Wärtsilä has won a contract to deliver the main engines for two liquefied natural gas (LNG) fuelled tugs being built for CNOOC Energy Technology & Services (CETS), a subsidiary of China National Offshore Oil (CNOOC).

Each of the tugs will be powered by a pair of six-cylinder Wärtsilä 34DF in line dual-fuel engines, which are claimed to be the first vessels to be equipped with the company’s dual-fuel engine technology.

Delivery of the vessels is expected to start at the beginning of 2013, while the first tug is scheduled to be delivered in June 2013. Wärtsilä said that its dual-fuel engine solution will help CNOOC to achieve cleaner energy use in its operations.

The technology offers low emission levels for vessels operating close to population centres, while high fuel efficiency will cut operating costs. The vessels will be operated along China’s coastline and fuel for the 6,500bhp tugs will be provided from CNOOC’s bunkering terminals.

Wärtsilä’s dual-fuel technology allows the engine to be operated on either natural gas, light fuel oil (LFO), or heavy fuel oil (HFO), and switching between fuels can take place seamlessly during operation, without loss of power or speed.

The company said that when operating in gas mode, nitrogen oxide (NOx) emissions are at least 85% below those specified in the current IMO regulations, and CO2 emissions are about 25% less than those of a conventional marine engine running on diesel fuel.

Since 2006, about 65% of all new LNG carriers have been equipped with Wärtsilä dual-fuel engines.