New two-stroke variable compression system

The variable compression ratio mechanism could have a dramatic impact on fuel efficiency The variable compression ratio mechanism could have a dramatic impact on fuel efficiency

The first variable compression ratio (VCR) mechanism for a two-stroke marine engine will unlock fuel efficiencies.

Diesel United's system is also expected to simplify the use of alternative fuels.

It comprises a hydraulic cylinder in the lower part of the piston rod which can be used to adjust compression ratio, optimising both for engine load and fuel type. The engine builder, which developed the system with IHI Corp, says the system can offer a fuel cost reduction of around Y100 million (US$887,000) a year for a large container ship.

“Although the effect of making compression ratio variable has been well known, it was technically difficult to develop due to complicated structure,” the company reported. “We have succeeded in the demonstration test, installing the VCR mechanism on an engine dedicated to low-speed testing.”

The system will be particularly useful for burning alternative fuels, where combustion properties of fuel components can vary. The company also noted that the improved fuel efficiency would enable CO2 emission reductions, while the greater combustion control – in conjunction with electronic engine management – would also contribute to low NOx formation.

Diesel United reported that it is developing engines incorporating the VCR system with Winterthur Gas & Diesel, from which it holds a license to build two-stroke engines. The companies are aiming for ‘early commercialisation’, a statement said.

Marcel Ott, programme manager dual-fuel technologies at WinGD, confirmed that the engine developer was in close cooperation with Diesel United. The company is reviewing possible procedures for industrialization of this technology and feasible application on production engines, he told The Motorship.

Ott explained that the concept has the potential to bring benefits in engine performance on both, diesel and dual fuel engines of all bore sizes. However at this stage, the company rather see it as an optional feature rather than a standard on all engines, since the benefits will not be equally significant for all applications and depends on trading routes and fuel mix.

“This development represents a major potential in further optimising the fuel performance of large combustion engines,” said Ott. “No such system has been commercialised before, and never before it was possible to optimise fuel consumption over the load range by adding a new degree of freedom for engine tuning as it is with the VCR.”

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