Japanese low-speed four-strokes
Japanese engine designer Niigata is continuing to develop its range of low-speed four-stroke engines, and announced plans to introduce a 340mm bore engine to the market in 2020.
There is an established market for low-speed four-stroke engines in the Japanese domestic fleet, where fishing vessels, oil tankers and bulk carriers use the engines. Some Japanese ferries have also adopted low-speed four-stroke engines.
The 6M34RT engine has a 340-mm bore, a stroke of 630 mm and rated output of 1,471 kW. It will be commercially available from next year.
Niigata has dubbed the new engine the ‘Galapagos engine’. The engine drives the propeller directly, while the lower speed improves the operational life of the engine’s components.
By extending the engine stroke, the compression ratio and maximum cylinder pressure have been increased, while the design also features a high pressure ratio turbocharger and high-pressure fuel injection. The design has also optimised the intake and exhaust timings.
Other low-pressure four-stroke engine designs are sold in the Japanese market. Hanshin Engine has developed a range of low speed four-stroke engines, the LA series. The series features five bore sizes, ranging from the 340mm bore LA34 down to the LA26, which was launched in 2018.
The Hanshin LA series also features high-pressure fuel injection. The inlet and exhaust valves are hydraulically opened and pneumatically closed. Small recesses in the underside of the top piston ring allow a controlled release of gases to obtain a more even pressure drop across the ring pack.
The design incorporates a separate cylinder lubrication system (similar to a two-stroke) which helps to limit oil consumption, while an 'L-ring' (piston cleaning ring) limits lube oil consumption.
For comparison, the LA34 has a stroke of 720 mm and rated output of 1,765 kW. A new variant, the LA-E, featuring electronic fuel injection has been developed which has improved fuel consumption at lower engine loads, but has only been made commercially available for 320mm, 410mm and 460mm bore sizes.
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