LNG Propulsion achieves master

LNG Propulsion achieves the next step in technological evolution

With the introduction of the Wärtsilä 46DF dual-fuel engine, the traditional design principles for LNG-powered vessels can be reviewed with substantial benefits to ship owners and operators.

Text: GIULIO TIRELLI Photo: -

Wärtsilä dual-fuel engines are already well-known in the marine market, and the technology they are based on is a daily reality for hundreds of owners all around the world. Vessels propelled with Wärtsilä dual-fuel (DF) engines are today operating in the most diversified global and environmental conditions, from Canada to China, from Korea to Norway, and from Brazil to Denmark.

Despite this wide acceptance from the marine market, innovation never stops and in March 2014, Wärtsilä launched the latest exemplar of the DF engine family: the Wärtsilä 46DF. 

Similarly to previously introduced DF engines, the Wärtsilä 46DF engine is derived from a well-established diesel engine, the Wärtsilä 46F, a market leader in applications such as cruise vessels, RO-RO and RO-Pax ferries. 

The cumulated experience from earlier DF engines made it possible for Wärtsilä for revisit the design of many of the engine’s working parameters, such as combustion spaces, fuel injection charge air, and automation. 

The results of such extensive work brought outstanding performances in power output and fuel consumption (both in gas and diesel mode) for the newly introduced engine, while also reducing its environmental footprint. 

In order to further improve its suitability for the multiplicity of applications where this engine could be applied, the Wärtsilä 46DF is available in two different versions. The high efficiency version offers drastically lower fuel consumption with a cylinder power of 1045kW, while the high power version is capable of a cylinder power of 1145kW with excellent engine thermal efficiency.

Compared to engines targeting similar applications, the Wärtsilä 46DF achieves 

a power output per cylinder that is up to 27% higher than the competition. In principle, this offers the chance to design an LNG-propelled vessel with 27% fewer installed cylinders than the available alternatives, with all the related benefits in onboard space demand, engine room arrangements, and reduced maintenance requirements (Figure 2.)

In this respect, it should be mentioned that the Wärtsilä 46DF is the first gas engine where basically no penalty in power output is imposed as a result of switching from traditional diesel propulsion to LNG. From this point of view, a new vessel design could, in principle, have the same engine configuration (and therefore similar engine room arrangements) regardless of whether it features a Wärtsilä 46F diesel engine or its DF “cousin”, theWärtsilä 46DF. This leads to benefits for both designers and owners, in that similar vessels in the fleet could be treated alike, irrespective of being diesel or LNG propelled. 

Another big achievement of the newly introduced design is the combination of the outstanding power output described above, with a drastic improvement in fuel consumption, both in gas and diesel mode.

Compared to the competition, when running in gas mode the Wärtsilä 46DF has up to 6% lower gas consumption. When in diesel mode, the benefits are even higher, reaching up to a 7% reduction in fuel consumption.

The implications for the economic and environmental impact to owners and operators are clear; lower fuel consumption implies lower fuel expenses and a reduced environmental footprint, thanks to less fuel being burned (Figure 3.) 

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Fig. 2 - The Wärtsilä 46DF power output per cylinder vs. its main competitors.
LNG Propulsion achieves 2
Fig. 3 - The Wärtsilä 46DF fuel consumption vs. its main competitors.

The Wärtsilä 46DF on LNG Carriers

One of the most important application fields for which the Wärtsilä 46DF engine has been developed is the LNG Carrier market. 

In a conventional installation for a large size LNG Carrier (i.e. featuring a cargo capacity above 150,000 m3), the selected engine configuration has been traditionally comprised of three 12-cylinder Wärtsilä 50DF V-engines, plus one 6-cylinder Wärtsilä 50DF in-line engine. The total amount of installed cylinders has, therefore, been 42 units.

With the introduction of the Wärtsilä 46DF engine, the installed configuration applied to a modern LNG Carrier design could be reduced down to four 8-cylinder Wärtsilä 46DF engines.

The reduction of ten installed cylinders offers clear direct benefits in reducing maintenance expenses, maintenance downtime, and onboard space demand without changing the high flexibility and operability of the vessel, factors that have led to the market leadership of DF-Electric propulsion. 

In addition, the selected engine configuration can now feature four engines that are exactly equal in all their aspects. This increases the possibilities for optimizing vessel efficiency, vessel flexibility, identical engine rooms design and the logistics and supply of spare parts. 

With its big improvements in liquid fuel consumption, the Wärtsilä 46DF is able to directly tackle the requirements of an increasingly common cargo trading scheme: the LNG Carrier spot market. 

With the remarkable increase in fleet size of LNG Carriers, the availability of LNG transportation services has been consequently rising. This has made the transportation offer and demand equilibrium more fluid. The result is that more owners are no longer chartering their LNG Carriers based on the traditional long time-charterer agreements (characterized by fixed routes, usually fixed export and import terminals, and remaining the same for a duration of about 20 years), but on a spot cargo basis. The spot market has the peculiarity of seeing a single vessel unloading all its traded cargo at the import terminal. This operation serves to maximize the benefits from the LNG purchase price vs. sell price differential. When totally empting its cargo tanks, the vessel will require the back haul trip to be performed on traditional liquid fuel, not having the chance to use Natural or Forced Boil-Off Gas (NBOG or FBOG). The Wärtsilä 46DF’s top of the class liquid fuel consumption consequently ensures the biggest savings also for LNG Carriers operating on a spot market. 

The Wärtsilä 46DF on RO-Pax

Ro-Pax represents another vessel family for which the Wärtsilä 46DF has been developed, and consequently where expectations are the highest. 

RO-Pax vessels are designed to transport cars, trucks, trailers and passengers, usually on very fixed routes during the entire life of the vessel. Thus, these ships typically operate at very constant speeds and their operating profile remains the same for years. Furthermore, they have a very tight turn-around time in port so as to maximize the volume of cargo and passengers transported, and they operate continuously, usually for 365 days a year, coping with all the variations in environmental conditions.

LNG propulsion is particularly suited to RO-Pax vessels thanks to the certainty of operations; a vessel would most likely call always at the same ports throughout its lifetime. If the LNG bunkering supply chain and infrastructure is in place and available in these same harbours, the vessel has almost certainly the capability of utilizing such a fuel continuously. 

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Fig. 4 - Comparisons between the M/S Viking Amorella, the M/S Viking Grace, and an ideal similar vessel powered by the Wärtsilä 46DF.

One of the most recent and most advanced LNG-powered references in the RO-Pax field is the M/S Viking Grace. In service since 15th January 2013, the vessel operates between Turku, Finland and Stockholm, Sweden with an open-sea operating speed of 22 kn. Sharing the same route with the M/S Viking Grace and operating in the opposite direction is the M/S Viking Amorella, a vessel built about 25 years ago and featuring a traditional propulsion system based on liquid fuel. 

Apart from the differences between the age of the two vessels and the “economy of scale” factor (the newest having almost double the dead-weight, with 13% more passenger capacity, and with the lane meter for car capacity increased by 11%), the M/S Viking Grace’s propulsion plant configuration was revised during the design phase to incorporate the most advanced technologies available at that time. As a result, the M/S Viking Grace features four 8-cylinder Wärtsilä 50DF engines, installed in diesel-electric configuration. 

Despite the fact that the two above mentioned vessels operate in the Baltic Sea with the same design speed, and although the newer ship is much bigger than the older one, the total installed power on the M/S Viking Grace has been remarkably reduced. The same reduction trend can be seen in the total number of cylinders installed, and the fuel consumption costs that have been cut by about 290,000 EUR/year. Finally, the NOX, SOX and CO2 emissions were reduced to the very low levels that LNG-based propulsion is capable of reaching. 

Let’s now imagine the possibility of introducing a new vessel totally equal to the M/S Viking Grace. Without taking into consideration possible improvements in the hull design, hull efficiency, dimensions, capacities, etc., but with the only difference being the use of Wärtsilä 46DF engines as the major power producers, numerous substantial additional benefits would immediately materialize.

Maintaining the vessel’s operational patterns (the same schedules, flexibility, safety and redundancy), the newly built vessel would see a further reduction of four installed cylinders, and lower fuel consumption accounting for an approximate EUR 300,000 saving per year compared to the reference vessel, and would have similar benefits regarding the NOX, SOX and CO2 emissions, thanks to the smaller amount of fuel utilized.

Dual-fuel propulsion is becoming a reality in all marine segments. Current DF references include highly diversified categories, such as tugs, navy vessels, offshore production and support vessels, dry and wet cargo ships, inland waterway, and passenger ships. Wärtsilä today counts more than 1000 DF engines sold and operating globally, with more than 10 million cumulated running hours of experience. 

The introduction of the Wärtsilä 46DF will certainly continue this trend. 

 

Press release was published 24 March 2014 Wärtsilä takes dual-fuel technology to next level by introducing Wärtsilä 46DF engine

Wärtsilä 46DF engine Wärtsilä 46DF product page on wartsila.com

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