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Lego for engineers

8/4/2014 | Words: Nina Felicitas Kunzi | Pictures: MTU


The world's first harbor tug powered by high-speed gas engines is due to enter service in Rotterdam port in 2016. She is being built by Dutch shipyard Damen, will be operated by the Danish shipping company Svitzer, and MTU is supplying her engines. The high power density of the engines together with the innovative vessel design will make the tug especially compact and maneuverable. For MTU engineers, the development process brought back fond childhood memories – because it allowed them to play a kind of Lego. Their job was to combine the crucial new engine components with existing modules from the Series 4000 unit, which is available as a diesel or stationary gas engine.   

It gives the impression of a closely monitored patient in an intensive care unit. Set up in a white-painted, sterile-looking room, the engine is closely observed by experts from behind a glass panel. Their gaze skips back and forth between the flickering colors on the PC screens and the subject on the other side of the glass. The newly developed MTU gas engine for mobile applications is rigged up on a new, ultra-modern and specialized test stand in Friedrichshafen. It is being put through its paces under near-real marine conditions to test its capabilities for the exacting demands of seagoing craft. 70 tonnes bollard pull, full load, acceleration, partial load, idling, turning – the 508 variously colored cables sprouting out of the test engine illustrate how many different readings the research engineers have to record. The advanced form of the engine will go into service in the very first harbor tug with high-speed natural gas propulsion to be  built by the Damen shipyard which will be used from 2016 for maneuvering gigantic ocean-going vessels within the confined space of a port. As yet, there are very few gas-powered tugs on the market. And they are mostly fitted with bigger and heavier medium-speed engines, which make them larger and less agile than the new Damen vessel.

Fuel of the future                                                                                                   "Natural gas will be an important fuel in the future. It will be available for longer, is cheaper in many parts of the world, and has less of an environmental impact than heavy oil or diesel," says Peter Friedl. He is product manager for gas engines at MTU Friedrichshafen. According to the maritime and offshore oil and gas classification society Det Norske Veritas, there are 42 ships running on liquefied natural gas (LNG ) on the world's oceans at present, while another 40 to 50 are on order or at the design stage. One of the main reasons for the apparently small number is the as yet moderate development level of the network of bunkers, i.e. filling stations for ships. So far there are only a few places where ships can fill up with liquefied or gaseous natural gas. Among the pioneers are ports in the USA, Norway, Denmark and the Netherlands. But that is set to change – the British marine classification society Lloyd's Register conducted a survey of 22 international ports for a bunker infrastructure study. According to the responses received, the ports in the ECAs (areas with particular environmental guidelines) expect LNG to make up about a quarter of total bunker capacity by 2025 – the figure for the coming year is predicted to be only 1.7%. The EU Commission has proposed that LNG bunker stations should be installed at all 139 sea and inland ports in the trans-European shipping network.

Lego for engineers                                                                                                    MTU research  engineers started work on a gas engine for mobile applications in 2011. They put together various components from the proven Series 4000 engine, which MTU offers in diesel and gas-fueled form. "The turbocharging system, running gear and easily modifiable exhaust system we carried over from the Ironmen diesel engines for marine applications. The cylinder heads, ignition system and throttle valves originate from the Series 4000 stationary gas engine for power generation," explains Dr Philippe Gorse. As team leader in the development of new engine concepts at MTU, he is in charge of the project. In addition, the research engineers introduced some components from C&I engines so that the future gas engine could also be operated safely under low loads. "The conceptual development of this new engine was basically like Lego for engineers," says Dr Gorse. In the space of two years, the project team developed the engine management concept and gas injection system and designed the engine for various gas qualities to achieve good transient response characteristics. By the end of 2014, the pilot engine is due to be handed over to MTU series production development.

Difference between diesel and gas engines                                                               "The new design of gas engine for mobile applications differs from an MTU diesel engine essentially in terms of the fuel system and engine management," explains Dr Gorse. While in a diesel engine the fuel is injected directly into the combustion chamber where it mixes with the air, evaporates and ultimately ignites, the natural gas used by a gas engine is injected into the intake air before it enters the cylinder head. That means that   the air and natural gas are mixed thoroughly before entering the combustion chamber, where the homogeneous mixture is compressed and ignited. Bottom line: virtually no soot particulates are produced. Similarly, the gas engine emits 25% less carbon dioxide (CO2), substantially less nitrogen oxide (NOx) and no sulfur oxides (SOx). The advantage of the fuel delivery system specific to the gas engine is that metering of the natural gas-air mixture can be varied according to the engine load. And that means, for instance, that if a tug with a gas engine is idling, the quantity of natural gas injected can be less than if it is pulling at full power to maneuver a colossal tanker inside the harbor. This is all made possible by the new gas injection system developed for the MTU engine. "So the challenge is to inject the gas so precisely that it burns efficiently and economically, enabling the engine to handle varying load conditions and at the same time meet the specified emissions limits," says Dr Gorse.

Full speed ahead without exceeding the limits
In terms of performance, the new high-speed gas engine from MTU easily matches its diesel equivalent. At 1,800 rpm the 12-cylinder version delivers 1,500 kW and the 16-cylinder version 2,000 kW. It safely satisfies the IMO Tier III emissions standard without exhaust gas aftertreatment. Peter Friedl explains: "When tighter environmental regulations are introduced in the ECAs in 2016, only ships that comply with the strict emission limits will be allowed into those areas. Gas engines are made for that."

First tug with high-speed gas engine                                                                          The world's first harbor tug powered by high-speed gas engines is being developed jointly by MTU, Damen and Svitzer. It is due to enter service in 2016. Besides MTU's 16-cylinder gas engine, it will also have Rolls-Royce azimuth thrusters. Martijn Smit, sales manager for Europe at the Damen shipyard says, "Damen is proud to be part of this project to build the world's first CNG harbor tug." Kristian Brauner, technology director at shipping company Svitzer, adds: "The ability to innovate in the area of reliable and environmentally safe operation is absolutely essential to us. So the decision to develop this new type of CNG tug is the logical continuation of our philosophy of combining the tug business and environmental protection." Experts expect the number of vessels running on natural gas to increase to around 3,200 by 2025. By then, the cable-sprouting gas engine on MTU's test stand will have long since demonstrated its ability to withstand the extreme conditions of everyday tug service.

The content of the stories reflects the status as of the respective date of publication. They are not updated. Further developments are therefore not taken into account.

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Having high speed GI engines in harbor tugs and maintaining the compact size and maneuverability is a substantial challenge. The introduction of GI engines for harbor tugs will certainly be a boon for the upcoming 2016 ECA regulations for emissions. This is some fantastic collabarative work.