The Naval Architect September 2020
Since its launch in 2013, WinGD’s X-DF has established itself as the world’s best selling low-speed dual-fuel engine. To date, there are some 60 vessels in operation and a further 320 on order. The XD/72DF has become a popular choice for LNG carriers, while in May the biggest engine in WinGD’s portfolio, the 12X92DF, received type approval for use onboard the very large container ship CMA CGM Jacques Saadé.
WinGD is now looking to build upon its success with a second generation, the X-DF2.0, developed with greenhouse gas reduction targets in mind and plans to incorporate a number of innovations. In June, the company unveiled the first of these, Intelligent Control by Exhaust Recycling (iCER), an exhaust recycling system that it claims will cut gas consumption by 3%, diesel fuel by 5% and achieve a reduction in methane slip by as much as 50%.
Marcel Ott, WinGD’s general manager for operations in China, has been involved in the development of the X-DF series since its beginnings nearly a decade ago. He explains: “The iCER technology reduces the reactivity of the cylinder charge by replacing oxygen with carbon dioxide. CO2 acts as an inert gas to combustion, moderating the combustion speed, and allows more control of combustion.”
In the Otto cycle, iCER extends the operating window between the rich limit and lean limits, meaning the engine can be optimised for the lowest possible consumption and emissions. The low-pressure exhaust recycling path, where part of the exhaust gas is recycled through a cooler into the engine, also allows the engine to operate at higher average mean pressure (BMEP) levels, allowing for a higher power output.
iCER, which is still undergoing testing, will be an optional technology available in two different arrangements. Should shipowners prefer a higher rate of steam production then this can be achieved by adding an economiser which has been developed in partnership with Alfa Laval.
WinGD’s VP of R&D Dominik Schneiter admits that the technology has been driven in part by concerns that developments in Otto cycle have been lagging behind those in diesel, while noting that the XDF has already achieved best in class results for emissions and fuel consumption.
He explains: “This is due mainly to the especially long cycle times we have on low-speed engines. The gas has more time to burn and that means the methane burns longer and there’s less methane slip compared to other Otto engines. The unique layering of the gas mixture in the cylinder leads to no flame quenching, crevices or gaps and helps to reduce and keep the methane slip under control.”
As the only two-stroke designer that has engines operating in diffusion and premixed cycles in the field, WinGD feels entitled to think of itself as the leading authority on dual-fuel technology. Following successful demonstrations, it has made it a standard for all X-DF engines to be able to demonstrate gas operation down to 5% engine load with minimum pilot fuel.
But according to Volkmar Galke, WinGD’s global sales director, the emphasis of the company’s research is aligned with industry expectations that LNG should be considered a bridging fuel in anticipation of carbon-free alternatives, such as ammonia, that may become more viable as 2050 draws closer.
Moreover, he believes the X-DF represents the best engine option for 2050 due to its combination of both the Otto and Diesel cycle in one engine, making it capable of handling all fuel types with the appropriate modifications. “The Otto cycle is digesting any gaseous fuel under low pressure, which means that it’s low capex. The diesel cycle in the same engine is ready for the liquid fuels to come.”
The company is planning additional efficiency features for the X-DF2.0, which it says will be announced in the near future. These are expected to include the variable compression ratio (VCR) technology which WinGD first published details of in a paper for last year’s CIMAC conference in Vancouver.
