Mercedes-Benz OM654 diesel engine

Daimler's new 2L inline four-cylinder modular diesel engines

2018/02/01

Summary

Since the VW emissions scandal in 2015 there is public concern about the harmful emissions of diesel engines. In response, Daimler announced its plans to develop a new modular diesel engine family, emphasizing its commitment to continue making diesel engines in the future. This report introduces the 2L inline 4-cylinder OM 654 engine, which is the first in its new family of modular diesel engines.

Outline of Daimler new modular engine

Daimler is developing a family of new generation internal combustion engines (ICE). The engine line-up will include 5 models: 2L four-cylinder inline gasoline & diesel engines, 3L 6-cylinder inline gasoline & diesel engines, and a 4L V8 gasoline engine.

The advantages of modularization includes the common use of components and the ability to share assembly lines, but one major objective is the reduction of development costs and time. By using a common bore diameter and stroke length it is possible to conduct a single test for time-consuming development tasks such as combustion analysis, emissions, and fuel efficiency testing. As a result, Daimler expects to introduce the five engine models to market more quickly.

Generally speaking, when the balance between output and fuel consumption is considered, the displacement per cylinder is 400 to 500cc for the gasoline engines and 500 to 600cc for the diesel engines. It is likely that Daimler decided on an engine displacement of 500cc to share components on both the gasoline and diesel engines and to share assembly lines.

A key characteristic of the new modular engine, the main variant for mass-market production, is that the engine displacement has been downsized from 3L to 2L. Another characteristic is that Daimler reverted to using an inline engine instead of a V-shaped 6-cylinder engine. There are two reasons for this. First, the overall length of a conventional inline 6-cylinder engine is long, so a V6 needs to be adopted for safety reasons in the event of a collision. However, the length of the engine can be shortened by decreasing the bore diameter to improve thermal efficiency, adopting a linerless aluminum cylinder block, and shortening the bore pitch, making it possible to use an inline six-cylinder engine configuration. Secondly, it is easier to develop a modular design for an inline 6-cylinder engine than it is for a V6 engine. In an inline 6-cylinder engine, it is only necessary to add two cylinders to an inline 4-cylinder engine to use a common layout for the auxiliary equipment. Conversely, in a V6 engine, the number of parts such as two pieces of cylinder-heads, increases the complexity and tightness of the auxiliary equipment layout because of shorter and wider characteristics of V6 engine.


Engine exterior (Source: Daimler)
New 2L inline four-cylinder diesel engine

 

Outline of the OM 654 engine

In the spring of 2016 Mercedes-Benz released the E220d Coupe equipped with a 2L four-cylinder inline diesel engine. The OM 654 engine was first engine of its new family of modular engines to be released, succeeding the predecessor OM 651 engine (2.2L displacement). The engine can be installed in both the longitudinal and transverse mounting positions and for 4WD vehicle applications. By reducing the engine displacement by about 10% and using an aluminum cylinder block, the packaging dimensions can be miniaturized and the weight of the engine can be reduced by about 35 kg. The exhaust aftertreatment system complies with the current Euro 6 emission standard, with a fuel consumption (CO2 emissions) of 102-112 g/km. Also, the front and upper sides of the engine are enclosed with a shielding plate to suppress engine noise.

The new 2L engine was designed to increase the potential to achieve a high specific output performance of up to 90 kW/L. In addition, the new diesel engine was designed to comply with the Worldwide harmonized Light vehicles Test Procedure (WLTP) cycle established in 2017 to measure real-world emissions and meet future Real Driving Emission (RDE) legislation and to make the engine smaller and lighter to improve fuel economy.


Engine exterior (Source: Daimler)
OM 654 engine with a cube-like compact layout

 

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