Wärtsilä is reporting close to a 50% reduction in methane slip in low-load ranges for a newer version of its four-stroke, LNG dual-fuel Wärtsilä 31DF engine, resulting from using well-proven engine technologies and “minor” modifications to some of components
The encouraging results, which were reported by the engine designer during a virtual press conference with trade media, were obtained in real-world conditions aboard Wasaline’s Aurora Botnia ferry, and verified independently by VTT, a Finnish research centre.
Wärtsilä said operating on LNG, this new version achieved a reduction of 56% in methane emissions and an 86% reduction in NOx emissions at a 50% load. On a weighted average, this new version can reduce methane emissions by 41% as compared with the standard Wärtsilä 31DF engine.
Juha Kytölä, director of R&D and engineering at Wärtsilä, said the results came through engine optimisation and taking full advantage of the engine’s advanced technologies.
“We have two-stage turbocharging [as] standard on this engine" he noted. "So, we get a lot of air in the cylinders when needed. We have variable valve timing, so we can control for each combustion, the volumes of air and exhaust gas. We have common rail for diesel operation and for the pilot fuel operation in gas mode. We have full electronic control, and the engine is tolerant for high maximum combustion pressures”.
Summed up Mr Kytölä: “What we now have done is we have utilised fully this opportunity that these technologies give for us, we have very stable combustion and even combustion in the cylinder so that all the fuel is evenly consumed”.
Besides its environmental benefits, reducing methane slip — essentially unburnt fuel that escapes through the exhaust — also yields better fuel economy, noted Mr Kytölä.
Calling it “a great step” to be able to operate on LNG and biogas in a more environmentally friendly manner, Wasaline technical director Jonas Teir said “It will also have a monetary effect” from 2026 when methane emissions will be a part of the EU ETS.
The newer version of the Wärtsilä 31DF engine is commercially available now, and legacy versions can be upgraded for the improved performance.
Methane slip, a bugbear for LNG dual-fuel engines, is a powerful greenhouse gas, representing a global warming potential of 28 on a 100-year timescale.
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