G90 – Introducing a New Design Platform

Malcolm Latarche
Malcolm Latarche

12 September 2016

The new G90ME-C10 has been added to MAN Diesel & Turbo’s large-bore engine programme. It is weight optimised, compared to the S90MEC9/10, and it forms the new design platform ready for a new generation of engines, when needed.

A new S70ME-C10, which is currently under consideration, will be based on this platform. The G90ME-C10.5 has been launched in addition to MAN Diesel & Turbo’s already very competitive S90ME-C9/10 and G95ME-C9 engine types. The G90 will be based on a much more mass-optimised design platform that results in a lighter engine with a specifi c mass of 26.5 kg/kW for the G90 compared to 29 kg/kW for the S90ME-C10. The overall length, width and height have also been reduced compared to the S90ME-C9/10. As the first engine in the engine programme, the G90 is from the beginning designed with FBIV (Fuel Booster Injection Valve) and TCEV (Top Controlled Exhaust Valve). This means that this engine does not have a hydraulic cylinder unit (HCU), a base plate and long high-pressure pipes between the actuators and the fuel and exhaust valves. The purpose of the TCEV is to integrate the exhaust actuator, the hydraulic push rod and the HCU block into the exhaust valve.

By doing so, the dynamic behaviour is improved (no long hydraulic push rod). The FBIV and the TCEV technologies are well-suited for integration on the cylinder cover of the engine. Similar to the G95, the control of the valves for fuel injection is separated from the control of the exhaust valve, however, now by using the well-known electronic fuel injection valve (ELFI) and the new proportional exhaust valve actuator (PEVA).

Integration of FBIV and TCEV will lead to a considerable weight reduction, because the baseplate, HCU, pressure booster, high-pressure fuel oil pipes and exhaust actuator can be eliminated. In combination, these two technologies also offer improved hydraulic dynamics and flexibility. Fig. 1 shows the top of the engine and the traditional HCU/actuator/booster solution to the right and the new TCEV/ FBIV integration to the left. The letters and numbers in Fig. 1 are explained in Table 1. For a G95, the weight reduction going from the traditional HCU setup to the TCEV/FBIV concept is about 2 tonnes per cylinder, as shown in Table 2.

The FBIV/TCEV design has been tested both on a test rig and on the test engine as well as service tested on a 50-cm bore size and shop tested on a 95-cm bore size. A new S70ME-C10 is under consideration. This new S70ME-C10 under consideration is based on the design platform created for the G90, which means less weight and smaller overall dimensions thanks to, among other things, the TCEV and FBIV, the fl ex rod, and the increased flexible main bearing supports. All data are still preliminary until the final design is in place.

New Technologies

For some years now, the primary target of R&D at MAN Diesel & Turbo in Copenhagen has been to develop the next generation of the ME platform. During this time, the goal has been to utilise the full potential of the ME engine concept by reducing the complexity of the hydraulic system and increase system performance, and the new TCEV and FBIV technologies have been developed within this scope. The two technologies were originally developed in parallel, however, it became apparent that a significant weight reduction could be realised by combining the two technologies, and today they are developed as a system with focus on the combined benefits. The TCEV/FBIV system is entering the final confirmation stage and has operated in service for more than 2,000 hours as a system, and the FBIVs for more than 10,000 hours – both on a 50-cm bore engine.Top Controlled Exhaust Valve

The ME low-force exhaust valve is the design foundation for the development of the TCEV. The exhaust valve movement is still a result of the pressure balance between the air spring and the actuator powered by the high pressure system. Furthermore, the actuator still has a two-step opening sequence where the hydraulic power is reduced after the initial opening, and thereby keeping the hydraulic oil consumption at a minimum. The TCEV is essentially an actuator piston placed directly on top of the exhaust valve spindle.

The high-pressure transmission from the HCU to the exhaust valve top has been removed, which means the high-pressure pipe along with all the components necessary to operate this hydraulic transmission. Furthermore, new design principles have also been introduced. One such example is the hydraulic actuator piston, which is designed in one single piece. The two-step actuation is achieved by cutting off the hydraulic oil supply for a ring area, called step 1. This is a significantly different principle compared to the actuator piston design in the present low-force exhaust valve actuator, where the reduction of hydraulic oil consumption is achieved by preventing the movement of one of the two acting pistons.

Cutting off the hydraulic oil supply is a general design feature of the TCEV replacing the low-force design elements of restricting movements. The result is hydraulic behaviour less sensitive to changes in viscosity and fewer pressure excitations. It is a general design challenge of a hydraulically actuated exhaust valve to achieve sufficient opening power at full load without exceeding the force limits on moving parts at low load due to excess of power. This is not different for the TCEV. In fact, it has become even more challenging with the increased dynamic behaviour.

A closed loop speed control has therefore been introduced to optimise the actuation power at all load points. The control valve reduces the fl ow area for the oil supply to the actuator piston based on an evaluation of the exhaust valve spindle speed. The slower exhaust valve opening reduced the excitation of pressure pulses, preventing cavitation from occurring.

Fuel Booster Injection Valve The key aspects of the fuel booster injection valve compared to the present fuel injection system are improved dynamic behaviour and system reliability. The main differences are the removal of the high-pressure pipe and the new position of the control valve closest possible to the fuel injection nozzle. Both design changes have a direct positive impact on the dynamic behaviour because the operating hydraulic volumes are reduced to an absolute minimum, thereby offering a more direct response to the control valve operation. A comparison between SFOC for the FBIV and the common rail system was conducted on test engines in Japan and complied with IMO NOX Tier II. The two systems showed comparable results across the whole load range, and the choice of injection system should therefore consider cost effectiveness more than performance. In many cases, the high-pressure pipe of the present fuel injection system has been a delicate component. Updates have been required, often in connection with the challenge of handling the significant forces acting on the long slender pipes, and these challenges have increased with the increasing stroke length. By removing it completely, the fuel injection system has become more robust and maintenance friendly. Another advantage is the upside-down position of the pressure booster piston. The risk of blending fuel and high-pressure oil may result in lubricating oil contamination. This situation has been eliminated in the new design by the upside-down arrangement. The umbrella sealing has therefore been removed on the newest design – further reducing the weight and complexity of the FBIV. The simplification is illustrated in Fig. 5. Finally, the piping connection to the FBIV was improved during the development of the FBIV for methanol injection. A sleeve solution was developed to enable easy maintenance of the valve and allow connection of fi ve individual pipes covering methanol supply, methanol circulation, cooling oil and umbrella drain. The sleeve solution is the basis for the latest FBIV design.

Combining TCEV and FBIV

Combining the TCEV and the FBIV was an obvious step when the control valves of both technologies were moved from the base plate level to the top of the cylinder. Furthermore, cost considerations regarding the FBIV called for the application of a combined control valve. FBIVs with individual control are costly, and the benefit of having individual control valves require significant software updates.

The integration was achieved by expanding the hydraulic interface of the TCEV with supply lines for the FBIVs and sufficient accumulator volume. A small control block was added to facilitate unity control of the FBIVs using a FIVA or ELFI control valve. The TCEV and FBIV as a system have been tested extensively both on test facilities in the Diesel Research Centre in Copenhagen, on test engines in Japan and in service. The dynamic behaviour of the FBIVs has been a main focus, as the displacement of the control valve of cause will attenuate the dynamic response behaviour. Both Design A and Design B have therefore been tested, and only a small difference can be seen on the most dynamic-demanding profile– double injection.

Technology Roll-Out

It has, furthermore, been decided that the G90ME-C will be equipped with TCEV and FBIV. Further engine upgrades in the two-stroke large-bore programme will include this new technology system as well.

Concluding Remarks

Five years of development on the new ME technologies has been concluded with the successful test in service over the past 12 months. MAN Diesel & Turbo is confident that the market will embrace the benefits of the new technologies, as they represent a simpler design with fewer components and a reduced total weight. It is an improvement not only for shipowners, but also for the company’s licensees.