For meeting EEDI purposes, the developments to the two-stroke crosshead engine in recent years have centred around increasing the stroke, reducing rpm and matching the engine to a larger propeller designed to match the operating profile of the vessel.
For many years, two-stroke engines were generally available in two variants – short or long stroke – the difference being self-explanatory. To meet the greater efficiency requirements demanded by EEDI regulations, most engine designers agree that a longer stroke which increases compression is advantageous. The designers and manufacturers have responded by designing super- and ultra- long stroke variants of their engines.
As these have been adopted by customers, the short and long stroke variants are gradually disappearing from engine catalogues although they are still available if required. The new longer stroke engines do raise some issues: engines are necessarily taller and manufacturing suitable crankshafts requires re-tooling by makers and sub-contractors.
With a larger catalogue of designs, MAN B&W engines delivered since 2016 have included models with long, super-long and ultra-long strokes, WinGD has lengthened the stroke of its main designs but does not offer the same choice of its rival.
Two-stroke crosshead engines are produced in a range of bore sizes from 35cm to 95cm. The smaller 35-45cm bore sizes are found on Handy and Handymax bulkers and similar size product tankers, the 50-60cm bores on Panamax size bulkers and tankers and the 70-80cm versions on larger bulkers and tankers. Most engines have five or six cylinders while the largest 90-95cm engines are found in 10- and 11-cylinder versions on the largest container ship types where more speed is still considered a desirable characteristic.
Today the focus of development is less on absolute power as on the need to meet EEDI rules. Different generations of engines appear from time to time with the improvements almost always aimed at improving efficiency as well as ease of maintenance and reducing complexity and weight.
In 2016, MAN B&W – as MAN Energy Solutions was then called – introduced the Mk 10 engine which included several new developments such as a complete redesign of the valve systems including the new FBIV (Fuel Booster Injection Valve) and TCEV (Top Controlled Exhaust Valve). This means that this engine does not have a hydraulic cylinder unit (HCU), a base plate and long high-pressure pipes between the actuators and the fuel and exhaust valves. In addition, the engine features a new bedplate design, optimised cylinder frame and a new connecting rod design. The overall benefits mean that the new version of a 90cm bore engine can deliver a 2.3% power increase for a 1g/kW SFOC decrease and a 10% weight reduction.
WinGD’s predecessor began development of a new range of engines designated X types in 2015 shortly before the transfer of business. Different variants have made their debuts since with the latest the WinGD X52 passing its factory and type approval tests in July 2017.
The reduced fuel consumption results primarily from the longer stroke configuration of WinGD’s Generation X engines, but they also have a relatively light structure and are designed to have low maintenance costs.
The X-prefix engines can also be offered with dual ratings which can be accessed via a minimum of modifications to engine and turbocharger components, enabling ship operators to readily employ a fuel-saving slow steaming mode, according to market and contract conditions.