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Tug Technology & Business

Dual-fuel workboat engines revealed

Fri 20 Jul 2018 by Martyn Wingrove

Dual-fuel workboat engines revealed
Wärtsilä was awarded EPA’s Tier 3 certification 34DF for both gas and diesel modes

Wärtsilä has gained certification from the US Environmental Protection Agency for its dual-fuel engine, while Yanmar is manufacturing dual-fuel and Tier III engines for tugs

The US Environmental Protection Agency (EPA) has certified Wärtsilä’s 34DF engine as compliant with its Tier 3 emission limits. This covers when the engine is running on natural gas and in diesel mode with a Wärtsilä selective catalytic reduction (SCR) system.

This is another milestone in engine development, as Wärtsilä was awarded EPA’s Tier 3 certification of emissions compliance for 34DF when operating in gas mode without an SCR system in 2017. 34DF engines have already been certified to meet IMO Tier III emissions requirements in both operating modes.

EPA Tier 3 requirements set limits for nitrogen oxide (NOx) and hydrocarbon emissions as well as acceptable levels of particulate matter. Wärtsilä’s NOx reducer system, like other SCR systems, uses a catalyst to convert NOx into diatomic nitrogen and water.

Tier 3 NOx requirements entered into force in 2016 for Category 3 engine sizes – engines with a cylinder displacement at or above 30 litres per cylinder – to be installed in US-flagged or registered vessels.

The Wärtsilä 34DF engine is manufactured in configurations from six to 16 cylinders covering a power range of 2,880 – 8,000 kW for marine applications.

Yanmar has manufactured IMO Tier III engines for tugs and workboats and has begun introducing dual-fuel four-stroke engines for tugboat projects in Asia.

The Japanese group’s Tier III engines emit 80% less NOx than Tier I by using a Yanmar SCR, which converts NOx into nitrogen gas and water by adding ammonia and oxygen, in this balanced chemical equation.

4NO + 4NH3 + O= 4N2 + 6H2O

Yanmar’s SCR uses a urea solution injector, an exhaust gas valve and a bypass of the catalyst chamber.

For tugs, Yanmar produces the 6EY26W series of engines with Y26SCR 6L or 8L for Tier III compliance, said Yanmar diesel engine design director Yohei Kamata. This four-stroke diesel engine series has a power range of 1,471-1,920 kW. They have six cylinders with a cylinder bore of 260 mm, a piston stroke of 385 mm, a piston speed of 9.63 m/s and mean effective pressure of 1.92-2.5 MPa (Mega Pascals).

There is also an eight-cylinder version, 8EY26W, with a power range of 2,060-2,560 kW for larger tug and workboat requirements. This has a similar cylinder bore, piston stroke and speed as the six cylinder version, but has a mean effective pressure of 2.02-2.5 MPa.

Mr Kamata told Tug Technology & Business that the 6EY26W series would be best for tug operations because these are “compact and tough engines” with four strokes and high speed. “We have supplied tug [shipyards] in Singapore, China and Japan,” he said at the Posidonia exhibition in Athens, Greece, in June. “We are also supplying dual-fuel engines to tugs being built in Japan and Singapore,” said Mr Kamata.

Yanmar’s dual-fuel engine uses diesel as a pilot and as a back-up to natural gas. The 6EY26DF engine has a shaft output of around 1,500 kW, while the 8EY26DF has about 2,050 kW, both at 750 rpm. Both types have cylinder bore of 260 mm, stroke of 385 mm and mean effective pressure of 2.0 MPa.

When running on natural gas, Yanmar said these engines emit 80% less NOx, 99% less sulphur and particulate matter and 25% less CO2 than conventional diesel engines.


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