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Two new large, 180,000-cubic-metre (cbm) liquefied natural gas (LNG) carriers being built by South Korea's Samsung Heavy Industries (SHI) on behalf of a collaboration between SK Shipping and Marubeni, are to be powered by six-cylinder Wärtsilä X62DF two-stroke dual-fuel engines.

The deal has been described by Finnish firm Wärtsilä as a "milestone order for the marine sector" as they will be the first large LNG carriers featuring Wärtsilä's two-stroke dual-fuel technology. The order was placed in September.

Wärtsilä has already supplied more than 150 ships with its four-stroke, low-pressure dual-fuel engines. The two-stroke development was introduced in November 2013. This engine technology is said to combine efficient fuel consumption and low investment costs.

In a statement Wärtsilä said: "The benefits already proven with the Wärtsilä four-stroke dual-fuel engines can now be applied to two-stroke engines, which are widely popular in merchant vessels. Importantly, both the Wärtsilä two-stroke and four-stroke, low-pressure dual-fuel engines are compliant with the International Maritime Organization's (IMO's) Tier III regulations without need of secondary exhaust treatment systems."

The scope of supply for these ships includes two six-cylinder Wärtsilä X62DF main engines per vessel together with the required electricity generator sets powered by Wärtsilä 34DF dual-fuel engines. The main engines are to be built by a Korean licensee and the deliveries are scheduled for the first quarter in 2016. The first ship is due for delivery in the first quarter of 2017.

"The selection of the Wärtsilä two-stroke, low-pressure, dual-fuel engine technology for these LNG carriers is indicative of the benefits this new technology will bring to the marine sector. We are able to meet the crucial requirements of today's shipping business, namely for fuel efficiency, environmental compliance at all engine loads, plus very competitive first time and running costs," remarked Mr Kang Seog-Hwan, COO of SK Shipping.

The vessels are to be chartered by a U.K. subsidiary of the French oil major, Total S.A. The ships will be the largest LNG carriers able to pass through the Panama Canal after its planned expansion in 2015.

Wärtsilä two-stroke low pressure dual-fuel engines

The Wärtsilä X62DF engine is the second engine - following the Wärtsilä RT-flex50DF - to be introduced with the low-pressure dual-fuel technology. The Finnish firm says its entire portfolio of Wärtsilä two-stroke engines will eventually be available as low-pressure dual-fuel (DF) versions. With this latest order, four X62DF and eight RT-flex50DF engines are currently under construction. Orders have now been received for tankers, container vessels as well as LNG Carriers.

"The benefits of this technology are significant. Compared to other technologies, studies show that Wärtsilä's low-pressure DF engines offer capital expenditure (CAPEX) reductions of 15-20 percent. This is achieved through a substantially simpler and lower cost LNG fuel gas handling system operating at pressures below 16 bar, and by the fact that no further exhaust gas cleaning systems are needed to meet future emission regulations," Wärtsilä said.

The new engines are claimed to be IMO Tier III emissions compliant in gas mode, and the minimum Tier II level is achieved in liquid fuel mode.

On the operating expenditure (OPEX) side, Wärtsilä says "significant gains" will be achieved with its technology, especially for LNG carriers. This is because no high-pressure gas compression system external to the engine needs to be operated onboard the vessel in order to use the boil off gas from the LNG cargo tanks as fuel.

Another main advantage, according to Wärtsilä, is that the technology allows stable operation on gas across the entire load range. This means that at low loads, there is no need to switch to diesel fuel.

"Moreover, the consumption of pilot fuel is approximately just one percent of the total fuel amount, and therefore much lower than with other technologies. This further reduces particulate emissions. Wärtsilä's low-pressure gas system fulfils all safety requirements. Since low-pressure gas technology is the standard for all four-stroke engine makers today, the merit of this concept is clearly proven," added Wärtsilä.

Wärtsilä will be featuring its latest dual-fuel technology at this week's SMM Conference in Hamburg, Germany. The company's stand is located in Hall A4, Booth number 305.