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Second contract for Wärtsilä’s new 2-stroke low-pressure dual-fuel engine as main propulsion

The recently introduced Wärtsilä low-pressure, 2-stroke, dual-fuel engine (DF) (earlier post) has received a second new order. A 5-cylinder Wärtsilä RT-flex50DF engine, together with the gas valve unit and other relevant equipment, has been ordered for a new liquefied natural gas (LNG) carrier vessel being built for the Chinese ship owner and operator, Zhejiang Huaxiang Shipping Co.Ltd.

Wärtsilä RT-flex50DF big
Wärtsilä RT-flex50DF. Click to enlarge.

The Qidong Fengshun Ship Heavy Industry Co., Ltd in China is building the new vessel according to the Chinese Class Society (CCS) standards. When delivered in August 2015, the 14,000 m3 LNG carrier will operate along the Chinese coastline to serve domestic LNG transportation lines.

Wärtsilä unveiled its low-pressure, dual-fuel technology for 2-stroke engines in November of last year. The technology offers significant both capital expenditure (CAPEX) and operating expenditure (OPEX) benefits, and in gas mode is compliant with the IMO’s Tier III emission regulations without need of any exhaust gas cleaning systems.

The 2-stroke dual-fuel concept. Click to enlarge.

Wärtsilä’s low pressure LNG concept is a lean burning Otto-cycle gas engine that has additional liquid fuel back-up capability, thereby enabling vessels to operate 100% on LNG. This is in contrast to other systems utilizing a high-pressure concept, which is merely a conventional diesel engine able to burn gas under certain conditions. Among other benefits, it offers simplicity, reliability, and the most economic gas supply system with the least number of components.

In addition to CAPEX and OPEX benefits, the new Wärtsilä low-pressure 2-stroke dual-fuel engine technology offers other competitive benefits. Most importantly, no investment is needed for exhaust gas cleaning systems in order to comply with the IMO’s Tier III environmental regulations. An important advantage of the Wärtsilä low pressure DF technology is also that it allows stable operation on gas across the entire load range. This means that at low loads (below 15%), there is no need to switch to diesel fuel.

The engine uses a low pressure gas handling system with a maximum 16 bar pressure. LNG and air are mixed in the cylinder prior to compression and, therefore, no additional external engine compressors are needed and additional parasitic load is avoided. Moreover, the consumption of pilot fuel is approximately just one per cent of the total energy at full load, and therefore the lowest for any low speed 2-stroke engine technology.

Studies show that compared to other technologies, Wärtsilä’s low pressure DF engines offer capital expenditure reductions of 15-20%. On the OPEX side, the ability of low pressure DF engines to operate on gas at all loads, including idling and maneuvering, substantially reduces costs.

The new 2-stroke DF application makes the use of LNG fuel available to virtually all vessel types. The Wärtsilä RT-flex50DF engine is the first of the new series to be manufactured.

This second contract for the Wärtsilä low-speed dual-fuel engines in a few months demonstrates the fast market acceptance of this “game-changer” technology. This is the first time that Wärtsilä low-speed DF engine will power an LNG carrier. It represents a very feasible solution for this vessel class. The extension of Wärtsilä low-speed DF engine portfolio to bigger bore sizes such as the Wärtsilä X62DF and Wärtsilä X72DF engines will further expand the range of applications for the low-speed DF engine family to larger container vessels, tankers, LNG carriers and bulk carriers.

—Martin Wernli, Vice President 2-stroke, Wärtsilä Ship Power

Zhejiang Huaxiang specializes in the safe transportation of LNG, and is one of the only two companies who have the Business Certificate of LNG transportation in coastal China issued by the Ministry of Transport of the People’s Republic of China.



This is a good achievement on costs and pollution. If ever a ship with this engine come to the montreal Canada port then I will like to go see it in action.

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