Glossary: Key technical terms

48 V electrical system: This supplies four times the power of its 12 V predecessor at the same current and allows the electrification of key components (e.g. air-conditioning compressor) or the introduction of new technologies (e.g. àelectric auxiliary compressor) and therefore fuel savings. The low-voltage system does not require the additional safety architecture of a high-voltage network.

EGR (exhaust gas recirculation): NOx formation is influenced primarily by the combustion temperature. Adding an inert gas to the combustion process lowers the maximum temperature in the combustion chamber, thereby reducing the formation of NOx. An example of such an inert gas is exhaust gas, a small proportion of which is recirculated to the combustion chamber. Mercedes-Benz employs multi-way EGR in the OM 654/656. This is a combination of low-pressure EGR (the exhaust gas is drawn off after it has been treated and is supplied ahead of the turbocharger) and high-pressure EGR (the exhaust gas is drawn off before the turbine of the turbocharger and before it has been treated; it is supplied behind the charge-air cooler and the throttle valve). At all operating points, this reduces the formation of both nitrogen oxides and particulates even before the exhaust gas undergoes treatment.

Multi-way EGR was used for the first time in the Mercedes-Benz OM 651 engine for the A-Class model series in the A 220 CDI/A 220 d.

Spectacle honing: With this process, the cylinder liners receive their mechanical surface treatment when already bolted in place. A jig resembling spectacles is bolted to the engine block in place of the cylinder head, which is mounted later. Any cylinder distortion that might occur during final assembly is therefore taken into account or eliminated as the cylinder liners are honed.

Closed-deck construction: The engine block cover plate is extensively closed in the area around the cylinders. It is penetrated only by small openings for the coolant. The advantage of this construction is the higher stiffness of the cover plate, which has positive effects on cover plate deformation, cylinder distortion and acoustics.

Common rail: Here, all the cylinders of the direct-injection diesel engine are supplied with fuel from a common distribution pipe (common rail). The high pressure line is under a permanent pressure of 2000 bar or higher, which stores diesel fuel and distributes it to the injectors.

Efficiency label: From December 2011, the Energy Consumption Labelling Directive for passenger cars (Pkw-EnVKV) requires every new car to carry such a label. The CO2 efficiency classes are assigned depending on the vehicle weight. To this end, the legislators have defined a reference value of the CO2 emissions for each vehicle weight. The heavier the car, the higher the reference value. Determining the efficiency class requires comparing the actual CO2 emissions with the reference value. If the CO2 emissions are exactly identical to the reference value, the car is assigned efficiency class E. Efficiency classes A+ to D are assigned to cars emitting less CO2 than the reference value. Vehicles with CO2 emissions that are clearly higher than the reference value are assigned efficiency class F or G.  

Electric auxiliary compressor (eZV): Part of the intelligent turbocharging of the new six-cylinder in-line petrol engine (M 256). This compressor, which is powered by the 48 V electrical system, delivers charge-air pressure independently of engine speed and engine load. Connected in tandem with a large exhaust turbocharger, the eZV ensures a balanced engine response in all rpm ranges and eliminates the turbo lag.

"Hot inside V": In this configuration, the (two) turbochargers are positioned not on the outside of the cylinder banks, but inside the "V" between the cylinders banks. The benefits are: compact engine design, remarkably spontaneous engine response and low exhaust emissions.

Diesel particulate filter: This removes over 95% of soot particles from the exhaust gas. The soot particles are trapped in the diesel particulate filter and burned off at cyclical intervals. From 2017, the àparticulate filter for petrol engines will be available from Mercedes-Benz.

Integrated Starter-Alternator (ISG): The functions of starter and alternator are combined in one electric machine. Unlike a àBSA, such a starter-alternator is not driven by a belt, but directly by the crankshaft. It is positioned between engine and transmission. Also, an ISG enables hybrid functions, such as boost, energy recovery and stop/start.

NANOSLIDE®: Innovative and economic process, developed by Mercedes-Benz and Gebr. Haller GmbH, for reducing fuel consumption and CO2 emissions in high-tech internal combustion engines. An extremely thin, low-friction coating is applied to the inner surfaces of the cylinders in an aluminium engine block. As up to 25 percent of the energy in fuel is used to overcome in-engine friction at part load, fuel savings of several percent are achievable with NANOSLIDE®.

NEDC: The New European Driving Cycle, introduced in the mid-1990s, is a standardised, around 20-minute exhaust gas measurement on the chassis dynamometer using a defined sequence of acceleration and braking. Urban driving is simulated two-thirds of the time, while extra-urban driving is simulated one-third of the time. The fuel consumption is calculated from the measured exhaust gas quantity. The objective of the NEDC was to define a standard for checking emission limits and to allow a cross-manufacturer comparison of fuel consumption.

Particulate filters for petrol engines: These reduce the emissions of particulate matter, especially in directly injected petrol engines. Used by Mercedes-Benz since 2014 in the S 500.

Piezo injection: Injection system in which the injectors are provided with a ceramic element. They make use of a piezo ceramic material's ability to change its crystal structure - and thus its thickness - in a matter of nanoseconds when under voltage. Piezo injectors allow smaller and more accurately dosed injected fuel quantities at high system pressures and operate up to three times faster than solenoid valves.

RDE: (Real Driving Emissions): Exhaust gas measurement under real on-road conditions. For this purpose, the vehicles are equipped with a portable emissions measurement system (PEMS) and the emissions (e.g. nitrogen oxides) are measured during operation on the road.

Energy recovery: The alternator converts kinetic energy into electrical energy, for example during braking or on overrun. The recovered energy is stored in the battery and is available for future acceleration.


Belt-driven starter-alternator (BSA): Combination of starter and alternator, which, like a conventional alternator, is connected to the crankshaft by a belt drive.

Offset: Offset between the longitudinal axis of the crankshaft and the centre axis of the cylinders. This offset has two advantages: the piston lateral force at the instant of ignition is reduced and the crankcase can be of more compact design.

Stepped combustion bowl: A characteristic feature of the pistons of a direct-injection diesel engine is a recess (bowl) in the piston crown in which the injected fuel is swirled and mixed with air. If the bowl is stepped (instead of having the conventional omega shape), this has a number of advantages, such as excellent air utilisation with low particulate emissions and higher efficiency thanks to a higher burning rate. The changed flow conditions in the combustion chamber result in reduced heat loss across the cylinder wall as well as in a more uniform temperature distribution at the cylinder head and reduced loading on the highly stressed valve lands. The overall result is reduced wall heat loss, which likewise contributes to increased efficiency.

Twin-scroll turbochargers: These differ from other turbochargers because of the different design of the turbine housing. They represent an alternative to twin-turbo concepts with two parallel-arranged turbochargers. The spiral housing of the twin-scroll turbine is divided by a flow separator into two parallel flow channels. In combination with a two-pipe exhaust manifold, this allows the exhaust gases to be separately supplied to the turbine wheel. The goal is, if possible, to prevent negative cross-influencing of the individual cylinders during the charge cycle.

WLTP: New global test procedure (Worldwide harmonized Light vehicles Test Procedure) for measuring emissions and consumption. The definition of the new test is based on extensive real driving data from all regions of the world. The measurements are carried out in order to guarantee reproducibility and comparability under clearly defined conditions on the chassis dynamometer. The main difference between the new test cycle and the NEDC is its more dynamic driving profiles at higher speeds, a longer distance and test duration as well as vehicle-specific shift points. In addition, major changes result from modified test temperature parameters, inclusion of optional equipment, determination of driving resistances and vehicle test weights. The European Commission plans to introduce the WLTP in September 2017.