ME ENGINES

MAN B&W ME-series engines, introduced to the market in2001, dispense with the camshaft and exploit hydraulic-mechanicalsystems supported by electronic hardware and software for activatingfuel injection and the exhaust valves.

Electronically-controlled fuel injection and exhaust valve actuation(Figure 10.36) allows individual and continuous adjustment of thetiming for each cylinder, securing these key benefits:

Reduced fuel consumption

∑Fuel injection characteristicscan be optimized at many different load conditions, while a conventional engine is optimized forthe guarantee load, typically at 90–100 per cent maximumcontinuous rating

∑Constant Pmax inthe upper load range can be achieved by acombination of fuel injection timing and variation of thecompression ratio (the latter by varying the closing of the exhaustvalve). As a result, the maximum pressure can be kept constantover a wider load range without overloading the engine, leading to significant reductions in specific fuel consumption at part load.

∑ On-line monitoringof the cylinder process ensures that the load distributionamong the cylinders and the individual cylinders firing pressure can be maintained at as newstandard over the lifetime of the engine.

Operational safety and flexibility

∑ Swifter acceleration of the engine, since the scavenge air pressure can be increased faster than normal by opening the exhaust valve earlier during acceleration.

∑ Dead slow running is improved significantly: the minimum rev/ min is substantially lower than for a conventional engine, dead slow running is much more regular, and combustion is improved thanks to the electronic control of fuel injection.

∑ The engines crash stop and reverse running performance is improved because the timing of the exhaust valves and fuel injection can be optimized for these manoeuvres as well.

∑ Engine brakingmay be obtained, reducing the ships stopping distance.

∑ Electronic monitoringof the engine (based on MAN B&Ws CoCoS-EDS system:  see MAN B&W Medium Speed Engines chapter) identifies running conditions that could lead to performance problems. Damage due to poor ignition-quality fuel can be prevented by injection control (pre-injection).

∑ The engine control system incorporates MAN B&Ws on-line Overload Protection System (OPS) feature, which ensures the engine complies with the load diagram and is not overloaded (often the case in shallow waters and with heavy propelleroperation).

∑ Maintenance costs will be lower (and maintenance easier) as a result of the protection against general overloading as well as overloading of individual cylinders; and also because of the as newrunning conditions for the engine, further enhanced by the ability of the diagnosis system to give early warning of faults and thus enable proper countermeasures to be taken in good time.

Exhaust gas emissions flexibility

∑ The engine can be changed over to various low emissionmodes, its NOx exhaust emissions reduced below the IMO limits if dictated by local regulations.

The following components of the conventional MC engine are eliminated in the ME engine: chain drive for camshaft; camshaft with fuel cams, exhaust cams and indicator cams; fuel pump actuating gear, including roller guides and reversing mechanism; conventional fuel injection pumps; exhaust valve actuating gear and roller guides; engine-driven starting air distributor; electronic governor with actuator; regulating shaft; mechanical engine-driven cylinder lubricators; and engine side control console.

These elements are replaced on the ME engine by an electro-hydraulic platform comprising: a hydraulic power supply (HPS); a hydraulic cylinder unit (HCU) with electronic fuel injection (ELFI) and electronic exhaust valve actuation (ELVA); an electronic Alpha cylinder lubricator (see above and Fuels and Lubes chapter); an electronically-controlled starting valve; a local control panel; a control system with governor; and a condition monitoring system.

ME engine systems

Valuable experience was gained by MAN B&W Diesel from its 4T50MX research engine at Copenhagen, operated from 1993 to 1997 with a first-generation Intelligent Engine (IE) system. Second-generation IE systems fitted to the engine in 1997 aimed for simplified design, production and installation of the key electronically-controlled fuel injection and exhaust valve actuation systems. Subsequent R&D focused on transforming the electronic elements into a modular system, whereby some of the individual modules could also be applied to conventional engines. This called for the development of a new computer unit and large software packages, both of which had to comply with the demands of classification societies for marine applications.

The second-generation IE system is based on an engine-driven high pressure servo oil system which provides the power for the hydraulicallyoperated fuel injection and exhaust valve actuation units on each cylinder. Before the engine is started the hydraulic power system (or servo oil system) is pressurized by a small electrically-driven high pressure pump. Fine-filtered main system lube oil is used as the actuating medium supplied by engine-driven multi-piston pumps at around 200 bar (Figure 10.37).

Fuel injection system

A common rail servo oil system applies this cool, clean and pressurized lube oil to power the fuel injection pump of each cylinder. Each cylinder unit is provided with a servo oil accumulator to ensure sufficiently swift delivery of oil in accordance with the requirements of the injection system, and to avoid heavy pressure oscillations in the associated servo oil pipe system. The movement of the pump plunger is controlled by a fast-acting proportional control valve (a so-called NC valve) which, in turn, is controlled by an electric linear motor that receives its control input from a cylinder control unit. The fuel injection pump features well proven technology and the fuel valves are of a standard design.

Second- and third-generation fuel injection pumps are much simpler than the first-generation design and their components are smaller and easier to manufacture (Figure 10.38). A major feature of the third-generation pump is its ability to operate on heavy fuel oil; the pump plunger is equipped with a modified umbrella design to prevent heavy fuel from entering the lube oil system. The driving piston and injection plunger are simple and kept in contact by the fuel pressure acting on the plunger and the hydraulic oil pressure acting on the driving piston. The beginning and end of the plunger stroke are both controlled solely by the fast-acting NC valve, which is computer controlled.

Optimum combustion (and thus optimum thermal efficiency) calls for an optimized fuel injection pattern, which in a conventional engine is generated by the fuel injection cam shape. Large two-stroke engines are designed for a specified maximum firing pressure and the fuel injection timing is controlled so as to reach that pressure with the given fuel injection system (cams, pumps, injection nozzles).

For modern engines, the optimum injection duration is around 18–20 degrees crank angle at full load, and the maximum firing pressure is reached in the second half of that period. To  secure the best thermal efficiency, fuel injected after the maximum firing pressure is reached must be injected (and burned) as quickly as possible in order to obtain the highest expansion ratio for that part of the heat released. From this it can be deduced that the optimum rate shapingof the fuel injection is one showing an increasing injection rate towards the end of injection, thus supplying the remaining fuel as quickly as possible. The camshaft of the conventional engine is designed accordingly, as is the fuel injection system of the ME engine. In contrast to the camshaftbased injection system, however, the ME system can be optimized at a large number of load conditions.

MAN B&W Diesel claims the fuel injection system for the ME engines can execute any sensible injection pattern needed to operate the engine. It can perform as a single-injection system as well as a preinjection system with a high degree of freedom to modulate the injection in terms of injection rate, timing, duration, pressure or single/double injection. In practice, a number of injection patterns are stored in the computer and selected by the control system for operating the engine with optimum injection characteristics from dead slow to overload, as well as during astern running and crash stop. Changeover from one to another of the stored injection characteristics may be effected from one injection cycle to the next.

Exhaust valve actuation system

The exhaust valve is driven by the same servo oil system as that for the fuel injection system, using cool pressurized lube oil as the working medium. The necessary  functionality of the exhaust valve is less complex than fuel injection, however, calling only for control of the timing of its opening and closing. This is arranged by a simple fast-acting on/ off control valve. Well proven technology from the established MC engine series is retained. The actuator for the exhaust valve system is of a simple, twostage design. The first-stage actuator piston is equipped with a collar for damping in both directions of movement. The second-stage actuator piston has no damper of its own and is in direct contact with a gear oil piston transforming the hydraulic system oil pressure into oil pressure in the oil push rod. The gear oil piston includes a damper collar that becomes active at the end of the opening sequence, when the exhaust valve movement will be stopped by the standard air spring.

RTA DESIGN FEATURES

The RTA design benefited from principles proven in earlier generations of Sulzer R-type engines. The key elements are:

A sturdy engine structure designed for low stresses and small deflections comprises a bedplate, columns and cylinder block pretensioned by vertical tie rods.

The single-wall bedplatehas an integrated thrust block and incorporates standardized large surface main bearing shells. The robust A-shaped columns are assembled with stiffening plates or are of monobloc design. The single cast iron cylinder jackets are bolted together to form a rigid cylinder block (multi-cylinder jacket units for smaller bore engines).

Lamellar cast iron, bore-cooled cylinder liners with back-pressure timed, load-dependent cylinder lubrication.

Solid, forged bore-cooled cylinder coverswith one large central exhaust valve arranged in a bolted-on valve cage; the valve is made from a heat- and corrosion-resistant material and its seat ring is bore-cooled.

Semi-built crankshaftdivided into two parts for larger bore engines with a large number of cylinders.

Running gearcomprising

connecting rod,

crosshead pin with very large surface crosshead bearingshells (with high pressure   lubrication) and

double-guided slippers,

piston rod and bore cooled piston crown using oil cooling.

short piston skirts.

All combustion chamber components are bore cooled, a traditional feature of Sulzer engines fostering optimum surface temperatures and preventing high temperature corrosion due to high temperatures on one side and sulphuric acid corrosion due to too low temperatures on the other.
   Comfortable working conditions for the exhaust valve are promoted by: hydraulic operation with controlled valve landing speed; air spring; full rotational symmetry of the valve seat, yielding well-balanced thermal and mechanical stresses and deformations of valve and valve seat, as well as uniform seating; extremely low and even temperatures in valve seat areas due to efficient bore cooling; valve rotation by simple vane impeller; valve actuation free from lateral forces, with axial symmetry; and simple guide bushes sealed by pressurized air. The low exhaust valve seating face temperature reportedly secures an ample safety margin to avoid corrosive attack from vanadium/ sodium compounds under all conditions. Efficient valve cooling is given by intimate contact with the bore-cooled seat, together with the appropriate excess air ratio in the cylinder. The specific design features of the valve assembly are also said to deter the build-up of seat deposits, seat distortion, misalignment and other factors which may accelerate seat damage.

Camshaft gear drive housed in a special double column or integrated into a monobloc column, placed at the driving end or in the centre of the engine for larger bore models with a large number of cylinders.

Balancer gear can be mounted on larger bore engines, when required, to counter second-order couples for four-, five- and sixcylinder models, and combined first- and second-order couples for four-cylinder models.

A compact integral axial detuner can be incorporated, if required, in the free end of the engine bedplate.

The fuel injection pump and exhaust valve actuator are combined in common units for each two cylinders.

The camshaft-driven injection pump with double valve-controlled variable injection timing delivers fuel to multiple uncooled injectors. The camshaftdriven actuators impart hydraulic drive to the single central exhaust valve working against an air spring.

Constant pressure turbocharging is based on high efficiency uncooled turbochargers; auxiliary blowers support uniflow scavenging during low load operation. In-service cleaning of the charge air coolers is possible. A standard optional three-stage charge air cooler unit can be specified for heat recovery.

RTA DESIGN DEVELOPMENTS

The reported benefits of the triple-valve configuration are a more uniform temperature distribution around the principal combustion space components (cylinder cover, liner and piston crown) at the increased maximum combustion pressures, along with even lower temperatures despite the higher loads. Three fuel valves also foster significantly lower exhaust valve and valve seat temperatures. Other spin-offs from the research engine included a modified cylinder liner bore-cooling geometry whose tangential outlets of the bores aim for optimum distribution of wall temperatures and thermal strains at higher specific loads. The geometry of the oil cooling arrangements of the piston crown was also modified to maintain an optimum temperature distribution. The good piston running behaviour was maintained by retaining established features of the RTA design: multilevel cylinder lubrication; die-casting technology for cylinder liners; and temperature-optimized cylinder liners. Advances in materials technology in terms of wear resistance have permitted engines to run at higher liner surface temperatures. This, in turn, allows a safe margin to be maintained above the increased dew point temperature and thus avoiding corrosive wear.