Brief Analysis of MAN B&W ME and Wärtsilä RT-flex EFI Main Engines

In the modern ship propulsion & power field, the two major EFI Main Engine, MAN B&W ME and Wärtsilä RT-flex, have attracted much attention.

The differences between them are reflected in the following four aspects:

1.Common Rail: The MAN B&W ME uses a single 20MPa common rail for hydraulic servo oil. The Wärtsilä RT-flex uses a dual rail system, with one 20MPa common rail for hydraulic servo oil and one 100MPa common rail for fuel.

2.Original Power:The MAN B&W ME uses a shaft-driven hydraulic pump to input servo oil to the oil rail.And an electric hydraulic pump is used to input oil before the diesel engine is started.The WärtsiläRT-flex uses a crankshaft-driven compound cam to drive a plunger oil pump to maintain a fuel pressure of 100 MPa in the oil rail, meanwhile driving an oil pump to maintain a servo oil pressure of 20 MPa.

3.High-pressure fuel pump: The MAN B&W ME engine uses a hydraulically driven high-pressure fuel pump with an additional oil pressure fluctuation buffer.There is no common fuel rail. The Wärtsilä RT-flex engine uses a shaft-belt blocked boost pump, driven by a compound camshaft, to achieve a common rail fuel.

4.Injection Control: The MAN B&W ME engine uses a dual-needle valve with oil re-circulation. Injection pressure is not adjustable and fuel injection is analog volume. Each cylinder control unit (CCU) controls the injection amount via a proportional valve.The Wärtsilä RT-flex engine electronically controlled common rail injection system can easily realize 1 to 3 fuel heads injection control as well as multiple injection control. The injection volume is controlled by the length of time that the common rail valve is energized.

Both of them have advantages and disadvantages.

1.MAN B&W ME EFI main engine:

It eliminates the traditional cam drive control mechanism, resulting in low mechanical losses and high mechanical efficiency.Easy to start. The fuel injection profile is optimized.The fuel consumption per unit power is low and the NOX as well as particle can be controlled.The electronic cylinder lubricator reduces cylinder oil consumption and provides a more complete real-time monitoring function.

However, the hydraulic system is relatively complex, and the working status of the hydraulic system has a great impact on the operating status of  engine. The hydraulic system and lubricating oil quality need to be well maintained and tracking management.

2.Wartsila RT-flex EFI engine:

It uses the digital common rail fuel injection system, achieving smokeless operation and low emissions on particulate matter.Variable valve timing allows precise adjustment at a load range of 15%-100% with strong operational flexibility.It has high power density , high power output per unit volume,less maintenance hours and long service intervals.

However, the structure is relatively complex, involving two common fuel rails and related drive systems, which may lead to relatively more failure points. It has high requirements for fuel quality as well as electronic control system accuracy and the maintenance cost will be high on such engine.

In short, MAN B&W ME and Wärtsilä RT-flex EFI engine have their own strengths.They both promote the sustainable development of global shipping industry.