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Marine Propulsion & Auxiliary Machinery

Marine Propulsion & Auxiliary Machinery

Electrically-assisted turbocharging boosts drive for hybrid

Tue 17 Oct 2017 by Paul Fanning

Electrically-assisted turbocharging boosts drive for hybrid
The ‘Cross-Charger’ is a hybrid turbocharger with which fuel consumption and gas emissions of combustion engines can be reduced

A new technology acquired exclusively by Rolls-Royce could cut fuel consumption, increase engine agility and facilitate hybridisation

Rolls-Royce has acquired electrically assisted turbocharging technology that promises to revolutionise the acceleration capability of marine engines.

The innovation comes from an invention devised by engineering services provider G+L Innotec, based in Laupheim in southern Germany. This is the ‘Cross-Charger,’ a hybrid turbocharger with which fuel consumption and gas emissions of combustion engines can be reduced.

Rolls-Royce has acquired the exclusive rights of use for the new technology, which allows for the electrically assisted charging of off-highway combustion engines in the power range above 450 KW. The new invention is protected by patents and so has not been available on the market to date.

The electrically assisted charging system comprises an electric drive combined with a traditional turbocharger developed and manufactured by MTU. As a result, the turbocharger can be accelerated electrically and the charge pressure built up earlier. In operating conditions in which the energy required for a faster charge pressure of the turbine would normally not be sufficient, it is possible to build up with the aid of the electric drive.

Using the technology developed by G+L innotec, MTU will be able to increase the acceleration capability of marine engines as well as the load-response capabilities of generator drives. In addition, it will be possible to reduce the engine’s fuel consumption and emissions in a variety of different applications. Due to the increased load-response capability, emergency standby gensets will be able to deliver their full output even faster than was previously the case. This technology is ideally suited to diesel and gas engines.

The story of the technology began when the predecessor company of G+L developed and produced turbocharger parts for gasoline engines. Speaking to Marine Propulsion, G+L  managing director Holger Gödeke said: “In this earlier development the high levels of effort which were needed to reach the requirements were recognised. For example, the turbocharger with variable turbine geometry required for the transient response of the engine got very complex and expensive. So they looked for an alternative to increase the agility of the turbocharger and with this the response of the engine."

In co-operation with experts on electric motors, the concept of this new technology was defined. In a publicly funded project, the first prototype was developed. Meanwhile, different prototype turbos were tested on various engines for on- and off-highway applications.

Cross Chargers are of great interest to marine applications, but also to the automotive sector – for which they were originally developed. Asked whether application to the marine sector presented any particular difficulties, MTU director of development turbocharging and fluid systems Dr Johannes Kech told Marine Propulsion: “For marine application the technology will be the same. The turbocharger will need the marine specific changes (for example, water-cooled housing). The major question will be the power supply in the vessel. Which voltage would be available in the future in this application (48 V or 600 V)? A further question is the availability of battery power to optimise the engine start.”

To provide the turbocharger with electrical assistance, a permanent magnet is installed upstream of the compressor wheel, and the electrical winding is integrated into the casing of the compressor. With this arrangement, the air drawn in by the compressor is not obstructed, and at the same time the electrical components are cooled by the air. The special feature of this arrangement is the large gap between the magnet and winding. This so-called media gap motor requires specially designed power electronics. This ensures that there is no aerodynamic impact on the charger, and also that existing chargers can be adapted easily to enable them to make use of this technology.

On the basis of a development collaboration agreement with G+L innotec, MTU has equipped turbochargers with this electric drive and has carried out component tests to determine its possible potential. In the next stage, the two partner companies will prepare the new products for series production, so that as of 2021 MTU will be able to launch engines equipped with this technology on the market. The first areas of application suitable for these engines include ships, emergency gensets and land vehicles.

Questioned on the tangible benefits on offer, Dr Kech said: “There will be the possibility to reduce fuel consumption. The amount of savings depends on the changes at the engine. We can use this technology to increase the agility as a major target, or we focus on fuel consumption. Especially if the load profile would allow the capacity to recuperate, the fuel consumption could be reduced.”  

In terms of target marine markets, the innovation is initally aimed at yachts, where the electrical assisted turbocharger will optimise the agility of the vessel. Dr Kech sees the innovation going beyond that, saying: “The ability to use the recuperation function could generate an advantage for all applications.”

Rolls-Royce plans to offer engines of its MTU brand with this technology as of 2021. “Electrically assisted charging is a milestone on the way to the hybridising of the engine. Using this technology, it will be possible for us to develop agile, low-consumption engines,” said Dr Kech, 

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