Chapter Sixteen - Medium-Speed Engines—Introduction

Abstract

New designs and upgraded versions of established models have maintained the dominance of medium-speed four-stroke diesel engines in the propulsion of smaller ships as well as larger specialist tonnage such as cruise vessels, car/passenger ferries and ro-ro freight carriers. The growth of the fast passenger and ropax ferry sector benefited those medium-speed enginebuilders who could offer designs with sufficiently high power/weight and volume ratios, an ability to function reliably at full load for sustained periods, and attractive through-life operating costs. Medium-speed engines further enjoy supremacy in the deep-sea vessel genset drive sector, challenged only in lower power installations by high-speed four-stroke engines. Designers now argue the merits of new generations of longer stroke medium-speed engines with higher specific outputs allowing a smaller number of cylinders to satisfy a given power demand and foster compactness, reliability, reduced maintenance and easier servicing. Progress in fuel and lubricating oil economy is also cited, along with enhanced pier-to-pier heavy fuel burning capability and better performance flexibility throughout the load range. Medium-speed engines can meet IMO limits on nitrogen oxide emissions in the exhaust gas comfortably. Lower production costs are also sought from design refinements and the wider exploitation of flexible manufacturing systems to produce components.