NYK will install a variable compression ratio system (VCR system) on two large LNG-fueled coal carriers to be built at Oshima Shipbuilding Co., Ltd. The vessels are scheduled to be delivered by the end of 2025. This will be the first time for VCR systems to be installed on vessels, including existing vessels that use heavy fuel oil as their main fuel.
The VCR mechanism adjusts the compression ratio CR continuously by varying the compression volume (Vc). This is achieved by moving the piston rod in vertical direction using a hydraulic cylinder located in the crosshead pin.
The piston position is controlled by the amount of lubricating oil in the lower chamber located below the piston rod. The oil amount is controlled by filling pressurized lubricating oil through a knee lever and by draining the lubricating oil from the lower chamber. The filling is controlled by a solenoid proportional valve located between the inlet of the knee lever and the lubricating oil feed manifold. The draining is controlled by designed leakage and by a solenoid relief valve located at a second connection of the knee lever.
The simple mechanical configuration has no impact on engine footprint or installation requirements. VCR can also be adjusted for part load operation, meaning that relatively larger savings can be achieved at the low speeds.
The VCR system can adjust the compression ratio in the engine combustion chamber to an optimal balance according to engine power and LNG fuel properties. This optimal adjustment will improve fuel efficiency during operation by about 3% in LNG gas mode and about 6% in diesel oil mode.
Cross section view of the VCR system. Source: WinGD.
The system is also expected to play an important role in reducing GHG emissions from existing ships and improving engine efficiency when decarbonized fuels are introduced.
Mitsui E&S DU Co., Ltd. developed the NYK VCR system together with Winterthur Gas & Diesel (WinGD). WinGD is making VCR available initially for X72DF, X62DF and short-stroke X62DF-S engines. WinGD says VCR will become a core engine technology of the future.
NYK Group’s vessel fuel conversion scenario towards 2050.