Camshaft less engines-ME & RT-FLEX

Camshaft Less Engine: 

In this engine, the camshaft functions are replaced by an electronically controlled set of actuators. These actuators control the Starting air valves. Start and Reversing sequences. Governor Function. Auxiliary blowers. Electronically Profiled Injection (EPIC) and Exhaust valve actuation. This is done with far greater precision than camshaft-controlled engines. The exhaust valves, as on the MC engines, are opened hydraulically and closed by an 'air spring'. The actuator is hydraulically driven by pressurized control oil via an on/off type valve. The Starting air distributor has now been replaced by electronically controlled on/off valve which, in conjunction with the ECU and the CCU. control the Starting air valves. The hydraulic power is provided by the Hydraulic Power Supply units placed at the aft end of the engine. The cam-less system, being electronically controlled, is fully integrated with other MAN B&W Diesel developments such as more efficient fuel and lube oil injection and the CoCoS engine diagnostic platform. This control makes the overall optimization of each system even more effective and reliable. The ECS can fully control and optimize the combustion process at any load by electronically controlling the valves according to the crankshaft position.

M.E Intelligent Engine vs RT Flex:

The two major manufacturers of two stroke crosshead engines have both introduced a camshaft-less engine. Sulzer call theirs the RT Flex engine, and MAN B&W call theirs the M.E intelligent engine. Both engines use electrical and engine driven axial piston pumps to pressurize servo oil rails to 200 bar which are then used for fuel injection and exhaust valve operation. In addition MAN B&W use the servo oil to drive the cylinder lubricator units (Alpha system). Although they both work without a camshaft and use computers to control fuel injection, exhaust valve operation and air starting, the method of fuel injection is different. Sulzer use a pressurized fuel rail using a set of jerk type pumps driven by a three lobe cam geared to the crankshaft. The pumps are variable delivery, based ,on the ZA40 fuel pump, controlled by an electrically driven fuel pump shaft linked to the engine computer. 

The engine computer system known as the Wartsila Engine Control System (WECS) controls the delivery from the common rail to the individual cylinders via the volumetric injection control system which uses finely filtered engine L.O pressurized by electric pumps to 200 bar. 

 When the Rail Valves are energized for injection by the Valve Driver Module, oil from the Control Rail opens the Injection Control Valves. The fuel injectors are pressurized and fuel oil pressure behind the Fuel Quantity Piston maintains this pressure at the injectors. As the Piston moves to the left a feedback signal is sent to the Cylinder Control Module. 

At low engine load the control system cuts out one of the three injection valves per cylinder. 

At very low load two of the three injection valves are cut out. This is used to avoid visible smoke emission and to reduce fuel consumption. It is possible to reduce engine load to 10% with engine revolutions as low as 7RPM. 

Unlike the Sulzer RT Flex engine the MAN B&W ME engine does not operate the fuel injection on a common rail system. 

Instead a solenoid operated proportioning valve (the FIVA valve - Fuel Injection Valve Activation) allows the pressurized servo oil under a hydraulic piston. This then moves the fuel pump piston upwards, raising the fuel pressure and opening the injection valves. A nitrogen filled accumulator maintains the hydraulic servo oil pressure during the operation of the pump. ' To be able to time the fuel injection the Control Systems must know the crank angle of the individual units. To do this two crank angle sensors are fitted at the free end of the the engine. These sensors are accurate to 0.1°.

 Cylinder pressures and powers are continually monitored by using strain gauges built into the cylinder head and the computer automatically compensates for twist in the crankshaft when relating crankshaft position to cylinder pressure, the systems give complete flexibility over start and end of injection and take into account fuel quality, dead time (the time between injection start command being given and actual injection), and Variable Injection Timing (VET). 

 The exhaust valve actuator replaces the cam operated exhaust valve hydraulic pump on both make of camshaft less engines. Both working on a similar principle, servo oil at 200 bar is used to operate a piston which operates the, exhaust 'valve "hydraulic push rod. The oil for operating the "hydraulic push rod" comes from the main engine LO supply via a non return valve. The air start system is similar to that on a conventional engine except there is no need for a mechanically driven distributor to open the air start valves at the correct time. 

 Instead of a camshaft driven, reversing air start distributor, each air start ..valve is opened at the correct time by the engine computers sending a signal to a solenoid controlled NC (normally closed) valve. 

 The timing of the air start valves will vary depending on the number of cylinders, but they will be open for a long enough period to allow overlap, so that a valve opens before the previous valve closes, allowing starting from any position of rest. The nominal opening can be considered as 0° (i.e. TDC) and closing at 110° After TDC. The computer knows when to send the signal because it is receiving information as to the crankshaft position from the angle encoders which measure crankshaft position and RPM. 

 When the engine has reached firing speed the computers shut off the air and introduce the fuel.

Difference between M.E. - M.C. engines. 

The ME series of engines have no camshaft. Instead, to provide power for fuel injection and exhaust valve lifting, they utilize a hydraulic oil loop with fine filtered oil from the main engine lubricating system at about 200 bar pressure. The advantages of the ME series of engines come from the fact that the timing and intensity of fuel oil injection and exhaust valve operating and Closing is optimal at all steady and transient loads, this giving lower part load fuel oil consumption, lower emissions and particularly smoother and better low load operation. The balance between cylinders will be easier to adjust for smoother operation. All this will eventually mean longer MTBO (Mean Time Between Overhauls). The engine can be changed over to different 'low emission modes' where its NOx exhaust emission can be reduced below the IMO limits if desirable due to local emission regulations. The electronic control of the fuel injection system and the exhaust valve operation, together with the fact that 'ME engines are normally delivered with on-line cylinder pressure measurement equipment and the engine diagnosis system CoCoS-EDS. provides a number of  benefits. 

Well-proven conventional fuel injection pattern and technology

Adjustable injection intensity by electronically variable cam "angle" and cam "length".

The control system offers more precise timing and thereby better engine balance with equalized thermal load in and between cylinders. 

Uniform combustion and heat load at any load. 

Lower rpm possible for maneuvering. 

Sequential cylinder cut-off at low load. 

High injection pressure at low load. 

Slide type zero-sack-volume fuel valves. 

Improved emission characteristics, i.e. lower NOx and less visible smoke at any load. 

System comprising performance monitoring for longer time between overhauls. 

Monitoring of the engine (based on CoCoS- EDS.) identifies running conditions which could lead to performance problems.

The Overload Protection System ensures compliance with the load diagram and ensures that the engine is not overloaded. 

Optimum crash stop and reverse running performance "Engine braking. may be obtained, reducing the stopping distance of the vessel Faster acceleration of the engine by opening the exhaust valves earlier during acceleration.

Significantly improved dead slow running with low minimum rpm and stable operation together With improved combustion due to the electronic control of fuel injection. 

The following parts are omitted: 

Chain drive 

Chain wheel frame 

Chain box on frame box 

Camshaft with cams 

Roller guides for fuel pumps and exhaust valves 

Fuel injection pumps 

Exhaust valve actuators 

Starting air distributor 

Governor

Regulating Shaft

Mechanical Cylinder Lubricator 

Local Control stand

The above-mentioned parts are replaced by: 

Hydraulic Power Supply (HPS)

Hydraulic Cylinder Units (HCU)

Engine Control System (ECS), controlling the following: 

    Electronically Profiled Injection (EPIC) 

    Exhaust valve actuation 

    Fuel oil pressure boosters 

    Start and reversing sequences 

    Governor function

    Starting air valves 

    Auxiliary blowers

    Crankshaft position sensing system 

    Electronically controlled Alpha Lubricator 

    Local Operating Panel (LOP) 

    Hydraulic cylinder unit 

The hydraulic cylinder unit, of which there is one per cylinder, consists of a hydraulic oil distributor block with pressure accumulators, an exhaust valve actuator with ELVA control valve and a fuel oil pressure booster with ELFI control valve. Each individual HCU is interconnected by double-wall piping, through which the hydraulic oil is led ELVA and ELFI valves were substituted by one common FIVA valve controlling both the exhaust valve actuation and the fuel oil injection. ELFI valves 

On the Print Circuit Board (PCB) components have come loose due to vibrations. Improvements by means of resilient mountings have been introduced on all vessels in service with ELFI valves, and performance has been Good ELVA valves Early service experience proved that low ambient temperatures, as often experienced during shop tests in the winter season, gave rise to sticking high response valve spools in the ELVA valve due to low hydraulic oil temperatures. The diameter of the spool was reduced in order to obtain correct functioning of the high-response valve Initially, the ME tacho system was designed on the basis of trigger segments with a sine-curved tooth profile mounted on the turning wheel. The total trigger ring was built from eight equal segments. Two redundant sets of sensors were applied.-This, initial tacho system is relatively expensive, and the system The new tacho system is based on optical angular encoders installed on the free end of the crankshaft. This system, consisting of two redundant encoders. 

Alpha Lubrication system The ME engine has the advantage of an integrated Alpha lubrication system, which utilizes the hydraulic oil as the medium for activation of the main piston in the lubricators. Thus, a separate pump station and control are not needed compared to the MC counterpart 

Comparison between ME- MC. engines. 

Power, speed and nominal Specific Fuel Oil Consumption (SFOC) are the same for the ME series as for their MC counterparts. The SFOC has been reduced significantly at part load as the maximum pressure can be maintained down to 65-70 percent of the engine load. SFOC is the same as for the mechanically controlled engines at nominal output At lower load, the SFOC is lower for the electronically controlled engines Easy to change between various running modes.

Development in Diesel Engine Technology.

Sophisticated methods of numerical analysis permit accurate predictions of the thermodynamic performance of the engine, the scavenging process. stresses, strains and deformations under both mechanical and thermal loads, heat transfer and temperature distributions in engine components and the vibration modes of complex structures, etc., 

Mechanical design concepts such as bore cooling of the combustion chamber components and permitted mechanical and thermal loads at unchanged, or even improved, reliability. 

 New measurement techniques on running engines for stresses, flow patterns, temperatures, etc. and on scale models led to a better understanding of the processes in the engine and their more efficient optimization. Improved turbocharger' performance, which led to higher working cycle efficiency and enabled a higher specific engine output. Wear and corrosion of the key Components such as exhaust valves, cylinder liners, etc. could be reduced or kept within acceptable limits in spite of higher specific output, through improved materials, better understanding of tribological problem and improved lubrication.