Commercial Marine

Pure propulsion

Posted on 16 March 2021 by Katrin Auernhammer, Images by WETA, Bilgin, Rolls-Royce

New developments in combination with an SCR system make engines more environmentally friendly

What is the marine propulsion of the future? Engineers around the world are working on it. In focus: Fuel cells, alternative fuels and batteries. But these technologies are not yet ready, and it will be years before they are market-tested. Clean engines, however, are already in demand today - and available. In combination with an SCR system that greatly reduces nitrogen oxides, the diesel engine is a clean alternative. 

Cleaner propulsion in San Francisco Bay

In the Bay of San Francisco, scrupulous care is taken with pollutant emissions, since the coastal region is under special protection and counts as California's most important ecosystem. Before Covid, daily shuttle services were provided by WETA Ferries using 15 passenger ferries that transported over 3 million commuters and tourists per year. WETA has added new catamarans to its fleet – and in doing so is stepping into the role of trailblazer, since these are the first vessels in the US to meet the new EPA Tier 4 emissions standard. Pyxis, the first, has even been awarded the 'Ship of the Year' accolade by American Ship Review magazine. One reason is its ferry propulsion system, which is equipped with twin 16-cylinder Series 4000 mtu units and an mtu SCR system developed by Rolls-Royce to ensure that the strict emissions regulations are complied with.

Current emissions requirements are challenging naval architects, shipyards, vessel operators and engine manufacturers alike. This is due to the add-on SCR systems that the engines require, and for which space must be found in the narrow engine rooms of the vessels. “It's not only the SCR system that needs accommodating. Customers have to find space for cables and reducing agent tanks, and you also need to make room for service work to be carried out,” explained Andreas Peters, mtu Applications Engineer at Rolls-Royce. 

Pyxis, a catamaran from WETA Ferries, was awarded 'Ship of the Year 2020' for its environmentally friendly propulsion system.

In the case of WETA's three new vessels, the shipyard Dakota Creek Industries, the design team at AMD Ferries and mtu engine experts from Rolls-Royce worked together very closely from scratch to find the solution that everyone could live with. “Not taking up any more space than absolutely necessary while still meeting all the criteria governing add-on modules and ease of maintenance was initially a headache. But we were a closely knit team and very focused from the start and made fast progress on planning and construction,” explained Jeff Sherman, from mtu marine engine sales at Rolls-Royce in the US.

The Pyxis plies the waters between Vallejo and San Francisco four times a day, carrying each way as many as 445 passengers who prefer to take a ferry rather than contend with traffic jams and overcrowded public transport. The crossing takes about an hour. The ferry's propulsion system comprises twin Series 4000 mtu engines, each with 2,560 kW power output, which can accelerate the vessel to 34 knots while still meeting environmental requirements. That is owing to advances in turbocharging, combustion and fuel injection, which, combined with the new SCR system, facilitate a 75% reduction in NOx emissions compared to IMO II, and a 65% reduction in particulates compared to EPA Tier 3. 

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Two solutions for yachts

No conditions are more cramped than in the engine room of a high-speed yacht, which can make a ferry or a tugboat seem roomy by comparison. Yet here as well, there are regulations to be followed, and Rolls-Royce has devised different ways of combining the mtu engine and SCR system. The SCR comes in two different designs: either cube-shaped or in the form of a flat box, which yacht customers usually find more attractive. Both designs are manufactured by Rolls-Royce at its mtu facility in Ruhstorf. The SCR systems are especially adapted to suit the mtu engines, allowing the customer to benefit from the reliability of a package solution.

Three 80-m yachts compliant with the IMO III directive are currently being built at Turkish shipyard Bilgin. They are powered by mtu Series 4000 M03 engines of the previous generation linked up to suitably adapted SCR systems. To achieve that, slight adjustments were made to the 16-cylinder engines in the form of modified turbochargers and new-generation engine controllers as well as optimized coordination. The mtu SCR system enables comprehensive control with nitrogen oxide measurements in real time upstream and downstream of the SCR box to ensure that the reactive substance is precisely dosed.

“In the yacht segment especially, ever stricter demands are being placed on the propulsion system. Customers want their engines to be powerful, but also as clean as possible so that they can sail around sensitive marine areas. That's why it's immensely important for us to have green credentials,” said Denise Kurtulus, head of yacht and commercial marine sales at Rolls-Royce. Many customers choose to install an additional diesel particulate filter, even though it is not actually stipulated in the standard.

The Bilgin 263 is not only the largest yacht built in Turkey, it is also the first to comply with the IMO-3 exhaust emissions standard.

The Bilgin yacht propulsion solution has already received IMO III certification, making these yachts the cleanest in their class. For the Pyxis catamaran and its sister vessels, certification took place in December 2020. “We were very confident about receiving approval. The engines installed in the Pyxis have run reliably over more than 2,800 hours of service and we're monitoring them very closely,” said Michael Drews, head of Series 4000 with exhaust aftertreatment for marine applications.

The energy turnaround in the maritime sector is just starting to take off. Rolls-Royce is examining various solutions – all the way from mobile gas engines and hybrid drives through to engines running on methane-based fuels from renewable sources, and fuel cells. “We've made it our mission to de-carbonize the marine propulsion,” summed up Daniel Chatterjee, head of the Green & Hightech program at RollsRoyce Power Systems.

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