Feature 3 | MEDIUM-SPEED ENGINES


Regulatory goals drive engine development


Medium-speed engine development is advancing on a broad front, motivated by the challenges of both intensifying environmental legislation and operators’ ever-more crucial need for efficiency from compact plant. David Tinsley reports.


T


he intensif ic at ion of environmental controls on shipping, with their particular


implications for coastal and intra-regional vessels, has stimulated considerable new interest in gas-fuelled machinery. In the case of the industry in Norway,


a very strict regime relating to emissions from ships operating along its shores, in combination with home-grown strengths in lean-burn gas engine technology, has fostered a growing uptake of medium- speed main machinery designed to operate on LNG bunkers. Although most notable in relation to


the modernisation of Norway’s extensive ford ferry fleet, the field of application has widened to other vessel types, as illustrated by the recent choice of machinery for two tugs ordered by Bukser og Berging. Each of the newbuilds will be powered by two Bergen C-type spark-ignition, lean-burn gas engines from Rolls-Royce, which is also supplying the LNG tank system and US35-type main azimuth thrusters. Te combined power and propulsion system is expected to produce 30% less emissions than similar, conventional tugs, and will ensure that the vessels comply with all known future emission regulations. Te newbuild project arises from Statoil’s


award of a contract to Bukser og Berging to provide two escort tugs to serve ships calling at the Kaarsto gas processing plant, run by Gassco, near Stavanger. Te charter period will be for 10 years, due to start in September 2013, with options covering a further 10 years. Each of the new-generation tugs will be fitted with two six-cylinder C26:33 gas engines, rated at 1620kW apiece at a crankshaſt speed of 1000rpm. Among the merits of the Bergen engines, besides their low-emission profiles, is their ability to accommodate direct-drive propulsion and the rapid load pick-up over the entire load range so vital to high-performance tugs.


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China’s inland and coastal fleets offer huge potential for the home-grown CS21 medium- speed engine.


Rolls-Royce has most recently extended


its medium-speed gas engine offering through the development of in-line models of the B35:40 design, complementing the B35:40 vee-type versions and the smaller C26:33 series. Te in-line B35:40 design has secured an opening deal in the shortsea sector of the Norwegian fleet. Te company’s gas engine portfolio as a


whole now covers unit power requirements from 1400 to 9000kW, in generator and mechanical propulsion drive applications. Te C26:33 is seen as the successor to the K-series gas engine, which has proved successful in land and marine applications through four generations before reaching its developmental limit. While the Bergen B32:40 and C25:33 diesel engines with Clean Design notation comfortably meet IMO Tier II emissions criteria


without necessitating additional exhaust cleaning measures, the B35:40 and C26:33 gas engine derivatives achieve a NOx emission level lower than that prescribed under the forthcoming IMO Tier III limits. Furthermore, the new-generation Bergen gas engines emit around 17% less greenhouse gases per unit of power produced than a


comparable diesel


engine, with a 92% reduction in NOx and negligible SOx and soot.


The option to switch Norway’s progressive expansion of


the


coastal LNG bunker supply infrastructure has provided the vital complement to the company’s latest engineering advances and helped nurture owners’ and charterers’ growing interest and investment in gas-fuelled vessels.


Ship & Boat International March/April 2012


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