which makes a major contribution to weight reduction. As a result, the new six-cylinder engine weighs a total of only around 208 kilogrammes (acc. to DIN) and achieves a remarkable power-to-weight ratio of 0.83 kW/kg; a major contribution to the outstanding agility and handling offered by the S 320 CDI by the new engine.

Piezo-injectors for finely metered fuel injection

Third-generation common-rail direct injection is a further technical highlight of this engine. It produces significant improvements in terms of fuel consumption, exhaust emissions and combustion noise.

Instead of the previous solenoid valves, the injectors are equipped with piezo-ceramics whose crystalline structure changes within milliseconds under an electric voltage.

This lifts the needle jet at the tip of the injector with a precision of only thousandths of a millimetre and thereby achieves an extremely fine jet of fuel.

Moreover, piezo injectors are considerably lighter and operate at twice the speed of conventional solenoid valves. With a response time of only 0.1 milliseconds, the fuel injection process can be even more precisely suited to the current load and engine speed situation, with favourable effects on emissions, fuel consumption and combustion noise.

Five fuel injections per power stroke at a peak pressure of up to 1,600 bar are possible thanks to this piezo-ceramic technology.

An electrically controlled intake port shut-off modifies the swirl characteristics of the air flowing into the cylinders, which also optimises the combustion process with the aim of reducing the fuel consumption and exhaust emissions even further.

The likewise newly developed electronic control unit manages all the engine functions – from the quick-start glow system and automatic start function to control of the high-pressure pump. The VNT turbocharger (Variable Nozzle Turbine) with electrically adjustable turbine blades, exhaust gas recirculation with a control valve and intake air throttling are also regulated as the situation requires on the basis of measured data.

Catalytic converters and a particulate filter for emission values below the EU-4 limits

Thanks to this precise engine management system, the nitrogen oxide and particulate emissions of the V6 engine are within the strict limits of the EU4 standard. Two oxidising catalytic converters are responsible for conversion of the carbon monoxide and hydrocarbons: a so-called starting converter located near the engine and a main converter in an under floor location.

To reduce soot emissions even further, Mercedes-Benz offers a maintenance-free particulate filter system which is standard equipment in the new S 320 CDI in various markets. The filter regenerates without the use of additives by selective adjustment of different engine functions.

Depending on the operating parameters and filter condition, the variable third-generation common-rail technology allows up to two precisely coordinated post-injections with the aim of specifically increasing the exhaust temperature. This means that the particles trapped in the filter are burned off in a controlled manner.

Key data for the V6 turbo-diesel engine in the new S 320 CDI: