Mercedes Benz
OM 656
Manufacturer:	Daimler AG
Production period:	since 2017
How it works:	diesel
Style:	Inline engine , six-cylinder
displacement:	2925 cc
Previous model:	OM 642

The OM 656 is a diesel engine from Mercedes-Benz , which was introduced 2017th The assembly takes place at MDC Power GmbH in Kölleda. 

The six-cylinder in - line engine OM 656 is the successor to the OM 642 and part of a modular engine generation comprising four- and six-cylinder diesel engines as well as four-cylinder and six-cylinder gasoline engines . Due to the same cylinder stroke (approx. 500 cm³) and distance (90 mm), a high number of identical parts is achieved. 

The first use of the engine was in 2017 in the facelift of the S-Class ( class 222 ).

Technology 

The displacement of the six-cylinder in - line engine is 2925 cc with a bore of 82 mm and a stroke of 92.4 mm, with a cylinder spacing of 90 mm. The compression ratiois 15.5. The crankcase of the engine is made of aluminum, the cylinder head of a high-strength aluminum alloy. Steel pistons and a so-called NANOSLIDE® cylinder coating are used. It is an iron-carbon layer by arc wire spraying is applied directly to the aluminum surface and high oil retention volumes of the cylinder liner made possible.

The change of charge is controlled by four valves per cylinder ( four-valve technology ) and two overhead camshafts driven by a timing chain . The engine has a switchable exhaust camshaft to assist in heating the exhaust system. 

Depending on the model, the engine has one or two turbochargers connected in series . The compressed fresh air is cooled in a charge air cooler .

The OM 656 has both a cooled low-pressure exhaust gas recirculation (EGR) and a cooled high-pressure exhaust gas recirculation. The exhaust gas of the low-pressure EGR is removed behind the particle filter, cooled and re-introduced before the compressor.

The exhaust aftertreatment of the OM 656 is system-identical to that of the OM 654 , is close to the engine and was designed for test procedures such as the WLTP cycle and Real Driving Emissions (RDE) . Behind the turbine of the turbocharger first a Dieseloxidationskatalysator (DOC) is used, afterwards with a falling-stream mixer the urea solution AdBlue necessary for the purification of the nitrogen oxides is metered. After a short mixing section, an SCR-coated diesel particulate filter (sDPF) and an SCR catalytic converter follow each other . 

The common-rail injection works with a fuel pressure of up to 2500 bar. As with the OM 654 , the step-well combustion process is used. In comparison to the previous omega-trough this should lead to a better efficiency with at the same time lower particle raw emissions.

Versions

The OM 656 is available in several performance levels.

OM 656 D 29 R SCR 

OM 656 D 29 SCR