Mercedes-Benz OM648 engine

In-line five -cylinder OM 647 In-line six -cylinder OM 648

The OM 646 Mercedes- Benz is a four-cylinder diesel engine with common - rail direct injection. It represents an evolution of the OM 611 dar. The article also discusses the engines OM 647 and OM 648 with five or six cylinders, also series engines which are technically related closely with the OM 646.



In the Mercedes -Benz OM 646 is a four-cylinder diesel engine with two overhead camshafts which operate the 16 valves via bucket tappets. For the first time, the OM 646 was sold to the market launch of the E-Class under the name E 220 CDI. In direct comparison to the predecessor of consumption was lowered again and the engine power can be increased. Responsible for this are modifications to more than 80 components. For continuous compliance with the emission values ​​an on- board diagnostic system was used, which monitors all emission-related components in the engine and exhaust system. The more powerful models (220 CDI) were equipped with two Lanchester balancer shafts to enhance smoothness. They rotate in opposite directions at twice the crankshaft speed and eliminate occurring mass forces caused by the piston movement.

The mechanical fuel pump has been replaced by an electric variant which performs its service in the tank. In order to ensure sufficient internal space heating, a PTC heater was installed. Compared to its predecessor, the coolant is not heated here, but only the air flowing into the interior air. As of 2003, it was initially optional, later as standard a soot particle filter in conjunction with the Euro 4 emissions standard offered.


For the first time comes with this type of engine, common rail direct injection of the second generation used. System suppliers is Bosch. The fuel distribution is carried out as previously via a common fuel line (common rail), in which the fuel pressure is kept up continuously by a high pressure pump. The system pressure was increased compared to the previous engine. Through the conduit of the fuel reaches the solenoid valve-controlled nozzles, from which it is injected at a pressure of up to 1600 bar by now seven holes in the combustion chamber. The new injectors with seven apertures distribute the fuel more finely in the combustion chamber. New from this type of engine are dual pilot injection, by means of which a small amount of fuel is introduced before the actual combustion in the cylinder and burned there. Wherein the combustion chamber heats up before effectively, whereby the temperature and pressure increase will be reduced in the main combustion. This makes for a smoother running. The control of the high -pressure fuel pump is pressure- and volumetric flow rate - controlled by a flow control valve and a pressure regulating valve.


The motor is charged as the OM 611 CDI Series II, by a turbocharger with variable turbine geometry. It has adjustable vanes on the exhaust side, which provide for a faster build up boost. Characterized the cylinder filling and thus the torque is improved. The so-called turbo lag is reduced. The boost pressure control is achieved by the adjustment of the vanes. This is in contrast to the previous model electronically controlled.

To cool the hot compressed charge air and to bring the more mass of oxygen in the combustion chamber, a charge air cooler is installed.

Intake tract

In the intake tract of the OM 646, as already known from the OM 611 FCOS (intake port shut-off ) will be used. The two inlet ducts per cylinder, at low speeds a passage tangential to be turned off. The sucked air then flows entirely through the specially shaped second passage ( swirl passage ). The resulting swirl leads to an improved mixture formation, resulting in better combustion. The CFST is controlled electronically and works continuously. In contrast to its predecessor, the pneumatically controlled exhaust gas recirculation valve has been replaced by an electronically controlled version. It reduces the excess air and lowers the temperature peaks by exhaust gases from the fresh intake air to be supplied. Characterized the emission of nitrogen oxides and combustion noise are reduced. To control the exhaust gas recirculation, a hot-film air mass meter is installed, which allows an accurate measurement of the air mass.

OM 646 EVO

In 2006, the OM 646 EVO was presented at the facelift of the E-Class. He is an evolved version of the OM 646, in which more than 90 components have been modified. The compression ratio was of 18.0 so far: 1 lowered by higher piston and connecting rod shorter were installed: 1 to 17.5. In addition, a new turbocharger with modified charge-air cooling was installed. An acoustic emission sensor in the injection system allows a needs-based dosage of the fuel. The cylinder head has been redesigned in order to achieve a more effective engine cooling. The air duct has also been redesigned. This allowed pressure loss and noise emissions are reduced. For an improved engine starting and cold running behavior, the glow plugs are made of ceramic instead of metal. They allow higher annealing temperatures. The previously known from the stronger variants balance shafts held in all OM 646 EVO engines feeder.

Five-cylinder OM 647 and OM 648 six-cylinder

The changes of the OM 611 OM 646 were for 612 ( five-cylinder ) and OM adopted with the exception of the balance shafts for the series OM 613 ( six-cylinder ). Thus, the series OM 647 and OM 648, which differ from the OM 646 constructively by the number of cylinders arose; Bore and stroke are the same for all the engines within that family. The modifications of the OM 646 EVO came the OM 647 and OM 648 series not benefit, as these were replaced by weaker versions of the new V6 engine OM 642.