Bosch Rexroth’s turbo hydraulic system saves up to 4 per cent of fuel

Bosch Rexroth’s turbo hydraulic system saves up to 4 per cent of fuel

Rexroth helps MES save fuel

Bosch Rexroth developed for the Mitsui shipyard a turbo hydraulic system using a Hägglunds radial piston motor leading to tonnes of fuel savings daily

October 2014

Seaways are the major arteries of international trade. Thousands of cargo vessels cruise across the seven seas and are responsible for around 90 per cent of global commodity exchange. With such an immense volume of traffic, the potential for a reduction in worldwide fuel consumption and thus emissions of greenhouse gases is correspondingly great.

Especially progressive propulsion systems can make an enormous difference here. Every per cent of increased efficiency prevents tonnes of fuel consumption and carbon dioxide emissions. Sufficient grounds for the Japanese government to institute a promotional programme for developments in this field in 2007.

Shipbuilding giant Mitsui Engineering and Shipbuilding (MES) took up the challenge. In the future, the Turbo Hydraulic System is to make an effective reduction in the fuel consumption of large-scale engines by recovering the energy from the exhaust gases.

When you realise that around 50 per cent of every litre of fuel combusted is dissipated as losses, you rapidly recognise the potential of the exhaust gases. At 25 per cent, they account for the greatest part of this waste heat. Up to now, it has not been possible to use that reservoir of energy satisfactorily.

There have been thermal waste heat recovery systems on the market for quite some time, but these solutions have been very expensive up to now and take up a lot of space in the engine room. Retrofitting, above all, is therefore often a complicated process.

Consequently, the MES team took a totally new route with a purely hydraulic solution. No simple task. This approach only became possible in the first place with the improvements in turbocharger efficiency in recent years. Nowadays, turbochargers can remove energy that is not needed to charge the engine from the flow of exhaust gas.

In order to be really interesting to shipowners, the Turbo Hydraulic System had to be capable of paying for itself in a reasonable period of time.

During intensive meetings between engineers from MES and Bosch Rexroth in Japan, a further pleasing development gradually emerged: The complete hydraulic system could be constructed using standard Rexroth components. The key component of the Turbo Hydraulic System is a Hägglunds radial piston motor from Rexroth, which is directly coupled to the crankshaft of the large engine.

Hydraulic axial piston pumps are connected to this turbocharger via a gearbox. By means of this connection, the pumps withdraw energy from the flow of exhaust gas and transform it into hydraulically usable energy which the hydraulic motor then feeds back into the engine.

At full engine load, the system saves up to four per cent of fuel – several tonnes per day at sea. Furthermore, the Turbo Hydraulic System fulfills all the demands of the developer team. The dimensions are compact and the complete system can be easily retrofitted to large engines which have already been installed.

As the investment costs are relatively low, the Turbo Hydraulic System is the optimum solution for small and medium-sized engines. Its suitability for use in practice was proven in extensive tests in 2012. These arguments have already convinced the first customers.

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