Dual-fuel engine is the diesel engine that can run on both gaseous and liquid fuels. When running in gas mode, the engine works according to the Otto process where the lean airfuel mixture is fed to cylinders during the suction stroke. Efficiencies exceeding 47% have been routinely recorded. When running in diesel mode, the engine works according to the Diesel process where the diesel fuel is fed to cylinders at the end of compression stroke. The engine is optimised for running on gaseous fuels and diesel fuel is used for back-up fuel operation.

Wärtsilä began development work with dual-fuel gas engines in 1987, the first concept being the gas-diesel (GD) engine with high-pressure gas injection. This was followed by the second generation of gas engines in the early 1990s, when the company introduced spark-ignited (SG) pure gas engines using low pressure gas. The real breakthrough, however, came when the dual-fuel (DF) engine was introduced by Wärtsilä in 1995. This resulted in the ability to combine fuel flexibility and efficiency with environmental performance.

The DF technology enables the engine to be operated on either natural gas, light fuel oil or HFO. Switching between fuels can take place seamlessly during operation, without loss of power or speed. The engine is designed to have the same output regardless of the fuel used.

The first dual-fuel Wärtsilä 32DF engines for marine application started operating in 2003. They are installed in the world’s first gas-driven PSV VIKING ENERGY and STRIL PIONER.

The first dual-fuel engines of the Wärtsilä 6L50DF type were ordered in 2002 for the world’s first dual-fuel-electric LNG tanker GAZ DE FRANCE ENERGY. Next engines were installed onboard of 154,000 m3 dual-fuel-electric LNG carrier GASELYS. She is powered by three 12-cylinder and one 6-cylinder 50DF engines with an aggregate power of 39.9 MW. The four dual-fuel engines drive generators to supply electricity for the two electric motors that drive the single propeller via a twin input/single output reduction gearbox. While making maximum use of the boil-off from LNG cargo to develop useful power, Wärtsilä 50DF engines have much lower fuel consumption overall and thus lower operating costs than the conventional steam turbine plant. Since the first the Wärtsilä 50DF engines were fitted on board LNG carriers about 65% of all new LNG tankers have been fitted with Wärtsilä dual-fuel engines. At the beginning of 2012, the 50DF engine was supplied to the 100th LNG carrier.

 In 2013, the Wärtsilä power packs, producing more than 100MW in total, in the new P-63 FPSO vessel have completed full 100% load tests at the Cosco shipyard in Dalian, China.

The FPSO has three separate power generation modules, each comprising two 18-cylinder Wärtsilä 50DF dual-fuel engines, alternators and auxiliary equipment. When in operation at the Papa-Terra oilfield, the modules will supply power to the drilling rig as well as the FPSO itself. The P-63 is said to be the first such ship to use gas engines to produce more than 100MWe of power.

The engines are capable of being run on treated well gas or treated crude, as well as marine diesel oil (MDO), which means that virtually no MDO will need to be shipped to the P-63, reducing operating costs. The gas-fired power solution offers significantly lower levels of CO2 emissions compared to conventional technologies. In real terms, the company estimates that the level of carbon emissions will be reduced by as much as 93,000t/year.

About three years ago, Wärtsilä initiated a major project to adapt its low pressure gas engine technology for use in its two-stroke engine portfolio. Subsequently, a new test engine, the RTX-5, based on a commercially available six-cylinder RT-flex50 engine, was installed in the Trieste engine laboratory in Italy in March 2011. The resulting tests with the low pressure low speed dual-fuel engine have demonstrated that low-speed engine performance can fully comply with IMO Tier III NOx limits when operating on gas.

Two 15,000dwt tankers under construction for Terntank Rederi Sweden will be provided with 5RT-flex50DF engines with CMCR of 5750kW at 99rpm

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