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First two-stroke low-pressure DF engine passes key test

Written by Nick Blenkey
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The 5RT-flex50DF is the first two-stroke low-pressure DF engine to pass the FAT

JUNE 23, 2015 — The first Wärtsilä low-speed two-stroke dual-fuel (DF) engine destined for a commercial application has successfully completed Factory Acceptance Testing (FAT) at Chinese licensee Yuchai Marine Power Co., Ltd. (YCMP), reports Winterthur Gas & Diesel Ltd. (WinGD), the Switzerland based designer, developer and licensor of Wärtsilä brand low-speed two-stroke engines.

The engine is a five cylinder, 50 cm bore, 5RT-flex50DF built at YCMP’s factory in Doumen, Zhuhai City, Guangdong Province, China.

The 5RT-flex50DF is the first two-stroke low-pressure DF engine to pass the FAT. It will power a handy-size 14,300 cu.m LNG carrier with a rated power of 6,000 kW being built for Zhejiang Huaxiang Shipping at shipbuilder Qidong Fengshun Ship Heavy Industry Co.

While designed to ocean-going standards, the ship will operate principally in Chinese coastal waters delivering LNG to terminals in the estuaries of major Chinese rivers.

WinGD’s scope-of-supply for the project also includes a gas valve unit (GVU), some ancillary equipment and the commissioning of both the engine and GVU aboard the LNG carrier.

With its Wärtsilä 5RT-flex50DF two-stroke dual-fuel engine burning the ship’s natural boil off gas, the vessel will comply with both the NOx and SOx requirements of the strictest IMO emissions regulations without exhaust after treatment.

The FAT took place earlier this month in the presence of representatives from the classification societies, the shipowners, the shipyard, YCMP and WinGD. It was organized by YCMP with the support of the WinGD testing team and gas engine specialists from WinGD headquarters in Winterthur, Switzerland.

Inspection of the engine and selected components according to classification society requirements took place on June 4.

“The system is based on the low-pressure gas admission system proven over more than two decades on Wärtsilä four-stroke DF engines,” said WinGD CEO Martin Wernli. “Our product objectives were to reduce both first and operating costs. The 5RT-flex50DF does not require the high-pressure electrically-driven compressor needed by two-stroke engines in which gas is injected under high pressure. Thus, not only can our fuel system be simpler and less expensive, it saves a considerable amount of onboard electrical power, which means that a vessel’s auxiliary generators can be dimensioned smaller. Such savings are, of course, of special interest on smaller LNG carriers such as the 14000 cu.m vessel which this engine will power.”

The WinGD dual-fuel technology, pioneered by Wärtsilä on medium-speed four-stroke engines in the mid-1990s, employs the lean burn Otto cycle with ignition of a lean air-gas mixture by injection of a small amount of liquid fuel. The gaseous fuel is admitted to the cylinders at low pressure via electronically controlled valves.

Lean burn combustion of gaseous fuels is an enabler of both the low emissions and high efficiencies of WinGD low-speed DF engines. Even without after treatment, NOx emissions in gas operation mode are within IMO Tier III limits for vessels operating in ECAs and, as natural gas is virtually sulfur-free, they also comply with IMO limits for SOx emissions in ECAs.
Since methane is the major constituent of natural gas and the simplest combination of hydrogen and carbon in the hydrocarbon series, in their gaseous fuel mode, the CO2 emissions of WinGD DF engines are lower than from diesel engines of comparable performance.

The lean burn combustion process is also an enabler of the excellent efficiencies attained by modern gas engines.

To provide back-up operation for emergencies and voyages where generation of boil off gas is insufficient, the 5RT-flex50DF is, like all WinGD marine DF engines, equipped with a fully dimensioned liquid fuel system capable of injecting either HFO or distillate fuels (e.g. MDO or MGO).

In its 100% liquid fuel mode the 5RT-flex50DF is compliant with IMO Tier II exhaust emissions regulations.

With its low-speed two-stroke DF engines, WinGD is responding to demand for high efficiency gas engines for both LNG carriers and tankers and containerships considering using LNG as a fuel to ensure IMO Tier III compliance in ECAs.

As the lifespan of ships is usually measured in decades, and gas is expected to gradually replace liquid fuels in many engine applications, WinGD is also stressing the “future proof” aspect of its low-pressure DF technology for two-stroke engines.

The system can be readily retroffited to Wärtsilä low speed two-stroke diesel engines that are already in service.

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