Mercedes-Benz OM 611 / OM 612 / OM 613 diesel engines

Mercedes Benz
OM 611, OM 612, OM 613
Manufacturer:	Mercedes Benz
Production period:	1997-2006
Style:	Four-cylinder OM 611 Inline five-cylinder OM 612  inline six-cylinder OM 613
Engines:	2.1 liters (2148 cc)  2.2 liters (2151 cc)  2.7 liters (2685 cc)  3.0 liters (2950 cc)  3.2 liters (3222 cc)
Previous model:	OM 604 (4-cylinder)  OM 605 (5-cylinder)  OM 606 (6-cylinder)
Successor:	OM 646 (4-cylinder)  OM 647 (5-cylinder)  OM 648 (6-cylinder)

The OM 611 by Mercedes-Benz is a four cylinder - diesel engine with common-rail direct injection . He was introduced in 1997 in the model C 220 CDI . Vehicles with this engine type carry mostly "200 CDI" and "220 CDI" in the sales name.

The article also covers the engines OM 612 and OM 613 with five or six cylinders, also in- line engines , which are technically closely related to the OM 611. Vehicles with five cylinders of this engine type carry mostly "270 CDI" in the sales description, with six-cylinder engine predominantly "320 CDI".

From 1997 to 2005, these engines were used predominantly in the C-Class W202 , the E-Class W210 , as a six-cylinder also in the S-Class W220 , and in vans (" Sprintern ").

Technology

The Mercedes-Benz OM 611 is a four-cylinder diesel engine with two overhead camshafts that actuate the 16 valves via tappets . For the first time, the OM 611 was sold in September 1997 in the C-Class under the name C 220 CDI.  Compared to its predecessor OM 604, the OM 611 has 30% more power, 50% more torque and 10% less fuel consumption. For emission control, an oxidation catalyst is used. Since the efficiency has been increased in the new generation of engines, at low outside temperatures is not enough heat for a sufficient interior heating available. This problem was encountered in the CDI Series II by an electric heater was installed and in the CDI Series I with a diesel-powered auxiliary heater. The camshaft drive is made by a duplex roller chain.

A special feature is the first-time use of common rail direct injection from Bosch in a Mercedes-Benz engine model. The fuel distribution takes place via a common fuel rail (common rail)in which the fuel pressure is kept continuously high by a high pressure pump. Through the line, the fuel reaches the solenoid valve-controlled injectors, from where it is injected with a pressure of up to 1350 bar through six holes in the combustion chamber. By the pilot injection, in which a small amount of fuel is introduced and burned before the actual combustion in the cylinder, the combustion chamber heats up, which is why the rise in temperature and pressure during the main combustion does not turn out so strongly. This ensures a significantly improved smoothness. In the CDI Series II, the injection system has been supplemented by a high-pressure control via pressure control valve, a flow control valve, a mechanical fuel feed pump and a fuel temperature sensor. 

The engine is ventilated via a turbocharger with a bypass valve (so-called wastegate ). Since the turbocharger with increasing engine speed is driven by the higher amount of exhaust more and more, the compressor itself promotes more and more air. This in turn leads to an even stronger exhaust gas flow, which in turn drives the turbine even more. In order to avoid damage due to mechanical or thermal overload, charging must be limited (charge pressure control). For this purpose, a bypass valve was used in the CDI series I, which is opened at a certain boost pressure and bypasses the exhaust gases past the loader into the exhaust tract. A further increase in the turbine speed is thus prevented. In the CDI Series II, the turbocharger was replaced by a VNT charger . VNT stands for Variable Nozzle Turbocharger (Eng. Variable Turbine Geometry Loader) and means that on the exhaust side adjustable vanesare attached. The control is done by means of negative pressure. This technology leads to a faster build-up of the boost pressure in the lower speed range. This is noticeable by better cylinder filling and thus higher torque. To cool the hot charge air to an optimal temperature, a charge air cooler was installed.

Intake tract 

The intake section of the OM 611 uses the EKAS (intake channel cut-off). Of the two inlet channels per cylinder, a channel (tangential channel) can be switched off at low speeds. The sucked air flows completely through the specially shaped second channel (swirl channel). The resulting swirl leads to a better mixture formation, whereby a better combustion is achieved. For the CDI Series I, the EKAS is pneumatically actuated, while the CDI Series II is equipped with an electronically controlled and stepless EKAS. Another new feature of the CDI Series II is the pneumatically controlled exhaust gas recirculation valve . It reduces the excess air and lowers the temperature peaks by producing exhaust gasesthe sucked fresh air are supplied. This reduces nitrogen oxide emissions and combustion noise. To regulate the exhaust gas recirculation, a hot-film air mass meter is installed, which allows an accurate determination of the intake air mass.

Five-cylinder OM 612 and six-cylinder OM 613 

Parallel to the OM 611, the OM 612 (five-cylinder) and OM 613 (six-cylinder) series were developed, forming an engine family with the four-cylinder OM 611 brother. So these engines have the same capacity per cylinder and are in-line engines. Their pistons, connecting rods, injectors, valves, glow plugs and other components are the same parts, with corresponding advantages in terms of procurement costs and warehousing. All engines of the OM 612 and OM 613 series are based on the CDI II series.

A special feature is the OM 612 DE 30 LA. This engine is based on the OM 612 DE 27 LA, but AMG has increased the lift in order to achieve a larger displacement. Due to the increased engine power and increased torque, numerous components had to be redesigned and adapted to the increased load. For example, the crank drive was strengthened, the cylinder head fitting optimized, an oil pump with greater pumping capacity used and reinforced pistons with oil spray cooling installed on the piston crowns. The glow system has been redesigned and ensures a shorter pre-glow time with the higher annealing temperature. The idling behavior could be optimized by an improved control of the afterglow behavior.

In order to ensure maximum output and torque output even at high outside temperatures, an unusual design was used for the intercooler : The intercooler is located directly next to the engine and equipped with an air-water heat exchanger. The heat is released via a separate low-temperature water circuit to two separate from the actual radiator radiator in the front.

Unlike the regular OM 612 engines, the VNT turbocharger's vanes are adjusted by the engine electronics; the adjustment is thus faster than in the pneumatic control. The exhaust gas recirculation valve was modified and also received an electronic control. Together with the close-coupled thin-walled front wall catalyst it provides for improved emission control. The exhaust system has a tube diameter of 76 mm and thus contributes to the increase in performance.